Datasets:

michaelsyao
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acrac

This dataset contains chunked guidelines and narratives from the ACR Appropriateness Criteria, an set of societal guidelines from the American College of Radiology (ACR) to help clinicians order appropriate diagnostic imaging studies for patients. The corpus is formatted similarly to the corpuses introduced in MedRAG by Xiong et al. (2024), and can therefore be similarly used for medical Retrieval-Augmented Generation (RAG).

Please abide by the ACR Terms and Conditions when using this dataset.

Dataset Structure

Each row of the dataset contains the following fields:

{
  "id": "A unique identifier for each chunk in the corpus",
  "title": "The title of the main document from which the chunk was extracted",
  "content": "The content of the chunk",
  "contents": "The title and content concatenated together into a single field",
  "ACRID": "The ACR topic identifier"
}

Of note, the contents field for each row does not exceed a maximum of 2048 characters in our implementation.

Dataset Curation

This dataset was curated by scraping the ACR Appropriateness Criteria website, downloading all the relevant PDF narratives, and using unstructured's open-source tooling to extract the content into chunks. The original source code used for the dataset curation can be found here. This dataset was constructed on July 17, 2024 - no updates to the ACR Appropriateness Criteria after this date are reflected in the most recent iteration.

Personal and Sensitive Information

The contents of this dataset consist of evidence-based guidelines written by a panel of experts for a medical audience. To our knowledge, no personal or sensitive information is contained in this dataset.

Dataset Card Contact

Please contact Michael Yao at michael.yao@pennmedicine.upenn.edu with any questions or comments.

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Size of downloaded dataset files:

13.5 MB

Size of the auto-converted Parquet files:

5.32 MB

Number of rows:

3,380

id stringlengths 13 16	title stringclasses 225 values	content stringlengths 1.09k 2.04k	contents stringlengths 1.12k 2.05k	ACRID stringclasses 225 values
acrac_70546_0	Acute Trauma to the Foot	Introduction/Background Acute injuries to the foot are frequently encountered in the setting of the emergency room and in general practice. The clinical indications for imaging (known as the Ottawa rules) have been developed to minimize unnecessary radiographs, and their utility is well documented by multiple studies. The most commonly accepted form of these rules is the following: A series of foot radiographs is required only if there is pain in the midfoot and any one of the following: 1) point bone tenderness of the navicular; 2) point bone tenderness of the base of the fifth metatarsal; or 3) inability to bear weight or to walk 4 steps (immediately after the injury or at the emergency department). A meta-analysis (10 studies encompassing 3,725 patients) of the Ottawa rules for the foot showed that these rules have a sensitivity of 99% and a median specificity of 26% for combined evaluation of the ankle and midfoot [1]. The Ottawa rules for the ankle and midfoot have been shown to be effective for the pediatric population (>5 years of age) [2]. Including the added criterion of swelling yields a sensitivity and specificity for fracture of 100% and 55% for the malleolar zone and 50% and 40% for the midfoot, respectively [3,4]. Exclusionary Criteria Multiple conditions or scenarios preclude the use of the Ottawa rules for determining if imaging is necessary [5,6]. It has been reported that the Ottawa rules for the foot should not be used or should be used with great caution in the following clinical situations: penetrating trauma, pregnancy, any skin wound, transferred with radiographs already taken, >10 days after trauma, a return visit for continued traumatic foot pain, in the setting of polytrauma, altered sensorium, neurologic abnormality affecting the foot, or underlying bone disease [7].	Acute Trauma to the Foot. Introduction/Background Acute injuries to the foot are frequently encountered in the setting of the emergency room and in general practice. The clinical indications for imaging (known as the Ottawa rules) have been developed to minimize unnecessary radiographs, and their utility is well documented by multiple studies. The most commonly accepted form of these rules is the following: A series of foot radiographs is required only if there is pain in the midfoot and any one of the following: 1) point bone tenderness of the navicular; 2) point bone tenderness of the base of the fifth metatarsal; or 3) inability to bear weight or to walk 4 steps (immediately after the injury or at the emergency department). A meta-analysis (10 studies encompassing 3,725 patients) of the Ottawa rules for the foot showed that these rules have a sensitivity of 99% and a median specificity of 26% for combined evaluation of the ankle and midfoot [1]. The Ottawa rules for the ankle and midfoot have been shown to be effective for the pediatric population (>5 years of age) [2]. Including the added criterion of swelling yields a sensitivity and specificity for fracture of 100% and 55% for the malleolar zone and 50% and 40% for the midfoot, respectively [3,4]. Exclusionary Criteria Multiple conditions or scenarios preclude the use of the Ottawa rules for determining if imaging is necessary [5,6]. It has been reported that the Ottawa rules for the foot should not be used or should be used with great caution in the following clinical situations: penetrating trauma, pregnancy, any skin wound, transferred with radiographs already taken, >10 days after trauma, a return visit for continued traumatic foot pain, in the setting of polytrauma, altered sensorium, neurologic abnormality affecting the foot, or underlying bone disease [7].	70546
acrac_70546_1	Acute Trauma to the Foot	Other clinical scenarios of foot trauma not directly addressed by the Ottawa rules include trauma to the metatarsal heads and toes and penetrating trauma with concern for a foreign body in the soft tissues. Also, there is little in the literature on medical decision making of when to order a radiographic study of the toes [8]. Discussion of Procedures by Variant Variant 1: Adult or child older than 5 years of age. Acute trauma to the foot. Ottawa rules can be evaluated without exclusionary criteria. Ottawa rules are negative. No suspected abnormalities in regions not evaluated by the Ottawa rules. Initial imaging. When assessing acute trauma to the foot, it is very important to determine that there are no exclusionary criteria for evaluation by Ottawa rules, in which case the rules cannot be applied; see Variant 3. In addition, there are clinical scenarios that are not specifically assessed by the Ottawa rules because the rules mainly address injuries to the midfoot. Such scenarios, for example, include injuries to the forefoot; see Variant 4. The American College of Radiology seeks and encourages collaboration with other organizations on the development of the ACR Appropriateness Criteria through society representation on expert panels. Participation by representatives from collaborating societies on the expert panel does not necessarily imply individual or society endorsement of the final document. Reprint requests to: publications@acr.org Acute Trauma to the Foot Radiography Foot The Ottawa rules were designed to minimize unnecessary radiographs for patients with acute ankle and foot injuries [6]. The Ottawa rules for acute trauma to the foot are fairly well established and have been validated by multiple institutional trials verifying the 99% sensitivity in determining the presence of a foot fracture [1,9,10].	Acute Trauma to the Foot. Other clinical scenarios of foot trauma not directly addressed by the Ottawa rules include trauma to the metatarsal heads and toes and penetrating trauma with concern for a foreign body in the soft tissues. Also, there is little in the literature on medical decision making of when to order a radiographic study of the toes [8]. Discussion of Procedures by Variant Variant 1: Adult or child older than 5 years of age. Acute trauma to the foot. Ottawa rules can be evaluated without exclusionary criteria. Ottawa rules are negative. No suspected abnormalities in regions not evaluated by the Ottawa rules. Initial imaging. When assessing acute trauma to the foot, it is very important to determine that there are no exclusionary criteria for evaluation by Ottawa rules, in which case the rules cannot be applied; see Variant 3. In addition, there are clinical scenarios that are not specifically assessed by the Ottawa rules because the rules mainly address injuries to the midfoot. Such scenarios, for example, include injuries to the forefoot; see Variant 4. The American College of Radiology seeks and encourages collaboration with other organizations on the development of the ACR Appropriateness Criteria through society representation on expert panels. Participation by representatives from collaborating societies on the expert panel does not necessarily imply individual or society endorsement of the final document. Reprint requests to: publications@acr.org Acute Trauma to the Foot Radiography Foot The Ottawa rules were designed to minimize unnecessary radiographs for patients with acute ankle and foot injuries [6]. The Ottawa rules for acute trauma to the foot are fairly well established and have been validated by multiple institutional trials verifying the 99% sensitivity in determining the presence of a foot fracture [1,9,10].	70546
acrac_70546_2	Acute Trauma to the Foot	The more serious potential problems in determining the need for imaging occurs in the patient who does not meet the inclusion criteria for imaging by the Ottawa rules of the foot. These inclusionary criteria are stated in the Introduction/Background section [5,6]; added criterion of swelling increases sensitivity and specificity [3,4]. One should carefully evaluate the patient to make sure they do not meet any of the exclusionary criteria before implementing the Ottawa rules. Radiographs may be appropriate in certain clinical scenarios when Ottawa rules cannot be applied. Also, trauma to the distal forefoot (metatarsal heads and toes) is not directly addressed by the Ottawa rules. In general, if a fracture of a toe is suspected, radiographs can document or rule out a fracture [11,12]. CT Foot In this clinical scenario and in absence of exclusionary criteria for the Ottawa rules, CT is not routinely used as the first imaging study for the evaluation of acute trauma to the foot. MRI Foot MRI is not routinely used as the first imaging study for the evaluation of acute trauma to the foot. US Foot A preliminary ultrasound (US) study has had less successful results compared with radiographic evaluation, with 90.9% sensitivity and specificity for detecting fracture [13]. A recent consensus paper from the European Society of Musculoskeletal Radiology [14] assigned low grading scores for US assessment of talus and bony avulsions. Variant 2: Adult or child older than 5 years of age. Acute trauma to the foot. Ottawa rules can be evaluated without exclusionary criteria. Ottawa rules are positive. Initial imaging. Radiography Foot Radiographs are indicated by positive Ottawa rules with 99% sensitivity in determining the presence of a foot fracture [1,9,10]. Radiographs are the mainstay of initial imaging in the setting of acute foot trauma. Initial imaging typically consists of a 3-view study with the possibility of additional views as indicated by the clinical setting [8].	Acute Trauma to the Foot. The more serious potential problems in determining the need for imaging occurs in the patient who does not meet the inclusion criteria for imaging by the Ottawa rules of the foot. These inclusionary criteria are stated in the Introduction/Background section [5,6]; added criterion of swelling increases sensitivity and specificity [3,4]. One should carefully evaluate the patient to make sure they do not meet any of the exclusionary criteria before implementing the Ottawa rules. Radiographs may be appropriate in certain clinical scenarios when Ottawa rules cannot be applied. Also, trauma to the distal forefoot (metatarsal heads and toes) is not directly addressed by the Ottawa rules. In general, if a fracture of a toe is suspected, radiographs can document or rule out a fracture [11,12]. CT Foot In this clinical scenario and in absence of exclusionary criteria for the Ottawa rules, CT is not routinely used as the first imaging study for the evaluation of acute trauma to the foot. MRI Foot MRI is not routinely used as the first imaging study for the evaluation of acute trauma to the foot. US Foot A preliminary ultrasound (US) study has had less successful results compared with radiographic evaluation, with 90.9% sensitivity and specificity for detecting fracture [13]. A recent consensus paper from the European Society of Musculoskeletal Radiology [14] assigned low grading scores for US assessment of talus and bony avulsions. Variant 2: Adult or child older than 5 years of age. Acute trauma to the foot. Ottawa rules can be evaluated without exclusionary criteria. Ottawa rules are positive. Initial imaging. Radiography Foot Radiographs are indicated by positive Ottawa rules with 99% sensitivity in determining the presence of a foot fracture [1,9,10]. Radiographs are the mainstay of initial imaging in the setting of acute foot trauma. Initial imaging typically consists of a 3-view study with the possibility of additional views as indicated by the clinical setting [8].	70546
acrac_70546_3	Acute Trauma to the Foot	Additional views, such as axial calcaneal view, can be useful in patients with suspected calcaneal fracture [15] because addition of this view increases specificity in diagnosing calcaneal fractures and sensitivity in distinguishing intra-articular calcaneal fractures. Radiography Foot with Weightbearing If there are clinical signs of a Lisfranc injury, obtaining weightbearing radiographs is recommended when possible because nonweightbearing radiographs are not reliable for detection of subtle injuries. Weightbearing views have been shown to increase the abnormal alignment at the Lisfranc joint, thus making it easier to identify a Lisfranc injury [16,19]. The inclusion of both feet on AP radiographs can help in the detection of subtle malalignment when compared with the uninjured side [20]. CT Foot CT is commonly used in evaluating the true extent of osseous injury in complex fractures and at times is used as the initial imaging study in polytrauma patients and in complex regions such as the midfoot [21,22]. CT is not routinely used as the first imaging study for the evaluation of acute trauma to the foot with positive Ottawa rules when exclusionary criteria do not apply. MRI Foot MRI is not routinely used as the first imaging study for the evaluation of acute trauma to the foot with positive Ottawa rules. Acute Trauma to the Foot US Foot A preliminary US study had less successful results compared with radiographic evaluation, with 90.9% sensitivity and specificity for detecting fracture [13]. In the presence of localized tenderness, one study reported US sensitivity and specificity of 100% and 96% for fifth metatarsal fractures and 40% and 93% for navicular fractures, respectively [23]. A recent consensus paper from European Society of Musculoskeletal Radiology [14] assigned low grading scores for US assessment of talus and bony avulsions. Variant 3: Adult or child older than 5 years of age. Acute trauma to the foot. Ottawa rules cannot be evaluated due to exclusionary criteria.	Acute Trauma to the Foot. Additional views, such as axial calcaneal view, can be useful in patients with suspected calcaneal fracture [15] because addition of this view increases specificity in diagnosing calcaneal fractures and sensitivity in distinguishing intra-articular calcaneal fractures. Radiography Foot with Weightbearing If there are clinical signs of a Lisfranc injury, obtaining weightbearing radiographs is recommended when possible because nonweightbearing radiographs are not reliable for detection of subtle injuries. Weightbearing views have been shown to increase the abnormal alignment at the Lisfranc joint, thus making it easier to identify a Lisfranc injury [16,19]. The inclusion of both feet on AP radiographs can help in the detection of subtle malalignment when compared with the uninjured side [20]. CT Foot CT is commonly used in evaluating the true extent of osseous injury in complex fractures and at times is used as the initial imaging study in polytrauma patients and in complex regions such as the midfoot [21,22]. CT is not routinely used as the first imaging study for the evaluation of acute trauma to the foot with positive Ottawa rules when exclusionary criteria do not apply. MRI Foot MRI is not routinely used as the first imaging study for the evaluation of acute trauma to the foot with positive Ottawa rules. Acute Trauma to the Foot US Foot A preliminary US study had less successful results compared with radiographic evaluation, with 90.9% sensitivity and specificity for detecting fracture [13]. In the presence of localized tenderness, one study reported US sensitivity and specificity of 100% and 96% for fifth metatarsal fractures and 40% and 93% for navicular fractures, respectively [23]. A recent consensus paper from European Society of Musculoskeletal Radiology [14] assigned low grading scores for US assessment of talus and bony avulsions. Variant 3: Adult or child older than 5 years of age. Acute trauma to the foot. Ottawa rules cannot be evaluated due to exclusionary criteria.	70546
acrac_70546_4	Acute Trauma to the Foot	Initial imaging. Multiple conditions or scenarios preclude the use of the Ottawa rules for determining if imaging is necessary [5,6]. It has been reported that the Ottawa rules for the foot should not be used or should be used with great caution in the following clinical situations: penetrating trauma, pregnancy, any skin wound, transferred with radiographs already taken, >10 days after trauma, a return visit for continued traumatic foot pain, in the setting of polytrauma, altered sensorium, neurologic abnormality affecting the foot, or underlying bone disease [7]. Radiography Foot If a foot fracture is suspected in a neurologically compromised patient, including patients with diabetic neuropathy, the foot should be radiographed. The Ottawa rules should not be applied in this clinical setting because pain perception may be diminished, no point tenderness will be elicited with palpation, and the patient may be able to ambulate even if a fracture is present [5]. Polytrauma and penetrating trauma also constitute exceptions to the implementations of the Ottawa rules. Both radiographs and US are useful imaging tools to exclude a foreign body in the setting of penetrating trauma to the foot [24]. The best initial imaging study for a foreign body in the foot depends on whether or not the suspected foreign body is radiopaque (eg, gravel, both leaded and nonleaded glass, or metal). Radiographic evaluation for a radiopaque foreign body has approximately 98% sensitivity [25]. If an unembedded fragment of the foreign body is available, then imaging it alongside the foot might provide more information as to the morphology and density of the foreign body. CT Foot CT is commonly used in evaluating the true extent of osseous injury in complex fractures and at times is used as the initial imaging study in polytrauma patients and in complex regions such as the midfoot [21,22]. In the polytrauma patient, approximately 25% of midfoot fractures identified on CT are overlooked on radiographs [21].	Acute Trauma to the Foot. Initial imaging. Multiple conditions or scenarios preclude the use of the Ottawa rules for determining if imaging is necessary [5,6]. It has been reported that the Ottawa rules for the foot should not be used or should be used with great caution in the following clinical situations: penetrating trauma, pregnancy, any skin wound, transferred with radiographs already taken, >10 days after trauma, a return visit for continued traumatic foot pain, in the setting of polytrauma, altered sensorium, neurologic abnormality affecting the foot, or underlying bone disease [7]. Radiography Foot If a foot fracture is suspected in a neurologically compromised patient, including patients with diabetic neuropathy, the foot should be radiographed. The Ottawa rules should not be applied in this clinical setting because pain perception may be diminished, no point tenderness will be elicited with palpation, and the patient may be able to ambulate even if a fracture is present [5]. Polytrauma and penetrating trauma also constitute exceptions to the implementations of the Ottawa rules. Both radiographs and US are useful imaging tools to exclude a foreign body in the setting of penetrating trauma to the foot [24]. The best initial imaging study for a foreign body in the foot depends on whether or not the suspected foreign body is radiopaque (eg, gravel, both leaded and nonleaded glass, or metal). Radiographic evaluation for a radiopaque foreign body has approximately 98% sensitivity [25]. If an unembedded fragment of the foreign body is available, then imaging it alongside the foot might provide more information as to the morphology and density of the foreign body. CT Foot CT is commonly used in evaluating the true extent of osseous injury in complex fractures and at times is used as the initial imaging study in polytrauma patients and in complex regions such as the midfoot [21,22]. In the polytrauma patient, approximately 25% of midfoot fractures identified on CT are overlooked on radiographs [21].	70546
acrac_70546_5	Acute Trauma to the Foot	Therefore, CT is essential for appropriate treatment planning and determining the true extent of osseous injuries in the polytrauma patient and can be used as primary imaging technique in high-energy polytrauma patients. Initial clinical experience suggests that cone-beam CT of the foot or ankle of pediatric patients is a viable lower- dose alternative to multidetector CT [26]. MRI Foot MRI is not routinely used as the first imaging study for the evaluation of acute trauma to the foot in the setting of peripheral neuropathy, penetrating trauma, or polytrauma. US Foot US is not routinely used as the first imaging study for the evaluation of acute trauma to the foot in the setting of peripheral neuropathy or polytrauma. Both radiographs and US are useful imaging tools to exclude a foreign body in the setting of penetrating trauma to the foot [24]. US is the imaging modality of choice if the foreign body is not radiopaque (eg, wood or plastic), with a reported 90% sensitivity for visualizing wooden foreign bodies in some clinical and experimental studies [27,28]. US can identify a foreign body and also help localize it and determine if it involves a tendon or a muscle and to evaluate for an abscess. Variant 4: Adult or child older than 5 years of age. Acute trauma to the foot. Ottawa rules can be evaluated without exclusionary criteria. Ottawa rules are negative. Suspected pathology in an anatomic area not addressed by Ottawa rules (not involving the midfoot; eg, metatarsal-phalangeal joint, metatarsal, toe, tendon, etc). Initial imaging. In clinical situations when Ottawa rules are applicable and negative, imaging may still be desired to evaluate for injuries not assessed by the Ottawa rules. For example, clinical scenarios of acute foot trauma not directly addressed by the Ottawa rules include trauma to the metatarsal heads and toes and acute tendon injury.	Acute Trauma to the Foot. Therefore, CT is essential for appropriate treatment planning and determining the true extent of osseous injuries in the polytrauma patient and can be used as primary imaging technique in high-energy polytrauma patients. Initial clinical experience suggests that cone-beam CT of the foot or ankle of pediatric patients is a viable lower- dose alternative to multidetector CT [26]. MRI Foot MRI is not routinely used as the first imaging study for the evaluation of acute trauma to the foot in the setting of peripheral neuropathy, penetrating trauma, or polytrauma. US Foot US is not routinely used as the first imaging study for the evaluation of acute trauma to the foot in the setting of peripheral neuropathy or polytrauma. Both radiographs and US are useful imaging tools to exclude a foreign body in the setting of penetrating trauma to the foot [24]. US is the imaging modality of choice if the foreign body is not radiopaque (eg, wood or plastic), with a reported 90% sensitivity for visualizing wooden foreign bodies in some clinical and experimental studies [27,28]. US can identify a foreign body and also help localize it and determine if it involves a tendon or a muscle and to evaluate for an abscess. Variant 4: Adult or child older than 5 years of age. Acute trauma to the foot. Ottawa rules can be evaluated without exclusionary criteria. Ottawa rules are negative. Suspected pathology in an anatomic area not addressed by Ottawa rules (not involving the midfoot; eg, metatarsal-phalangeal joint, metatarsal, toe, tendon, etc). Initial imaging. In clinical situations when Ottawa rules are applicable and negative, imaging may still be desired to evaluate for injuries not assessed by the Ottawa rules. For example, clinical scenarios of acute foot trauma not directly addressed by the Ottawa rules include trauma to the metatarsal heads and toes and acute tendon injury.	70546
acrac_70546_6	Acute Trauma to the Foot	Acute Trauma to the Foot Radiography Foot Metatarsal-Phalangeal Joint Injury The best initial imaging study for evaluating hallux plantar plate disruption after metatarsal-phalangeal (MTP) joint injury is weightbearing AP, lateral, and sesamoid axial views, with addition of comparison radiographs of the contralateral foot [29]. Radiographs may also indirectly evaluate lesser metatarsophalangeal plantar plate injury [30]. The combination of a positive drawer test coupled with transverse deviation of the third MTP joint on radiographs can be used to diagnose high-grade plantar plate tear of the second MTP joint [31]. A forced dorsiflexion lateral view of the hallux MTP joint is recommended if there is clinical suspicion of plantar plate injury of the first MTP joint [29]. Radiography Foot with Weightbearing The best initial imaging study for evaluating hallux plantar plate disruption after MTP joint injury is weightbearing AP, lateral, and sesamoid axial views with addition of comparison radiographs of the contralateral foot [29,32]. MRI Foot MRI is the most sensitive modality for the detection of occult fracture and acute bone stress changes [34,35]. MRI is not routinely used as the first imaging study for the evaluation of acute trauma to the foot in setting of suspected MTP joint injury or occult fracture. Both MRI and US are used in evaluating soft-tissue injuries of the foot in the setting of acute trauma, especially when radiographs are noncontributory. Both modalities have a similar sensitivity for acute soft-tissue trauma about the ankle and foot such as ligamentous and tendinous disruption [36- 38]. US Foot US is not routinely used as the first imaging study for the evaluation of acute trauma to the foot in the setting of suspected MTP joint injury or occult fracture. US has been shown to be sensitive for the diagnosis of acute tendon rupture or tendon dislocation in the foot [36,39,40].	Acute Trauma to the Foot. Acute Trauma to the Foot Radiography Foot Metatarsal-Phalangeal Joint Injury The best initial imaging study for evaluating hallux plantar plate disruption after metatarsal-phalangeal (MTP) joint injury is weightbearing AP, lateral, and sesamoid axial views, with addition of comparison radiographs of the contralateral foot [29]. Radiographs may also indirectly evaluate lesser metatarsophalangeal plantar plate injury [30]. The combination of a positive drawer test coupled with transverse deviation of the third MTP joint on radiographs can be used to diagnose high-grade plantar plate tear of the second MTP joint [31]. A forced dorsiflexion lateral view of the hallux MTP joint is recommended if there is clinical suspicion of plantar plate injury of the first MTP joint [29]. Radiography Foot with Weightbearing The best initial imaging study for evaluating hallux plantar plate disruption after MTP joint injury is weightbearing AP, lateral, and sesamoid axial views with addition of comparison radiographs of the contralateral foot [29,32]. MRI Foot MRI is the most sensitive modality for the detection of occult fracture and acute bone stress changes [34,35]. MRI is not routinely used as the first imaging study for the evaluation of acute trauma to the foot in setting of suspected MTP joint injury or occult fracture. Both MRI and US are used in evaluating soft-tissue injuries of the foot in the setting of acute trauma, especially when radiographs are noncontributory. Both modalities have a similar sensitivity for acute soft-tissue trauma about the ankle and foot such as ligamentous and tendinous disruption [36- 38]. US Foot US is not routinely used as the first imaging study for the evaluation of acute trauma to the foot in the setting of suspected MTP joint injury or occult fracture. US has been shown to be sensitive for the diagnosis of acute tendon rupture or tendon dislocation in the foot [36,39,40].	70546
acrac_70546_7	Acute Trauma to the Foot	Fluoroscopy Foot In addition to routine radiographs, fluoroscopy has been suggested in assessment of a hallux MTP joint injury with direct fluoroscopic evaluation of sesamoid tracking distally with great toe extension at the MTP joint on forced dorsiflexion lateral view or fluoroscopy [29]. Variant 5: Adult or child older than 5 years of age. Acute trauma to the foot. Suspect Lisfranc injury, tendon injury, or occult fracture or dislocation. Radiographs are normal or equivocal. Next imaging study. CT Foot Lisfranc Injury CT has been advocated as the primary imaging technique in acute hyperflexion injury and high-energy polytrauma (especially if the patient is not able to bear weight) [33,38,41-45]. CT is useful in demonstrating the multiple metatarsal and cuneiform fractures that can be associated with a ligamentous Lisfranc injury [21,22,33]. CT is typically used for preoperative planning for fracture treatment and evaluation. In the patient with a suspected Lisfranc injury and normal radiographs, the literature supports further advanced imaging by MRI and CT [21,33,43,46]. Acute Tendinous Injury CT imaging has been shown to be an effective way of documenting various tendon entrapment and dislocations, in particularly peroneal dislocations and peroneal retinacular injuries, which are associated with comminuted calcaneal fractures [47-50]. MRI Foot MRI can show osseous injuries that are not visible radiographically including fractures and high-grade contusions associated with prolonged recovery times in elite athletes [51]. MRI can demonstrate ligamentous and osseous Acute Trauma to the Foot injuries in midtarsal (Chopart) sprains, which frequently accompany acute ankle injuries [52,53]. If radiographs are negative, MRI can be obtained in select patients with forefoot pain because of its increased sensitivity for the early detection of metatarsal head subchondral fracture [54].	Acute Trauma to the Foot. Fluoroscopy Foot In addition to routine radiographs, fluoroscopy has been suggested in assessment of a hallux MTP joint injury with direct fluoroscopic evaluation of sesamoid tracking distally with great toe extension at the MTP joint on forced dorsiflexion lateral view or fluoroscopy [29]. Variant 5: Adult or child older than 5 years of age. Acute trauma to the foot. Suspect Lisfranc injury, tendon injury, or occult fracture or dislocation. Radiographs are normal or equivocal. Next imaging study. CT Foot Lisfranc Injury CT has been advocated as the primary imaging technique in acute hyperflexion injury and high-energy polytrauma (especially if the patient is not able to bear weight) [33,38,41-45]. CT is useful in demonstrating the multiple metatarsal and cuneiform fractures that can be associated with a ligamentous Lisfranc injury [21,22,33]. CT is typically used for preoperative planning for fracture treatment and evaluation. In the patient with a suspected Lisfranc injury and normal radiographs, the literature supports further advanced imaging by MRI and CT [21,33,43,46]. Acute Tendinous Injury CT imaging has been shown to be an effective way of documenting various tendon entrapment and dislocations, in particularly peroneal dislocations and peroneal retinacular injuries, which are associated with comminuted calcaneal fractures [47-50]. MRI Foot MRI can show osseous injuries that are not visible radiographically including fractures and high-grade contusions associated with prolonged recovery times in elite athletes [51]. MRI can demonstrate ligamentous and osseous Acute Trauma to the Foot injuries in midtarsal (Chopart) sprains, which frequently accompany acute ankle injuries [52,53]. If radiographs are negative, MRI can be obtained in select patients with forefoot pain because of its increased sensitivity for the early detection of metatarsal head subchondral fracture [54].	70546
acrac_70546_8	Acute Trauma to the Foot	Lisfranc Injury MRI has been advocated as a sensitive diagnostic test in evaluation of Lisfranc ligamentous complex (especially if the patient is not able to bear weight), and 3-D volumetric acquisitions have proven superiority over orthogonal proton density fat-suppressed imaging [33,38,41-45]. There is a high correlation between MRI and intraoperative findings for an unstable Lisfranc injury [44]. In the patient with a suspected Lisfranc injury and normal radiographs, the literature supports further advanced imaging by MRI and CT [21,33,43,46]. Acute Tendinous Rupture MRI tends to be used as a screening tool when one is not certain of the specific tendon injury or if concomitant osseous injury is suspected. Both MRI and US have been shown to be sensitive for the diagnosis of acute tendon rupture or dislocation in the foot [39]. In a surgically confirmed study, MRI was shown to have 83% sensitivity for diagnosing tendon and ligament traumatic injuries about the foot and ankle [37]. US Foot The importance of focused US examinations is emphasized in the literature [57,58]. Protocol-based US evaluation identified 97.4% of symptomatic abnormalities in the distal extremities (including the foot), with additional accuracy obtained with focused examination [57]. Lisfranc Injury Although the literature evidence is limited, US may hold promise as an alternative method to accurately evaluate for a significant Lisfranc injury providing direct and indirect assessment of the Lisfranc ligamentous complex as well as dynamic evaluation with weightbearing as demonstrated in a series of 10 patients [59]. Dorsal component of Lisfranc ligament is amenable to direct US evaluation [59,60], although this structure may not be critical for stability for the Lisfranc joint [20,32]. The physiologic deformation of the dorsal Lisfranc ligament resulting from functional loading emphasized the need for normative US data as well as proper positioning when bilateral evaluation is performed [61,62].	Acute Trauma to the Foot. Lisfranc Injury MRI has been advocated as a sensitive diagnostic test in evaluation of Lisfranc ligamentous complex (especially if the patient is not able to bear weight), and 3-D volumetric acquisitions have proven superiority over orthogonal proton density fat-suppressed imaging [33,38,41-45]. There is a high correlation between MRI and intraoperative findings for an unstable Lisfranc injury [44]. In the patient with a suspected Lisfranc injury and normal radiographs, the literature supports further advanced imaging by MRI and CT [21,33,43,46]. Acute Tendinous Rupture MRI tends to be used as a screening tool when one is not certain of the specific tendon injury or if concomitant osseous injury is suspected. Both MRI and US have been shown to be sensitive for the diagnosis of acute tendon rupture or dislocation in the foot [39]. In a surgically confirmed study, MRI was shown to have 83% sensitivity for diagnosing tendon and ligament traumatic injuries about the foot and ankle [37]. US Foot The importance of focused US examinations is emphasized in the literature [57,58]. Protocol-based US evaluation identified 97.4% of symptomatic abnormalities in the distal extremities (including the foot), with additional accuracy obtained with focused examination [57]. Lisfranc Injury Although the literature evidence is limited, US may hold promise as an alternative method to accurately evaluate for a significant Lisfranc injury providing direct and indirect assessment of the Lisfranc ligamentous complex as well as dynamic evaluation with weightbearing as demonstrated in a series of 10 patients [59]. Dorsal component of Lisfranc ligament is amenable to direct US evaluation [59,60], although this structure may not be critical for stability for the Lisfranc joint [20,32]. The physiologic deformation of the dorsal Lisfranc ligament resulting from functional loading emphasized the need for normative US data as well as proper positioning when bilateral evaluation is performed [61,62].	70546
acrac_70546_9	Acute Trauma to the Foot	Turf Toe and Plantar Plate Injuries US in the sagittal plane best visualizes the plantar plate between the flexor tendon and hyaline cartilage of the metatarsal head [63]. US has shown a 96% sensitivity compared with 87% sensitivity for MRI for the detection of lesser toe plantar plate tears; however, both modalities have poor specificity [64]. Acute Tendinous Rupture Both MRI and US have been shown to be sensitive for the diagnosis of acute tendon rupture or dislocation in the foot [39]. US has also been reported to have a high sensitivity for peroneal tendon tears [65]. Variant 6: Adult or child older than 5 years of age. Acute trauma to the foot. Suspect penetrating trauma with a foreign body. Radiographs of the foot are negative. Next imaging study. CT Foot An experimental study for detection of a variety of foreign bodies (eg, fresh wood, dry wood, glass, porcelain, and plastic fragments) reported 63% sensitivity and 98% specificity for CT for detecting a foreign body [66]. CT was superior to MRI in identifying water-rich fresh wood. MRI Foot An experimental study reported 58% sensitivity and 100% specificity for MRI for detecting a foreign body [66]. In a clinical study including 8 patients with wooden foreign bodies, MRI showed the surrounding inflammatory response in all patients [28]. US Foot Both radiographs and US are useful imaging tools to exclude a foreign body in the setting of penetrating trauma to the foot [24]. US is the imaging modality of choice if the foreign body is not radiopaque (eg, wood or plastic), Acute Trauma to the Foot with a reported 90% sensitivity for visualizing wooden foreign bodies in some clinical and experimental studies [27,28]. US can be used effectively to locate wooden foreign bodies as small as 2.5 mm in length [27]. However, some experimental studies utilizing soft-tissue phantom models report lower overall sensitivity (<50%) for US for detection of foreign bodies [25].	Acute Trauma to the Foot. Turf Toe and Plantar Plate Injuries US in the sagittal plane best visualizes the plantar plate between the flexor tendon and hyaline cartilage of the metatarsal head [63]. US has shown a 96% sensitivity compared with 87% sensitivity for MRI for the detection of lesser toe plantar plate tears; however, both modalities have poor specificity [64]. Acute Tendinous Rupture Both MRI and US have been shown to be sensitive for the diagnosis of acute tendon rupture or dislocation in the foot [39]. US has also been reported to have a high sensitivity for peroneal tendon tears [65]. Variant 6: Adult or child older than 5 years of age. Acute trauma to the foot. Suspect penetrating trauma with a foreign body. Radiographs of the foot are negative. Next imaging study. CT Foot An experimental study for detection of a variety of foreign bodies (eg, fresh wood, dry wood, glass, porcelain, and plastic fragments) reported 63% sensitivity and 98% specificity for CT for detecting a foreign body [66]. CT was superior to MRI in identifying water-rich fresh wood. MRI Foot An experimental study reported 58% sensitivity and 100% specificity for MRI for detecting a foreign body [66]. In a clinical study including 8 patients with wooden foreign bodies, MRI showed the surrounding inflammatory response in all patients [28]. US Foot Both radiographs and US are useful imaging tools to exclude a foreign body in the setting of penetrating trauma to the foot [24]. US is the imaging modality of choice if the foreign body is not radiopaque (eg, wood or plastic), Acute Trauma to the Foot with a reported 90% sensitivity for visualizing wooden foreign bodies in some clinical and experimental studies [27,28]. US can be used effectively to locate wooden foreign bodies as small as 2.5 mm in length [27]. However, some experimental studies utilizing soft-tissue phantom models report lower overall sensitivity (<50%) for US for detection of foreign bodies [25].	70546
acrac_3158175_0	Osteomyelitis or Septic Arthritis Child Excluding Axial Skeleton PCAs	Introduction/Background Pediatric musculoskeletal infections can result in significant morbidity, particularly given ongoing skeletal maturation, and delayed diagnosis may result in premature physeal arrest or joint damage. Among osteoarticular infections, osteomyelitis occurs twice as frequently as septic arthritis [1]. Estimates of the incidence of pediatric osteomyelitis vary widely but have been cited between 2 to 20 per 100,000 [1-4]. Concomitant joint and bone or other extra-articular infections are common in children and may occur in >50% of cases [5-7]. Septic arthritis, which most commonly occurs in the knee and hip joints, is considered an orthopedic emergency because bacterial proliferation and metabolites can rapidly result in cartilage damage [11]. The Kocher criteria, first described in 1999, are widely applied in evaluation of the hip joint as a means to distinguish septic arthritis (surgical emergency) from transient synovitis (expectant management) [14]. The criteria include fever >101.3oF, erythrocyte sedimentation rate of at least 40 mm/hour, white blood cell (WBC) count of at least 12,000 cells/mm3, and an inability to bear weight on the affected side. Satisfying more of these criteria results in higher likelihood of septic arthritis, with near 100% likelihood in patients who meet all four criteria. More recently, elevated C-reactive protein >2.0 mg/dL has been described as an accurate predictor of septic arthritis [15]. Clinical suspicion of septic arthritis is of paramount importance in management because diagnosis is made by arthrocentesis. The distribution of septic arthritis and osteomyelitis varies by age. Children <2 years of age have been reported to be more likely to have septic arthritis than osteomyelitis (P = . 0003). In children between 2 and 10 years old, osteomyelitis is slightly more common than septic arthritis, and in children from 10 to 18 years old, septic arthritis is slightly more common [6].	Osteomyelitis or Septic Arthritis Child Excluding Axial Skeleton PCAs. Introduction/Background Pediatric musculoskeletal infections can result in significant morbidity, particularly given ongoing skeletal maturation, and delayed diagnosis may result in premature physeal arrest or joint damage. Among osteoarticular infections, osteomyelitis occurs twice as frequently as septic arthritis [1]. Estimates of the incidence of pediatric osteomyelitis vary widely but have been cited between 2 to 20 per 100,000 [1-4]. Concomitant joint and bone or other extra-articular infections are common in children and may occur in >50% of cases [5-7]. Septic arthritis, which most commonly occurs in the knee and hip joints, is considered an orthopedic emergency because bacterial proliferation and metabolites can rapidly result in cartilage damage [11]. The Kocher criteria, first described in 1999, are widely applied in evaluation of the hip joint as a means to distinguish septic arthritis (surgical emergency) from transient synovitis (expectant management) [14]. The criteria include fever >101.3oF, erythrocyte sedimentation rate of at least 40 mm/hour, white blood cell (WBC) count of at least 12,000 cells/mm3, and an inability to bear weight on the affected side. Satisfying more of these criteria results in higher likelihood of septic arthritis, with near 100% likelihood in patients who meet all four criteria. More recently, elevated C-reactive protein >2.0 mg/dL has been described as an accurate predictor of septic arthritis [15]. Clinical suspicion of septic arthritis is of paramount importance in management because diagnosis is made by arthrocentesis. The distribution of septic arthritis and osteomyelitis varies by age. Children <2 years of age have been reported to be more likely to have septic arthritis than osteomyelitis (P = . 0003). In children between 2 and 10 years old, osteomyelitis is slightly more common than septic arthritis, and in children from 10 to 18 years old, septic arthritis is slightly more common [6].	3158175
acrac_3158175_1	Osteomyelitis or Septic Arthritis Child Excluding Axial Skeleton PCAs	The American College of Radiology seeks and encourages collaboration with other organizations on the development of the ACR Appropriateness Criteria through representation of such organizations on expert panels. Participation on the expert panel does not necessarily imply endorsement of the final document by individual contributors or their respective organization. Reprint requests to: publications@acr.org Osteomyelitis or Septic Arthritis-Child Typical management of uncomplicated osteomyelitis in the pediatric population consists initially of intravenous (IV) antibiotic therapy followed by a prolonged course of outpatient antibiotics, either oral or IV. However, surgical debridement may be indicated in certain scenarios, such as in the setting of subperiosteal collections, necrosis, or failure to respond to initial management. Typical management of septic arthritis consists of antibiotics, arthrotomy, irrigation, and debridement [16]. Imaging plays a critical role in characterizing and differentiating septic arthritis from osteomyelitis. Please note that chronic recurrent multifocal osteomyelitis, which affects the pediatric population and typically manifests with multiple sites of involvement, is a nonbacterial autoinflammatory disorder and as such will not be discussed in this document, which will focus on acute musculoskeletal infection. Special Imaging Considerations Evaluation for pediatric musculoskeletal infection in the setting of existing orthopedic hardware can be impacted by artifact. On CT, beam hardening artifact occurs, which can be reduced on conventional CT by corrective software, as well as filtration and calibration connection [18,19]. With the advent of dual-energy CT, metal artifact reduction can be performed to reduce beam hardening by acquisition of data at two distinct energy spectra in order to create a virtual monochromatic image to optimize visualization of bone or soft tissue [19].	Osteomyelitis or Septic Arthritis Child Excluding Axial Skeleton PCAs. The American College of Radiology seeks and encourages collaboration with other organizations on the development of the ACR Appropriateness Criteria through representation of such organizations on expert panels. Participation on the expert panel does not necessarily imply endorsement of the final document by individual contributors or their respective organization. Reprint requests to: publications@acr.org Osteomyelitis or Septic Arthritis-Child Typical management of uncomplicated osteomyelitis in the pediatric population consists initially of intravenous (IV) antibiotic therapy followed by a prolonged course of outpatient antibiotics, either oral or IV. However, surgical debridement may be indicated in certain scenarios, such as in the setting of subperiosteal collections, necrosis, or failure to respond to initial management. Typical management of septic arthritis consists of antibiotics, arthrotomy, irrigation, and debridement [16]. Imaging plays a critical role in characterizing and differentiating septic arthritis from osteomyelitis. Please note that chronic recurrent multifocal osteomyelitis, which affects the pediatric population and typically manifests with multiple sites of involvement, is a nonbacterial autoinflammatory disorder and as such will not be discussed in this document, which will focus on acute musculoskeletal infection. Special Imaging Considerations Evaluation for pediatric musculoskeletal infection in the setting of existing orthopedic hardware can be impacted by artifact. On CT, beam hardening artifact occurs, which can be reduced on conventional CT by corrective software, as well as filtration and calibration connection [18,19]. With the advent of dual-energy CT, metal artifact reduction can be performed to reduce beam hardening by acquisition of data at two distinct energy spectra in order to create a virtual monochromatic image to optimize visualization of bone or soft tissue [19].	3158175
acrac_3158175_2	Osteomyelitis or Septic Arthritis Child Excluding Axial Skeleton PCAs	On MRI, susceptibility artifact limits regional visualization and directly correlates with magnetic field strength. Basic metal artifact reduction can be performed by increasing bandwidth, decreasing slice thickness, increasing echo train length, and increasing matrix size [20]. Advanced MR software packages and sequences have been developed for more robust through-section and in-plane artifact reduction. Osteomyelitis commonly occurs in young children, with half of cases reportedly in children <5 years of age [13,21]. Although hematogenous bacterial seeding is the most common underlying cause for osteomyelitis, a history of trauma, often minor, is frequently elicited [11,13]. Infants and toddlers with septic arthritis or osteomyelitis often present with a limp, though it is often difficult in this population to localize a site of involvement on physical examination. In these cases, imaging is often utilized to help identify the affected site [22]. Concurrent osteomyelitis and septic arthritis are common. 3-Phase Bone Scan Area of Interest There is no relevant literature regarding the use of 3-phase bone scan of the area of interest in the initial evaluation of osteomyelitis or septic arthritis in children <5 years of age. Osteomyelitis or Septic Arthritis-Child Bone Scan Whole Body There is no relevant literature regarding the use of whole-body bone scan in the initial evaluation of osteomyelitis or septic arthritis in children <5 years of age. Bone Scan Whole Body and 3-Phase Bone Scan Area of Interest There is no relevant literature regarding the use of whole-body bone scan with 3-phase bone scan of the area of interest in the initial evaluation of osteomyelitis or septic arthritis in children <5 years of age. CT Area of Interest There is no relevant literature regarding the use of CT in the initial evaluation of osteomyelitis or septic arthritis in children <5 years of age.	Osteomyelitis or Septic Arthritis Child Excluding Axial Skeleton PCAs. On MRI, susceptibility artifact limits regional visualization and directly correlates with magnetic field strength. Basic metal artifact reduction can be performed by increasing bandwidth, decreasing slice thickness, increasing echo train length, and increasing matrix size [20]. Advanced MR software packages and sequences have been developed for more robust through-section and in-plane artifact reduction. Osteomyelitis commonly occurs in young children, with half of cases reportedly in children <5 years of age [13,21]. Although hematogenous bacterial seeding is the most common underlying cause for osteomyelitis, a history of trauma, often minor, is frequently elicited [11,13]. Infants and toddlers with septic arthritis or osteomyelitis often present with a limp, though it is often difficult in this population to localize a site of involvement on physical examination. In these cases, imaging is often utilized to help identify the affected site [22]. Concurrent osteomyelitis and septic arthritis are common. 3-Phase Bone Scan Area of Interest There is no relevant literature regarding the use of 3-phase bone scan of the area of interest in the initial evaluation of osteomyelitis or septic arthritis in children <5 years of age. Osteomyelitis or Septic Arthritis-Child Bone Scan Whole Body There is no relevant literature regarding the use of whole-body bone scan in the initial evaluation of osteomyelitis or septic arthritis in children <5 years of age. Bone Scan Whole Body and 3-Phase Bone Scan Area of Interest There is no relevant literature regarding the use of whole-body bone scan with 3-phase bone scan of the area of interest in the initial evaluation of osteomyelitis or septic arthritis in children <5 years of age. CT Area of Interest There is no relevant literature regarding the use of CT in the initial evaluation of osteomyelitis or septic arthritis in children <5 years of age.	3158175
acrac_3158175_3	Osteomyelitis or Septic Arthritis Child Excluding Axial Skeleton PCAs	Although some studies have shown no significant difference in sensitivity and specificity in diagnosis of osteomyelitis or septic arthritis with or without the use of gadolinium-based contrast agents, IV contrast has been shown to improve detection of abscesses [32,33]. Decreased femoral head enhancement on early postcontrast imaging has been noted as a reliable feature of septic arthritis not seen in transient synovitis, and diminished femoral head enhancement on MRI in the setting of septic arthritis in children <12 months of age correlated with development of secondary osteomyelitis [34,35]. Contrast has been shown to markedly improve detection of infection of unossified growth cartilage (chondritis) in children <6 years of age, in which the cartilage most commonly appeared normal on unenhanced sequences; hypoenhancement was more commonly noted with infection [36,37]. In one study of children <18 months of age with community acquired S aureus infection of the unossified epiphyseal cartilage, 7 of 9 cases demonstrated normal cartilage signal on noncontrast sequences; hypoenhancement or nonenhancement of involved foci was used for diagnosis [36]. In another study of children <6 years of age, focal or global cartilage nonenhancement was demonstrated in 71% of 14 patients with surgically confirmed epiphyseal osteomyelitis, compared with 21% of controls [37]. Global enhancement defects were more sensitive, noted in 43% of cases but not seen in any control cases. MRI Extremity Area of Interest In one study, a large field-of-view MRI was performed to encompass both lower extremities rather than the area of concern [38]. In patients who were later found to have osteomyelitis, 11% had contralateral extremity findings, including contralateral osteomyelitis, and 20% had ipsilateral septic arthritis.	Osteomyelitis or Septic Arthritis Child Excluding Axial Skeleton PCAs. Although some studies have shown no significant difference in sensitivity and specificity in diagnosis of osteomyelitis or septic arthritis with or without the use of gadolinium-based contrast agents, IV contrast has been shown to improve detection of abscesses [32,33]. Decreased femoral head enhancement on early postcontrast imaging has been noted as a reliable feature of septic arthritis not seen in transient synovitis, and diminished femoral head enhancement on MRI in the setting of septic arthritis in children <12 months of age correlated with development of secondary osteomyelitis [34,35]. Contrast has been shown to markedly improve detection of infection of unossified growth cartilage (chondritis) in children <6 years of age, in which the cartilage most commonly appeared normal on unenhanced sequences; hypoenhancement was more commonly noted with infection [36,37]. In one study of children <18 months of age with community acquired S aureus infection of the unossified epiphyseal cartilage, 7 of 9 cases demonstrated normal cartilage signal on noncontrast sequences; hypoenhancement or nonenhancement of involved foci was used for diagnosis [36]. In another study of children <6 years of age, focal or global cartilage nonenhancement was demonstrated in 71% of 14 patients with surgically confirmed epiphyseal osteomyelitis, compared with 21% of controls [37]. Global enhancement defects were more sensitive, noted in 43% of cases but not seen in any control cases. MRI Extremity Area of Interest In one study, a large field-of-view MRI was performed to encompass both lower extremities rather than the area of concern [38]. In patients who were later found to have osteomyelitis, 11% had contralateral extremity findings, including contralateral osteomyelitis, and 20% had ipsilateral septic arthritis.	3158175
acrac_3158175_4	Osteomyelitis or Septic Arthritis Child Excluding Axial Skeleton PCAs	Among patients who did not have osteomyelitis, 20% had contralateral abnormalities; most common diagnoses included stress reaction, soft-tissue edema, myositis, sterile joint effusion, and leukemia. Radiography Area of Interest Features of acute osteomyelitis on radiographs include periosteal reaction, a well-circumscribed focal bone lucency, and frank bone destruction. Radiographs are not sensitive in assessment of early osteomyelitis because bone destruction does not typically occur until 7 to 10 days into the disease course, and radiographs are normal until >30% osseous matrix destruction has occurred [24,40]. Radiographs, however, do have initial utility in all populations in excluding other entities that may mimic acute osteomyelitis, such as fracture or neoplasm and can be used to direct subsequent imaging evaluation [3,25,31,40]. A particularly challenging subset of patients to Osteomyelitis or Septic Arthritis-Child evaluate is those with sickle cell disease. One study found that 63% of patients with known hand or wrist osteomyelitis and underlying sickle cell disease had lytic radiographic changes or periosteal reaction, compared with 23% of patients without sickle cell disease, with the greater frequency in the sickle cell population attributed to either marrow infarction or osteomyelitis as the underlying cause for radiographic changes [41]. Radiographs are highly variable in identifying hip joint effusions, with sensitivity ranging from 20% to 73% [40,42,43]. Radiographs are also variable for identifying fluid in joints other than the hip. US Area of Interest Ultrasonography (US) is a highly sensitive method of diagnosing joint effusions, with the bulk of literature addressing the hip joint. US can reportedly detect hip effusions as small as 1 mL [44].	Osteomyelitis or Septic Arthritis Child Excluding Axial Skeleton PCAs. Among patients who did not have osteomyelitis, 20% had contralateral abnormalities; most common diagnoses included stress reaction, soft-tissue edema, myositis, sterile joint effusion, and leukemia. Radiography Area of Interest Features of acute osteomyelitis on radiographs include periosteal reaction, a well-circumscribed focal bone lucency, and frank bone destruction. Radiographs are not sensitive in assessment of early osteomyelitis because bone destruction does not typically occur until 7 to 10 days into the disease course, and radiographs are normal until >30% osseous matrix destruction has occurred [24,40]. Radiographs, however, do have initial utility in all populations in excluding other entities that may mimic acute osteomyelitis, such as fracture or neoplasm and can be used to direct subsequent imaging evaluation [3,25,31,40]. A particularly challenging subset of patients to Osteomyelitis or Septic Arthritis-Child evaluate is those with sickle cell disease. One study found that 63% of patients with known hand or wrist osteomyelitis and underlying sickle cell disease had lytic radiographic changes or periosteal reaction, compared with 23% of patients without sickle cell disease, with the greater frequency in the sickle cell population attributed to either marrow infarction or osteomyelitis as the underlying cause for radiographic changes [41]. Radiographs are highly variable in identifying hip joint effusions, with sensitivity ranging from 20% to 73% [40,42,43]. Radiographs are also variable for identifying fluid in joints other than the hip. US Area of Interest Ultrasonography (US) is a highly sensitive method of diagnosing joint effusions, with the bulk of literature addressing the hip joint. US can reportedly detect hip effusions as small as 1 mL [44].	3158175
acrac_3158175_5	Osteomyelitis or Septic Arthritis Child Excluding Axial Skeleton PCAs	The absence of hip joint effusion virtually excludes septic arthritis; a false negative rate of 5% has been described, noted in patients with a shorter duration of symptoms (<1 day) [40,43,45-47]. Hip US for the purpose of identifying joint effusion can be performed with high sensitivity and specificity [48]. In one study, nearly 80% of pediatric patients with septic arthritis of the hip required US imaging alone to guide their management [45]. US can also be used to identify joint fluid in extremity joints other than the hip. US in evaluation of osteomyelitis is limited in its ability to assess the osseous structures but can identify abutting inflammatory changes such as periosteal elevation, subperiosteal collections, and soft-tissue edema [40,49,50]. Bone Scan Whole Body and 3-Phase Bone Scan Area of Interest Skeletal scintigraphy has been traditionally used to accurately detect disease in cases of suspected acute osteomyelitis with normal radiographs because scintigraphic changes are present within the first 1 to 2 days of symptoms [8]. Although multiple studies have documented the success of scintigraphy in identifying acute osteomyelitis in children, there is limited data with studies in which only the area of interest was imaged. In one study in which blood pool and delayed imaging of only the area of interest were performed, 70 of 71 cases of osteomyelitis were identified [51]. However, multifocal osteomyelitis is common in the pediatric population, particularly among young children, and as a result, whole-body bone scan is typically advocated [52]. One study, in which a 3-phase bone scan was performed followed by a whole-body scan, delayed imaging noted 19% of cases of acute osteomyelitis were noted to be multifocal osteomyelitis, with over half of those cases noted in patients <6 years of age, the majority of which were neonates [52].	Osteomyelitis or Septic Arthritis Child Excluding Axial Skeleton PCAs. The absence of hip joint effusion virtually excludes septic arthritis; a false negative rate of 5% has been described, noted in patients with a shorter duration of symptoms (<1 day) [40,43,45-47]. Hip US for the purpose of identifying joint effusion can be performed with high sensitivity and specificity [48]. In one study, nearly 80% of pediatric patients with septic arthritis of the hip required US imaging alone to guide their management [45]. US can also be used to identify joint fluid in extremity joints other than the hip. US in evaluation of osteomyelitis is limited in its ability to assess the osseous structures but can identify abutting inflammatory changes such as periosteal elevation, subperiosteal collections, and soft-tissue edema [40,49,50]. Bone Scan Whole Body and 3-Phase Bone Scan Area of Interest Skeletal scintigraphy has been traditionally used to accurately detect disease in cases of suspected acute osteomyelitis with normal radiographs because scintigraphic changes are present within the first 1 to 2 days of symptoms [8]. Although multiple studies have documented the success of scintigraphy in identifying acute osteomyelitis in children, there is limited data with studies in which only the area of interest was imaged. In one study in which blood pool and delayed imaging of only the area of interest were performed, 70 of 71 cases of osteomyelitis were identified [51]. However, multifocal osteomyelitis is common in the pediatric population, particularly among young children, and as a result, whole-body bone scan is typically advocated [52]. One study, in which a 3-phase bone scan was performed followed by a whole-body scan, delayed imaging noted 19% of cases of acute osteomyelitis were noted to be multifocal osteomyelitis, with over half of those cases noted in patients <6 years of age, the majority of which were neonates [52].	3158175
acrac_3158175_6	Osteomyelitis or Septic Arthritis Child Excluding Axial Skeleton PCAs	Single-photon emission computed tomography (SPECT)/CT offers improved characterization of osseous pathology compared to planar imaging [53]. MRI is generally considered preferable in detection of early manifestations of osteomyelitis, as well as infection of the surrounding soft tissues, because of the rapid progression of disease [53]. Whole-body bone scan is typically helpful when scintigraphy is used for suspected osteomyelitis, particularly if there is a fever of unknown origin or bacteremia [54]. One study assessed the accuracy of bone scan for the diagnosis of suspected acute hematogenous osteomyelitis and septic arthritis in 86 children, using whole-body and selected static images, without blood flow or blood pool views [55]. Bone scan findings were correlated with the final diagnosis in 34 sites of septic arthritis and in 62 sites of osteomyelitis. Bone scan accuracy was 81%. Positive predictive value was 82% for those sites with increased activity and 100% for those sites with decreased activity. Negative predictive value was 63%. In another smaller study, 9 patients who underwent whole-body scan, 100% (7 of 7) patients with osteomyelitis had increased uptake corresponding to the site of involvement [56]. In one study of 213 children referred for skeletal scintigraphy because of suspicion for acute hematogenous osteomyelitis who underwent a 3-phase bone scan of the area of interest along with whole-body delayed images, accurate diagnosis was made in 84% of cases without the need for MRI, including 92% of those diagnosed with osteomyelitis, although it should be noted that bone scan was limited regarding soft- tissue and articular pathology [57]. In another study of 65 children who underwent whole-body scan with focused evaluations of the area of interest and the contralateral side, 23 patients who were classified as having osteomyelitis all had abnormal bone scans [58].	Osteomyelitis or Septic Arthritis Child Excluding Axial Skeleton PCAs. Single-photon emission computed tomography (SPECT)/CT offers improved characterization of osseous pathology compared to planar imaging [53]. MRI is generally considered preferable in detection of early manifestations of osteomyelitis, as well as infection of the surrounding soft tissues, because of the rapid progression of disease [53]. Whole-body bone scan is typically helpful when scintigraphy is used for suspected osteomyelitis, particularly if there is a fever of unknown origin or bacteremia [54]. One study assessed the accuracy of bone scan for the diagnosis of suspected acute hematogenous osteomyelitis and septic arthritis in 86 children, using whole-body and selected static images, without blood flow or blood pool views [55]. Bone scan findings were correlated with the final diagnosis in 34 sites of septic arthritis and in 62 sites of osteomyelitis. Bone scan accuracy was 81%. Positive predictive value was 82% for those sites with increased activity and 100% for those sites with decreased activity. Negative predictive value was 63%. In another smaller study, 9 patients who underwent whole-body scan, 100% (7 of 7) patients with osteomyelitis had increased uptake corresponding to the site of involvement [56]. In one study of 213 children referred for skeletal scintigraphy because of suspicion for acute hematogenous osteomyelitis who underwent a 3-phase bone scan of the area of interest along with whole-body delayed images, accurate diagnosis was made in 84% of cases without the need for MRI, including 92% of those diagnosed with osteomyelitis, although it should be noted that bone scan was limited regarding soft- tissue and articular pathology [57]. In another study of 65 children who underwent whole-body scan with focused evaluations of the area of interest and the contralateral side, 23 patients who were classified as having osteomyelitis all had abnormal bone scans [58].	3158175
acrac_3158175_7	Osteomyelitis or Septic Arthritis Child Excluding Axial Skeleton PCAs	SPECT/CT offers improved characterization of osseous pathology compared with planar imaging [59]. MRI is generally considered preferable in detection of early manifestations of osteomyelitis, as well as infection of the surrounding soft tissues, because of the rapid progression of the disease [53]. Osteomyelitis or Septic Arthritis-Child CT Area of Interest There is no relevant literature regarding the use of CT as the next imaging study in evaluation of osteomyelitis or septic arthritis in children under 5 years of age. Image-Guided Aspiration Area of Interest Primary differential considerations when a joint effusion is present in the absence of trauma are transient synovitis and septic arthritis. Although the most common locations of septic arthritis are the knee and hip joints, this can affect any joint [60]. Although most nontraumatic hip joint effusions are secondary to transient synovitis, early diagnosis of septic arthritis is extremely important in preventing complications, and US-guided hip aspiration is considered highly accurate for diagnosis [43,61]. In one study, 100% of children were confirmed to have septic hip arthritis via bedside joint aspiration and were able to avoid arthrotomy. However, it should be noted than US guidance for aspiration was only provided in one case, and the remainder were performed using anatomic landmarks without imaging guidance [62]. In the setting of confirmed transient synovitis, children who underwent US-guided joint aspiration experienced shorter duration of stay and shorter duration of a limp compared with those who did not undergo joint aspiration [61]. In patients with suspected or confirmed septic arthritis, femoral neck aspiration performed at the time of incision and drainage was noted to improve diagnosis of concurrent osteomyelitis compared with preoperative MRI alone [63].	Osteomyelitis or Septic Arthritis Child Excluding Axial Skeleton PCAs. SPECT/CT offers improved characterization of osseous pathology compared with planar imaging [59]. MRI is generally considered preferable in detection of early manifestations of osteomyelitis, as well as infection of the surrounding soft tissues, because of the rapid progression of the disease [53]. Osteomyelitis or Septic Arthritis-Child CT Area of Interest There is no relevant literature regarding the use of CT as the next imaging study in evaluation of osteomyelitis or septic arthritis in children under 5 years of age. Image-Guided Aspiration Area of Interest Primary differential considerations when a joint effusion is present in the absence of trauma are transient synovitis and septic arthritis. Although the most common locations of septic arthritis are the knee and hip joints, this can affect any joint [60]. Although most nontraumatic hip joint effusions are secondary to transient synovitis, early diagnosis of septic arthritis is extremely important in preventing complications, and US-guided hip aspiration is considered highly accurate for diagnosis [43,61]. In one study, 100% of children were confirmed to have septic hip arthritis via bedside joint aspiration and were able to avoid arthrotomy. However, it should be noted than US guidance for aspiration was only provided in one case, and the remainder were performed using anatomic landmarks without imaging guidance [62]. In the setting of confirmed transient synovitis, children who underwent US-guided joint aspiration experienced shorter duration of stay and shorter duration of a limp compared with those who did not undergo joint aspiration [61]. In patients with suspected or confirmed septic arthritis, femoral neck aspiration performed at the time of incision and drainage was noted to improve diagnosis of concurrent osteomyelitis compared with preoperative MRI alone [63].	3158175
acrac_3158175_8	Osteomyelitis or Septic Arthritis Child Excluding Axial Skeleton PCAs	Although some studies have shown no significant difference in sensitivity and specificity in the diagnosis of osteomyelitis or septic arthritis with or without the use of gadolinium-based contrast agents, IV contrast has been shown to improve detection of abscesses [32,33]. Decreased femoral head enhancement on early postcontrast imaging has been noted as a reliable feature of septic arthritis not seen in transient synovitis, and diminished femoral head enhancement on MRI has been noted in the setting of septic arthritis in children under 12 months of age correlated with development of secondary osteomyelitis [34,35]. Contrast has been shown to markedly improve detection of infection of unossified growth cartilage (chondritis) in children <6 years of age, in which the cartilage most commonly appeared normal on unenhanced sequences; hypoenhancement was more commonly noted with infection [36,37]. In one study of children <18 months of age with community acquired S aureus infection of the unossified epiphyseal cartilage, 7 of 9 cases demonstrated normal cartilage signal on noncontrast sequences; hypoenhancement or nonenhancement of involved foci was used for diagnosis [36]. In another study of children <6 years of age, focal or global cartilage nonenhancement was demonstrated in 71% of 14 patients with surgically confirmed epiphyseal osteomyelitis, compared with 21% of controls [37]. Global enhancement defects were more sensitive, noted in 43% of cases but not seen in any control cases. Repeat MRI of the area of interest performed for worsening or persistent symptoms resulted in clinical management changes in 21% of patients [64]. In one study on septic elbow arthritis, 40% of patients did not respond to antibiotic therapy and were noted on subsequent elbow MRI to have concurrent osteomyelitis [60].	Osteomyelitis or Septic Arthritis Child Excluding Axial Skeleton PCAs. Although some studies have shown no significant difference in sensitivity and specificity in the diagnosis of osteomyelitis or septic arthritis with or without the use of gadolinium-based contrast agents, IV contrast has been shown to improve detection of abscesses [32,33]. Decreased femoral head enhancement on early postcontrast imaging has been noted as a reliable feature of septic arthritis not seen in transient synovitis, and diminished femoral head enhancement on MRI has been noted in the setting of septic arthritis in children under 12 months of age correlated with development of secondary osteomyelitis [34,35]. Contrast has been shown to markedly improve detection of infection of unossified growth cartilage (chondritis) in children <6 years of age, in which the cartilage most commonly appeared normal on unenhanced sequences; hypoenhancement was more commonly noted with infection [36,37]. In one study of children <18 months of age with community acquired S aureus infection of the unossified epiphyseal cartilage, 7 of 9 cases demonstrated normal cartilage signal on noncontrast sequences; hypoenhancement or nonenhancement of involved foci was used for diagnosis [36]. In another study of children <6 years of age, focal or global cartilage nonenhancement was demonstrated in 71% of 14 patients with surgically confirmed epiphyseal osteomyelitis, compared with 21% of controls [37]. Global enhancement defects were more sensitive, noted in 43% of cases but not seen in any control cases. Repeat MRI of the area of interest performed for worsening or persistent symptoms resulted in clinical management changes in 21% of patients [64]. In one study on septic elbow arthritis, 40% of patients did not respond to antibiotic therapy and were noted on subsequent elbow MRI to have concurrent osteomyelitis [60].	3158175
acrac_3158175_9	Osteomyelitis or Septic Arthritis Child Excluding Axial Skeleton PCAs	MRI Extremity Area of Interest In one study, a large field-of-view MRI was performed to encompass both lower extremities rather than the area of concern [38]. In patients who were later found to have osteomyelitis, 11% had contralateral extremity findings, including contralateral osteomyelitis, and 20% had ipsilateral septic arthritis. Among patients who did not have osteomyelitis, 20% had contralateral abnormalities; most common diagnoses included stress reaction, soft-tissue edema, myositis, sterile joint effusion, and leukemia. Osteomyelitis or Septic Arthritis-Child US Area of Interest US is a highly sensitive method of diagnosing hip joint effusion, and the absence of hip joint effusion virtually excludes septic arthritis; a false negative rate of 5% has been described, noted in patients with a shorter duration of symptoms (<1 day) [40,43,45-47]. US can reportedly detect hip effusions as small as 1 mL [44]. Hip US for the purpose of identifying joint effusion can be performed with high sensitivity and specificity [48]. In one study, nearly 80% of pediatric patients with hip septic arthritis required US imaging alone to guide their management [45]. US in evaluation of osteomyelitis is limited in its ability to assess the osseous structures but can identify abutting inflammatory changes affecting the soft tissues such as periosteal elevation and subperiosteal collections [40,49,50]. Although some studies have shown no significant difference in sensitivity and specificity in diagnosis of osteomyelitis or septic arthritis with or without the use of gadolinium-based contrast agents, contrast has been shown to improve detection of abscesses [32,33]. Decreased femoral head enhancement on early postcontrast imaging has been noted as a reliable feature of septic arthritis not seen in transient synovitis [34]. In addition, MRI has been shown to be useful in evaluating for concurrent musculoskeletal infection.	Osteomyelitis or Septic Arthritis Child Excluding Axial Skeleton PCAs. MRI Extremity Area of Interest In one study, a large field-of-view MRI was performed to encompass both lower extremities rather than the area of concern [38]. In patients who were later found to have osteomyelitis, 11% had contralateral extremity findings, including contralateral osteomyelitis, and 20% had ipsilateral septic arthritis. Among patients who did not have osteomyelitis, 20% had contralateral abnormalities; most common diagnoses included stress reaction, soft-tissue edema, myositis, sterile joint effusion, and leukemia. Osteomyelitis or Septic Arthritis-Child US Area of Interest US is a highly sensitive method of diagnosing hip joint effusion, and the absence of hip joint effusion virtually excludes septic arthritis; a false negative rate of 5% has been described, noted in patients with a shorter duration of symptoms (<1 day) [40,43,45-47]. US can reportedly detect hip effusions as small as 1 mL [44]. Hip US for the purpose of identifying joint effusion can be performed with high sensitivity and specificity [48]. In one study, nearly 80% of pediatric patients with hip septic arthritis required US imaging alone to guide their management [45]. US in evaluation of osteomyelitis is limited in its ability to assess the osseous structures but can identify abutting inflammatory changes affecting the soft tissues such as periosteal elevation and subperiosteal collections [40,49,50]. Although some studies have shown no significant difference in sensitivity and specificity in diagnosis of osteomyelitis or septic arthritis with or without the use of gadolinium-based contrast agents, contrast has been shown to improve detection of abscesses [32,33]. Decreased femoral head enhancement on early postcontrast imaging has been noted as a reliable feature of septic arthritis not seen in transient synovitis [34]. In addition, MRI has been shown to be useful in evaluating for concurrent musculoskeletal infection.	3158175
acrac_3158175_10	Osteomyelitis or Septic Arthritis Child Excluding Axial Skeleton PCAs	In assessment of septic arthritis, the majority of pediatric patients with septic arthritis were noted on MRI to have infection beyond the joint space, though this may vary based on population factors such as geography [7,46,60,65,66]. Conversely, in metaphyseal osteomyelitis, >50% in one study were noted on MRI to have concomitant joint effusions, 75% of which were confirmed to be septic arthritis [67]. Osteomyelitis or Septic Arthritis-Child MRI Extremity Area of Interest In one study, a large field-of-view MRI was performed to encompass both lower extremities rather than the area of concern [38]. In patients who were later found to have osteomyelitis, 11% had contralateral extremity findings, including contralateral osteomyelitis, and 20% had ipsilateral septic arthritis. Among patients who did not have osteomyelitis, 20% had contralateral abnormalities, most commonly stress reaction, soft-tissue edema, myositis, joint effusion (not septic), and leukemia. Radiography Area of Interest Radiographs are not sensitive in assessment of early osteomyelitis because bone destruction does not typically occur until 7 to 10 days into the disease course, and radiographs are normal until >30% osseous matrix destruction has occurred [24,40]. Radiographs, however, do have utility in all populations in excluding other entities that may mimic acute osteomyelitis, such as fracture or neoplasm [3,25,31,40]. Radiographs are highly variable in identifying hip joint effusions, with sensitivity ranging from 20% to 73% [40,42,43]. US Area of Interest US is a highly sensitive method of diagnosing hip joint effusion, and the absence of hip joint effusion virtually excludes septic arthritis; a false negative rate of 5% has been described, noted in patients with a shorter duration of symptoms (<1 day) [40,43,45-47]. US can reportedly detect hip effusions as small as 1 mL [44].	Osteomyelitis or Septic Arthritis Child Excluding Axial Skeleton PCAs. In assessment of septic arthritis, the majority of pediatric patients with septic arthritis were noted on MRI to have infection beyond the joint space, though this may vary based on population factors such as geography [7,46,60,65,66]. Conversely, in metaphyseal osteomyelitis, >50% in one study were noted on MRI to have concomitant joint effusions, 75% of which were confirmed to be septic arthritis [67]. Osteomyelitis or Septic Arthritis-Child MRI Extremity Area of Interest In one study, a large field-of-view MRI was performed to encompass both lower extremities rather than the area of concern [38]. In patients who were later found to have osteomyelitis, 11% had contralateral extremity findings, including contralateral osteomyelitis, and 20% had ipsilateral septic arthritis. Among patients who did not have osteomyelitis, 20% had contralateral abnormalities, most commonly stress reaction, soft-tissue edema, myositis, joint effusion (not septic), and leukemia. Radiography Area of Interest Radiographs are not sensitive in assessment of early osteomyelitis because bone destruction does not typically occur until 7 to 10 days into the disease course, and radiographs are normal until >30% osseous matrix destruction has occurred [24,40]. Radiographs, however, do have utility in all populations in excluding other entities that may mimic acute osteomyelitis, such as fracture or neoplasm [3,25,31,40]. Radiographs are highly variable in identifying hip joint effusions, with sensitivity ranging from 20% to 73% [40,42,43]. US Area of Interest US is a highly sensitive method of diagnosing hip joint effusion, and the absence of hip joint effusion virtually excludes septic arthritis; a false negative rate of 5% has been described, noted in patients with a shorter duration of symptoms (<1 day) [40,43,45-47]. US can reportedly detect hip effusions as small as 1 mL [44].	3158175
acrac_3158175_11	Osteomyelitis or Septic Arthritis Child Excluding Axial Skeleton PCAs	Hip US for the purpose of identifying joint effusion can be performed with high sensitivity and specificity [48]. In one study, nearly 80% of pediatric patients with hip septic arthritis required US imaging alone to guide their management [45]. US in evaluation of osteomyelitis is limited in its ability to assess the osseous structures but can identify abutting inflammatory changes affecting the soft tissues such as periosteal elevation and subperiosteal collections [40,49,50]. Bone Scan Whole Body Whole-body bone scan is typically recommended when scintigraphy is used for suspected osteomyelitis, particularly if there is a fever of unknown origin or bacteremia [54]. One study assessed the accuracy of bone scan for the diagnosis of suspected acute hematogenous osteomyelitis and septic arthritis in 86 children, using whole- body and selected static images, without blood flow or blood pool views [55]. Bone scan findings were correlated with the final diagnosis in 34 sites of septic arthritis and in 62 sites of osteomyelitis. Bone scan accuracy was 81%. Positive predictive value was 82% for those sites with increased activity and 100% for those sites with decreased activity. Negative predictive value was 63%. In another smaller study, 9 patients who underwent whole-body scan, Osteomyelitis or Septic Arthritis-Child 100% (7 of 7) patients with osteomyelitis had increased uptake corresponding to the site of involvement [56]. SPECT/CT offers improved characterization of osseous pathology compared to planar imaging [59]. MRI is generally considered preferable in detection of early manifestations of osteomyelitis, as well as infection of the surrounding soft tissues, because of the rapid progression of the disease [53]. Bone Scan Whole Body and 3-Phase Bone Scan Area of Interest Whole-body bone scan is typically recommended when scintigraphy is used for suspected osteomyelitis, particularly if there is a fever of unknown origin or bacteremia [54].	Osteomyelitis or Septic Arthritis Child Excluding Axial Skeleton PCAs. Hip US for the purpose of identifying joint effusion can be performed with high sensitivity and specificity [48]. In one study, nearly 80% of pediatric patients with hip septic arthritis required US imaging alone to guide their management [45]. US in evaluation of osteomyelitis is limited in its ability to assess the osseous structures but can identify abutting inflammatory changes affecting the soft tissues such as periosteal elevation and subperiosteal collections [40,49,50]. Bone Scan Whole Body Whole-body bone scan is typically recommended when scintigraphy is used for suspected osteomyelitis, particularly if there is a fever of unknown origin or bacteremia [54]. One study assessed the accuracy of bone scan for the diagnosis of suspected acute hematogenous osteomyelitis and septic arthritis in 86 children, using whole- body and selected static images, without blood flow or blood pool views [55]. Bone scan findings were correlated with the final diagnosis in 34 sites of septic arthritis and in 62 sites of osteomyelitis. Bone scan accuracy was 81%. Positive predictive value was 82% for those sites with increased activity and 100% for those sites with decreased activity. Negative predictive value was 63%. In another smaller study, 9 patients who underwent whole-body scan, Osteomyelitis or Septic Arthritis-Child 100% (7 of 7) patients with osteomyelitis had increased uptake corresponding to the site of involvement [56]. SPECT/CT offers improved characterization of osseous pathology compared to planar imaging [59]. MRI is generally considered preferable in detection of early manifestations of osteomyelitis, as well as infection of the surrounding soft tissues, because of the rapid progression of the disease [53]. Bone Scan Whole Body and 3-Phase Bone Scan Area of Interest Whole-body bone scan is typically recommended when scintigraphy is used for suspected osteomyelitis, particularly if there is a fever of unknown origin or bacteremia [54].	3158175
acrac_3158175_12	Osteomyelitis or Septic Arthritis Child Excluding Axial Skeleton PCAs	In one study of 213 children referred for skeletal scintigraphy because of a suspicion for acute hematogenous osteomyelitis who underwent a 3-phase bone scan of the area of interest along with whole-body delayed images, accurate diagnosis was made in 84% of cases without the need for MRI, including 92% of those diagnosed with osteomyelitis [57]. In another study of 65 children who underwent whole-body scan with focused evaluations of the area of interest and the contralateral side, 23 patients who were classified as having osteomyelitis all had abnormal bone scans [58]. SPECT/CT offers improved characterization of osseous pathology compared with planar imaging [59]. MRI is generally considered preferable in detection of early manifestations of osteomyelitis, as well as infection of the surrounding soft tissues, because of the rapid progression of the disease, but SPECT/CT offers improved characterization of osseous pathology compared with planar imaging [53,59]. Image-Guided Aspiration Area of Interest Primary differential considerations when a joint effusion is present in the absence of trauma are transient synovitis and septic arthritis. Though most nontraumatic hip joint effusions are secondary to transient synovitis, early diagnosis of septic arthritis is extremely important in preventing complications, and US-guided hip aspiration is considered highly accurate for diagnosis [43,61]. In one study, 100% of children were confirmed to have septic hip arthritis via bedside joint aspiration and were able to avoid arthrotomy. However, it should be noted than US guidance for aspiration was only provided in one case, and the remainder were performed using anatomic landmarks and without imaging guidance [62]. In the setting of confirmed transient synovitis, children who underwent US- guided joint aspiration experienced shorter duration of stay and shorter duration of a limp compared with those who did not undergo joint aspiration [61].	Osteomyelitis or Septic Arthritis Child Excluding Axial Skeleton PCAs. In one study of 213 children referred for skeletal scintigraphy because of a suspicion for acute hematogenous osteomyelitis who underwent a 3-phase bone scan of the area of interest along with whole-body delayed images, accurate diagnosis was made in 84% of cases without the need for MRI, including 92% of those diagnosed with osteomyelitis [57]. In another study of 65 children who underwent whole-body scan with focused evaluations of the area of interest and the contralateral side, 23 patients who were classified as having osteomyelitis all had abnormal bone scans [58]. SPECT/CT offers improved characterization of osseous pathology compared with planar imaging [59]. MRI is generally considered preferable in detection of early manifestations of osteomyelitis, as well as infection of the surrounding soft tissues, because of the rapid progression of the disease, but SPECT/CT offers improved characterization of osseous pathology compared with planar imaging [53,59]. Image-Guided Aspiration Area of Interest Primary differential considerations when a joint effusion is present in the absence of trauma are transient synovitis and septic arthritis. Though most nontraumatic hip joint effusions are secondary to transient synovitis, early diagnosis of septic arthritis is extremely important in preventing complications, and US-guided hip aspiration is considered highly accurate for diagnosis [43,61]. In one study, 100% of children were confirmed to have septic hip arthritis via bedside joint aspiration and were able to avoid arthrotomy. However, it should be noted than US guidance for aspiration was only provided in one case, and the remainder were performed using anatomic landmarks and without imaging guidance [62]. In the setting of confirmed transient synovitis, children who underwent US- guided joint aspiration experienced shorter duration of stay and shorter duration of a limp compared with those who did not undergo joint aspiration [61].	3158175
acrac_3158175_13	Osteomyelitis or Septic Arthritis Child Excluding Axial Skeleton PCAs	In patients with suspected or confirmed septic arthritis, femoral neck aspiration performed at the time of incision and drainage was noted to improve diagnosis of concurrent osteomyelitis compared with preoperative MRI alone [63]. Although the bulk of literature on image-guided joint aspiration in the pediatric population refers to the hip joint, aspiration could also be considered in other joints. Although some studies have shown no significant difference in sensitivity and specificity in the diagnosis of osteomyelitis or septic arthritis with or without the use of gadolinium-based contrast agents, contrast has been shown to improve detection of abscesses [32,33]. Decreased femoral head enhancement on early postcontrast imaging has been noted as a reliable feature of septic arthritis not seen in transient synovitis [34]. In addition, MRI has been shown to be useful in evaluating for concurrent musculoskeletal infection. In assessment of septic arthritis, the majority of pediatric patients with septic arthritis were noted on MRI to have infection beyond the joint space, although this may vary based on population factors such as geography [7,46,60,65,66]. Conversely, in metaphyseal osteomyelitis, over 50% in one study were noted on MRI to have concomitant joint effusions, 75% of which were confirmed to be septic arthritis [67]. Osteomyelitis or Septic Arthritis-Child Repeat MRI of the area of interest performed for worsening or persistent symptoms resulted in clinical management changes in 21% of patients [64]. In one study on septic elbow arthritis, 40% of patients did not respond to antibiotic therapy and were noted on subsequent elbow MRI to have concurrent osteomyelitis [60]. MRI Extremity Area of Interest In one study, a large field-of-view MRI was performed to encompass both lower extremities rather than the area of concern [38].	Osteomyelitis or Septic Arthritis Child Excluding Axial Skeleton PCAs. In patients with suspected or confirmed septic arthritis, femoral neck aspiration performed at the time of incision and drainage was noted to improve diagnosis of concurrent osteomyelitis compared with preoperative MRI alone [63]. Although the bulk of literature on image-guided joint aspiration in the pediatric population refers to the hip joint, aspiration could also be considered in other joints. Although some studies have shown no significant difference in sensitivity and specificity in the diagnosis of osteomyelitis or septic arthritis with or without the use of gadolinium-based contrast agents, contrast has been shown to improve detection of abscesses [32,33]. Decreased femoral head enhancement on early postcontrast imaging has been noted as a reliable feature of septic arthritis not seen in transient synovitis [34]. In addition, MRI has been shown to be useful in evaluating for concurrent musculoskeletal infection. In assessment of septic arthritis, the majority of pediatric patients with septic arthritis were noted on MRI to have infection beyond the joint space, although this may vary based on population factors such as geography [7,46,60,65,66]. Conversely, in metaphyseal osteomyelitis, over 50% in one study were noted on MRI to have concomitant joint effusions, 75% of which were confirmed to be septic arthritis [67]. Osteomyelitis or Septic Arthritis-Child Repeat MRI of the area of interest performed for worsening or persistent symptoms resulted in clinical management changes in 21% of patients [64]. In one study on septic elbow arthritis, 40% of patients did not respond to antibiotic therapy and were noted on subsequent elbow MRI to have concurrent osteomyelitis [60]. MRI Extremity Area of Interest In one study, a large field-of-view MRI was performed to encompass both lower extremities rather than the area of concern [38].	3158175
acrac_3158175_14	Osteomyelitis or Septic Arthritis Child Excluding Axial Skeleton PCAs	In patients who were later found to have osteomyelitis, 11% had contralateral extremity findings, including contralateral osteomyelitis, and 20% had ipsilateral septic arthritis. Among patients who did not have osteomyelitis, 20% had contralateral abnormalities, most commonly stress reaction, soft-tissue edema, myositis, joint effusion (not septic), and leukemia. US Area of Interest US is a highly sensitive method of diagnosing hip joint effusion, and the absence of hip joint effusion virtually excludes septic arthritis; a false negative rate of 5% has been described, noted in patients with a shorter duration of symptoms (<1 day) [40,43,45-47]. US can reportedly detect hip effusions as small as 1 mL [44]. Hip US for the purpose of identifying joint effusion can be performed with high sensitivity and specificity [48]. In one study, nearly 80% of pediatric patients with hip septic arthritis required US imaging alone to guide their management [45]. US in evaluation of osteomyelitis is limited in its ability to assess the osseous structures but can identify abutting inflammatory changes affecting the soft tissues such as periosteal elevation and subperiosteal collections [40,49,50]. 3-Phase Bone Scan Area of Interest There is limited data regarding the use of 3-phase bone scan of area of interest as the next imaging study in evaluation of septic arthritis. In one study in which blood pool and delayed imaging of only the area of interest were performed, 8 of 9 cases of septic arthritis were identified [51]. Bone Scan Whole Body There is limited data regarding the use of whole-body bone scan as the next imaging study in the evaluation of septic arthritis. One study assessed the accuracy of bone scan for the diagnosis of suspected acute hematogenous osteomyelitis and septic arthritis in 86 children, using whole-body and selected static images, without blood flow or blood pool views [55].	Osteomyelitis or Septic Arthritis Child Excluding Axial Skeleton PCAs. In patients who were later found to have osteomyelitis, 11% had contralateral extremity findings, including contralateral osteomyelitis, and 20% had ipsilateral septic arthritis. Among patients who did not have osteomyelitis, 20% had contralateral abnormalities, most commonly stress reaction, soft-tissue edema, myositis, joint effusion (not septic), and leukemia. US Area of Interest US is a highly sensitive method of diagnosing hip joint effusion, and the absence of hip joint effusion virtually excludes septic arthritis; a false negative rate of 5% has been described, noted in patients with a shorter duration of symptoms (<1 day) [40,43,45-47]. US can reportedly detect hip effusions as small as 1 mL [44]. Hip US for the purpose of identifying joint effusion can be performed with high sensitivity and specificity [48]. In one study, nearly 80% of pediatric patients with hip septic arthritis required US imaging alone to guide their management [45]. US in evaluation of osteomyelitis is limited in its ability to assess the osseous structures but can identify abutting inflammatory changes affecting the soft tissues such as periosteal elevation and subperiosteal collections [40,49,50]. 3-Phase Bone Scan Area of Interest There is limited data regarding the use of 3-phase bone scan of area of interest as the next imaging study in evaluation of septic arthritis. In one study in which blood pool and delayed imaging of only the area of interest were performed, 8 of 9 cases of septic arthritis were identified [51]. Bone Scan Whole Body There is limited data regarding the use of whole-body bone scan as the next imaging study in the evaluation of septic arthritis. One study assessed the accuracy of bone scan for the diagnosis of suspected acute hematogenous osteomyelitis and septic arthritis in 86 children, using whole-body and selected static images, without blood flow or blood pool views [55].	3158175
acrac_3158175_15	Osteomyelitis or Septic Arthritis Child Excluding Axial Skeleton PCAs	Bone scan findings were correlated with the final diagnosis in 34 sites of septic arthritis and in 62 sites of osteomyelitis. Bone scan accuracy was 81%. Positive predictive value was 82% for those sites with increased activity and 100% for those sites with decreased activity. Negative predictive value was 63%. Bone Scan Whole Body and 3-Phase Bone Scan Area of Interest There is no relevant recent regarding the use of whole-body bone scan and 3-phase bone scan of area of interest as the next imaging study in the evaluation of suspected septic arthritis. CT Area of Interest There is no relevant literature regarding the use of CT as the next imaging study in the evaluation of suspected septic arthritis. Image-Guided Aspiration Area of Interest Early diagnosis of septic arthritis is extremely important in preventing complications, and US-guided hip aspiration is considered highly accurate [43,61]. In one study, 100% of children were confirmed to have septic hip arthritis via bedside joint aspiration and were able to avoid arthrotomy. However, it should be noted that US guidance for Osteomyelitis or Septic Arthritis-Child aspiration was only provided in one case, and the remainder performed using anatomic landmarks without imaging guidance [62]. In the setting of confirmed transient synovitis, children who underwent US-guided joint aspiration experienced shorter duration of stay and shorter duration of limp compared with those who did not undergo joint aspiration [61]. In patients with suspected or confirmed septic arthritis, femoral neck aspiration performed at the time of incision and drainage was noted to improve diagnosis of concurrent osteomyelitis compared with preoperative MRI alone [63].	Osteomyelitis or Septic Arthritis Child Excluding Axial Skeleton PCAs. Bone scan findings were correlated with the final diagnosis in 34 sites of septic arthritis and in 62 sites of osteomyelitis. Bone scan accuracy was 81%. Positive predictive value was 82% for those sites with increased activity and 100% for those sites with decreased activity. Negative predictive value was 63%. Bone Scan Whole Body and 3-Phase Bone Scan Area of Interest There is no relevant recent regarding the use of whole-body bone scan and 3-phase bone scan of area of interest as the next imaging study in the evaluation of suspected septic arthritis. CT Area of Interest There is no relevant literature regarding the use of CT as the next imaging study in the evaluation of suspected septic arthritis. Image-Guided Aspiration Area of Interest Early diagnosis of septic arthritis is extremely important in preventing complications, and US-guided hip aspiration is considered highly accurate [43,61]. In one study, 100% of children were confirmed to have septic hip arthritis via bedside joint aspiration and were able to avoid arthrotomy. However, it should be noted that US guidance for Osteomyelitis or Septic Arthritis-Child aspiration was only provided in one case, and the remainder performed using anatomic landmarks without imaging guidance [62]. In the setting of confirmed transient synovitis, children who underwent US-guided joint aspiration experienced shorter duration of stay and shorter duration of limp compared with those who did not undergo joint aspiration [61]. In patients with suspected or confirmed septic arthritis, femoral neck aspiration performed at the time of incision and drainage was noted to improve diagnosis of concurrent osteomyelitis compared with preoperative MRI alone [63].	3158175
acrac_69482_0	Headache PCAs	Initial Imaging Definition Initial imaging is defined as imaging at the beginning of the care episode for the medical condition defined by the variant. More than one procedure can be considered usually appropriate in the initial imaging evaluation when: aColumbia University Medical Center, New York, New York. bPanel Chair, Uniformed Services University, Bethesda, Maryland. cOhio State University, Columbus, Ohio. dWake Forest School of Medicine, Winston Salem, North Carolina; American Geriatrics Society. eStanford University, Stanford, California, Primary care physician. fIndiana University School of Medicine, Indianapolis, Indiana; Committee on Emergency Radiology-GSER. gMayo Clinic, Rochester, Minnesota; Commission on Nuclear Medicine and Molecular Imaging. hWeill Cornell Medical College, New York, New York. iUniversity of California Los Angeles, Los Angeles, California. jEinstein Healthcare Network, Philadelphia, Pennsylvania. kFort Belvoir Community Hospital, Fort Belvoir, Virginia; American Academy of Family Physicians. lUniversity of California San Diego, San Diego, California. mOregon Health & Science University, Portland, Oregon. nSouthern California Permanente Medical Group, Pasadena, California; American Academy of Neurology. oWeill Cornell Medical College, New York, New York; American Academy of Otolaryngology-Head and Neck Surgery. pSchmidt College of Medicine, Florida Atlantic University, Boca Raton, Florida; American College of Emergency Physicians. qThe University of Vermont Medical Center, Burlington, Vermont. rOakland University William Beaumont School of Medicine, Rochester, Michigan; American Association of Neurological Surgeons/Congress of Neurological Surgeons. sUniversity of Cincinnati Medical Center, Cincinnati, Ohio. tSpecialty Chair, Montefiore Medical Center, Bronx, New York.	Headache PCAs. Initial Imaging Definition Initial imaging is defined as imaging at the beginning of the care episode for the medical condition defined by the variant. More than one procedure can be considered usually appropriate in the initial imaging evaluation when: aColumbia University Medical Center, New York, New York. bPanel Chair, Uniformed Services University, Bethesda, Maryland. cOhio State University, Columbus, Ohio. dWake Forest School of Medicine, Winston Salem, North Carolina; American Geriatrics Society. eStanford University, Stanford, California, Primary care physician. fIndiana University School of Medicine, Indianapolis, Indiana; Committee on Emergency Radiology-GSER. gMayo Clinic, Rochester, Minnesota; Commission on Nuclear Medicine and Molecular Imaging. hWeill Cornell Medical College, New York, New York. iUniversity of California Los Angeles, Los Angeles, California. jEinstein Healthcare Network, Philadelphia, Pennsylvania. kFort Belvoir Community Hospital, Fort Belvoir, Virginia; American Academy of Family Physicians. lUniversity of California San Diego, San Diego, California. mOregon Health & Science University, Portland, Oregon. nSouthern California Permanente Medical Group, Pasadena, California; American Academy of Neurology. oWeill Cornell Medical College, New York, New York; American Academy of Otolaryngology-Head and Neck Surgery. pSchmidt College of Medicine, Florida Atlantic University, Boca Raton, Florida; American College of Emergency Physicians. qThe University of Vermont Medical Center, Burlington, Vermont. rOakland University William Beaumont School of Medicine, Rochester, Michigan; American Association of Neurological Surgeons/Congress of Neurological Surgeons. sUniversity of Cincinnati Medical Center, Cincinnati, Ohio. tSpecialty Chair, Montefiore Medical Center, Bronx, New York.	69482
acrac_69482_1	Headache PCAs	The American College of Radiology seeks and encourages collaboration with other organizations on the development of the ACR Appropriateness Criteria through representation of such organizations on expert panels. Participation on the expert panel does not necessarily imply endorsement of the final document by individual contributors or their respective organization. Reprint requests to: publications@acr.org OR Headache Discussion of Procedures by Variant Variant 1: Sudden onset severe headache that reaches maximal severity within one hour. Initial imaging. Many of the headaches presenting to the emergency department are benign or primary; however, a subset of headaches defined as TCH warrant further investigation. The most important feature of TCH is the abrupt onset of a severe headache that reaches maximum intensity in <1 minute, although for the purposes of this discussion, the term will be used more loosely to encompass the sudden onset of a severe headache that reaches maximum intensity in <1 hour. Initially used in reference to the pain associated with leaking or ruptured intracranial aneurysms, other etiologies of TCH have since been identified [10,11]. Ruptured aneurysm resulting in subarachnoid hemorrhage (SAH) is the primary concern because of significant morbidity and mortality, although it accounts for only 4% to 12% of acute severe headaches [11]. Reversible cerebral vasoconstriction syndrome (RCVS) is the second most common cause of TCH and is the most common cause of TCH without aneurysmal SAH. Associated complications include intracranial hemorrhage and ischemic infarction [12]. RCVS is an important cause of recurrent TCH; half of RCVS headaches can be attributed to a specific trigger [10,12].	Headache PCAs. The American College of Radiology seeks and encourages collaboration with other organizations on the development of the ACR Appropriateness Criteria through representation of such organizations on expert panels. Participation on the expert panel does not necessarily imply endorsement of the final document by individual contributors or their respective organization. Reprint requests to: publications@acr.org OR Headache Discussion of Procedures by Variant Variant 1: Sudden onset severe headache that reaches maximal severity within one hour. Initial imaging. Many of the headaches presenting to the emergency department are benign or primary; however, a subset of headaches defined as TCH warrant further investigation. The most important feature of TCH is the abrupt onset of a severe headache that reaches maximum intensity in <1 minute, although for the purposes of this discussion, the term will be used more loosely to encompass the sudden onset of a severe headache that reaches maximum intensity in <1 hour. Initially used in reference to the pain associated with leaking or ruptured intracranial aneurysms, other etiologies of TCH have since been identified [10,11]. Ruptured aneurysm resulting in subarachnoid hemorrhage (SAH) is the primary concern because of significant morbidity and mortality, although it accounts for only 4% to 12% of acute severe headaches [11]. Reversible cerebral vasoconstriction syndrome (RCVS) is the second most common cause of TCH and is the most common cause of TCH without aneurysmal SAH. Associated complications include intracranial hemorrhage and ischemic infarction [12]. RCVS is an important cause of recurrent TCH; half of RCVS headaches can be attributed to a specific trigger [10,12].	69482
acrac_69482_2	Headache PCAs	Less common causes of TCH include cerebral venous thrombosis (CVT), cervical arterial dissection, posterior reversible encephalopathy syndrome (PRES), spontaneous intracranial hypotension (SIH), pituitary apoplexy, perimesencephalic hemorrhage, arteriovenous malformations (AVM), dural arteriovenous fistulas, and intraventricular colloid cyst. A subset of patients will not have a causative disorder and will be diagnosed as suffering from primary TCH; this is a diagnosis of exclusion [10,11,13]. Arteriography Cervicocerebral There is no relevant literature to support the use of cervicocerebral arteriography in the initial evaluation of TCH; it may have utility in follow-up evaluation after initial neuroimaging. Digital subtraction angiography (DSA) can assess vessel diameters as small as 0.4 mm compared with 0.7 mm for CT angiography (CTA). This may be useful for further workup of etiologies such as RCVS, which primarily impacts the smaller vessels and provides the opportunity for intravascular therapy. For example, intraarterial nimodipine has been used to demonstrate reversibility, a diagnostic criterion for RCVS [12]. Likewise, DSA may have a role in the workup of aneurysm rupture associated with SAH, when no aneurysm is detected on the initial multidetector CTA. The American Heart Association and the American Stroke Association guidelines also suggest that DSA may not be necessary if a classic perimesencephalic pattern of hemorrhage is present on CT with a negative CTA. In cases of suspected CVT or AVM based on initial neuroimaging, catheter angiography may be used for further characterization and for endovascular therapy [11]. CT Head With IV Contrast There is no relevant literature to support the use of CT head with intravenous (IV) contrast in the initial imaging evaluation of TCH. CT Head Without and With IV Contrast There is no relevant literature to support the use of CT head without and with IV contrast in the initial imaging evaluation of TCH. Headache	Headache PCAs. Less common causes of TCH include cerebral venous thrombosis (CVT), cervical arterial dissection, posterior reversible encephalopathy syndrome (PRES), spontaneous intracranial hypotension (SIH), pituitary apoplexy, perimesencephalic hemorrhage, arteriovenous malformations (AVM), dural arteriovenous fistulas, and intraventricular colloid cyst. A subset of patients will not have a causative disorder and will be diagnosed as suffering from primary TCH; this is a diagnosis of exclusion [10,11,13]. Arteriography Cervicocerebral There is no relevant literature to support the use of cervicocerebral arteriography in the initial evaluation of TCH; it may have utility in follow-up evaluation after initial neuroimaging. Digital subtraction angiography (DSA) can assess vessel diameters as small as 0.4 mm compared with 0.7 mm for CT angiography (CTA). This may be useful for further workup of etiologies such as RCVS, which primarily impacts the smaller vessels and provides the opportunity for intravascular therapy. For example, intraarterial nimodipine has been used to demonstrate reversibility, a diagnostic criterion for RCVS [12]. Likewise, DSA may have a role in the workup of aneurysm rupture associated with SAH, when no aneurysm is detected on the initial multidetector CTA. The American Heart Association and the American Stroke Association guidelines also suggest that DSA may not be necessary if a classic perimesencephalic pattern of hemorrhage is present on CT with a negative CTA. In cases of suspected CVT or AVM based on initial neuroimaging, catheter angiography may be used for further characterization and for endovascular therapy [11]. CT Head With IV Contrast There is no relevant literature to support the use of CT head with intravenous (IV) contrast in the initial imaging evaluation of TCH. CT Head Without and With IV Contrast There is no relevant literature to support the use of CT head without and with IV contrast in the initial imaging evaluation of TCH. Headache	69482
acrac_69482_3	Headache PCAs	CT Head Without IV Contrast CT head without IV contrast is useful in the setting of TCH because of its high sensitivity for detecting intracranial hemorrhage. Several studies have demonstrated a high negative predictive value of a noncontrast head CT performed within 6 hours of headache onset in detecting aneurysmal SAH, ranging between 99.9% and 100%. When it is performed within the first 24 hours, the sensitivity ranges between 90% and 100% [16,17]. Ten percent of patients with CVT present with SAH; associated CT abnormalities include venous infarcts, parenchymal edema, or hyperdense thrombus within the occluded sinus. Although SAH is less common in cases of ruptured AVMs, lobar hemorrhage and serpiginous structures representing dilated vasculature can be seen on a noncontrast head CT [11]. In addition, a CTA head with IV contrast may be useful in the setting of TCH when performed in conjunction with a noncontrast head CT (not as an independent initial imaging technique in isolation). There is literature supporting the usefulness of obtaining a head CTA at the same time as a head CT in a patient with TCH, especially when a patient presents with sudden onset severe headache >6 hours, because the sensitivity of head CT for SAH diminishes over time. For suspected cases of RCVS, a noncontrast head CT with special attention to the presence of convexity SAH has been shown to be useful [12] CTA Head With IV Contrast CTA head with IV contrast may be useful in the setting of TCH when performed in conjunction with a noncontrast head CT (not as an independent initial imaging technique in isolation). There is literature supporting the usefulness of obtaining a head CTA at the same time as a head CT in a patient with TCH, especially when a patient presents with sudden onset severe headache >6 hours, because the sensitivity of head CT for SAH diminishes over time.	Headache PCAs. CT Head Without IV Contrast CT head without IV contrast is useful in the setting of TCH because of its high sensitivity for detecting intracranial hemorrhage. Several studies have demonstrated a high negative predictive value of a noncontrast head CT performed within 6 hours of headache onset in detecting aneurysmal SAH, ranging between 99.9% and 100%. When it is performed within the first 24 hours, the sensitivity ranges between 90% and 100% [16,17]. Ten percent of patients with CVT present with SAH; associated CT abnormalities include venous infarcts, parenchymal edema, or hyperdense thrombus within the occluded sinus. Although SAH is less common in cases of ruptured AVMs, lobar hemorrhage and serpiginous structures representing dilated vasculature can be seen on a noncontrast head CT [11]. In addition, a CTA head with IV contrast may be useful in the setting of TCH when performed in conjunction with a noncontrast head CT (not as an independent initial imaging technique in isolation). There is literature supporting the usefulness of obtaining a head CTA at the same time as a head CT in a patient with TCH, especially when a patient presents with sudden onset severe headache >6 hours, because the sensitivity of head CT for SAH diminishes over time. For suspected cases of RCVS, a noncontrast head CT with special attention to the presence of convexity SAH has been shown to be useful [12] CTA Head With IV Contrast CTA head with IV contrast may be useful in the setting of TCH when performed in conjunction with a noncontrast head CT (not as an independent initial imaging technique in isolation). There is literature supporting the usefulness of obtaining a head CTA at the same time as a head CT in a patient with TCH, especially when a patient presents with sudden onset severe headache >6 hours, because the sensitivity of head CT for SAH diminishes over time.	69482
acrac_69482_4	Headache PCAs	For example, a concurrent or follow-up CTA is useful in suspected cases of intracranial aneurysm (ruptured or unruptured), arterial dissection, and RCVS [10-12,18]. CTV Head With IV Contrast There is no relevant literature to support the use of CT venography (CTV) head with IV contrast in the initial imaging evaluation of TCH. Following initial evaluation with a noncontrast head CT, head CTV can be useful when there are clinical or imaging findings suspicious for CVT, which is a less common cause of TCH [11,13]. MRA Head With IV Contrast There is no relevant literature to support the use of MR angiography (MRA) head with IV contrast in the initial imaging evaluation of TCH. MRA Head Without and With IV Contrast There is no relevant literature to support the use of MRA head without and with IV contrast in the initial imaging evaluation of TCH. MRA Head Without IV Contrast There is no relevant literature to support the use of MRA head without IV contrast in the initial imaging evaluation of TCH. However, similar to head CTA, brain MRA can be obtained as a follow-up imaging study when there are clinical or imaging findings concerning for aneurysm, dissection, RCVS, or AVM [11]. MRI Head With IV Contrast There is no relevant literature to support the use of MRI head with IV contrast in the initial imaging evaluation of TCH. MRI Head Without and With IV Contrast There is no relevant literature to support the use of MRI head without and with IV contrast in the initial imaging evaluation of TCH; it may have utility in follow-up evaluation after initial neuroimaging. Contrast-enhanced brain MRI can be useful in the diagnosis of SIH, pituitary apoplexy, and intraventricular colloid cyst, which are rare causes of TCH [11]. High-resolution MRI using vessel wall imaging may be useful in differentiating various vasculitides from RCVS and in identifying dissection of the intracranial vessels, compared with standard MRI.	Headache PCAs. For example, a concurrent or follow-up CTA is useful in suspected cases of intracranial aneurysm (ruptured or unruptured), arterial dissection, and RCVS [10-12,18]. CTV Head With IV Contrast There is no relevant literature to support the use of CT venography (CTV) head with IV contrast in the initial imaging evaluation of TCH. Following initial evaluation with a noncontrast head CT, head CTV can be useful when there are clinical or imaging findings suspicious for CVT, which is a less common cause of TCH [11,13]. MRA Head With IV Contrast There is no relevant literature to support the use of MR angiography (MRA) head with IV contrast in the initial imaging evaluation of TCH. MRA Head Without and With IV Contrast There is no relevant literature to support the use of MRA head without and with IV contrast in the initial imaging evaluation of TCH. MRA Head Without IV Contrast There is no relevant literature to support the use of MRA head without IV contrast in the initial imaging evaluation of TCH. However, similar to head CTA, brain MRA can be obtained as a follow-up imaging study when there are clinical or imaging findings concerning for aneurysm, dissection, RCVS, or AVM [11]. MRI Head With IV Contrast There is no relevant literature to support the use of MRI head with IV contrast in the initial imaging evaluation of TCH. MRI Head Without and With IV Contrast There is no relevant literature to support the use of MRI head without and with IV contrast in the initial imaging evaluation of TCH; it may have utility in follow-up evaluation after initial neuroimaging. Contrast-enhanced brain MRI can be useful in the diagnosis of SIH, pituitary apoplexy, and intraventricular colloid cyst, which are rare causes of TCH [11]. High-resolution MRI using vessel wall imaging may be useful in differentiating various vasculitides from RCVS and in identifying dissection of the intracranial vessels, compared with standard MRI.	69482
acrac_69482_5	Headache PCAs	For example, recent studies have demonstrated concentric thickening of the vessel wall with minimal or no enhancement in RCVS, compared with more eccentric wall thickening and significant wall enhancement in cases of vasculitis [12]. In addition, vessel wall imaging can be used to help identify the ruptured lesion when initial CTA reveals multiple aneurysms [11]. Headache MRI Head Without IV Contrast There is no relevant literature to support the use of MRI head without IV contrast in the initial imaging evaluation of TCH; it may have utility in follow-up evaluation after initial neuroimaging. Brain MRI has been shown to have high sensitivity for SAH when using fluid-attenuated inversion recovery (FLAIR) and T2* or susceptibility-weighted images, especially in the acute phase. FLAIR has been demonstrated to be useful for detecting peripheral or sulcal SAH, and T2* has been demonstrated to be useful for detecting cisternal or intraventricular hemorrhage. However, other studies have identified additional causes of sulcal FLAIR hyperintensity, which is therefore not a specific finding for SAH. Brain MRI has higher contrast resolution than head CT, and as a follow-up examination, it can help delineate parenchymal changes from various other non-SAH etiologies of TCH including RCVS, CVT, and pituitary apoplexy [13,19,20]. MRV Head With IV Contrast There is no relevant literature to support the use of MR venography (MRV) head with IV contrast in the initial imaging evaluation of TCH. Brain MRV can be used as a follow-up imaging study in cases of suspected CVT [11]. MRV Head Without and With IV Contrast There is no relevant literature to support the use of MRV head without and with IV contrast in the initial imaging evaluation of TCH. Brain MRV can be used as a follow-up imaging study in cases of suspected CVT [11]. MRV Head Without IV Contrast There is no relevant literature to support the use of MRV head without IV contrast in the initial imaging evaluation of TCH.	Headache PCAs. For example, recent studies have demonstrated concentric thickening of the vessel wall with minimal or no enhancement in RCVS, compared with more eccentric wall thickening and significant wall enhancement in cases of vasculitis [12]. In addition, vessel wall imaging can be used to help identify the ruptured lesion when initial CTA reveals multiple aneurysms [11]. Headache MRI Head Without IV Contrast There is no relevant literature to support the use of MRI head without IV contrast in the initial imaging evaluation of TCH; it may have utility in follow-up evaluation after initial neuroimaging. Brain MRI has been shown to have high sensitivity for SAH when using fluid-attenuated inversion recovery (FLAIR) and T2* or susceptibility-weighted images, especially in the acute phase. FLAIR has been demonstrated to be useful for detecting peripheral or sulcal SAH, and T2* has been demonstrated to be useful for detecting cisternal or intraventricular hemorrhage. However, other studies have identified additional causes of sulcal FLAIR hyperintensity, which is therefore not a specific finding for SAH. Brain MRI has higher contrast resolution than head CT, and as a follow-up examination, it can help delineate parenchymal changes from various other non-SAH etiologies of TCH including RCVS, CVT, and pituitary apoplexy [13,19,20]. MRV Head With IV Contrast There is no relevant literature to support the use of MR venography (MRV) head with IV contrast in the initial imaging evaluation of TCH. Brain MRV can be used as a follow-up imaging study in cases of suspected CVT [11]. MRV Head Without and With IV Contrast There is no relevant literature to support the use of MRV head without and with IV contrast in the initial imaging evaluation of TCH. Brain MRV can be used as a follow-up imaging study in cases of suspected CVT [11]. MRV Head Without IV Contrast There is no relevant literature to support the use of MRV head without IV contrast in the initial imaging evaluation of TCH.	69482
acrac_69482_6	Headache PCAs	Brain MRV can be used as a follow-up imaging study in cases of suspected CVT [11]. Variant 2: Primary migraine or tension-type headache. Normal neurologic examination. Initial imaging. In a single year, more than half of the adult population suffers from a headache, most often a primary headache such as TTH and migraine, with a prevalence of 21% and 15%, respectively [21]. Based on the 2016 Global Burden of Diseases study, TTHs and migraines have been ranked in the top 10 causes, with the greatest prevalence. Moreover, migraines are ranked as the second leading cause of years living with disability, especially in high- income, high-middle-income, and middle-socio-demographic index quintile countries. Migraine was also ranked as the second leading cause of years living with disability for women in 35 countries [22]. Two major types of migraines are documented: migraine with aura and migraine without aura. Although less disabling than migraine, TTH has a higher lifetime prevalence of 30% to 78% and, therefore, a high socioeconomic impact. The clinical criteria classify TTH into subtypes based on the frequency of headaches (number of days per month) and the presence or absence of pericranial tenderness [23]. Despite the clinical and social impact of the 2 most common primary headaches, various studies have demonstrated very few significant structural abnormalities on neuroimaging in patients presenting to the emergency department and outpatient clinics. The HUNT MRI study performed in middle-aged patients demonstrated that headache sufferers in general demonstrated an increased incidence of intracranial abnormalities, mostly attributed to small nonspecific white matter hyperintensities. This association was near zero when white matter hyperintensities were removed from the analysis [21]. Studies were also conducted examining the incidence of intracranial abnormalities in patients suffering from migraine with and without aura.	Headache PCAs. Brain MRV can be used as a follow-up imaging study in cases of suspected CVT [11]. Variant 2: Primary migraine or tension-type headache. Normal neurologic examination. Initial imaging. In a single year, more than half of the adult population suffers from a headache, most often a primary headache such as TTH and migraine, with a prevalence of 21% and 15%, respectively [21]. Based on the 2016 Global Burden of Diseases study, TTHs and migraines have been ranked in the top 10 causes, with the greatest prevalence. Moreover, migraines are ranked as the second leading cause of years living with disability, especially in high- income, high-middle-income, and middle-socio-demographic index quintile countries. Migraine was also ranked as the second leading cause of years living with disability for women in 35 countries [22]. Two major types of migraines are documented: migraine with aura and migraine without aura. Although less disabling than migraine, TTH has a higher lifetime prevalence of 30% to 78% and, therefore, a high socioeconomic impact. The clinical criteria classify TTH into subtypes based on the frequency of headaches (number of days per month) and the presence or absence of pericranial tenderness [23]. Despite the clinical and social impact of the 2 most common primary headaches, various studies have demonstrated very few significant structural abnormalities on neuroimaging in patients presenting to the emergency department and outpatient clinics. The HUNT MRI study performed in middle-aged patients demonstrated that headache sufferers in general demonstrated an increased incidence of intracranial abnormalities, mostly attributed to small nonspecific white matter hyperintensities. This association was near zero when white matter hyperintensities were removed from the analysis [21]. Studies were also conducted examining the incidence of intracranial abnormalities in patients suffering from migraine with and without aura.	69482
acrac_69482_7	Headache PCAs	It was found that patients with migraine with aura were imaged more frequently and demonstrated an increased incidence of minor intracranial abnormalities such as lacunar infarcts and microvascular ischemic changes. No abnormalities were detected that were of major clinical significance [24]. A study performed in China in 2018 examined 1,070 healthy control patients and 1,070 primary headache sufferers; imaging evaluation included either CT or MRI and found no statistical difference in the detection of intracranial abnormalities: 0.58% in patients with headache and 0.78% in healthy controls [25]. Headache Arteriography Cervicocerebral There is no relevant literature to support the use of cervicocerebral arteriography in the initial imaging evaluation of primary migraine or TTH with a normal neurologic examination. CT Head With IV Contrast There is no relevant literature to support the use of CT head with IV contrast in the initial imaging evaluation of primary migraine or TTH with a normal neurologic examination. CT Head Without and With IV Contrast There is no relevant literature to support the use of CT head without and with IV contrast in the initial imaging evaluation of primary migraine or TTH with a normal neurologic examination. CT Head Without IV Contrast There is no relevant literature to support the use of CT head without IV contrast in the initial imaging evaluation of primary migraine or TTH with a normal neurologic examination. Most studies demonstrate a very low incidence of clinically significant intracranial abnormalities in patients presenting with migraine or TTH and a normal neurological examination [25,26]. CTA Head With IV Contrast There is no relevant literature to support the use of CTA head with IV contrast in the initial imaging evaluation of primary migraine or TTH with a normal neurologic examination.	Headache PCAs. It was found that patients with migraine with aura were imaged more frequently and demonstrated an increased incidence of minor intracranial abnormalities such as lacunar infarcts and microvascular ischemic changes. No abnormalities were detected that were of major clinical significance [24]. A study performed in China in 2018 examined 1,070 healthy control patients and 1,070 primary headache sufferers; imaging evaluation included either CT or MRI and found no statistical difference in the detection of intracranial abnormalities: 0.58% in patients with headache and 0.78% in healthy controls [25]. Headache Arteriography Cervicocerebral There is no relevant literature to support the use of cervicocerebral arteriography in the initial imaging evaluation of primary migraine or TTH with a normal neurologic examination. CT Head With IV Contrast There is no relevant literature to support the use of CT head with IV contrast in the initial imaging evaluation of primary migraine or TTH with a normal neurologic examination. CT Head Without and With IV Contrast There is no relevant literature to support the use of CT head without and with IV contrast in the initial imaging evaluation of primary migraine or TTH with a normal neurologic examination. CT Head Without IV Contrast There is no relevant literature to support the use of CT head without IV contrast in the initial imaging evaluation of primary migraine or TTH with a normal neurologic examination. Most studies demonstrate a very low incidence of clinically significant intracranial abnormalities in patients presenting with migraine or TTH and a normal neurological examination [25,26]. CTA Head With IV Contrast There is no relevant literature to support the use of CTA head with IV contrast in the initial imaging evaluation of primary migraine or TTH with a normal neurologic examination.	69482
acrac_69482_8	Headache PCAs	CTV Head With IV Contrast There is no relevant literature to support the use of CTV head with IV contrast in the initial imaging evaluation of primary migraine or TTH with a normal neurologic examination. MRA Head With IV Contrast There is no relevant literature to support the use of MRA head with IV contrast in the initial imaging evaluation of primary migraine or TTH with a normal neurologic examination. MRA Head Without and With IV Contrast There is no relevant literature to support the use of MRA head without and with IV contrast in the initial imaging evaluation of primary migraine or TTH with a normal neurologic examination. MRA Head Without IV Contrast There is no relevant literature to support the use of MRA head without IV contrast in the initial imaging evaluation of primary migraine or TTH with a normal neurologic examination. Brain MRA in primary patients with headache has demonstrated no increased incidence of vascular abnormalities [21]. MRI Head With IV Contrast There is no relevant literature to support the use of MRI head with IV contrast in the initial imaging evaluation of primary migraine or TTH with a normal neurologic examination. MRI Head Without and With IV Contrast There is no relevant literature to support the use of MRI head without and with IV contrast in the initial imaging evaluation of primary migraine or TTH with a normal neurologic examination. MRI Head Without IV Contrast There is no relevant literature to support the use of MRI head without IV contrast in the initial imaging evaluation of primary migraine or TTH with a normal neurologic examination. Several studies in primary headache sufferers demonstrated no significant increase in the incidence of major intracranial abnormalities that would require further action or are clinically significant. The most prevalent findings were an increased incidence of small nonspecific white matter hyperintensities, especially in TTH [21,24-26].	Headache PCAs. CTV Head With IV Contrast There is no relevant literature to support the use of CTV head with IV contrast in the initial imaging evaluation of primary migraine or TTH with a normal neurologic examination. MRA Head With IV Contrast There is no relevant literature to support the use of MRA head with IV contrast in the initial imaging evaluation of primary migraine or TTH with a normal neurologic examination. MRA Head Without and With IV Contrast There is no relevant literature to support the use of MRA head without and with IV contrast in the initial imaging evaluation of primary migraine or TTH with a normal neurologic examination. MRA Head Without IV Contrast There is no relevant literature to support the use of MRA head without IV contrast in the initial imaging evaluation of primary migraine or TTH with a normal neurologic examination. Brain MRA in primary patients with headache has demonstrated no increased incidence of vascular abnormalities [21]. MRI Head With IV Contrast There is no relevant literature to support the use of MRI head with IV contrast in the initial imaging evaluation of primary migraine or TTH with a normal neurologic examination. MRI Head Without and With IV Contrast There is no relevant literature to support the use of MRI head without and with IV contrast in the initial imaging evaluation of primary migraine or TTH with a normal neurologic examination. MRI Head Without IV Contrast There is no relevant literature to support the use of MRI head without IV contrast in the initial imaging evaluation of primary migraine or TTH with a normal neurologic examination. Several studies in primary headache sufferers demonstrated no significant increase in the incidence of major intracranial abnormalities that would require further action or are clinically significant. The most prevalent findings were an increased incidence of small nonspecific white matter hyperintensities, especially in TTH [21,24-26].	69482
acrac_69482_9	Headache PCAs	Imaging techniques continue to evolve and improve, and recent developments in advanced MRI techniques are allowing the clinical community to better understand the underlying pathophysiology of migraines, which remains less well characterized than the clinical phenotype. Early research with novel structural imaging techniques such as voxel based morphometry and surface based morphometry suggest consistent variations in gray matter volume in regions of the brain responsible for pain processing and modulation in patients with migraine and other chronic Headache pain. White matter hyperintensities have been the most common minor intracranial abnormality in patients with migraine. Recent studies have investigated the correlation of white matter volume changes (eg, corpus callosum) and microstructural alterations on diffusion tensor imaging to symptoms in patients with migraine with and without aura, especially those with a depressive/anxious comorbidity. Functional neuroimaging studies have also been used to investigate the brain activation changes during and between migraine attacks. In addition to functional imaging, research using arterial spin labeling imaging to measure perfusion without necessitating IV contrast is providing useful insignts into the transient perfusion changes during the acute phase of an aura and following an attack. Arterial spin labeling has also proved in separating mirgraine with aura from cerebral ischemia, which can have a direct impact on clinical decision making. This ongoing research may help us understand attack ignition/propagation and provide targets for future therapy [27,28]. MRV Head With IV Contrast There is no relevant literature to support the use of MRV head with IV contrast in the initial imaging evaluation of primary migraine or TTH with a normal neurologic examination.	Headache PCAs. Imaging techniques continue to evolve and improve, and recent developments in advanced MRI techniques are allowing the clinical community to better understand the underlying pathophysiology of migraines, which remains less well characterized than the clinical phenotype. Early research with novel structural imaging techniques such as voxel based morphometry and surface based morphometry suggest consistent variations in gray matter volume in regions of the brain responsible for pain processing and modulation in patients with migraine and other chronic Headache pain. White matter hyperintensities have been the most common minor intracranial abnormality in patients with migraine. Recent studies have investigated the correlation of white matter volume changes (eg, corpus callosum) and microstructural alterations on diffusion tensor imaging to symptoms in patients with migraine with and without aura, especially those with a depressive/anxious comorbidity. Functional neuroimaging studies have also been used to investigate the brain activation changes during and between migraine attacks. In addition to functional imaging, research using arterial spin labeling imaging to measure perfusion without necessitating IV contrast is providing useful insignts into the transient perfusion changes during the acute phase of an aura and following an attack. Arterial spin labeling has also proved in separating mirgraine with aura from cerebral ischemia, which can have a direct impact on clinical decision making. This ongoing research may help us understand attack ignition/propagation and provide targets for future therapy [27,28]. MRV Head With IV Contrast There is no relevant literature to support the use of MRV head with IV contrast in the initial imaging evaluation of primary migraine or TTH with a normal neurologic examination.	69482
acrac_69482_10	Headache PCAs	MRV Head Without and With IV Contrast There is no relevant literature to support the use of MRV head without and with IV contrast in the initial imaging evaluation of primary migraine or TTH with a normal neurologic examination. MRV Head Without IV Contrast There is no relevant literature to support the use of MRV head without IV contrast in the initial imaging evaluation of primary migraine or TTH with a normal neurologic examination. Variant 3: Primary trigeminal autonomic cephalalgias (eg, cluster headache). Initial imaging. The ICHD-3 describes TACs as attacks of severe, strictly unilateral pain, which are orbital, supraorbital, temporal, or in any combination of these sites, lasting 15 to 180 minutes and occurring from once every other day to 8 times a day. Associated symptoms include ipsilateral conjunctival injection, lacrimation, nasal congestion, rhinorrhea, forehead and facial sweating, miosis, ptosis and/or eyelid edema, with or without restlessness or agitation. This predilection for the ophthalmic nerve (V1) distribution and associated autonomic symptoms help differentiate TACs from trigeminal neuralgia, which is a different disease. They are further classified as chronic or episodic, with 10% to 15% of patients suffering from chronic cluster headaches. Other subtypes include paroxysmal hemicranias (2-30 minutes), short-lasting unilateral neuralgiform headache attacks (1-600 seconds), hemicrania continua, and probable TAC. The short-lasting unilateral headache attacks are further characterized in 2 types: short-lasting unilateral neuralgiform headache attacks with conjunctival injection and tearing and short-lasting unilateral neuralgiform headache attacks with cranial autonomic symptoms [23]. TACs are, as a group, an uncommon primary headache disorder, with cluster headaches being the most common, characterized by a prevalence of 0.1% to 0.4% and a male predominance [29,30].	Headache PCAs. MRV Head Without and With IV Contrast There is no relevant literature to support the use of MRV head without and with IV contrast in the initial imaging evaluation of primary migraine or TTH with a normal neurologic examination. MRV Head Without IV Contrast There is no relevant literature to support the use of MRV head without IV contrast in the initial imaging evaluation of primary migraine or TTH with a normal neurologic examination. Variant 3: Primary trigeminal autonomic cephalalgias (eg, cluster headache). Initial imaging. The ICHD-3 describes TACs as attacks of severe, strictly unilateral pain, which are orbital, supraorbital, temporal, or in any combination of these sites, lasting 15 to 180 minutes and occurring from once every other day to 8 times a day. Associated symptoms include ipsilateral conjunctival injection, lacrimation, nasal congestion, rhinorrhea, forehead and facial sweating, miosis, ptosis and/or eyelid edema, with or without restlessness or agitation. This predilection for the ophthalmic nerve (V1) distribution and associated autonomic symptoms help differentiate TACs from trigeminal neuralgia, which is a different disease. They are further classified as chronic or episodic, with 10% to 15% of patients suffering from chronic cluster headaches. Other subtypes include paroxysmal hemicranias (2-30 minutes), short-lasting unilateral neuralgiform headache attacks (1-600 seconds), hemicrania continua, and probable TAC. The short-lasting unilateral headache attacks are further characterized in 2 types: short-lasting unilateral neuralgiform headache attacks with conjunctival injection and tearing and short-lasting unilateral neuralgiform headache attacks with cranial autonomic symptoms [23]. TACs are, as a group, an uncommon primary headache disorder, with cluster headaches being the most common, characterized by a prevalence of 0.1% to 0.4% and a male predominance [29,30].	69482
acrac_69482_11	Headache PCAs	The exact pathophysiology of TACs is not well understood; current investigations suggest the involvement of the trigeminovascular system, the autonomic nervous system, and the hypothalamus. Recent functional and anatomic neuroimaging studies have demonstrated changes in the pain neuromatrix including the trigeminal nerve, trigeminovascular complex, and general pain system [30]. TACs are a primary headache disorder; however, the differential diagnosis includes structural lesions affecting the trigeminal autonomic reflex and pain pathways. Therefore, it is usually recommended to rule out a secondary cause of these headaches with neuroimaging. The most common structural lesions are primary pituitary lesions. Other reported lesions include parasellar meningiomas, posterior fossa lesions, vascular lesions such as carotid or vertebral artery dissection, cerebral AVMs, and sinus infections. Possible underlying causes of hemicrania continua include CVT and intracranial metastases [30-33]. Arteriography Cervicocerebral There is no relevant literature to support the use of cervicocerebral arteriography in the initial imaging evaluation of TACs. CT Head With IV Contrast There is no relevant literature to support the use of CT head with IV contrast in the initial imaging evaluation of TACs. Headache CT Head Without and With IV Contrast There is no relevant literature to support the use of CT head without and with IV contrast in the initial imaging evaluation of TACs. CT Head Without IV Contrast There is no relevant literature to support the use of CT head without IV contrast in the initial imaging evaluation of TACs. CTA Head With IV Contrast There is no relevant literature to support the use of CTA head with IV contrast in the initial imaging evaluation of TACs; it may have utility in follow-up evaluation after initial neuroimaging. Vascular lesions including carotid/vertebral dissections, AVMs, and aneurysms are a rare, secondary cause of TACs [30,31,33].	Headache PCAs. The exact pathophysiology of TACs is not well understood; current investigations suggest the involvement of the trigeminovascular system, the autonomic nervous system, and the hypothalamus. Recent functional and anatomic neuroimaging studies have demonstrated changes in the pain neuromatrix including the trigeminal nerve, trigeminovascular complex, and general pain system [30]. TACs are a primary headache disorder; however, the differential diagnosis includes structural lesions affecting the trigeminal autonomic reflex and pain pathways. Therefore, it is usually recommended to rule out a secondary cause of these headaches with neuroimaging. The most common structural lesions are primary pituitary lesions. Other reported lesions include parasellar meningiomas, posterior fossa lesions, vascular lesions such as carotid or vertebral artery dissection, cerebral AVMs, and sinus infections. Possible underlying causes of hemicrania continua include CVT and intracranial metastases [30-33]. Arteriography Cervicocerebral There is no relevant literature to support the use of cervicocerebral arteriography in the initial imaging evaluation of TACs. CT Head With IV Contrast There is no relevant literature to support the use of CT head with IV contrast in the initial imaging evaluation of TACs. Headache CT Head Without and With IV Contrast There is no relevant literature to support the use of CT head without and with IV contrast in the initial imaging evaluation of TACs. CT Head Without IV Contrast There is no relevant literature to support the use of CT head without IV contrast in the initial imaging evaluation of TACs. CTA Head With IV Contrast There is no relevant literature to support the use of CTA head with IV contrast in the initial imaging evaluation of TACs; it may have utility in follow-up evaluation after initial neuroimaging. Vascular lesions including carotid/vertebral dissections, AVMs, and aneurysms are a rare, secondary cause of TACs [30,31,33].	69482
acrac_69482_12	Headache PCAs	The European Headache Federation recommends vascular imaging especially when 3 consecutive preventative treatments fail [34]. CTV Head With IV Contrast There is no relevant literature to support the use of CTV head with IV contrast in the initial imaging evaluation of TACs. Brain CTV can be used as a follow-up imaging study in cases of suspected CVT, which is in the differential diagnosis for TACs, especially hemicrania continua. [30,31,33,34]. MRA Head With IV Contrast There is no relevant literature to support the use of MRA head with IV contrast in the initial imaging evaluation of TACs. MRA Head Without and With IV Contrast There is no relevant literature to support the use of MRA head without and with IV contrast in the initial imaging evaluation of TACs. MRA Head Without IV Contrast There is no relevant literature to support the use of MRA head without IV contrast in the initial imaging evaluation of TACs; it may have utility in follow-up evaluation after initial neuroimaging. Vascular lesions including carotid/vertebral dissections, AVMs, and aneurysms are a rare, secondary cause of TACs [30,31,33]. The European Headache Federation recommends vascular imaging especially when 3 consecutive preventative treatments fail [34]. MRI Head With IV Contrast There is no relevant literature to support the use of MRI head with IV contrast in the initial imaging evaluation of TACs; the most common recommendation for initial imaging evaluation is MRI head without and with IV contrast. MRI Head Without and With IV Contrast MRI head without and with IV contrast is the most common recommendation for initial imaging evaluation of TACs; it is useful to help exclude a secondary headache due to a sellar region or posterior fossa mass. MRI Head Without IV Contrast There is no relevant literature to support the use of MRI head without IV contrast in the initial imaging evaluation of TACs; the most common recommendation for initial imaging evaluation is MRI head without and with IV contrast.	Headache PCAs. The European Headache Federation recommends vascular imaging especially when 3 consecutive preventative treatments fail [34]. CTV Head With IV Contrast There is no relevant literature to support the use of CTV head with IV contrast in the initial imaging evaluation of TACs. Brain CTV can be used as a follow-up imaging study in cases of suspected CVT, which is in the differential diagnosis for TACs, especially hemicrania continua. [30,31,33,34]. MRA Head With IV Contrast There is no relevant literature to support the use of MRA head with IV contrast in the initial imaging evaluation of TACs. MRA Head Without and With IV Contrast There is no relevant literature to support the use of MRA head without and with IV contrast in the initial imaging evaluation of TACs. MRA Head Without IV Contrast There is no relevant literature to support the use of MRA head without IV contrast in the initial imaging evaluation of TACs; it may have utility in follow-up evaluation after initial neuroimaging. Vascular lesions including carotid/vertebral dissections, AVMs, and aneurysms are a rare, secondary cause of TACs [30,31,33]. The European Headache Federation recommends vascular imaging especially when 3 consecutive preventative treatments fail [34]. MRI Head With IV Contrast There is no relevant literature to support the use of MRI head with IV contrast in the initial imaging evaluation of TACs; the most common recommendation for initial imaging evaluation is MRI head without and with IV contrast. MRI Head Without and With IV Contrast MRI head without and with IV contrast is the most common recommendation for initial imaging evaluation of TACs; it is useful to help exclude a secondary headache due to a sellar region or posterior fossa mass. MRI Head Without IV Contrast There is no relevant literature to support the use of MRI head without IV contrast in the initial imaging evaluation of TACs; the most common recommendation for initial imaging evaluation is MRI head without and with IV contrast.	69482
acrac_69482_13	Headache PCAs	Headache MRV Head With IV Contrast There is no relevant literature to support the use of MRV head with IV contrast in the initial imaging evaluation of TACs. Brain MRV can be used as a follow-up imaging study in cases of suspected CVT, which is in the differential diagnosis for TACs, especially hemicrania continua [30,31,33,34]. MRV Head Without and With IV Contrast There is no relevant literature to support the use of MRV head without and with IV contrast in the initial imaging evaluation of TACs. Brain MRV can be used as a follow-up imaging study in cases of suspected CVT, which is in the differential diagnosis for TACs, especially hemicrania continua [30,31,33,34]. MRV Head Without IV Contrast There is no relevant literature to support the use of MRV head without IV contrast in the initial imaging evaluation of TACs. Brain MRV can be used as a follow-up imaging study in cases of suspected CVT, which is in the differential diagnosis for TACs, especially hemicrania continua [30,31,33,34]. Variant 4: Headache with features of intracranial hypertension (eg, papilledema, pulsatile tinnitus, visual symptoms worse on Valsalva). Initial imaging. Headache attributed to increased cerebrospinal fluid (CSF) pressure can be accompanied by nausea/vomiting and exacerbated by the Valsalva maneuver (inhibits venous return) or by lying down (redistributes CSF into head). Elevated intracranial pressure can be due to various secondary etiologies such as structural lesions including mass, hydrocephalus, and venous sinus thrombosis [35]. Primary idiopathic intracranial hypertension (IIH), also known previously as pseudotumor cerebri, is characterized as an elevation of intracranial pressure with no identifiable cause. The etiology remains unknown. IIH predominantly impacts women, especially obese women of childbearing age. The prevalence of IIH in the general population ranges between 0.5 and 2 per 100,000. Due to the overlap of symptoms with several other primary headache syndromes, IIH is likely underdiagnosed.	Headache PCAs. Headache MRV Head With IV Contrast There is no relevant literature to support the use of MRV head with IV contrast in the initial imaging evaluation of TACs. Brain MRV can be used as a follow-up imaging study in cases of suspected CVT, which is in the differential diagnosis for TACs, especially hemicrania continua [30,31,33,34]. MRV Head Without and With IV Contrast There is no relevant literature to support the use of MRV head without and with IV contrast in the initial imaging evaluation of TACs. Brain MRV can be used as a follow-up imaging study in cases of suspected CVT, which is in the differential diagnosis for TACs, especially hemicrania continua [30,31,33,34]. MRV Head Without IV Contrast There is no relevant literature to support the use of MRV head without IV contrast in the initial imaging evaluation of TACs. Brain MRV can be used as a follow-up imaging study in cases of suspected CVT, which is in the differential diagnosis for TACs, especially hemicrania continua [30,31,33,34]. Variant 4: Headache with features of intracranial hypertension (eg, papilledema, pulsatile tinnitus, visual symptoms worse on Valsalva). Initial imaging. Headache attributed to increased cerebrospinal fluid (CSF) pressure can be accompanied by nausea/vomiting and exacerbated by the Valsalva maneuver (inhibits venous return) or by lying down (redistributes CSF into head). Elevated intracranial pressure can be due to various secondary etiologies such as structural lesions including mass, hydrocephalus, and venous sinus thrombosis [35]. Primary idiopathic intracranial hypertension (IIH), also known previously as pseudotumor cerebri, is characterized as an elevation of intracranial pressure with no identifiable cause. The etiology remains unknown. IIH predominantly impacts women, especially obese women of childbearing age. The prevalence of IIH in the general population ranges between 0.5 and 2 per 100,000. Due to the overlap of symptoms with several other primary headache syndromes, IIH is likely underdiagnosed.	69482