Dysphagia

Dysphagia. Functional abnormalities of the esophagus include gastroesophageal reflux and motility disorders. The most important structural lesion is carcinoma of the esophagus or gastroesophageal junction. In one study, biphasic esophagography was found to have 96% sensitivity in diagnosing cancer of the esophagus or esophagogastric junction [20] comparable to the reported sensitivity of endoscopy for diagnosing these lesions. In two other large patient series, endoscopy failed to reveal any cases of esophageal carcinoma that had been missed on the barium studies [21,22]. The findings in these series suggest that endoscopy is not routinely warranted to rule out missed tumors in patients who have normal findings on radiologic examinations. Although double-contrast views best detect mucosal lesions (eg, tumors, esophagitis), prone single-contrast views of patients who continuously drink a low-density barium suspension best detect lower esophageal rings or strictures. Lower esophageal rings are two to three times more likely to be diagnosed on prone single-contrast views than on upright double-contrast views because of inadequate distention of the distal esophagus when the patient is upright [11,23]. In one study, the biphasic esophagram was found to depict about 95% of all lower esophageal rings, whereas endoscopy detected only 76% of these rings [23]. Similarly, biphasic esophagrams have been found to have a sensitivity of about 95% for the detection of peptic strictures, sometimes revealing strictures that are missed with endoscopy [24,25]. The biphasic esophagram is also a useful test in patients with esophageal motility disorders causing dysphagia. Videofluoroscopy of discrete swallows of a low-density barium suspension in the prone right antero-oblique position permits detailed assessment of esophageal motility.


Dysphagia

Dysphagia. In various studies, videofluoroscopy has been found to have an overall sensitivity of 80% to 89% and specificity of 79% to 91% for diagnosing esophageal motility disorders (eg, achalasia, diffuse esophageal spasm) compared with esophageal manometry [17,26]. Occasionally, barium studies may even reveal dysmotility not seen at manometry (eg, some patients with the beak-like distal esophageal narrowing of achalasia are found to have complete relaxation of the lower esophageal sphincter on manometry) [27]. Even for those patients with a significant esophageal motility disorder detected on a barium study, manometry may be performed to further elucidate the nature of this motility disorder. Endoscopy performed to evaluate the esophagus for structural abnormalities in patients with dysphagia is a highly accurate test for esophageal cancer when multiple endoscopic biopsy specimens and brushings are obtained. It is also more sensitive than double-contrast esophagography for detecting mild reflux esophagitis or other subtle forms of esophagitis. However, endoscopy is a much more invasive test than the barium study. It is also less sensitive than the barium study for detecting lower esophageal rings or strictures [11,23-25] and does not permit evaluation of esophageal motility disorders. For these reasons, a biphasic esophagram is often recommended as the initial diagnostic test for patients with dysphagia [3,5,28]. Dysphagia Fluoroscopy Single-Contrast Esophagram Although the biphasic esophagram provides superior mucosal detail, allowing for earlier detection of subtle lesions, patient cooperation and mobility are required. For debilitated, immobile patients or patients who are limited in their ability to cooperate, a single-contrast esophagram may be necessary. Fluoroscopy Barium Swallow Modified In patients with retrosternal dysphagia, the entire esophagus and the gastric cardia should be assessed. Therefore, the modified barium swallow may not be appropriate.


Dysphagia

Dysphagia. Fluoroscopy Pharynx Dynamic and Static Imaging Dynamic and static imaging of the pharynx may not be appropriate as the only examination performed in a patient with retrosternal dysphagia because the entire esophagus and gastric cardia should be assessed. This study does not evaluate the thoracic esophagus or gastric cardia. CT Neck and Chest CT is not usually indicated as an initial imaging modality in this clinical scenario because it does not assess esophageal mucosa and motility. CT may be helpful in the subsequent evaluation of patients if initial studies are not revealing. Esophageal Transit Nuclear Medicine Scan Specific protocols to assess esophageal emptying may be useful in patients with known or suspected achalasia but does not provide anatomic detail [29,30]. Radionuclide esophageal transit scintigraphy is a simple, noninvasive, and quantitative test of esophageal emptying that can be useful in these patients [3,31,32]. Variant 4: Retrosternal dysphagia in immunocompromised patients. Initial imaging. The major consideration in immunocompromised patients with dysphagia or odynophagia (painful swallowing) is infectious esophagitis, most commonly due to Candida albicans or herpes simplex virus. In HIV-positive patients, Candida is most often the cause of esophageal symptoms; cytomegalovirus, herpes simplex, and idiopathic ulcers (also known as HIV ulcers) are the other most common etiologies [33]. HIV-positive patients with esophageal symptoms may be treated empirically with antifungal therapy without first undergoing a diagnostic examination. However, most gastroenterologists prefer that those who have severe symptoms at presentation or persistent symptoms be evaluated by endoscopy. Endoscopy is preferred because of the ability to obtain specimens (eg, histology, cytology, immunostaining, or culture) [3,33].


Dysphagia

Dysphagia. The endoscopic or radiographic appearance alone usually does not accurately predict diseases other than Candida esophagitis; diagnosis requires specimen acquisition for laboratory study [33,34]. Fluoroscopy Biphasic Esophagram Esophagrams are preferred by some as an initial diagnostic study and can be useful in guiding management. A biphasic esophagram is more accurate than single-contrast esophagram for detecting ulcers or plaques associated with infectious esophagitis [35-37]. However, a single-contrast esophagram may be performed if the patient is too sick or debilitated to tolerate a double-contrast examination. Patients with radiographically diagnosed Candida or herpes esophagitis may be treated with antifungal or antiviral agents, respectively, without endoscopic evaluation. Endoscopy is warranted for patients with giant esophageal ulcers to differentiate cytomegalovirus and HIV and begin appropriate therapy [34]. Fluoroscopy Single-Contrast Esophagram Although the biphasic esophagram provides superior mucosal detail, allowing for earlier detection of subtle lesions, patient cooperation and mobility are required. For debilitated, immobile patients or patients who are limited in their ability to cooperate, a single-contrast esophagram may be necessary. Fluoroscopy Barium Swallow Modified A modified barium swallow does not evaluate esophageal anatomy and structure. It may not be appropriate because it may fail to reveal the etiology of retrosternal dysphagia. However, it may be useful to evaluate swallowing function in the setting of pharyngeal infection. Fluoroscopy Pharynx Dynamic and Static Imaging Dynamic and static imaging evaluates swallowing and oropharyngeal motility and structure. Performed alone, it may not be appropriate because it may fail to reveal the etiology of retrosternal dysphagia. Dysphagia CT Neck and Chest CT is usually not indicated as an initial imaging modality in this clinical scenario because it does not assess esophageal mucosa and motility.


Dysphagia

Dysphagia. CT may be helpful in the subsequent evaluation of patients if initial studies are not revealing. Esophageal Transit Nuclear Medicine Scan Scintigraphy is usually not indicated in this clinical scenario. Variant 5: Early postoperative dysphagia. Oropharyngeal or retrosternal. Initial imaging. Dysphagia is a common complaint following surgery on the oropharynx, soft tissues of the neck, cervical spine, esophagus, or stomach. Imaging should be tailored to the type and location of surgery (oropharyngeal versus retrosternal) and the time of onset of symptoms following surgery. In the immediate or early postoperative period, fluid collections, anastomotic leaks, perforation, and abscess may be of clinical concern [38]. Fluoroscopy Single-Contrast Esophagram A single-contrast esophagram is the study of choice for patients presenting with dysphagia following surgery to the neck, c-spine, esophagus, or stomach [1,39]. When there is a question of leak or fistula, the study is ideally performed by utilizing water-soluble contrast followed by barium if necessary. Esophagrams are highly specific for the detection of leaks but not sensitive. Roh et al [39] showed that the sensitivity of the esophagram in diagnosing a leak was 36% and specificity was 97%. For this reason, a CT examination may be ordered if there is a high clinical suspicion following a negative esophagram. Lantos et al [40] showed that esophagography had a sensitivity of 79%, specificity of 73%, positive predictive value of 73%, and negative predictive value of 79% for detecting leaks, and esophagography and CT combined had a sensitivity of 100%, specificity of 27%, positive predictive value of 56%, and negative predictive value of 100%. The sensitivity of esophagography increased when high-density barium was administered after water-soluble contrast, whereas the sensitivity of CT was the same with and without oral contrast agent.


Dysphagia

Dysphagia. Esophagrams have a slightly lower sensitivity and substantially higher specificity compared with CT for detecting leaks after esophagectomy [41]. Fluoroscopy Biphasic Esophagram Biphasic esophagram is not usually indicated when a patient has dysphagia in the immediate postoperative period. Single-contrast technique utilizing water-soluble contrast is preferable because evaluation for postoperative leak is the primary concern. Fluoroscopy Barium Swallow Modified When oropharyngeal dysphagia occurs postoperatively and there is a high index of suspicion for swallowing dysfunction, a modified barium swallow is the study of choice, especially if leak has been excluded clinically or with imaging. In the immediate postoperative period, if a leak or perforation is of clinical concern, a single-contrast esophagram with water-soluble contrast may be more appropriate because it is better suited to evaluate postoperative structural abnormalities. However, a modified swallow performed with water-soluble contrast material has been shown to be effective in the diagnosis of leakage [41]. In this study there were no adverse events associated with aspiration of iohexol as water-soluble contrast material [41]. A modified barium swallow examination does not evaluate the entire esophagus. It is not appropriate for postoperative retrosternal dysphagia because it does not evaluate the retrosternal anatomy. Fluoroscopy Pharynx Dynamic and Static Imaging Pharynx dynamic and static imaging is usually not appropriate because it is a double-contrast barium evaluation of the pharynx alone. A single-contrast esophagram with water-soluble contrast possibly followed with barium is more appropriate to evaluate for postoperative leak or fistula in a patient who has had surgery in the neck and is complaining of oropharyngeal dysphagia [42]. Furthermore, this study does not evaluate the thoracic esophagus and gastric cardia.


Dysphagia

Dysphagia. Alone, pharynx dynamic and static imaging is not appropriate for postoperative retrosternal dysphagia because it does not evaluate the retrosternal anatomy but may be useful combined with esophageal evaluation. CT Neck and Chest For oropharyngeal and retropharyngeal dysphagia, CT of the neck and chest with intravenous (IV) contrast is Dysphagia indicated when there is concern of early postoperative complications, such as leak, fluid collection, abscess, or hematoma [40,43]. CT has a slightly higher sensitivity and substantially lower specificity than esophagography for detecting clinically relevant leaks after esophagectomy [40,43]. The use of CT as the initial imaging test in these patients can lead to earlier diagnosis and treatment of leaks missed on esophagography. In many patients, both CT and esophagrams are performed especially when the clinical concern is high. Lantos et al [40] showed that esophagography had a sensitivity of 79%, specificity of 73%, positive predictive value of 73%, and negative predictive value of 79% for detecting leaks, whereas CT had a sensitivity of 86%, specificity of 33%, positive predictive value of 55%, and negative predictive value of 71%; esophagography and CT combined had a sensitivity of 100%, specificity of 27%, positive predictive value of 56%, and negative predictive value of 100%. CT may be useful to assess the position of surgical hardware or complication related to surgical hardware with respect to the oropharynx and airway. Oral contrast administered immediately before the examination may be a helpful adjunct to facilitate interpretation of esophageal integrity and anatomy, though one study showed the use of oral contrast did not change the sensitivity of CT for detection of leaks [40]. CT scan with IV contrast better defines the anatomic structures of the neck and chest compared to CT without IV contrast because normal soft-tissue and blood vessel enhancement are better delineated from postoperative fluid collections, such as hematomas and abscesses.


Dysphagia

Dysphagia. Obtaining a CT scan with and without IV contrast offers little additional benefit compared to a CT with IV contrast alone. Esophageal Transit Nuclear Medicine Scan Scintigraphy is usually not indicated in this clinical scenario. Variant 6: Delayed (greater than 1 month) postoperative development of dysphagia. Oropharyngeal or retrosternal. Initial imaging. Dysphagia occurring weeks or months following surgery may be due to dysmotility, gastroesophageal reflux, or structural abnormalities, such as anastomotic strictures, diverticula, or recurrent disease [38]. The incidence of dysphagia after laryngectomy is reported to occur in up to 72% of patients [44], and aspiration occurs in 65% of patients [45]. In addition to patients who have undergone operations to the oropharynx, larynx, and esophagus, operative procedures on the cervical spine may also cause dysphagia and significant disability. In the latter group of patients, dysphagia may be caused by structural abnormalities (displaced surgical hardware or bone graft) or functional abnormalities resulting in aspiration or penetration [1]. Patients following esophageal and gastric surgery can also experience dysphagia related to many potential complications. Fluoroscopy Pharynx Dynamic and Static Imaging Pharynx dynamic and static imaging is usually not appropriate because it is a double-contrast barium evaluation of the pharynx alone. A single-contrast esophagram with water-soluble contrast possibly followed with barium is more appropriate to evaluate for postoperative leak or fistula in a patient who has had surgery in the neck and is complaining of oropharyngeal dysphagia [42]. Furthermore, this study does not evaluate the thoracic esophagus Dysphagia and gastric cardia. Alone, pharynx dynamic and static imaging is not appropriate for postoperative retrosternal dysphagia because it does not evaluate the retrosternal anatomy but may be useful combined with esophageal evaluation.


Lower Extremity Arterial Revascularization Post Therapy Imaging.  Over the past several decades, a paradigm shift away from surgical treatment and toward endovascular therapy for PAD has occurred, with many now advocating surgical treatments only after one or more failed endovascular revascularization attempts. The BASIL trial demonstrated that patients with critical limb ischemia (CLI) presenting with rest pain, ulceration, and gangrene of the leg due to infrainguinal disease had similar amputation- free survival and quality-of-life outcomes whether they were randomized to a surgery-first or angioplasty-first treatment strategy. Furthermore, first-year costs associated with bypass surgery were about one-third higher than those associated with angioplasty [5]. The long-term outcomes following surgical and endovascular therapy in the setting of CLI are the subject of the ongoing BEST-CLI trial, which has an estimated primary endpoint completion date in December 2018. Whether endovascular or surgical revascularization is used, restenosis is a pervasive issue. As target lesion restenosis and adjacent segment disease typically precede frank occlusion and CLI, surveillance has been advocated for many years in the setting of bypass, and there is increasing evidence to support its use following angioplasty and stenting. Additionally, there has been a steady increase in the investigative tools available to the vascular specialist to diagnose and stratify lesions in the lower extremity arteries. Because of the plethora of testing options available, it can be difficult for physicians to determine the most appropriate test to obtain in the setting of recurrent symptoms after therapy. Overview of Imaging Modalities Noninvasive Hemodynamic Testing Noninvasive testing (NIVT), both before and after intervention, has been used for decades as a first-line investigatory tool in the diagnosis and categorization of PAD.


Lower Extremity Arterial Revascularization Post Therapy Imaging. It is widely available and provides a large amount of information at low cost without the use of ionizing radiation [6]. NIVT can consist of one or more of the following components: the ABI, segmental pressure measurements (SPMs), pulse-volume recordings (PVRs), photoplethysmography (PPG), and transcutaneous oxygen pressure measurement (TcPO2). aResearch Author, University of Michigan Health System, Ann Arbor, Michigan. bPrincipal Author and Panel Vice-chair, University of Michigan Health System, Ann Arbor, Michigan. cPanel Chair, UT Southwestern Medical Center, Dallas, Texas. dScripps Green Hospital, La Jolla, California; Society for Vascular Surgery. eNorthwestern Medicine, Chicago, Illinois. fUniversity of Wisconsin, Madison, Wisconsin. gMassachusetts General Hospital, Boston, Massachusetts. hCleveland Clinic Heart and Vascular Institute, Cleveland, Ohio; American College of Cardiology. iMayo Clinic, Rochester, Minnesota. jUniversity of Michigan Health System, Ann Arbor, Michigan. kUniversity of California San Diego, San Diego, California. lUniversity of Virginia Health System, Charlottesville, Virginia. mLoyola University Medical Center, Maywood, Illinois. nColumbia University Medical Center, New York, New York. oUT Southwestern Medical Center, Dallas, Texas. pSpecialty Chair, Ottawa Hospital Research Institute and the Department of Radiology, The University of Ottawa, Ottawa, Ontario, Canada. 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 PVRs provide a qualitative (rather than quantitative) measurement of limb perfusion.


Lower Extremity Arterial Revascularization Post Therapy Imaging. PVRs are created by inflating pneumoplethysmography cuffs to a specified pressure at predetermined levels on each limb. Each cuff measures the miniscule change in the volume of the limb under the cuff with each pulse, creating a tracing of volume versus time. The resultant waveforms can be compared to determine segmental disease, providing insight into the quality of arterial blood flow at each station simultaneously. PVRs are also useful in patients with noncompressible vessels, as this modality relies on limb volume change rather than the pressure required impeding flow through the vessel being interrogated. PPG involves the detection of a transmitted infrared signal through each of the digits. The degree of transmitted signal varies depending on blood volume within the digit, blood vessel wall movement, and the orientation of red blood cells [12]. PPG is useful for detection of disease below the knee as well as disease isolated to the forefoot and digits. As such, it has been demonstrated to be a complementary test to ABI, which has limited use in these segments. TcPO2 measurement allows the determination of the oxygen tension within tissue. An improvement in the TcPO2 value postintervention compared with preintervention has been validated as an excellent marker of tissue reperfusion [13]. TcPO2 values >40 mmHg in the area surrounding the ulcer or amputation site are considered predictive of successful healing. This test is not limited by noncompressible vessels, and, in patients without pedal Doppler signals, it is one of the few NIVTs that is helpful [14]. The test is limited by its availability in the office setting, patient resistance to avoiding smoking and caffeine prior to the test, as well as the time and cost constraints associated with providing the temperature-controlled environment required to standardize the test.


Lower Extremity Arterial Revascularization Post Therapy Imaging. US Peripheral duplex ultrasound (DUS) imaging, which consists of grayscale 2-D imaging, color Doppler, and spectral waveform analysis, has been a mainstay of vascular imaging for decades. This technology is widely available, portable, does not require contrast agents, and can be used in the angiography suite or operating room. DUS has been validated as a screening tool [15], a first-line study for clinically suspected PAD [16], and as a tool to plan the approach for both endovascular and surgical intervention [17]. In most situations, it is complimentary to NIVT, such as the ABI [18]. US has a high sensitivity for the detection of patent tibial arteries but is less accurate in detecting complete occlusions, particularly in the peroneal artery [19]. DUS has also been used to quantify the firmness of occlusions to determine the degree of chronicity to some success [20]. Lower Extremity Arterial Revascularization correlate well with symptom recurrence [26]. When planning interventions, the anticipated intervention based on US alone was unchanged after angiogram in femoropopliteal and iliac lesions in >80% of patients, but only 59% in lesions below the knee [27]. In critical limbs, close surveillance shows significant improvement in limb salvage rates over clinical follow-up alone [28]. Unfortunately, of all the noninvasive imaging techniques, US is also the most operator dependent and time consuming [29]. The DIPAD trial, which evaluates the cost-benefit ratio of DUS compared with computed tomography angiography (CTA) and contrast-enhanced magnetic resonance angiography (CE-MRA), showed that although the initial cost of US is lower, this does not take into account the time-related expense and operator experience required to produce satisfactory imaging. Additionally, practitioner confidence in the results is often lower than with the more advanced techniques, leading to a greater number of follow-up studies prior to intervention [30].


Lower Extremity Arterial Revascularization Post Therapy Imaging. CTA Modern CTA has been demonstrated to be comparable to the gold standard (catheter-based angiography) for the detection of hemodynamically significant stenoses (>50%) with sensitivity, specificity, and accuracy of 99%, 98%, and 98%, respectively [31]. Refinements in CT protocols have also compared favorably to MRA with no statistically significant difference between the two modalities in the evaluation of claudication or CLI [32]. Arterial opacification is significantly improved by using high-density compact contrast boluses, which is rapidly becoming the standard of care with equivalent iodine dose to previous standard bolus technique [33]. Potential drawbacks of CTA include the exposure to ionizing radiation and the use of iodinated contrast, which presents the potential for allergic reaction or contrast-induced nephropathy, particularly in those patients who already possess some degree of renal impairment. Metallic streak artifact is often problematic in patients with postsurgical changes or implanted hardware. Additionally, in extremely obese patients, the signal-to-noise ratio becomes somewhat prohibitive. Evaluation of densely calcified vessels can be difficult with CTA because of the similar density between plaque and contrast and the blooming artifact created by the former, leading to overestimation of the degree of stenosis in many cases, as well as the inability to determine patency in stented vessels. Because of the density of calcified plaque in relation to the relatively small lumen of the tibial vessels, CTA has traditionally suffered in the infrageniculate distribution [34]. Multiple studies have now validated dual-energy CTA as a practical and effective method for subtraction of calcified plaque and soft tissues, allowing for simultaneous creation of conventional CTA data sets and angiogram-like composite images of the vasculature alone.


Lower Extremity Arterial Revascularization Post Therapy Imaging. These subtraction images have been demonstrated to be nearly equivalent in diagnostic accuracy to those of conventional angiograms, with similar or less radiation using newer protocols [35]. This technique has been improved at some institutions by subtracting the extravascular tissues in multiple segments rather than the entire study at once [36]. Relatively recent advances in CTA technology include the use of dynamic (time-resolved) imaging of the tibial arteries [37], selective ultra- low-dose intra-arterial contrast-enhanced CTA [38], and CO2-enhanced high-pitch CTA [39], all of which show promise in certain circumstances. MRA MRA has been used for many years in patients with PAD for both treatment planning and assessment of procedural success. Continued evolution of this technology and imaging protocols has improved image quality and increased the potential applications. Most MRA protocols provide both source images with excellent soft- tissue differentiation and subtracted images demonstrating the vasculature in 2-D and 3-D representations similar to those provided during conventional angiography. In the current era, the accuracy of CTA and CE-MRA for the detection of hemodynamically significant PAD has become essentially equivalent, with an edge for CTA in the aortoiliac segment and for MRA in the infrageniculate distribution [32]. In diabetics, MRA is considered particularly helpful for runoff evaluation because of its superior ability to detect flow in small, calcified vessels, approaching the sensitivity of digital subtraction angiography (DSA) [40]. Lower Extremity Arterial Revascularization at which each segment is optimally opacified [42]. This technique increases sensitivity, specificity, and accuracy for PAD in all segments of the lower extremity arteries, but most importantly below the knee [43,44]. Time- resolved imaging of the whole limb has also been reported [45].


Lower Extremity Arterial Revascularization Post Therapy Imaging. MRA provides imaging quality similar to DSA for the evaluation of lower extremity bypass conduits [46,47]. It also allows for excellent evaluation of previously angioplastied segments and has a high specificity for in-stent patency; however, sensitivity for occlusion is still poor because of blooming artifact, particularly in stainless steel stents [48]. Newer generation nitinol stents are less affected by this limitation. There are several important limitations of MRA. Patients with most types of defibrillators, spinal cord stimulators, intracerebral shunts, cochlear implants, and other devices are excluded, as are patients affected by claustrophobia that is not overcome by sedation. Open-field 1.0T MRA has been used for claustrophobic patients, with imaging quality approaching that of DSA above the knee; however, below the knee, the technology is still quite limited [49]. It takes longer to acquire images with MRA than with CTA, and the studies themselves are considerably more expensive. However, with MRA, patients are not exposed to ionizing radiation, and the risk of nephrotoxicity from gadolinium-based contrast is considerably less than that of iodinated contrast agents. For a time, CE-MRA was considered an alternative to CTA in patients with renal impairment; however, since the association between renal failure and nephrogenic systemic fibrosis after gadolinium administration was discovered, it fell out of favor [50]. This led to copious research of noncontrast MRA. Time-of-flight imaging is one such method, which, with current technology, provides images with equivalent accuracy to CE-MRA for popliteal and runoff assessment, but still lags behind in the aortoiliac and femoral segments [51,52]. It is less expensive than CE-MRA, and has been proposed as a potential PAD screening test [53].


Lower Extremity Arterial Revascularization Post Therapy Imaging. Quiescent-interval single-shot MRA and flow-spoiled fresh-blood imaging are newer techniques, which may show promise in combination with conventional time-of-flight techniques [54-56]. Quiescent-interval single-shot currently provides similar imaging quality and diagnostic accuracy to CE-MRA in runoff vessels of diabetics, suggesting that perhaps a combination of noncontrast MRA techniques may provide equivalent whole-body vascular imaging to those provided by CE-MRA [57]. Many newer techniques in MRA show excellent promise in certain circumstances. Perfusion imaging using arterial spin labeling has been used to quantify arterial flow in the thigh and calf musculature, which has been shown to have equal or greater sensitivity for PAD compared with ABI, independent of the amount of preimaging exercise time [58,59]. Arterial peak flow velocity measurements can be obtained using phase-contrast techniques, comparing well to those obtained using spectral Doppler [60,61]. The vessel wall itself can be evaluated using blood-suppression, allowing for quantification and characterization of plaque and restenosis [62]. Continuous table movement MRA is a newer method that promises similar imaging quality to conventional multi-station MRA, with 30% faster imaging acquisition [63]. Arteriography DSA is the reference standard to which CTA and MRA are compared. DSA can localize and quantify obstructive lesions, permits physiological evaluation by the determination of pressure gradients, and allows for intervention at the time of diagnosis. In high-acuity settings, such as a thrombosed bypass graft, where immediate catheter-based intervention is likely to be indicated, direct referral to catheter angiography is a valid option. However, DSA is an invasive technique with a small but definite risk in every patient.


Lower Extremity Arterial Revascularization Post Therapy Imaging. Access-site hematoma, arterial dissection, thrombosis, and limb loss are known complications that can result from the procedure and occur in up to 2.0% of patients in this population [64]. These occur less frequently with increasing operator experience. For this document, it is assumed the procedure is performed and interpreted by an expert. Serious systemic complications are also possible, with increased risk in patients with severe widespread vascular disease, diabetes, renal insufficiency, or other contraindications to the use of iodinated contrast media. Carbon dioxide angiography may be of value in these patients. In light of the risk of nephrogenic systemic fibrosis in patients with severe renal disease, gadolinium chelates serve a very limited role as DSA contrast agents. Although DSA remains the gold standard for diagnosing PAD at the time of intervention, it generally plays no role in the surveillance of arterial segments previously treated with endovascular methods and in grafts without clinical evidence of malfunction. Discussion of Procedures by Variant Variant 1: Previous infrainguinal endovascular therapy or bypass. Asymptomatic. Surveillance. The most important indicator of restenosis or occlusion in the setting of previous revascularization is recurrence of symptoms. There is limited data to suggest that treatment of asymptomatic patients after endovascular therapy Lower Extremity Arterial Revascularization provides any long-term benefit [65]. As such, patients presenting to the clinic for follow-up of previous endovascular therapy or bypass for PAD should be evaluated for symptoms of claudication and rest pain, and should be examined closely for evidence of lower extremity ulceration or gangrene. ABI should be determined at each follow-up visit in all previously treated patients with PAD [66].


Lower Extremity Arterial Revascularization Post Therapy Imaging. PVRs can provide insight into subtle changes in arterial flow quality between segments, often preceding detectable anatomic changes on other modalities; however, they are fraught with reader subjectivity, poor patient cooperation, and baseline abnormalities in poor cardiac output [9]. A recent paper has also called into question whether they provide any benefit over ABIs and SPMs alone [67]. MRA Although both CE-MRA and nonenhanced MRA have been proposed as potential screening tests for PAD, particularly in patients in whom NIVT is limited (ie, diabetics) and time constraints remain prohibitive [77], there is no convincing evidence in the literature arguing for the use of CE-MRA or nonenhanced MRA for surveillance of previously treated PAD, either with endovascular or surgical methods. False positives suggesting recurrent disease in asymptomatic patients could lead to unnecessary procedures. CTA Because of availability, the use of ionizing radiation and the risks inherent to iodinated contrast, CTA is not recommended for routine follow-up of asymptomatic patients with nonaneurysmal PAD. Arteriography As an invasive test, lower extremity arteriography is completely inappropriate for surveillance of asymptomatic patients. There is no evidence to support its use in this setting. Lower Extremity Arterial Revascularization US DUS has a very high correlation with clinical deterioration after both endovascular therapy and bypass for lower-extremity PAD [26]. Following angioplasty, DUS has been validated as accurate for determining the specific levels of hemodynamically significant disease, although it often underestimates the extent of disease beyond the first significant stenosis. The aortoiliac segment can be evaluated in some patients, although obesity and bowel gas artifact are a pervasive problem.


Lower Extremity Arterial Revascularization Post Therapy Imaging. In combination with spectral Doppler, inflow disease can often be excluded and can guide the interventional approach (ie, retrograde contralateral versus antegrade ipsilateral access). Duplex is valuable in the determination of flow within and beyond stented and stent-grafted segments, and is slightly less limited than CTA and MRA, particularly in smaller-caliber stents [22]. The identification and treatment of symptomatic restenosis associated with a previously treated segment has been shown to provide improved long-term outcomes and patency in both endovascular and surgical patients [79]. In many cases, patients can proceed directly to intervention with Duplex arterial mapping alone [16,17]. In the setting of bypass, Duplex can determine whether the graft is patent, threatened, or occluded, and often can identify specific segments of disease to guide either endovascular repair or surgical revision. Although nonenhanced MRA can provide imaging quality and diagnostic confidence levels similar to that from CE-MRA, protocols and image quality vary significantly between institutions. Additionally, the lack of time- resolved imaging limits evaluation in the infrageniculate segment. Its use is generally reserved for patients who require evaluation of suspected aortoiliac and femoropopliteal lesions in the setting of renal insufficiency. The use of this modality is likely to evolve over the next decade given the vast amount of research in this area over the past few years. CTA In the era of modern CTA, vascular imaging quality is similar to that of DSA, albeit with a modest limitation in the infrageniculate distribution due to contrast-timing issues and the frequency of tibial calcification. Through the acquisition of isotropic voxels on new scanners, images can be reconstructed in any plane, including curved planar reformats along the lumen of the vessel [80].


Lower Extremity Arterial Revascularization Post Therapy Imaging. Particularly suited for aortoiliac and femoropopliteal evaluation, CTA is an excellent choice for the evaluation of claudicants, in which tibial disease is both less frequently present and less frequently treated. Similar to MRA, it is best suited in combination with tests providing data on the hemodynamic significance of identified lesions (NIVT and DUS). Arteriography Given the similar sensitivity and specificity of MRA and CTA compared with DSA, this invasive modality is generally reserved for immediate pretreatment evaluation of PAD and is rarely used solely for diagnostic purposes. The ability to acquire pressure measurements can help determine whether a previously identified stenosis is truly hemodynamically significant, which can sometimes be difficult to determine with NIVT and DUS in the setting of multilevel disease. It is occasionally used to determine surgical targets for infrageniculate bypass in patients with densely calcified runoff vessels who are deemed to be poor endovascular candidates, although noninvasive cross-sectional imaging has essentially replaced angiography for this indication as well. Lower Extremity Arterial Revascularization Variant 3: Previous infrainguinal endovascular therapy or bypass, presenting with cold, painful extremity and diminished pulses (acute limb ischemia). Initial imaging. Physical examination is critical in suspected acute limb ischemia/threatened limb, which is, at its core, a clinical diagnosis. The temperature and appearance of the limb, absence of palpable pulses or arterial signals by Doppler, loss of sensation, and decreased or absent strength in the affected extremity all provide insight into the urgency of the event. There is little evidence regarding the use of imaging in the setting of a threatened limb, and no tests should be performed that would significantly delay therapy in a patient with impending limb loss.


Lower Extremity Arterial Revascularization Post Therapy Imaging. Patients with severe ischemia, as indicated by motor loss or severe sensory deficits (Rutherford class IIb or III), should likely proceed directly to definitive therapy, usually surgical thromboembolectomy or bypass [81]. Although a full spectrum of NIVT may be too time consuming in an acutely threatened limb, the determination of the ABI and SPM can assist in the determination of both the etiology of the symptoms and can also guide the level of necessary intervention. US DUS may provide the ability to determine whether the patient has an acute event associated with a previously treated segment or not. Brief evaluation of the venous system can also exclude other potential causes for acute lower extremity ischemia, such as phlegmasia cerulea dolens. Limited US evaluation for the evaluation of bilateral common femoral patency, the determination of inflow quality, and the patency of lower extremity bypass conduits can help guide expeditious treatment. Given portability and ubiquity in the hospital system, this can potentially be performed by physicians in the emergency department to triage patients to appropriate vascular specialists [82]. For this document, it is assumed the procedure is performed and interpreted by an expert. There is increasing focus on training vascular specialists to perform point-of-care DUS to quickly determine the etiology and extent of limb ischemia during the initial consultation [83]. This is particularly true for bypass conduits, which are generally located superficially and easily assessed sonographically. However, these tests should not delay definitive therapy if it is immediately available. Arteriography Immediately threatened limbs (Rutherford class IIb and early presentations of class III) require rapid definitive therapy, and generally should proceed directly to emergency thromboembolectomy to prevent limb loss [84].


Lower Extremity Arterial Revascularization Post Therapy Imaging. In the setting of viable or marginally threatened limbs (Rutherford class I or IIa), immediate arteriography for the evaluation of anatomic relationships between diseased segments is the preferred procedure [85]. Angiography provides detailed and accurate information regarding the etiology and extent of the insult that has caused acute limb ischemia and may allow a catheter-based treatment in some patients [86]. This can allow patients to be appropriately triaged to either surgery or endovascular therapy, the latter of which may involve thrombolysis or percutaneous thrombectomy, angioplasty, stenting, etc. If performed without prior NIVT or US, there is the potential for longer procedure times, increased contrast use and possibly multiple access sites to provide definitive therapy. CTA In patients with acute limb ischemia and viable or marginally threatened limbs, CTA may be considered for preprocedural evaluation given its near-equivalent accuracy compared to diagnostic angiography [36]. CTA is a rapid modality that can provide insight into the precise location of vessel occlusion, and in some centers it is supplanting arteriography as the test of choice prior to intervention [87]. It is particularly useful in patients who present with bilateral symptoms where inflow disease is suspected. However, its use should not delay definitive therapy. Additionally, the use of iodinated contrast agent for this modality can limit the ability to provide subsequent angiographic therapy because of the risk of contrast-induced nephropathy [88]. Similar to CE-MRA, nonenhanced MRA is time consuming and should only be used in patients with renal insufficiency where the determination between endovascular and surgical therapy remains obscure. Although there are references that report on studies with design limitations, 28 well-designed or good-quality studies provide good evidence.


Rib Fractures

Rib Fractures.  Introduction/Background Rib fracture is the most common thoracic injury and is present in 10% of all traumatic injuries and in almost 40% of patients who sustain severe nonpenetrating trauma [1,2]. Rib fractures typically affect the fifth through ninth ribs. This may be due to the fact that the shoulder girdle affords relative protection to the upper ribs, and the lower ribs are relatively mobile and may deflect before fracturing [1]. Although rib fractures can produce significant morbidity, the diagnosis of associated complications (such as pneumothorax, hemothorax, pulmonary contusion, atelectasis, flail chest, cardiovascular injury, and injuries to solid and hollow abdominal organs) is arguably more important as these complications are likely to have the most significant clinical impact [1,2]. When isolated, rib fractures have a relatively low morbidity and mortality [2,3]. Treatment of rib fractures is generally aimed at pain control and avoidance of respiratory distress and intubation, but the presence of multiple rib fractures, underlying organ injury, or in an elderly patient especially, may warrant transfer from a community hospital to tertiary care center [2,4-6]. Radiography Chest In combination with the physical examination, a standard posteroanterior (PA) chest radiograph should be the initial diagnostic test for detection of rib fractures. Despite the low sensitivity of the chest radiograph, which may miss 50% of rib fractures [2], studies suggest that failure to detect fractures does not necessarily alter patient management or outcome in uncomplicated cases. A review of 271 patients who presented to a community hospital emergency department after minor trauma showed no difference in treatment (use of pain medications, etc) between patients who did and did not have rib fractures diagnosed on physical examination or radiographs [3].


Rib Fractures

Rib Fractures. In a study of 552 patients who had blunt chest trauma and resultant rib fracture (diagnosed on clinical or radiographic grounds), 93% of affected patients ultimately resumed daily activities without significant disability [2]. The chest radiograph may detect complications that are more important than the rib fractures themselves, such as pneumothorax, hemothorax, flail chest, or contusion [1,2]. Although a flail chest can usually be diagnosed at physical examination, it is conceivable that in a heavy patient a flail chest could be missed by clinical examination, but a chest radiograph almost always shows the displaced fragments. Dual-energy chest radiography with bone subtraction imaging has failed to show improved detection when aPanel Vice-Chair, University of California San Francisco, San Francisco, California. bPanel Chair, Vanderbilt University Medical Center, Nashville, Tennessee. cCharles E. Schmidt College of Medicine, Florida Atlantic University, Boca Raton, Florida. dSouthern Illinois University School of Medicine, Springfield, Illinois; Society of Thoracic Surgeons. eUniversity of Iowa, Iowa City, Iowa; Society of Thoracic Surgeons. fMayo Clinic, Rochester, Minnesota. gUniversity of Michigan Medical Center, Ann Arbor, Michigan. hUniversity of Iowa Hospitals and Clinics, Iowa City, Iowa. iVanderbilt University Medical Center, Nashville, Tennessee; American College of Chest Physicians. jRadiology Imaging Associates, Englewood, Colorado. kUniversity of Texas Health Science Center at San Antonio, San Antonio, Texas. lJohn H. Stroger, Jr. Hospital of Cook County, Chicago, Illinois; American College of Physicians. mNational Institutes of Health, Bethesda, Maryland. nUniversity of Texas MD Anderson Cancer Center, Houston, Texas. oSpecialty Chair, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin. Reprint requests to: publications@acr.org Rib Fractures compared with standard radiographs.


Rib Fractures

Rib Fractures. A review of 39 patients with a total of 204 rib fractures showed no statistically significant difference in sensitivity, specificity, or level of confidence between standard images and dual-energy subtraction images [9]. Radiography Rib Views While still performed in many practices, rib detail radiograph series rarely add additional information to the PA film that would change treatment as has been shown in two retrospective studies. In a review of 422 patients presenting to a university-affiliated emergency department for suspected rib fracture, Shuaib et al [10] found that rib series resulted in a change of management in only one patient (0.23%). Moreover, these authors found that, compared to standard PA radiographs, rib series negatively impacted patient care by prolonging report turnaround time [10]. Hoffstetter et al [11] retrospectively reviewed 609 patients that underwent rib series in the emergency department and found that while diagnosing a higher number of rib fractures as compared to PA radiographs alone, there was no statistically significant difference in the number of patients who received medical treatment. If rib series are to be performed, Park et al [12] showed that interpreting images with both conventional grayscale and inverted grayscale views may improve detection of rib fractures, although this study did not assess if the improved detection had an effect on outcomes. CT Chest The increased sensitivity of CT for the detection of rib fractures does not necessarily alter the management or clinical outcomes of patients without associated injuries. Kea et al [13] reported that CT detected rib fractures in 66 of 589 patients (11%) who had initial chest radiographs interpreted as normal at a level I trauma center, but none of the rib fractures were considered of major clinical significance. The presence and number of rib fractures, and the degree of displacement of the fractures, may carry prognostic significance.


Rib Fractures

Rib Fractures. Thus, detection of rib fractures by CT may be indicated under certain circumstances (especially if severe injury is suspected). Bugaev et al [14] retrospectively reviewed 245 patients that presented to a level 1 trauma center for a number of rib fractures and degree of displacement. They found that the number of rib fractures and the degree of fracture fragment displacement accurately predicted subsequent opioid requirements. Patients with rib fractures from a high-energy mechanism or with a high clinical suspicion of intrathoracic or intra-abdominal injury may warrant further evaluation with contrast-enhanced CT, whereas a low-energy injury or normal physical examination may obviate further testing. Dubinsky and Low [17] studied 69 patients with nonthreatening trauma (stable vital signs with no evidence of cardiac injury, solid or hollow viscus rupture, or fractures associated with significant blood loss) and found that neither rib studies nor chest radiographs were of clinical benefit in this scenario, but they concluded that clinical evidence of a complicated injury, such as pneumothorax, hemothorax, or flail chest, may warrant further evaluation. Similarly, Schurink et al [18] studied patients with lower rib fractures (ribs 7 through 12) and found that the negative predictive value of a negative physical examination for abdominal injury that is due to low-energy impact was 100%, but in patients with multiple injuries, lower rib fractures were associated with abdominal organ injury in 67% of patients. Matthes et al [19] found no association between right-sided lower rib fractures in 55 Rib Fractures trauma patients with hepatic injury when matched with 55 trauma patients without hepatic injury (there was a slight negative association of hepatic laceration with left-sided fractures) but ultimately concluded that the absence of rib fractures could not rule out hepatic injury.


Rib Fractures

Rib Fractures. Thus, in patients with multiple injuries and lower rib fractures, contrast-enhanced CT might be indicated even in the setting of a normal clinical examination. Several studies have demonstrated a high prevalence of radiographically detected rib fractures in patients with aortic injury, although the positive predictive value is low. In a large prospective multicenter trial involving 50 trauma centers in North America, Fabian et al [20] reported multiple rib fractures in 46% of 274 patients with blunt aortic injury. Mirvis et al [21] found fractures of ribs 1 through 4 in 18% of 41 patients with traumatic aortic injury proved by angiography but with a positive predictive value of only about 21%. Lee et al [22] studied 548 patients who underwent angiography to evaluate for aortic injury and concluded that rib fractures were the only type of thoracic skeletal injury that had a higher incidence in patients with aortic injury (58%) versus those without aortic injury (43%), but the positive predictive value was only 14.8%. This has also been shown at autopsy, where Williams et al [23] retrospectively reviewed 530 motor vehicle fatalities. In 90 victims, 105 aortic injuries were found, and 78% had multiple rib fractures, including 42% with fractures of the first rib. In contrast, there is some evidence that rib fractures detected with CT (given the increased sensitivity) may not be associated with an increased risk of aortic injury. A review of 185 patients with rib fractures detected on spine CT found no association between presence of first-rib or second-rib fracture and the incidence of aortic injury on subsequent CT [24]; however, ribs 3 through 12 were not assessed. Increased likelihood of injury to the adjacent subclavian and innominate vessels has been reported with displaced first-rib and second-rib fractures, but this injury can usually be suspected on clinical grounds or from a chest radiograph [25].


Rib Fractures

Rib Fractures. US Chest Several articles have noted that ultrasound (US) can detect fractures not seen on conventional radiographs [26- 28]. Griffith et al [28] compared US and radiography (chest radiography plus one oblique rib radiograph) in 50 patients and found that radiographs detected only 8 of 83 (10%) sonographically detected rib fractures and were positive in only 6 of the 39 patients who had demonstrated fractures. In this study, US allowed evaluation of the costochondral junction, the costal cartilage, and the ribs and was able to show nondisplaced fractures. Kara et al [26] found rib fractures in 40.5% of 37 patients with minor blunt chest trauma and negative radiographs by using US; osseous fractures were more common in the elderly, and duration of pain was significantly longer in these patients compared to those with chondral injuries [26-28]. However, Hurley et al [29] found US to be only marginally superior to conventional radiographs, and its routine use was not indicated because of the lengthy time of the examination, averaging 13 minutes in this series, and patient discomfort from the pressure of the US probe, particularly since identification of the fracture was unlikely to impact patient care. Bone Scan Whole Body Nuclear medicine bone scans are sensitive but not specific for detection of rib fracture [30]. Bone scans are most commonly used for detection of osseous involvement in systemic processes (eg, metastatic disease) and may result in false-positive diagnosis of malignancy in a patient with rib fractures, although the pattern of tracer uptake can often help differentiate the two processes [30]. Bone scans have limited use in distinguishing acute and subacute or chronic rib fractures as they will usually be positive within 24 hours after an injury, but the return to normal can be slow (79% by 1 year, 93% by 2 years, and 100% in 3 years) [31].


Rib Fractures

Rib Fractures. Furthermore, patients with known malignancy and benign rib fractures may exhibit false-positive findings on PET using the tracer fluorine- 18-2-fluoro-2-deoxy-D- glucose (FDG) studies performed 17 days to 8 weeks after injury [32]. Variant 2: Suspected rib fractures after cardiopulmonary resuscitation (CPR). Initial imaging. Radiography Chest Multiple studies [33-35] have shown that rib fractures are under-reported on radiography performed following cardiopulmonary resuscitation (CPR). In a retrospective analysis of 40 patients who survived CPR, Kim et al [33] reported that CT detected rib fractures in 26 patients (65%); whereas, anteroposterior chest radiography detected fractures in only 10 of the patients. Lederer et al [34] found that radiography detected only 14% of rib fractures compared to autopsy in 19 patients. Rib fractures from CPR are more commonly anterior, on the left side, and are more numerous in the elderly [34]. The diagnosis of such fractures in CPR survivors may be important since approximately half of CPR survivors with rib fractures experience complications, and the presence of rib fractures in these patients may impair Rib Fractures ventilation and compromise recovery. It should be noted that many of these patients are examined with portable supine radiography, which may contribute to underdiagnosis. Radiography Rib Views There is no strong indication in the literature that radiography rib series serves any significant use as an initial imaging modality to detect rib fractures after CPR. US Chest While focused US of the chest wall is more sensitive for detection of rib fractures than radiography in trauma patients [28], there is no direct evidence assessing the use of US in patients after CPR. Bone Scan Whole Body There is no strong indication in the literature that bone scan serves any significant use as an initial imaging modality to detect rib fractures after CPR.


Rib Fractures

Rib Fractures. CT Chest As described above, chest CT is more sensitive than radiography for the detection of rib fractures after CPR. Moreover, CT may show fracture-related complications that are radiographically occult. Kim et al [33] reported that CT found fracture-related complications in 6 of 40 patients (15%) who received CPR, including 1 pneumothorax, 1 subclavian vein injury, and 4 chest wall hematomas. This study did not indicate whether intravenous (IV) contrast was used, nor did it indicate whether CT was performed specifically for evaluation of rib fractures, or if the rib fractures were an incidental finding on a CT performed for other means (eg, suspected pulmonary embolism). Variant 3: Suspected pathologic rib fracture. Initial imaging. Radiography Chest Pathologic fractures may result from metabolic disorders or neoplasm, including primary bone tumor, metastatic disease of intrathoracic or extrathoracic primary, hematologic malignancy (eg, multiple myeloma, lymphoma), or direct extension of a tumor in the thorax. A PA chest radiograph may be sufficient for diagnosis of a pathologic fracture (or provide clues to an underlying diagnosis), but further evaluation using such modalities as CT, bone scan, or FDG-PET may be necessary to further characterize a lesion detected on radiography or to search for radiographically occult lesions [36-38]. Radiography Rib Views There is no strong indication in the literature that radiography rib series serves any significant use as an initial imaging modality to detect suspected pathologic rib fractures. US Chest There is no strong indication in the literature that US serves any significant use as an initial imaging modality to detect rib fractures. CT Chest CT may be useful for characterizing a pathologic fracture, and some features may be helpful in differentiating a primary malignant tumor of bone from metastasis [36].


Inflammatory Back Pain Known or Suspected Axial Spondyloarthropathy PCAs.  Introduction/Background Axial spondyloarthritis or axial spondyloarthropathy (axSpA) describes a heterogeneous group of inflammatory disorders affecting the axial skeleton that were historically classified separately as ankylosing spondylitis (AS), reactive arthritis, psoriatic spondyloarthritis, enteropathic spondyloarthritis, juvenile spondyloarthritis, and undifferentiated spondyloarthritis [1]. The prevalence of axSpA is estimated to be between 0.9% to 1.4% in the United States adult population [2]. There is a genetic component to axSpA, including a strong association with HLA-B27, which is positive in 74% to 89% of patients [1]. Patients with axSpA often present before age 45 with chronic back pain and stiffness and may have elevated inflammatory markers [3]. A clinical hallmark is the presence of inflammatory back pain, which is present in 70% to 80% of patients [4]. There are varying definitions for inflammatory back pain, although characteristically this pain includes the following features: insidious onset, improvement with exercise, no improvement with rest, occurring at night, and age of onset <40 years of age [4]. Inflammatory back pain symptoms, depending on the criteria used, have been reportedly been present in 5% to 6% of the general adult population [5], and in up to 15% of patients in the primary care setting [6]. Although recognition of axSpA is improving, a mean delay of 4.9 years from onset of symptoms to diagnosis was recently reported, highlighting the challenge of establishing this diagnosis early in the disease course [7]. Imaging plays a critical role in the diagnosis of axSpA. Historically, imaging diagnosis was based on radiographs using the modified New York criteria [15]; however, the radiographic changes of axSpA were subsequently found to evolve slowly over the course of years [16,17].


Inflammatory Back Pain Known or Suspected Axial Spondyloarthropathy PCAs. Additionally, some patients with symptomatic AS did not have radiographic evidence of axSpA [18], driving the search for additional imaging biomarkers of early disease. As evolving literature accumulated on the utility of MRI in axSpA, the Assessment of SpondyloArthritis international Society (ASAS) established diagnostic criteria in 2009 for axSpA that included MRI in the diagnostic algorithm, promoting the diagnosis of both patients with radiographically evident axSpA (radiographic-axSpA or classic AS) as well as patients with negative radiographs who may have inflammatory changes demonstrated on MRI (nonradiographic-axSpA) [17,19]. It was later shown that a portion of patients with nonradiographic-axSpA will Reprint requests to: publications@acr.org Inflammatory Back Pain progress to radiographic-axSpA over the course of years [20], although it is uncertain if radiographic-axSpA and nonradiographic-axSpA represent a continuum of the same entity or if they are truly separate disease subsets. This is the topic of some debate [1,21-23]. The development of the ASAS criteria facilitated diagnosis of patients at an earlier stage of disease and allowed more patients with axSpA to be considered for biologic therapy [17,19,22]. However, care should be taken to acknowledge that the ASAS criteria are designed for use in clinical research, not for definitive clinical diagnosis. Beyond the important roles of imaging in early diagnosis and treatment in axSpA patients, those with advanced axSpA resulting in ankylosis are a subset of patients that warrants further discussion. These patients, classically considered to have AS, develop spinal rigidity combined with osteoporosis resulting in a risk of fracture even with low energy trauma or no apparent trauma [1,31-33]. These fractures are often unstable and involve all 3 spinal columns [31,34]. The cervical spine is most frequently involved [32,33,35].


Inflammatory Back Pain Known or Suspected Axial Spondyloarthropathy PCAs. Associated neurologic deficits have been reported in 21% to 100% of patients, and other complications reported in 84% of patients [32]. The diagnosis can be delayed in 15% to 41% of cases, and therefore, clinical suspicion for fracture must be elevated in the appropriate setting given the severity of these injuries. Many patients undergo surgical fixation of these injuries, although unfavorable outcomes with relatively high morbidity and mortality are reported [32,35]. Early use of advanced imaging modalities is crucial in these patients to facilitate a timely diagnosis. OR Discussion of Procedures by Variant Variant 1: Inflammatory back pain. Suspected axial spondyloarthritis. Initial imaging. The body regions covered in this clinical scenario are the sacroiliac joints, cervical, thoracic, and lumbar spine. These body regions might be evaluated separately or in combination as guided by physical examination findings, patient history, and other available information. Bone Scan with SPECT or SPECT/CT Sacroiliac Joints Bone scintigraphy with single-photon emission computed tomography (SPECT) or SPECT/CT is not routinely obtained as the initial imaging modality in the evaluation of suspected axSpA, and there is no relevant literature supporting its use in this setting. Bone Scan with SPECT or SPECT/CT Spine Area of Interest Bone scintigraphy with SPECT or SPECT/CT is not routinely obtained as the initial imaging modality in the evaluation of suspected axSpA, and there is no relevant literature supporting its use in this setting. CT Sacroiliac Joints CT is not routinely obtained as the initial imaging modality in the evaluation of suspected axSpA, and there is no relevant literature supporting its use in this setting. Inflammatory Back Pain CT Spine Area of Interest CT is not routinely obtained as the initial imaging modality in the evaluation of suspected axSpA, and there is no relevant literature supporting its use in this setting.


Inflammatory Back Pain Known or Suspected Axial Spondyloarthropathy PCAs. Fluoride PET/CT Skull Base to Mid-Thigh F-18-fluoride PET/CT is not routinely obtained as the initial imaging modality in the evaluation of suspected axSpA, and there is no relevant literature supporting its use in this setting. MRI Sacroiliac Joints MRI is not routinely obtained as the initial imaging modality in the evaluation of suspected axSpA; however, it is known that the inflammatory changes of sacroiliitis on MRI can precede radiographic structural findings of sacroiliitis by three to seven years [36,37], resulting in a low sensitivity of radiographs for detection of early disease [16,17]. In cases of those with a short duration of symptoms, MRI of the sacroiliac joints could be considered as the initial imaging modality [22]. MRI Spine Area of Interest MRI is not routinely obtained as the initial imaging modality in the evaluation of suspected axSpA, and there is no relevant literature supporting MRI of the spine in this setting. US Sacroiliac Joints Ultrasound (US) is not routinely obtained as the initial imaging modality in the evaluation of suspected axSpA, and there is no relevant literature supporting its use in this setting. US Spine Area of Interest US is not routinely obtained as the initial imaging modality in the evaluation of suspected axSpA, and there is no relevant literature supporting its use in this setting. Variant 2: Inflammatory back pain. Suspected axial spondyloarthritis. Additional imaging following radiographs. Next imaging study. The body regions covered in this clinical scenario are the sacroiliac joints, cervical, thoracic, and lumbar spine. These body regions might be evaluated separately or in combination as guided by physical examination findings, patient history, and other available information. Inflammatory Back Pain Bone Scan with SPECT or SPECT/CT Sacroiliac Joints Bone scintigraphy is not routinely suggested in the evaluation of patients with suspected axSpA [22].


Inflammatory Back Pain Known or Suspected Axial Spondyloarthropathy PCAs. Conventional bone scintigraphy has low to moderate sensitivity and variable specificity for the diagnosis of axSpA [41,42,50]. If bone scintigraphy is used, SPECT should be performed during the examination because of the complexity of the sacroiliac joint anatomy [51]. Although bone scintigraphy is not typically performed during the evaluation of suspected axSpA because of its limited diagnostic utility, there is recent data that hybrid SPECT/CT has higher sensitivity than conventional bone scintigraphy in the detection of sacroiliitis [52,53]. However, there is not enough evidence currently to support its routine use for evaluation of the sacroiliac joints and spine. Bone Scan with SPECT or SPECT/CT Sacroiliac Joints and Spine Area of Interest Bone scintigraphy is not routinely suggested in the evaluation of patients with suspected axSpA [22]. Conventional bone scintigraphy has low to moderate sensitivity and variable specificity for the diagnosis of axSpA [41,42,50]. If bone scintigraphy is used, because of the complexity of the sacroiliac joint anatomy, the use of SPECT should be performed during the examination [51]. Although bone scintigraphy is not typically performed during the evaluation of suspected axSpA because of its limited diagnostic utility, there is recent data that hybrid SPECT/CT has higher sensitivity than conventional bone scintigraphy in the detection of sacroiliitis [52,53]. However, there is not enough evidence currently to support its routine use for evaluation of the sacroiliac joints and spine. CT Sacroiliac Joints CT demonstrates the structural changes of sacroiliitis in patients with axSpA that may not be apparent on radiographs [22]. These structural changes, including erosions, sclerosis, bone formation, and ankylosis, are best demonstrated on sacroiliac protocol examinations that include obliquely oriented reformatted images prescribed parallel and perpendicular to the long axis of the sacrum [54].


Inflammatory Back Pain Known or Suspected Axial Spondyloarthropathy PCAs. Several studies have shown CT to have higher sensitivity for detection of sacroiliitis than radiography [43,44,47,55]. Low-dose CT is increasingly being performed and can demonstrate the fine structural changes of axSpA better than radiography [45]. Additionally, the interreader reliability has shown to be excellent for grading sacroiliitis on CT, higher than for radiography, because of the increased level of structural detail demonstrated by CT [47]. Although conventional CT has the ability to demonstrate the chronic structural changes of sacroiliitis, it cannot demonstrate active inflammation, and therefore MRI remains the technique of choice for the diagnosis of axSpA [1,3,19,22]. There is evolving literature on the use of dual-energy CT (DECT) in the evaluation of sacroiliitis in axSpA, with early studies showing the ability of DECT to demonstrate bone marrow edema in patients with axSpA in addition to the inherent ability of CT to demonstrate the chronic structural changes of sacroiliitis [56,57]. One study shows that DECT has a sensitivity of 87% to 93% and specificity of 91% to 94% for detection of bone marrow edema using MRI as the reference standard, but more data are needed to support the diagnostic utility of DECT in the evaluation of axSpA [56]. There is no role for intravenous (IV) contrast in CT evaluation of axSpA. CT Sacroiliac Joints and Spine Area of Interest CT demonstrates structural changes in the sacroiliac joints and spine in patients with axSpA that may not be apparent on radiographs [22]. These structural changes include erosions, sclerosis, bone formation, syndesmophytes, and ankylosis [49,54]. In addition to its diagnostic utility in assessment of the sacroiliac joints, CT of the spine has the ability to demonstrate syndesmophytes with higher sensitivity than radiographs, and low-dose protocols can be utilized [58].


Inflammatory Back Pain Known or Suspected Axial Spondyloarthropathy PCAs. CT is especially helpful for evaluation of the thoracic spine and facet joints, which can be challenging to evaluate on radiography [49]. There is not a consistently established convention to guide the clinician on whether to image only the sacroiliac joints or both the sacroiliac joints and spine in patients with suspected axSpA. However, spinal involvement is common, and numerous studies have shown that axSpA involvement can be isolated to the spine, isolated to the sacroiliac joints, or can involve both the sacroiliac joints and spine [19,59-63]. Therefore, if CT is performed, imaging the spine in addition to the sacroiliac joints is beneficial in the setting of symptoms referable to the spine. There is no role for IV contrast in the CT evaluation of axSpA. Fluoride PET/CT Skull Base to Mid-Thigh There is not enough data to support the routine use of F-18-fluoride PET/CT in the evaluation of patients with suspected axSpA. F-18-fluoride has been shown to be a potentially useful tracer in identifying sites of osteoblastic activity in axSpA patients [64], with uptake corresponding to sites of active bone formation on histology [65]. Uptake on PET/CT has also been shown to correlate with clinical disease activity in patients with axSpA [66,67]; however, there is conflicting evidence regarding the extent to which tracer uptake correlates with specific Inflammatory Back Pain inflammatory and structural lesions seen on CT and MRI resulting in uncertainty about its diagnostic utility [64,67- 72]. In one study, the interreader reliability of diagnosing sacroiliitis on PET/CT was poor and substantially lower than that for MRI or CT [67]. In a small study using radiographs as the reference standard, F-18-fluoride PET/CT had a sensitivity of 80% and specificity of 77% for the detection of sacroiliitis in AS, although there are inherent limitations in the use of radiographs as the reference standard for diagnosing axSpA [73].


Inflammatory Back Pain Known or Suspected Axial Spondyloarthropathy PCAs. Given the available data, the utility of PET/CT in the diagnosis of axSpA is uncertain at this time. MRI Sacroiliac Joints After radiography is performed, MRI of the sacroiliac joints is the next imaging technique of choice in the evaluation of patients with suspected axSpA [1,3,19,22]. MRI of the sacroiliac joints is widely recognized as an important tool in the evaluation of patients with suspected axSpA, resulting in improved diagnostic confidence and yielding findings that stimulate changes in both diagnosis and treatment plans for patients [1,3,19,22,74]. Additionally, MRI findings have been shown to be predictive of both subsequent radiographic disease progression and the likelihood of response to therapy [36,63,75,76]. MRI, utilizing short tau inversion recovery (STIR) and T1-weighted images, can identify both active inflammatory lesions of the sacroiliac joints (bone marrow edema, capsulitis, synovitis, and enthesitis) and chronic structural lesions (sclerosis, erosions, fat deposition, and ankylosis) that are typical for sacroiliitis [38,77]. MRI demonstrates active sacroiliitis with higher sensitivity and earlier than radiography because of its ability to detect inflammatory lesions of axSpA [13,36,37,78]. The inflammatory changes of sacroiliitis on MRI have been shown to precede structural radiographic findings by three to seven years [36,37]. MRI can also detect the chronic structural lesions of the sacroiliac joints with higher accuracy than radiographs [45]. It is important to recognize that the sensitivity and specificity of MRI for axSpA depends on the imaging criteria used, patient population, and reference standard for diagnosis. Early literature showed 95% sensitivity and 100% specificity of MRI for sacroiliitis, substantially higher than radiographs or bone scintigraphy, although that study included a small number of patients, and most subsequent studies demonstrate smaller yields [41].


Inflammatory Back Pain Known or Suspected Axial Spondyloarthropathy PCAs. The ASAS criteria developed in 2009 utilize the presence of bone marrow edema to define a positive MRI of the sacroiliac joints in axSpA [79]. Using solely the imaging arm of the ASAS algorithm (which includes positive radiographs or positive MRI with one clinical axSpA feature), the ASAS criteria were initially shown to have a sensitivity of 66.2% and specificity of 97.3%, although by combining both imaging and clinical arms of the algorithm the sensitivity was 82.9% and specificity was 84.4% for axSpA [19]. Subsequently, in an inception cohort followed for 8 years, the ASAS definition of a positive MRI demonstrated a sensitivity of 79% and a specificity of 89% for the diagnosis of axSpA [80]. Although the presence of bone marrow edema provides a sensitive evaluation for inflammatory changes in axSpA, bone marrow edema can also be seen in noninflammatory conditions such as in age-related degenerative changes, postpartum patients, patients with chronic back pain, athletes, and in up to 30% of healthy controls [81-85]. As a result, the ASAS MRI criteria have been criticized for decreased specificity of bone marrow edema as the sole MRI diagnostic criterion [82]. Importantly, although bone marrow edema may be nonspecific in some cases, one study found that the presence of a deep bone marrow edema lesion which extends at least 1 cm deep to the articular surface is more specific and found almost exclusively in axSpA [86]. Structural changes of axSpA including erosions, sclerosis, fatty deposition, and ankylosis are not accounted for in the ASAS definition of a positive MRI, although they are important findings in axSpA and should be identified in clinical practice [38].


Inflammatory Back Pain Known or Suspected Axial Spondyloarthropathy PCAs. Two related studies on a group of 187 patients demonstrated high sensitivity of 90% to 92% and specificity of 94% to 97% for the diagnosis of AS by using global assessment of both inflammatory and structural lesions [83,87], and subsequently this group of authors showed that identifying erosions and/or bone marrow edema increases sensitivity for axSpA compared with bone marrow edema alone, without decreasing specificity [85]. They also showed that identifying erosions and/or bone marrow edema on MRI increased both sensitivity and specificity for axSpA compared with the diagnostic criterion of solely bone marrow edema [88]. Subchondral fatty deposition, another chronic finding of structural marrow remodeling, is an additional helpful and highly specific finding in axSpA with reported specificities up to 95% to 98% [89,90]. Finally, intra-articular signal changes including increased T1 signal, T2 hyperintense joint fluid, and ankylosis are highly specific findings for axSpA, and when found together with bone marrow edema can increase the positive predictive value for a diagnosis of axSpA compared with bone marrow edema alone [91,92]. Overall, it is clear that interrogation of sacroiliac joint MRI using both STIR and T1-weighted images is critical to identify both the inflammatory and structural changes of axSpA in clinical practice. MRI has long been considered inferior to CT in demonstrating the structural changes of axSpA, although evolving literature demonstrates that a specific MRI sequence, volumetric interpolated breath-hold examination (VIBE), can Inflammatory Back Pain demonstrate erosions with higher sensitivity and similar specificity compared to conventional T1-weighted imaging, and may be comparable to CT [93,94], making it a promising technique for identifying structural lesions of axSpA on MRI.


Inflammatory Back Pain Known or Suspected Axial Spondyloarthropathy PCAs. Multiple studies have examined diffusion-weighted imaging and dynamic contrast-enhanced MRI to determine their diagnostic utility and performance as imaging biomarkers of inflammation. Although these studies show correlation between diffusion-weighted imaging, dynamic contrast-enhanced, and conventional sequences, there is no evidence that these MRI techniques provide additional diagnostic utility compared with conventional MRI sequences [95- 106]. Contrast-enhanced MRI can demonstrate active inflammatory changes of the sacroiliac joints in axSpA, although multiple studies show that noncontrast and contrast-enhanced MRI have overall similar diagnostic utility for axSpA [107-111]. Contrast-enhanced MRI has been reported to increase the diagnostic confidence of MRI interpretation in 1 study [107]. MRI Sacroiliac Joints and Spine Area of Interest After radiography is performed, MRI is the next imaging technique of choice in the evaluation of suspected axSpA [1,3,19,22]. MRI of the sacroiliac joints and spine is associated with improved diagnostic confidence in axSpA and yields findings that stimulate changes in both diagnosis and treatment plans for patients [74]. Although there is agreement in the literature and among experts that MRI should include the sacroiliac joints, there is not a consistently established convention to guide the clinician on whether to image only the sacroiliac joints or both the sacroiliac joints and the spine in patients with suspected axSpA [1,3,19,22]. Not unexpectedly, there is heterogeneity in clinical practice regarding the use of MRI to evaluate the sacroiliac joints and/or spine in these patients [112]. One study has shown that the majority of patients can be diagnosed with axSpA by obtaining MRI of the sacroiliac joints only [60]. Another study shows that the addition of spine MRI to sacroiliac joint MRI adds little incremental value in the diagnosis of nonradiographic axSpA [113].


Inflammatory Back Pain Known or Suspected Axial Spondyloarthropathy PCAs. However, axSpA often involves the axial skeleton proximal to the sacroiliac joints and may exhibit findings isolated to the spine. For example, in a study of whole-body MRI in active axSpA, 99% of patients were found to have active inflammatory lesions in the axial skeleton, with inflammatory changes isolated to the sacroiliac joints in 52% of patients, inflammatory changes isolated to the spine in 5% of patients, and with inflammatory changes at both the sacroiliac joints and spine in 41% of patients [59]. Other studies have shown widely varying degrees of isolated spinal involvement on MRI ranging from 1% to 49% [19,60-63,114,115]. In early axSpA, it has been shown that inflammation involving both the sacroiliac joints and spine can be seen in 28.3% of patients [116]. Therefore, it can be useful in some cases to image both the sacroiliac joints and the spine to help ensure MRI yields the highest diagnostic utility and establishes the extent of disease burden. The decision on whether to image the spine as well as the sacroiliac joints could be based on the site of symptoms. Although there is some disagreement about the extent to which inflammatory changes in the axial skeleton correspond with symptoms, imaging the spine in the clinical region of interest is beneficial in the setting of referable symptoms [62,117-119]. Multiple authors utilize whole-spine or whole-body MRI to identify the burden of disease throughout the spine rather than imaging specific segments because findings may potentially be found in any portion of the spine [10,59,63,89,114,120-122]. The spine MRI findings of axSpA include the active inflammatory changes of spondylitis and spondylodiscitis, inflammatory changes of the costovertebral joints, costotransverse joints, and facet joints, and areas of enthesitis along other vertebral ligamentous attachments [123].


Inflammatory Back Pain Known or Suspected Axial Spondyloarthropathy PCAs. The chronic structural changes of fatty deposition, erosions, and syndesmophytes are also characteristic findings [123]. One study showed that the presence of two or more corner inflammatory lesions had a sensitivity of 69% and specificity of 94% for AS and that lateral vertebral inflammatory lesions had high specificity of 97% [120]. The presence of multiple lesions in the spine has shown to be useful; specifically the presence of at least 5 inflammatory lesions or 5 fatty lesions in the spine has been shown to have a specificity of 95% for axSpA [89]. One study shows that the corner sign in the lumbar spine on T1- weighted or T2-weighted images without fat saturation has a sensitivity of 62% and specificity of 96% for AS [12]. Furthermore, it has been shown that the presence of multiple fatty corner lesions in the spine has a high specificity of 98% and can be useful in the absence of active inflammatory lesions [11]. The ASAS considers a spine MRI positive for axSpA if there are three or more sites of inflammatory spondylitis and considers fatty corner deposition at several sites suggestive of axSpA especially in younger adults [123]. A subsequent study confirmed that the presence of multiple corner lesions has high specificity for axSpA, although it showed a low diagnostic utility because of low sensitivity [121]. Importantly, the findings on spine MRI should be interpreted alongside sacroiliac joint MRI to ensure the highest diagnostic utility. Additionally, MRI findings should be interpreted with specific Inflammatory Back Pain attention to identify associated morphologic findings such as disc degeneration or osteophytes that favor degenerative changes rather than axSpA, because both inflammatory and fatty lesions can occur in degenerative changes [124].


Inflammatory Back Pain Known or Suspected Axial Spondyloarthropathy PCAs. Contrast-enhanced MRI can demonstrate active inflammatory changes of the sacroiliac joints and spine in axSpA, although multiple studies show that noncontrast and contrast-enhanced MRI have overall similar diagnostic utility for axSpA [9,107-111,125-129]. Contrast-enhanced MRI has been reported to increase the diagnostic confidence and reliability of MRI interpretation in 2 studies [9,107]. US Sacroiliac Joints US is not suggested as a routine diagnostic modality for the evaluation of sacroiliitis in patients with suspected axSpA because of its lack of established diagnostic utility [22]. Importantly, US provides evaluation limited to the superficial posterior margins of the sacroiliac joints, and therefore many structural details are not demonstrated. Many of the available studies examine the utility of Doppler evaluation. It has been shown that patients with active sacroiliitis because of axSpA have lower Doppler US resistive indices than healthy controls or patients with osteoarthritis at the sacroiliac joints [130-132]. Using MRI as the reference standard in a study of 51 patients with AS, a pulsatile monophasic waveform was shown to have a sensitivity of 82% and specificity of 92% for active disease, although 18.5% of active AS patients, 70.8% of inactive AS patients, and 63.3% of normal patients had no Doppler flow identified, and the sensitivity for detection of AS patients overall was only 43% [133]. One study reported higher sensitivity of contrast-enhanced US compared with conventional US [134,135]. A recent systematic review of US of the sacroiliac joints in spondyloarthritis reported a median sensitivity of 90% and specificity of 89% in seven of those studies, although with variation in the method of evaluation and reference standard. The authors concluded that there is not enough evidence to support the use of US for the diagnosis of axSpA [136].


Inflammatory Back Pain Known or Suspected Axial Spondyloarthropathy PCAs. US Sacroiliac Joints and Spine Area of Interest US is not suggested as a routine diagnostic modality for the evaluation of sacroiliitis in patients with suspected axSpA because of its lack of established diagnostic utility [22]. Importantly, US provides evaluation limited to the superficial posterior margins of the sacroiliac joints and spine, and therefore many structural details are not demonstrated. Many of the available studies examine the utility of Doppler evaluation. In addition to data showing decreased resistive indices at the sacroiliac joints in patients with active sacroiliitis joints [130-132], there is evidence that resistive indices of the thoracolumbar paraspinal areas are also decreased in patients with AS [132]. However, there is not enough evidence to support the use of US for the diagnosis of axSpA. Variant 3: Inflammatory back pain. Suspected axial spondyloarthritis. Negative radiographs and negative MRI of the sacroiliac joints. Next imaging study. The body regions covered in this clinical scenario are the sacroiliac joints, cervical, thoracic, and lumbar spine. These body regions might be evaluated separately or in combination as guided by physical examination findings, patient history, and other available information. Bone Scan with SPECT or SPECT/CT Spine Area of Interest Bone scintigraphy is not routinely suggested in the evaluation of patients with suspected axSpA because of its lack of established diagnostic utility [22]. Conventional bone scintigraphy has low to moderate sensitivity and variable specificity for the diagnosis of axSpA [41,42,50]. If bone scintigraphy is used, because of the complexity of the spine anatomy, the use of SPECT should be performed during the examination [51].


Inflammatory Back Pain Known or Suspected Axial Spondyloarthropathy PCAs. Although bone scintigraphy is not typically performed during the evaluation of suspected axSpA because of its limited diagnostic utility, there is recent data that hybrid SPECT/CT has higher sensitivity than conventional bone scintigraphy in the detection of sacroiliitis [52,53], although there is not enough evidence at this time to support its routine use for evaluating the sacroiliac joints or spine. CT Spine Area of Interest CT demonstrates structural changes in the spine that may not be apparent on radiographs [22], including structural changes such as erosions, sclerosis, bone formation, syndesmophytes, and ankyloses [49,54]. CT has been shown to demonstrate syndesmophytes with higher sensitivity than radiographs and low-dose protocols can be utilized [58]. CT is especially helpful for evaluation of the thoracic spine and facet joints, which can be challenging to evaluate on radiography [49]. Although MRI remains the technique of choice for the diagnosis of axSpA [1,3,19,22], CT can be useful in patients in the setting of prior negative radiographic and negative CT evaluation of Inflammatory Back Pain the sacroiliac joints in order to identify patients with axSpA who have disease isolated to the spine, which has been shown to occur in a variable percentage of patients based on data from MRI studies [19,59-63]. There is no role for contrast-enhanced CT in the evaluation of axSpA. Fluoride PET/CT Skull Base to Mid-Thigh There is not enough data to support the routine use of PET/CT in the evaluation of patients with suspected axSpA. F-18-fluoride has been shown to be a potentially useful tracer in identifying sites of osteoblastic activity in axSpA patients [64,65].


Inflammatory Back Pain Known or Suspected Axial Spondyloarthropathy PCAs. Uptake on PET/CT has also been shown to correlate with clinical disease activity in patients with axSpA [66,67]; however, there is conflicting evidence regarding the extent to which tracer uptake correlates with specific inflammatory and structural lesions seen on CT and MRI resulting in uncertainty about its diagnostic utility [64,67-72]. In one study, the interreader reliability of diagnosing sacroiliitis on PET/CT was poor and substantially lower than that for MRI or CT [67]. In a small study using radiographs as the reference standard, F-18-fluoride PET/CT had a sensitivity of 80% and specificity of 77% for the detection of sacroiliitis in AS, although there are inherent limitations in the use of radiographs as the reference standard for diagnosing axSpA [73]. Given the available data, the utility of PET/CT in the diagnosis of axSpA, including its utility in assessment of the spine, is uncertain at this time. MRI Spine Area of Interest Although MRI of the sacroiliac joints has high utility for the diagnosis of axSpA, some patients will not demonstrate imaging features of axSpA in the sacroiliac joints on MRI as indicated by sensitivities of all studies to varying degrees below 100% [22], and therefore some patients may need further imaging evaluation with MRI given that it is the imaging modality of choice for the diagnosis of axSpA [1,3,19,22]. Studies have shown widely varying degrees of isolated spinal involvement on MRI in axSpA ranging from 1% to 49% [19,59-63,114,115]. Therefore, imaging of the spine is beneficial for patients in whom there is suspicion for axSpA but imaging of the sacroiliac joints has been negative. Some authors have shown the utility of using whole-spine or whole-body MRI to identify the burden of disease rather than selecting specific areas of the spine to image because findings may be potentially isolated to any portion of the spine [10,59,63,89,114,120-122].


Inflammatory Back Pain Known or Suspected Axial Spondyloarthropathy PCAs. The spine MRI findings of axSpA include the active inflammatory changes of spondylitis and spondylodiscitis, the inflammatory changes of the costovertebral joints, costotransverse joints, and facet joints and areas of enthesitis along other vertebral ligamentous attachments [123]. The chronic structural changes of fatty deposition, erosions, and syndesmophytes are also characteristic findings [123]. One study showed that the presence of two or more corner inflammatory lesions had a sensitivity of 69% and specificity of 94% for AS and that lateral vertebral inflammatory lesions had high specificity of 97% [120]. The presence of multiple lesions in the spine has shown to be useful; specifically the presence of at least five inflammatory lesions or five fatty lesions in the spine has been shown to have a specificity of 95% for axSpA [89]. One study shows that the corner sign in the lumbar spine on T1-weighted or T2-weighted images without fat saturation has a sensitivity of 62% and specificity of 96% for AS [12]. Furthermore, it has been shown that the presence of multiple fatty corner lesions in the spine has a high specificity of 98% and can be useful in the absence of active inflammatory lesions [11]. The ASAS considers a spine MRI positive for axSpA if there are three or more sites of inflammatory spondylitis and considers fatty corner deposition at several sites suggestive of axSpA especially in younger adults [123]. A subsequent study confirmed that the presence of multiple corner lesions has a high specificity for axSpA, although it showed a low diagnostic utility because of low sensitivity [121]. Importantly, the findings on spine MRI should be interpreted alongside sacroiliac joint MRI to ensure the highest diagnostic utility.


Inflammatory Back Pain Known or Suspected Axial Spondyloarthropathy PCAs. Additionally, MRI findings should be interpreted with specific attention to identify associated morphologic findings such as disc degeneration or osteophytes that favor degenerative changes rather than axSpA, because both inflammatory and fatty lesions can occur in degenerative changes [124]. Contrast-enhanced MRI can demonstrate active inflammatory changes of the spine in axSpA, although multiple studies show that noncontrast and contrast-enhanced MRI have overall similar diagnostic utility for axSpA [9,125- 129]. Contrast-enhanced MRI has been reported to increase reliability of MRI interpretation in 1 study [9]. Radiography Spine Area of Interest If radiographs and MRI of the sacroiliac joints have been negative, radiographic evaluation of the spine can be obtained to evaluate for the structural imaging findings of axSpA, including syndesmophytes, erosions, shiny corners, vertebral body squaring, and ankylosis [38]. Although radiographs show structural changes, they will not demonstrate the inflammatory changes or fatty infiltration that can be demonstrated on MRI. Inflammatory Back Pain US Spine Area of Interest US is not beneficial as a diagnostic tool for the evaluation of sacroiliitis in patients with suspected axSpA because of its lack of established diagnostic utility [22]. Importantly, US provides limited evaluation of the superficial posterior margins of the spine, and therefore many structural details are not demonstrated. There is a paucity of evidence literature evaluating US in the spine in patients with axSpA. One study demonstrates that resistive indices of the thoracolumbar paraspinal areas are also decreased in patients with AS, similar to findings reported at the sacroiliac joints [132]. Variant 4: Known axial spondyloarthritis. Follow-up for treatment response or disease progression. The body regions covered in this clinical scenario are the sacroiliac joints, cervical, thoracic, and lumbar spine.


Inflammatory Back Pain Known or Suspected Axial Spondyloarthropathy PCAs. These body regions might be evaluated separately or in combination as guided by physical examination findings, patient history, and other available information. Bone Scan with SPECT or SPECT/CT Sacroiliac Joints Bone scintigraphy is not routinely obtained to evaluate for treatment response or disease progression in axSpA patients, and there is no relevant literature supporting its use in this setting. Bone Scan with SPECT or SPECT/CT Sacroiliac Joints and Spine Area of Interest Bone scintigraphy is not routinely obtained to evaluate for treatment response or disease progression in axSpA patients, and there is no relevant literature supporting its use in this setting. CT Sacroiliac Joints CT demonstrates structural changes of the sacroiliac joints in axSpA that may not be apparent on radiographs [22]; however, it is not routinely used for follow-up or assessing disease progression. CT Sacroiliac Joints and Spine Area of Interest CT demonstrates structural changes of the sacroiliac joints in axSpA that may not be apparent on radiographs [22] and can better demonstrate spinal syndesmophyte growth than radiographs using low-dose techniques [49,58]. However, it is not routinely used for follow-up or assessing disease progression. Fluoride PET/CT Skull Base to Mid-Thigh F-18-fluoride PET/CT is not routinely obtained to evaluate for treatment response or disease progression in axSpA patients, and there is no relevant literature supporting its use in this setting. MRI Sacroiliac Joints There is no standard method of following patients with MRI to evaluate for treatment response or disease progression [22,30]. Although multiple studies demonstrate decreasing inflammation on MRI following treatment with TNF-inhibitors, including some long-term studies showing sustained reduction in inflammation, the degree to which MRI findings correlate with disease activity is variable [30].


Inflammatory Back Pain Known or Suspected Axial Spondyloarthropathy PCAs. The American College of Rheumatology and European League Against Rheumatism agree that the decision to repeat MRI to assess disease activity or monitor for disease response depends on the clinical circumstances [22,30]. Specifically, MRI of the sacroiliac joints may be helpful for cases in which the disease activity is unclear, available clinical or laboratory data are conflicting, or knowledge of MRI findings is expected to alter treatment [30]. MRI can also detect chronic structural changes on axSpA in the sacroiliac joints, although the clinical utility of follow-up for that purpose is not established [137]. Noncontrast and contrast-enhanced MRI have overall similar diagnostic utility for evaluation of the sacroiliac joints in axSpA [107-111]. The Spondyloarthritis Research Consortium of Canada method has been utilized as a scoring system for quantification and follow-up of lesions at the sacroiliac joints on MRI [138]. MRI Sacroiliac Joints and Spine Area of Interest There is no standard method of following patients with MRI to evaluate for treatment response or disease progression [22,30]. Although multiple studies demonstrate decreasing inflammation on MRI following treatment with TNF-inhibitors, including some long-term studies showing sustained reduction in inflammation, the degree to which MRI findings correlate with disease activity is variable [30]. The American College of Rheumatology and European League Against Rheumatism agree that the decision to repeat MRI to assess disease activity or monitor for disease response depends on the clinical circumstances [22,30]. Specifically, MRI of the sacroiliac joints and spine may be helpful for cases in which the disease activity is unclear, available clinical or laboratory data are conflicting, or knowledge of MRI findings is expected to alter treatment [30].