Cerebrovascular Diseases Stroke and Stroke Related Conditions PCAs. MRV Head Without IV Contrast There is no relevant literature to support the use of MRV of the head in the evaluation of the asymptomatic patient with a carotid bruit.


Cerebrovascular Diseases Stroke and Stroke Related Conditions PCAs. US Duplex Doppler Carotid Artery Duplex carotid Doppler is a very accurate and useful screening test in the evaluation of the extracranial vasculature for carotid stenosis in the asymptomatic patient with a carotid bruit, which stratifies patients into groups of mild (<50%), moderate (50%-69%), and severe (>70%) stenosis. Specifically, carotid Doppler has a 90% sensitivity and a 94% specificity in the identification of clinically significant >70% stenosis, which might warrant surgical intervention [111,112,120]. The lack of need for IV contrast decreases the risk to the patient. However, caution must be observed when evaluating patients with either extremely severe stenosis or multivessel involvement because Doppler can overestimate the degree of stenosis in the setting of contralateral disease or multivessel disease or underestimate the stenosis in the setting of critical high-grade stenosis, which may result in artifactual elevation of velocity or reduction in velocity, respectively. Clinically significant carotid disease may trigger further anatomic imaging to characterize stenosis and exclude confounding multivessel disease; however, there is no consensus on this matter. In otherwise uncomplicated cases, US imaging alone may be the only necessary examination in a patient with carotid bruit.


Cerebrovascular Diseases Stroke and Stroke Related Conditions PCAs. US Duplex Doppler Transcranial Transcranial Doppler may be useful, both in the detection of microembolic events and in determining the hemodynamic significance of a known carotid stenosis. However, there is no literature to support transcranial Doppler in the initial workup of the asymptomatic patient with a carotid bruit.


Cerebrovascular Diseases Stroke and Stroke Related Conditions PCAs. Variant 10: Adult. Asymptomatic carotid stenosis. Surveillance imaging. Asymptomatic carotid stenosis is an important diagnostic finding, which may progress to symptomatic stenosis. For asymptomatic patients, advances in medical therapy have rendered data from older clinical trials on the benefit of endarterectomy out of date, and thus the value of determining the degree of stenosis in these patients is less clear and currently the subject of a large randomized clinical trial [108-110]. Currently, guidelines from professional societies continue to recommend CEA for certain selected patients with asymptomatic stenosis in which the degree of stenosis is an important deciding factor [111,112]. Surveillance imaging is an important tool in the management


Cerebrovascular Diseases Stroke and Stroke Related Conditions PCAs. Cerebrovascular Diseases-Stroke of asymptomatic carotid stenosis. From a management prospective, carotid stenosis is divided into 3 categories based on the degree of stenosis including mild (<50%), moderate (50%-69%), and severe (>70%) stenosis, with the latter 2 categories having a higher probability of hemodynamic significance subsequent ipsilateral stroke [121,122]. The risk for progression of carotid stenosis is poorly characterized. In small case-controlled studies, the risk of mild or moderate stenosis to progress is between 30% and 40% within the ensuing 3 years [123]. The type of surveillance imaging indicated is informed by the degree of stenosis and, thereby, concern of the hemodynamic significance of the stenosis. In most cases, surveillance imaging of asymptomatic carotid disease focuses on the area of stenosis guided by the character of the stenosis and presence of involvement of the other cerebrovascular territories. However, if hemodynamically significant stenosis is suspected, parenchymal imaging, physiologic imaging, and invasive imaging may be useful to guide management of asymptomatic carotid disease [112]. For symptomatic carotid disease, please see Variants 1 to 5 for indicated imaging procedures.


Cerebrovascular Diseases Stroke and Stroke Related Conditions PCAs. Arteriography Cervicocerebral Catheter-directed cerebral angiography has the highest spatial resolution and temporal resolution of any vascular study. Catheter-directed angiography accurately measures the degree of vascular stenosis and can also be useful in the evaluation of collateral circulation. However, the usefulness of this technique for surveillance imaging is obviated by the invasive nature of the examination and availability of both sensitive and specific noninvasive tests. Although cerebral angiography is not used as routine surveillance imaging for asymptomatic carotid disease, angiography can be useful in some cases of known, hemodynamically significant stenosis to determine appropriate treatment options.


Cerebrovascular Diseases Stroke and Stroke Related Conditions PCAs. CT Head Perfusion With IV Contrast CT head perfusion imaging may help delineate the hemodynamic significance of a known asymptomatic carotid lesion and the collateral support in each distribution. More specifically, perfusion imaging may be helpful in cases of moderate stenosis, approaching 70% or severe stenosis [124]. However, there is no literature to support the use of CTP as the initial imaging test in surveillance imaging of asymptomatic carotid disease. The need for IV contrast and relative lack of sensitivity for white matter ischemic changes detracts from the routine use of this study in surveillance imaging.


Cerebrovascular Diseases Stroke and Stroke Related Conditions PCAs. CT Head With IV Contrast There is no relevant literature to support the use of contrast-enhanced CT of the head in the surveillance imaging of asymptomatic carotid stenosis.


Cerebrovascular Diseases Stroke and Stroke Related Conditions PCAs. CT Head Without and With IV Contrast There is no relevant literature to support the use of contrast-enhanced CT of the head in the surveillance imaging of asymptomatic carotid stenosis.


Cerebrovascular Diseases Stroke and Stroke Related Conditions PCAs. CT Head Without IV Contrast There is no literature to support noncontrast CT of the head in the routine surveillance imaging of asymptomatic carotid disease. Noncontrast CT of the head is useful in evaluating for the sequela of carotid stenosis such as clinically silent strokes or microvascular ischemic changes in the setting of an established diagnosis of carotid stenosis, which is particularly important in cases of hemodynamically significant stenosis. However, MRI is much more sensitive in evaluating microvascular ischemic changes or recent strokes. Symptomatic carotid disease should be evaluated relative to the underlying symptoms. Please see Variants 1 to 5 for a discussion of appropriate imaging.


Cerebrovascular Diseases Stroke and Stroke Related Conditions PCAs. CTA Head With IV Contrast There is no literature to support CTA of the head in routine surveillance imaging of known asymptomatic carotid disease with no future treatment plans. CTA of the head may be useful in treatment planning for patients with an established diagnosis of hemodynamically significant asymptomatic carotid stenosis. Specifically, intracranial collateral characterization may be important when considering both the initial decision to treat and treatment involving proximal embolic protection strategies.


Cerebrovascular Diseases Stroke and Stroke Related Conditions PCAs. CTA Neck With IV Contrast CTA of the neck is useful in the surveillance imaging of some patients with asymptomatic carotid stenosis owing to the anatomic assessment of stenosis. Specifically, CTA of the neck is helpful when multivessel cerebrovascular disease or very severe stenosis is present, which might result in artifactual over or underestimation of the degree of disease by carotid Doppler, respectively [113]. CTA of the neck is also useful for treatment planning [114]. However, CTA of the neck may also underestimate the degree of stenosis in the setting of tortuosity or calcifications similar in density to contrast media [80]. Conversely, CTA may overestimate stenosis in the setting of very severe


Cerebrovascular Diseases Stroke and Stroke Related Conditions PCAs. Cerebrovascular Diseases-Stroke near occlusive stenosis [115]. Dual-energy CT may help limit the overestimation of stenosis in some instances [116].


Cerebrovascular Diseases Stroke and Stroke Related Conditions PCAs. CTV Head With IV Contrast There is no relevant literature to support the use of CTV of the head in the surveillance imaging of asymptomatic carotid stenosis.


Cerebrovascular Diseases Stroke and Stroke Related Conditions PCAs. MRA Head Without and With IV Contrast There is no relevant literature to support the use of contrast-enhanced MRA of the head in the surveillance imaging of asymptomatic carotid stenosis.


Cerebrovascular Diseases Stroke and Stroke Related Conditions PCAs. MRA Head Without IV Contrast There is no literature to support MRA of the head as in ongoing routine surveillance imaging of known asymptomatic carotid disease. MRA of the head may be useful in treatment planning for patients with an established diagnosis of asymptomatic carotid stenosis. Specifically, intracranial collateral characterization may be important when considering both the initial decision to treat and treatment involving proximal embolic protection strategies.


Cerebrovascular Diseases Stroke and Stroke Related Conditions PCAs. MRA Neck Without and With IV Contrast MRA of the neck is useful in the surveillance imaging of some patients with asymptomatic carotid stenosis owing to the anatomic assessment of stenosis and can be useful for treatment planning. Specifically, MRA of the neck is helpful when multivessel cerebrovascular disease or very severe stenosis is present, which might result in artifactual over or underestimation of the degree of disease by carotid Doppler, respectively [113]. Noncontrast MRA of the neck may overestimate the degree of stenosis when severe and/or near occlusive. Contrast administration can reduce the degree of overestimation of the degree of stenosis in some cases. However, contrast-enhanced and TOF MRA of the neck have similar sensitivity for the detection of >70% stenosis of the carotid when 2-D and 3-D techniques of TOF are combined [27,117]. MRA of the neck may also be useful for treatment planning. However, the anatomic definition of the surrounding structures may be inadequate for treatment planning in some cases depending on the sequences used [114]. Additionally, anatomical features of carotid plaque including intraplaque high-intensity signal on 3-D TOF source images can be useful predictors of future stroke risk, beyond assessing the degree of luminal narrowing [85,118,119].


Cerebrovascular Diseases Stroke and Stroke Related Conditions PCAs. MRA Neck Without IV Contrast MRA of the neck is useful in the surveillance imaging of some patients with asymptomatic carotid stenosis owing to the anatomic assessment of stenosis and can be useful for treatment planning. Specifically, MRA of the neck is helpful when multivessel cerebrovascular disease or very severe stenosis is present, which might result in artifactual over- or underestimation of the degree of disease by carotid Doppler, respectively [113]. Noncontrast MRA of the neck may overestimate the degree of stenosis when severe and/or near occlusive. Contrast administration can reduce the degree of overestimation of the degree of stenosis in some cases. However, contrast-enhanced and TOF MRA of the neck have a similar sensitivity for the detection of >70% stenosis of the carotid when 2-D and 3-D techniques of TOF are combined [27,117]. MRA of the neck may also be useful for treatment planning. However, the anatomic definition of the surrounding structures may be inadequate for treatment planning in some cases depending on the sequences used [114]. Additionally, anatomical features of carotid plaque including intraplaque high-intensity signal on 3-D TOF source images can be useful predictors of future stroke risk, beyond assessing the degree of luminal narrowing [85,118,119].


Cerebrovascular Diseases Stroke and Stroke Related Conditions PCAs. MRI Head Perfusion With IV Contrast Contrast-enhanced MRI head perfusion imaging (or, if available, noncontrast ASL perfusion) may help delineate the hemodynamic significance of a known asymptomatic carotid lesion and the collateral support in each distribution. More specifically, perfusion imaging may be helpful in cases of moderate stenosis, approaching 70% or severe stenosis [124].


Cerebrovascular Diseases Stroke and Stroke Related Conditions PCAs. MRI Head Without and With IV Contrast There is no relevant literature to support the use of contrast-enhanced MRI of the head in the surveillance imaging of asymptomatic carotid stenosis.


Cerebrovascular Diseases Stroke and Stroke Related Conditions PCAs. MRI Head Without IV Contrast MRI of the head is useful in evaluating for the sequela of carotid stenosis such as clinically silent strokes or microvascular ischemic changes in the setting of an established diagnosis of carotid stenosis, which is particularly important in cases of hemodynamically significant stenosis. There may be a role for noncontrast MRI of the head


Cerebrovascular Diseases Stroke and Stroke Related Conditions PCAs. Cerebrovascular Diseases-Stroke when monitoring patients with risk factors for stroke or known carotid stenosis. However, symptomatic carotid disease should be evaluated relative to the underlying symptoms. Please see Variants 1 to 5 for a discussion of appropriate imaging.


Cerebrovascular Diseases Stroke and Stroke Related Conditions PCAs. MRV Head Without and With IV Contrast There is no relevant literature to support the use of MRV of the head in the surveillance imaging of asymptomatic carotid stenosis.


Cerebrovascular Diseases Stroke and Stroke Related Conditions PCAs. MRV Head Without IV Contrast There is no relevant literature to support the use of MRV of the head in the surveillance imaging of asymptomatic carotid stenosis.


Cerebrovascular Diseases Stroke and Stroke Related Conditions PCAs. US Duplex Doppler Carotid Artery Duplex carotid Doppler is a very accurate and useful test in the evaluation of the extracranial vasculature in the setting of carotid stenosis, which stratifies patients into groups of mild (<50%), moderate (50%-69%), and severe (>70%) stenosis. Specifically, carotid Doppler has a 90% sensitivity and a 94% specificity in the identification of clinically significant >70% stenosis, which might warrant surgical intervention [120]. The lack of need for IV contrast decreases the risk to the patient. However, caution must be observed when evaluating patients with either extremely severe stenosis or multivessel involvement because Doppler can overestimate the degree of stenosis in the setting of contralateral disease or multivessel disease or underestimate the stenosis in the setting of critical high- grade stenosis, which may result in artifactual elevation of velocity or reduction in velocity, respectively. In the absence of suspected confounding factors that might result in Doppler error or active treatment plan, US imaging may be the only indicated examination in a patient with carotid bruit.


Cerebrovascular Diseases Stroke and Stroke Related Conditions PCAs. US Duplex Doppler Transcranial Transcranial Doppler may be useful, both in the detection of microembolic events and in determining the hemodynamic significance of a known carotid stenosis. However, there is no literature to support transcranial Doppler in the surveillance imaging of asymptomatic carotid stenosis.


Cerebrovascular Diseases Stroke and Stroke Related Conditions PCAs. Arteriography Cervicocerebral Catheter-directed cerebral angiography has the highest spatial resolution and temporal resolution of any vascular study. As such, catheter-directed angiography is the most accurate means of grading a cervical dissection, delineating the degree of associated stenosis, and may also be useful in assessment of collateral circulation. Additionally, some subtle dissections may be more apparent due to higher spatial resolution. However, the usefulness of this technique in screening for dissection is obviated by the invasive nature of the test. There is no literature supporting cerebral angiography as the initial imaging test for suspected cervical vascular dissection. Cervicocerebral angiography may influence treatment options after the initial diagnosis of dissection in patients with severe presenting symptoms such as focal neurological deficits [126]; however, the degree of stenosis may not influence the rate of further stroke [127,128].


Cerebrovascular Diseases Stroke and Stroke Related Conditions PCAs. Cerebrovascular Diseases-Stroke CT Head Perfusion With IV Contrast There is no literature to support the use of CTP in the initial imaging of suspected cervical vascular dissection or injury.


Cerebrovascular Diseases Stroke and Stroke Related Conditions PCAs. CT Head With IV Contrast There is no relevant literature to support the use of contrast-enhanced CT of the head in the initial imaging of suspected cervical vascular dissection or injury.


Cerebrovascular Diseases Stroke and Stroke Related Conditions PCAs. CT Head Without and With IV Contrast There is no relevant literature to support the use of contrast-enhanced CT of the head in the initial imaging of suspected cervical vascular dissection or injury.


Cerebrovascular Diseases Stroke and Stroke Related Conditions PCAs. CT Head Without IV Contrast Noncontrast CT may be useful in the setting of a known dissection to evaluate for complications such as hemorrhagic conversion, mass effect, and herniation or in the exclusion of ICH before the initiation of anticoagulation or antiplatelet therapy for a known dissection. However, MRI is much more sensitive in evaluating recent strokes.


Cerebrovascular Diseases Stroke and Stroke Related Conditions PCAs. CTA Head With IV Contrast CTA of the head may be useful in the evaluation for intracranial extension of a known cervical dissection. CTA of the head may also be useful for evaluation of intracranial collaterals of the circle of Willis and excluding associated intracranial LVO, which is important in stroke risk stratification and treatment strategies. As such, although a CTA of the head may be necessary in the workup of a known cervical artery dissection, there is no literature to support CTA of the head in the initial screening examination for a suspected cervical artery dissection.


Cerebrovascular Diseases Stroke and Stroke Related Conditions PCAs. CTA Neck With IV Contrast CTA of the neck is useful in the initial screening examination for suspected cervical vascular dissection owing to rapid acquisition and high spatial resolution of the examination. Rapid examination is important in the evaluation for suspected cervical dissection due to the stroke risk associated with treatment delays. The high resolution of CTA neck allows for the detection of fairly subtle dissections with high sensitivity for both cervical carotid and vertebral artery dissections with a sensitivity and specificity approaching 98% [129]. CTA neck can rapidly and accurately grade the degree of luminal narrowing, vessel irregularity, wall thickening/hematoma, pseudoaneurysm, and intimal flap, which may make it preferable to MRA [130]. CTA neck also allows for fairly accurate grading of dissections comparable to digital subtraction angiography, which may be helpful in clinical management [131]. The potential detractors from CTA of the neck are the requirements for iodinated contrast and ionizing radiation.


Cerebrovascular Diseases Stroke and Stroke Related Conditions PCAs. CTV Head With IV Contrast There is no relevant literature to support the use of CTV of the head in the initial imaging of suspected cervical vascular dissection or injury.


Cerebrovascular Diseases Stroke and Stroke Related Conditions PCAs. MRA Head Without and With IV Contrast There is no relevant literature to support the use of contrast-enhanced MRA of the head in the initial imaging of suspected cervical vascular dissection or injury.


Cerebrovascular Diseases Stroke and Stroke Related Conditions PCAs. MRA Head Without IV Contrast MRA of the head may be useful in evaluation for intracranial extension of a known cervical dissection. MRA of the head may also be useful for evaluation of intracranial collaterals of the circle of Willis, which is important in stroke risk stratification and treatment strategies. As such, although an MRA of the head may be useful in the workup of a known cervical dissection, there is no literature to support MRA of the head in the initial imaging of suspected cervical arterial dissection.


Cerebrovascular Diseases Stroke and Stroke Related Conditions PCAs. MRA Neck Without and With IV Contrast MRA of the neck is useful in the initial screening examination for suspected cervical vascular dissection owing to high tissue contrast, especially incorporating fat-saturated T1-weighted sequences, which may be helpful in delineation of subtle intramural hematomas improving visibility to the examiner. The sensitivity of MRI neck is similar to CTA neck for cervical carotid dissections. However, the sensitivity for detection of cervical vertebral artery dissections is significantly reduced compared with CTA neck to as low as 60%, with some variability depending on the technique and sequences employed [129]. Limitations of MRA neck include longer acquisition times and lower spatial resolution, which may delay care or miss subtle intimal irregularities associated with suspected cervical vascular dissections, particularly those involving the vertebral artery. Additionally, an


Cerebrovascular Diseases Stroke and Stroke Related Conditions PCAs. Cerebrovascular Diseases-Stroke unenhanced MRA of the neck may also overestimate the degree of stenosis in more severe dissections, and the anatomic definition of the surrounding structures may be inadequate for treatment planning in some cases depending on the sequences used. Contrast administration can reduce the degree of overestimation of the degree of stenosis in many cases [132].


Cerebrovascular Diseases Stroke and Stroke Related Conditions PCAs. MRA Neck Without IV Contrast MRA of the neck is useful in the initial screening examination for suspected cervical vascular dissection owing to high tissue contrast, especially incorporating fat-saturated T1-weighted sequences, which may be helpful in the delineation of subtle intramural hematomas, improving visibility to the examiner. The sensitivity of MRI neck is similar to CTA neck for cervical carotid dissections. However, the sensitivity for the detection of cervical vertebral artery dissections is significantly reduced compared with CTA neck to as low as 60%, with some variability depending on the technique and sequences employed [129]. Limitations of MRA neck include longer acquisition times and lower spatial resolution, which may delay care or miss subtle intimal irregularities associated with suspected cervical vascular dissections, particularly those involving the vertebral artery. Additionally, an unenhanced MRA of the neck may also overestimate the degree of stenosis in more severe dissections, and the anatomic definition of the surrounding structures may be inadequate for treatment planning in some cases depending on the sequences used. Contrast administration can reduce the degree of overestimation of the degree of stenosis in many cases [132].


Cerebrovascular Diseases Stroke and Stroke Related Conditions PCAs. MRI Head Perfusion With IV Contrast There is no literature to support the use of MRI head perfusion as the initial imaging test in the detection of a suspected cervical artery dissection.


Cerebrovascular Diseases Stroke and Stroke Related Conditions PCAs. MRI Head Without and With IV Contrast There is no relevant literature to support the use of contrast-enhanced MRI of the head in the initial imaging of suspected cervical vascular dissection or injury.


Cerebrovascular Diseases Stroke and Stroke Related Conditions PCAs. MRI Head Without IV Contrast MRI of the head may be useful in evaluating strokes in the setting of a known dissection or in the exclusion of ICH before the initiation of anticoagulation or antiplatelet therapy for a known dissection. As such, although an MRI of the head may be useful in the workup of a known dissection, there is no literature to support an MRI of the head in the initial screening examination for a suspected cervical artery dissection.


Cerebrovascular Diseases Stroke and Stroke Related Conditions PCAs. MRV Head Without and With IV Contrast There is no relevant literature to support the use of MRV of the head in the initial imaging of suspected cervical vascular dissection or injury.


Cerebrovascular Diseases Stroke and Stroke Related Conditions PCAs. MRV Head Without IV Contrast There is no relevant literature to support the use of MRV of the head in the initial imaging of suspected cervical vascular dissection or injury.


Cerebrovascular Diseases Stroke and Stroke Related Conditions PCAs. US Duplex Doppler Carotid Artery There is no literature that supports duplex Doppler examination of the carotid in the initial imaging of suspected cervical vascular dissection or injury.


Cerebrovascular Diseases Stroke and Stroke Related Conditions PCAs. US Duplex Doppler Transcranial Transcranial Doppler may be useful, both in the detection of microembolic events and in determining the hemodynamic significance of a known cervical vascular dissection. However, there is no literature to support transcranial Doppler in the initial imaging of suspected cervical vascular dissection or injury.


Cerebrovascular Diseases Stroke and Stroke Related Conditions PCAs. Variant 12: Adult. Known cervical vascular dissection or injury. Surveillance imaging. Cervical cerebrovascular dissections are an important stroke etiology across all age ranges with an incidence of 2 per 100,000, accounting for 15% of all strokes [125]. The indications for neurologic imaging in the surveillance of vascular dissection vary based on the cause and severity of dissection, stability of the patient, and presence of ongoing or worsening symptoms. Cerebrovascular dissections associated with major nonpenetrating trauma are typically graded on the Biffl scale, which is in most cases colloquially referred to as the Denver grading scale. Higher-grade dissections are more likely to result in ischemic complications [126]. For these dissections associated with major nonpenetrating trauma, repeat imaging with CTA neck is recommend at 7 days and again at 3 months [133]. For patients with minor or no trauma, outcome is not correlated with the degree of subsequent recanalization


Cerebrovascular Diseases Stroke and Stroke Related Conditions PCAs. Cerebrovascular Diseases-Stroke so a role of follow-up imaging has not been established [134-136]. The subsequent surveillance imaging of cervical vascular dissections centers on the evaluation of healing of the dissection, risk stratification, and development for ongoing ischemic and hemorrhagic complications. Surveillance imaging is less focused on screening for intracranial complication of known dissection beyond the early stages of vascular injury. For indicated imaging in patients with focal neurological deficits relative to cervicocerebral dissections, please see Variants 1 to 5 for additional indicated imaging procedures. Dissection may also be the result of suspected connective tissue disorder, which may also warrant further imaging workup.


Cerebrovascular Diseases Stroke and Stroke Related Conditions PCAs. Arteriography Cervicocerebral Catheter-directed cerebral angiography may be useful in the surveillance imaging of some selected cases of known vascular dissection. Specifically, assessment for complete healing of a previously symptomatic dissection or assessment of progression of a known dissection with new or ongoing focal neurological symptom may be more completely assessed by catheter-directed angiography owing to higher spatial and temporal resolution compared with other vascular studies.


Cerebrovascular Diseases Stroke and Stroke Related Conditions PCAs. CT Head Perfusion With IV Contrast For indicated imaging in patients with focal neurological deficits relative to cervicocerebral cervical dissections, please see Variants 1 to 5 for additional indicated imaging procedures. However, there is no literature to support the use of CTP as a routine surveillance imaging test in the ongoing evaluation of cervical artery dissections.


Cerebrovascular Diseases Stroke and Stroke Related Conditions PCAs. CT Head With IV Contrast There is no relevant literature to support the use of contrast-enhanced CT of the head in the surveillance imaging of cervical vascular dissection.


Cerebrovascular Diseases Stroke and Stroke Related Conditions PCAs. CT Head Without and With IV Contrast There is no relevant literature to support the use of contrast-enhanced CT of the head in the surveillance imaging of cervical vascular dissection.


Cerebrovascular Diseases Stroke and Stroke Related Conditions PCAs. CT Head Without IV Contrast In the absence of ongoing symptoms, there is no literature to support routine surveillance imaging of the brain parenchyma in the setting of cervical vascular dissection. Noncontrast CT may be useful in the setting of a known dissection in the patient with ongoing or new symptoms to evaluate for new ischemic stroke and complications such as hemorrhagic conversion, mass effect, and herniation or in the exclusion of ICH in the setting of ongoing medical treatment of vascular dissections. However, MRI is much more sensitive in evaluating recent strokes.


Cerebrovascular Diseases Stroke and Stroke Related Conditions PCAs. CTA Head With IV Contrast There is no literature to support CTA of the head in the routine surveillance of known dissections isolated to the cervical vasculature. CTA of the head may be useful in the surveillance of cervical vascular dissections that are known to extend into the intracranial vasculature. CTA of the head may also be useful for the evaluation of intracranial collaterals of the circle of Willis and excluding associated intracranial LVO in patients with ongoing symptoms, which is important in stroke risk stratification and treatment strategies.


Cerebrovascular Diseases Stroke and Stroke Related Conditions PCAs. CTA Neck With IV Contrast CTA of the neck is useful in ongoing surveillance imaging of cervical vascular dissection owing to high spatial resolution of the examination. The high resolution of CTA allows for the detection of subtle dissections with high sensitivity for both cervical carotid and vertebral artery dissections with a sensitivity and specificity approaching 98%, which informs the usefulness of CTA in follow-up surveillance imaging [129]. CTA can rapidly and accurately grade the degree of luminal narrowing, vessel irregularity, wall thickening/hematoma, pseudoaneurysm, and intimal flap, which may make it preferable to MRA [130]. CTA also allows for accurate grading of dissections comparable to digital subtraction angiography, which may be helpful in clinical management [131]. The potential detractors from CTA of the neck are the requirements for iodinated contrast and ionizing radiation.


Cerebrovascular Diseases Stroke and Stroke Related Conditions PCAs. CTV Head With IV Contrast There is no relevant literature to support the use of CTV of the head in the surveillance imaging of cervical vascular dissection.


Cerebrovascular Diseases Stroke and Stroke Related Conditions PCAs. MRA Head Without and With IV Contrast There is no relevant literature to support the use of contrast-enhanced MRA of the head in the surveillance imaging of cervical vascular dissection.


Cerebrovascular Diseases Stroke and Stroke Related Conditions PCAs. Cerebrovascular Diseases-Stroke MRA Head Without IV Contrast There is no literature to support MRA of the head in the routine surveillance of known dissections isolated to the cervical vasculature. MRA of the head may be useful in the surveillance of cervical vascular dissections that are known to extend into the intracranial vasculature. MRA of the head may also be useful for the evaluation of intracranial collaterals of the circle of Willis and excluding associated intracranial LVO in patients with ongoing symptoms, which is important in stroke risk stratification and treatment strategies.


Cerebrovascular Diseases Stroke and Stroke Related Conditions PCAs. MRA Neck Without and With IV Contrast MRA of the neck may be useful in the surveillance imaging of known cervical vascular dissections owing to high tissue contrast, especially incorporating fat-saturated T1-weighted sequences, which may better demonstrate subtler intramural hematomas that may not be visible on other noninvasive studies. However, some dissections may be too subtle to follow by MRA of the neck due to lower spatial resolution compared with CTA. Specifically, the sensitivity of MRI is similar to CTA for cervical carotid dissections; however, the sensitivity for the detection of cervical vertebral artery dissections is significantly reduced compared with CTA to as low as 60% with some variability depending on the technique and sequences employed [129]. Unenhanced MRA of the neck may also overestimate the degree of stenosis in more severe dissections, and the anatomic definition of the surrounding structures may be inadequate for treatment planning in some cases depending on the sequences used. Contrast administration can reduce the degree of overestimation of the degree of stenosis in many cases [132].


Cerebrovascular Diseases Stroke and Stroke Related Conditions PCAs. MRA Neck Without IV Contrast MRA of the neck may be useful in the surveillance imaging of known cervical vascular dissections owing to high tissue contrast, especially incorporating fat-saturated T1-weighted sequences, which may better demonstrate subtler intramural hematomas that may not be visible on other noninvasive studies. However, some dissections may be too subtle to follow by MRA of the neck due to lower spatial resolution compared with CTA. Specifically, the sensitivity of MRI is similar to CTA for cervical carotid dissections; however, the sensitivity for detection of cervical vertebral artery dissections is significantly reduced compared with CTA to as low as 60% with some variability depending on the technique and sequences employed [129]. Unenhanced MRA of the neck may also overestimate the degree of stenosis in more severe dissections, and the anatomic definition of the surrounding structures may be inadequate for treatment planning in some cases depending on the sequences used. Contrast administration can reduce the degree of overestimation of the degree of stenosis in many cases [132].


Cerebrovascular Diseases Stroke and Stroke Related Conditions PCAs. MRI Head Perfusion With IV Contrast There is no literature to support the use of MRI head perfusion in the surveillance imaging of cervical vascular dissection.


Cerebrovascular Diseases Stroke and Stroke Related Conditions PCAs. MRI Head Without and With IV Contrast There is no relevant literature to support the use of contrast-enhanced MRI of the head in the surveillance imaging of cervical vascular dissection.


Cerebrovascular Diseases Stroke and Stroke Related Conditions PCAs. MRI Head Without IV Contrast There is no literature to support an MRI of the head in the surveillance imaging of cervical vascular dissection. MRI of the head may be useful in the setting of a known dissection in the patient with ongoing or new symptoms to evaluate for new ischemic stroke and complications such as hemorrhagic conversion, mass effect, and herniation or in the exclusion of ICH in the setting of ongoing medical treatment of vascular dissections.


Cerebrovascular Diseases Stroke and Stroke Related Conditions PCAs. MRV Head Without and With IV Contrast There is no relevant literature to support the use of MRV head in the surveillance imaging of cervical vascular dissection.


Cerebrovascular Diseases Stroke and Stroke Related Conditions PCAs. MRV Head Without IV Contrast There is no relevant literature to support the use of MRV head in the surveillance imaging of cervical vascular dissection.


Cerebrovascular Diseases Stroke and Stroke Related Conditions PCAs. US Duplex Doppler Carotid Artery Limited studies have used US in follow-up of known cervical carotid dissection [137]. There is no relevant literature to support the use of US duplex Doppler examination of the carotid in the surveillance imaging of cervical vascular dissection.


Cerebrovascular Diseases-Stroke

Cerebrovascular Diseases Stroke and Stroke Related Conditions PCAs. Cerebrovascular Diseases-Stroke


Cerebrovascular Diseases Stroke and Stroke Related Conditions PCAs. Cerebrovascular Diseases-Stroke Acknowledgement The panel would like to thank Dr. William J. Powers for his valued contribution to the literature review and for his careful review during the narrative drafting portions of topic development.


Cerebrovascular Diseases Stroke and Stroke Related Conditions PCAs. Supporting Documents The evidence table, literature search, and appendix for this topic are available at https://acsearch.acr.org/list. The appendix includes the strength of evidence assessment and the final rating round tabulations for each recommendation.


Cerebrovascular Diseases Stroke and Stroke Related Conditions PCAs. For additional information on the Appropriateness Criteria methodology and other supporting documents go to www.acr.org/ac.


Cerebrovascular Diseases-Stroke


Renal Failure

Renal Failure. AKI is common, affecting up to 20% of hospital inpatients and between 30% to 60% of critically ill patients [3] with a rising incidence worldwide. Hospital-acquired AKI is 5 to 10 times more common than community-acquired AKI. AKI has a significant impact on patient morbidity and mortality with increased health care costs. AKI may be reversible or can lead to CKD.


Renal Failure

Renal Failure. AKI is often multifactorial but generally categorized as prerenal, renal, or postrenal. Prerenal factors include impaired blood flow from any cause including hypotension, hypovolemia, decreased cardiac output, or renal artery occlusion. Renal causes include any disease that damages renal parenchyma, such as vasculitis, acute tubular necrosis, glomerulonephritis, interstitial nephritis, renal infection or infiltration, drugs, and toxins. Postrenal AKI results from ureteral, bladder, or urethral obstruction. Renal and prerenal etiologies far outweigh obstruction as a cause of AKI, accounting for >97% of AKI [4].


Renal Failure

Renal Failure. For appropriate intervention, identification of the specific cause of AKI is critical, as there are different treatments for diseases such as glomerulonephritis, vasculitis, and ureteral obstruction. Evaluation of the patient with AKI includes a thorough history, physical examination, and laboratory analysis of blood (for serum creatinine, blood urea nitrogen, complete blood count, and differential) and urine (microscopy for casts and epithelial cells, chemistry, and biomarkers) [3]. Renal biopsy may be indicated for differentiation of nephritic and nephrotic syndromes [3].


Renal Failure

Renal Failure. CKD is common, affecting 10% of the world population. It is defined as an abnormality of kidney structure or function, present for >3 months, with health consequences [5]. The definition requires knowledge of laboratory values in the preceding 3 months. Hypertension and diabetes are the predominant risk factors for CKD [6]. Five stages of CKD are based on estimated GFR calculated using serum creatinine and standard equations such as the Modification of Diet in Renal Disease study equation or CKD Epidemiology Collaboration equation [7]. Stage 5 with a GFR <15 mL/min per 1.73 m2 body surface area is considered kidney failure [5]. CKD may be silent, progressing through stages of CKD to renal failure. Patients with CKD are at increased risk for hypertension, cardiovascular disease, bone disease, and anemia with increased morbidity and mortality.


Renal Failure

Renal Failure. Evaluation of the patient with CKD will include a thorough history, physical examination, laboratory, and serologic workups. Markers of kidney damage include measurement of albuminuria and urinary sediment; urinary albumin-


Renal Failure

Renal Failure. aUniversity of Maryland School of Medicine, Baltimore, Maryland. bPanel Chair, Northwestern University, Chicago, Illinois. cPanel Vice-Chair, UT Southwestern Medical Center, Dallas, Texas. dUniversity of Rochester Medical Center, Rochester, New York. eThe University of Texas MD Anderson Cancer Center, Houston, Texas. fUniversity of Pennsylvania School of Medicine, Philadelphia, Pennsylvania; American Society of Nephrology. gUniversity of Washington, Seattle, Washington; American Urological Association. hDuke University Medical Center, Durham, North Carolina. iEmory University School of Medicine, Atlanta, Georgia. jThomas Jefferson University Hospital, Philadelphia, Pennsylvania. kUT Health San Antonio, San Antonio, Texas. lCleveland Clinic, Cleveland, Ohio. mMedical University of South Carolina, Charleston, South Carolina; American Urological Association. nUniversity of Alabama at Birmingham, Birmingham, Alabama. oUniversity of California San Francisco School of Medicine, San Francisco, California. pJohns Hopkins University School of Medicine, Washington, District of Columbia. qSpecialty Chair, University of Alabama at Birmingham, Birmingham, Alabama.


Renal Failure

Renal Failure. The American College of Radiology seeks and encourages collaboration with other organizations on the development of the ACR Appropriateness Criteria through representation of such organizations on expert panels. Participation on the expert panel does not necessarily imply endorsement of the final document by individual contributors or their respective organization.


Renal Failure

Renal Failure. Reprint requests to: publications@acr.org


Renal Failure

Renal Failure. Renal Failure to-creatinine ratio is a sensitive and specific marker for CKD. Abnormal histology on kidney biopsy or structural abnormalities on imaging (small echogenic kidneys, dysplastic or polycystic kidneys, renal scarring, hydronephrosis) will also qualify as CKD [8].


Renal Failure

Renal Failure. Special Imaging Considerations The use of iodinated contrast or gadolinium-based contrast agents merits special discussion in the context of renal failure. Generally, iodinated contrast is avoided in AKI unless there is an over-riding clinical question that cannot be answered with an alternative imaging modality or when an intravascular intervention is required [9]. Avoidance of other nephrotoxic drugs, adequate hydration, and close assessment are part of the management. In CKD, the risk- benefit ratio is determined by the level and acuity of kidney disease, specifically weighing the benefits versus risks of any contrast agent. Patients already on hemodialysis or peritoneal dialysis may undergo contrast-enhanced CT if there is no residual renal function.


Renal Failure

Renal Failure. For MRI, there are risk-benefit considerations with respect to the type of gadolinium-based contrast agents. Unenhanced MR angiography (MRA) techniques may be diagnostic. Group II gadolinium-based contrast agents, and lowest diagnostic contrast dose should be standard for contrast-enhanced MRA. Patients already on hemodialysis may undergo contrast-enhanced MRI with group II agents if safety guidelines are followed. For more details please refer to the ACR Manual on Contrast Media [9].


Renal Failure

Renal Failure. Ultrasound (US) contrast media are not nephrotoxic, which makes these potentially ideal agents for microvascular imaging in AKI or CKD [10]. Contrast-enhanced US has the potential to provide dynamic quantitative information about renal perfusion and can diagnose acute cortical necrosis and infarction in allografts and native kidneys [11- 13].


Renal Failure

Renal Failure. All elements are essential: 1) timing, 2) reconstructions/reformats, and 3) 3-D renderings. Standard CTs with contrast also include timing issues and reconstructions/reformats. Only in CTA, however, is 3-D rendering a required element. This corresponds to the definitions that the CMS has applied to the Current Procedural Terminology codes.


Renal Failure

Renal Failure. CT urography (CTU) is an imaging study that is tailored to improve visualization of both the upper and lower urinary tracts. There is variability in the specific parameters, but it usually involves unenhanced images followed by intravenous (IV) contrast-enhanced images, including nephrographic and excretory phases acquired at least 5 minutes after contrast injection. Alternatively, a split-bolus technique uses an initial loading dose of IV contrast and then obtains a combined nephrographic-excretory phase after a second IV contrast dose; some sites include arterial phase. CTU should use thin-slice acquisition. Oral hydration, IV saline hydration, compression bands, and low- dose furosemide have all been reported as methods to improve urinary distension. Reconstruction methods commonly include maximum intensity projection or 3-D volume rendering. For the purposes of this document, we make a distinction between CTU and CT abdomen and pelvis without and with IV contrast. CT abdomen and pelvis without and with IV contrast is defined as any protocol not specifically tailored for evaluation of the upper and lower urinary tracts and without both the precontrast and excretory phases.


Renal Failure

Renal Failure. MR urography (MRU) is also tailored to improve imaging of the urinary system. Unenhanced MRU relies upon heavily T2-weighted imaging of the intrinsic high signal from urine for evaluation of the urinary tract. IV contrast is administered to provide additional information regarding obstruction, urothelial thickening, focal lesions, and stones. Contrast-enhanced T1-weighted series should include corticomedullary, nephrographic, and excretory phase. Thin-slice acquisition and multiplanar imaging should be obtained. MRU is most commonly performed on a 1.5T machine, but imaging at 3T has become more widely used; however, comparison of 3T MRU and CTU has not been published in the literature. For the purposes of this document, we make a distinction between MRU and MR abdomen and pelvis without and with IV contrast. MR abdomen and pelvis without and with IV contrast is defined as any protocol not specifically tailored for evaluation of the upper and lower urinary tracts, without both the precontrast and excretory phases and without heavily T2-weighted images of the urinary tract.


Renal Failure

Renal Failure

Renal Failure. Renal Failure


Renal Failure

Renal Failure. OR Discussion of Procedures by Variant Variant 1: Renal failure. Acute kidney injury (AKI), unspecified. Initial imaging. Arteriography Kidney Arteriography is reserved for intervention rather than for the initial diagnosis of AKI. Renal revascularization may be considered in a very select group of patients with AKI. There is no relevant literature regarding the use of arteriography in the evaluation of AKI.


Renal Failure

Renal Failure. CT Abdomen and Pelvis Unenhanced CT abdomen and pelvis is useful for further evaluation of US-detected hydronephrosis by determining level and cause of obstruction. CT is the most sensitive modality for urinary tract calculi and more sensitive than US for retroperitoneal pathology [15]. Although CT can also provide an assessment of renal size and volume, it is generally not considered the first-line imaging modality for AKI [16]. CT may be considered if US is not feasible or is nondiagnostic because body habitus.


Renal Failure

Renal Failure. The use of iodinated contrast hinges on renal function and specific indication. CT with IV contrast is not appropriate for the diagnosis of and determination of the cause of AKI. There is no relevant literature regarding the use of CT abdomen and pelvis with IV contrast in the evaluation of AKI.


Renal Failure

Renal Failure. CT abdomen and pelvis without and with IV contrast is not appropriate for the diagnosis of and determination of the cause of AKI. There is no relevant literature regarding the use of CT abdomen and pelvis without and with IV contrast in the evaluation of AKI.


Renal Failure

Renal Failure. CT Abdomen There is no relevant literature regarding the use of CT abdomen in the evaluation of AKI.


Renal Failure

Renal Failure. CTA Abdomen and Pelvis Contrast-enhanced CTA is very rarely indicated for initial diagnosis of AKI given the potential nephrotoxicity. The risk-benefit ratio should be carefully evaluated if CTA is necessary to diagnose vascular thrombosis or stenosis. The lowest dose of contrast needed for a diagnostic study should be used and supplemented with adequate volume expansion [9]. There is no relevant literature regarding the use of CTA in the evaluation of AKI.


Renal Failure

Renal Failure. CTU There is no relevant literature regarding the use of CTU in the evaluation of AKI. The requirement for IV contrast limits its utility.


Renal Failure

Renal Failure. MRA Abdomen MRA may be considered when there is a high suspicion of a renovascular cause of AKI such as renal artery stenosis, thrombosis, or arterial injury after trauma, all of which are rare [4,17].


Renal Failure

Renal Failure. However, there is no relevant literature regarding the use of MRA abdomen without and with IV contrast in the evaluation of AKI. If contrast-enhanced MRA is needed after consideration of the risks and benefits, group II contrast agents should be used [9]. Contrast-enhanced MRA has a sensitivity of 93% and a specificity of 93% compared with 85% and 84%, respectively, for Doppler US for diagnosis of >60% stenosis [18].


Renal Failure

Renal Failure. Unenhanced MRA techniques, such as time-spatial labeling inversion pulse or steady-state free precession, may be considered in AKI. These techniques have a sensitivity of 73% to 100%, specificity of 82% to 99%, and negative predictive value of 88% to 100% for the diagnosis of >50% renal artery stenosis [19,20].


Renal Failure

Renal Failure. MRI Abdomen and Pelvis MRI with IV contrast is generally not indicated in AKI. Unenhanced MRI may be used to evaluate extent and cause of suspected distal urinary tract obstruction. However, there is no relevant literature regarding the use of MRI abdomen and pelvis without IV contrast in the evaluation of AKI.


Renal Failure

Renal Failure. There is no relevant literature regarding the use of MRI abdomen and pelvis without and with IV contrast in the evaluation of AKI.


Renal Failure

Renal Failure. MRI with IV contrast is generally no t indicated in AKI. However, acute cortical necrosis can be specifically diagnosed when there is a low T2 signal rim at the corticomedullary junction and absence of cortical enhancement [23].


Renal Failure

Renal Failure. MR Urography There is no relevant literature regarding the use of MRU in the evaluation of AKI. However, a nonenhanced contrast MRU may provide additional information in patients with renal failure secondary to obstruction.


Renal Failure

Renal Failure. Radiography Abdomen and Pelvis There is no role for radiography in AKI, other than for evaluation of renal stone disease, which acknowledges that radiography is less sensitive than CT for stone disease [24].


Renal Failure

Renal Failure. DMSA Renal Scan Tc-99m dimercaptosuccinic acid (DMSA) scintigraphy is ideal for functional renal cortical imaging and is most useful for detection of focal renal parenchymal abnormalities and scars in the setting of acute or chronic pyelonephritis or for differential renal function. There is no relevant literature regarding its use in the evaluation of AKI.


Renal Failure

Renal Failure. MAG3 Renal Scan Tc-99m mercaptoacetyltriglycine (MAG3) is the most frequently used renal tubular agent, specifically to quantify renal tubular extraction. Its rate of clearance can be used as an independent measure of renal function. The Tc-99m MAG3 radionuclide angiogram assesses renal perfusion, and the following scintigraphic renogram can quantity split renal function. Diuretic furosemide renography can help to confirm a dilated obstructed versus a dilated nonobstructed renal collecting system. A persistent nephrogram without excretion suggests acute tubular necrosis [25]. Measurement of effective renal plasma flow may provide prognostic information. However, Tc-99m MAG3 is not widely used in the differentiation of causes of AKI.


Renal Failure

Renal Failure. US Kidneys Retroperitoneum US has the greatest diagnostic value in the detection of hydronephrosis associated with acute urinary tract obstruction [4]. Grayscale US is highly sensitive (>90%) for hydronephrosis and bladder distension, allowing localization of the level of obstruction and guiding intervention such as Foley catheter placement or nephrostomy/stenting [26]. However, even in hospitalized patients with AKI, the prevalence of hydronephrosis is low, ranging from 5% to 10%, with obstruction being the cause of AKI in <45.2% of patients with hydronephrosis [4,27-29]. The highest yield for US is in patients with risk factors for urinary obstruction, such as pelvic tumors, bladder disorders, prostate hypertrophy, stone disease, and pelvic surgery. In patients without risk factors for obstruction, <1% of patients had US-detected obstruction [4]. Hydronephrosis does not necessarily indicate obstruction; a distended bladder, reflux, pregnancy, postobstructive dilation, or diuresis may cause ureteral and collecting system dilatation. When the bladder is distended, the patient should be re-evaluated after the bladder has been decompressed by voiding or catheterization. False-negative US studies may be secondary to suboptimal image quality, dehydration, early obstruction, or compression of the renal pelvis or ureters by tumor or fibrosis.


Renal Failure

Renal Failure. A secondary role of US is the evaluation of renal size, echogenicity, and morphology to differentiate AKI from CKD and allow determination of prognosis. Normal renal length is >10 cm in the third decade, but renal length correlates with height, sex, age (negative correlation), and weight in normal patients and varies with the state of hydration or presence of an obstruction [3]. Renal size/volume correlates with creatinine clearance [30]. Both kidney


Renal Failure

Renal Failure

Renal Failure. Renal Failure


Renal Failure

Renal Failure. size and parenchymal thickness decrease in CKD [31]. Therefore, a normal kidney size suggests AKI rather than CKD. However, infiltrative and inflammatory diseases, as well as renal vein thrombosis, may increase kidney size and parenchymal thickness in AKI or CKD. Increased renal echogenicity is associated with acute and chronic medical renal disease, but this is nonspecific and does not correlate well with renal function. Patients with AKI have only a 30% to 40% chance of increased echogenicity [4,28]. Alternatively, small echogenic kidneys are diagnostic of CKD.


Renal Failure

Renal Failure. Color Doppler is routinely used to assess global perfusion and confirm arterial and venous patency. Color Doppler will differentiate a dilated pelvis from prominent renal veins in the renal sinus and can confirm presence or absence of ureteral jets in the bladder.


Renal Failure

Renal Failure. If there is contemporaneous imaging such as CT or MRI showing normal kidneys and no new risk factors for obstruction, additional US is not indicated.


Renal Failure

Renal Failure. US Duplex Doppler Kidneys Retroperitoneal Renovascular causes of AKI are rare; renal artery stenosis was found in 1.5% of cases with AKI even when it was not the cause of AKI [4]. In an older series of intensive care patients, AKI was attributed to renal artery thrombosis, stenosis, or trauma in 1% [17]. The diagnosis of significant renal artery stenosis can be made by obtaining angle- corrected measurements of the peak systolic velocities in the aorta and main renal arteries. Using a cutoff value of 285 cm/s achieved sensitivity, specificity, and overall accuracy of 67%, 90%, and 81%, respectively, for >60% stenosis [32]. In a smaller series, using a cutoff value of 180 cm/s, the sensitivity and specificity of US were 85% and 84%, respectively, for >60% stenosis [18]. Renal artery duplex Doppler studies may be appropriate in selected patients with a high clinical suspicion of renal artery stenosis.


Renal Failure

Renal Failure. Resistive index (RI) has been studied in patients with AKI as a means to detect intrarenal vasoconstriction and differentiate renal from prerenal AKI. An elevated RI has been reported to be an early predictor of early or persistent postoperative AKI after cardiac or hip surgery [33,34] or persistent AKI in critically ill patients [35] and is associated with intensive care unit mortality [36]. An elevated RI can predict progression to CKD [37]. However, an elevated intrarenal RI is not specific to the cause of AKI as RI depends on multiple physiologic and pathologic factors, including vascular compliance, age, atherosclerosis, renal damage, hypertension, heart rate, as well as intrinsic renal disease [33,37]. Serial RI measurement is largely a research tool at this time.


Renal Failure

Renal Failure. Variant 2: Renal failure. Chronic kidney disease (CKD). Initial imaging. Arteriography Kidney Arteriography is reserved for intervention rather than for initial diagnosis. Treatment of renal artery stenosis may be considered, but a recent meta-analysis does not indicate a benefit in the preservation of renal function [38].


Renal Failure

Renal Failure. CT Abdomen and Pelvis Unenhanced CT is useful for further evaluation of US-detected hydronephrosis by determining level and cause of obstruction. CT is the most sensitive modality for urinary tract calculi [15]. Although CT can determine if there is hydronephrosis and assess renal size/volume, it is generally not considered the first-line imaging modality [16]. CT may be considered if US is not feasible or is nondiagnostic because of body habitus.


Renal Failure

Renal Failure. There is no relevant literature regarding the use of CT abdomen and pelvis without and with IV contrast for initial evaluation of CKD. Although CT with IV contrast may be feasible depending on the stage of CKD, it is not appropriate for the diagnosis of and determination of the cause of CKD.


Renal Failure

Renal Failure. There is no relevant literature regarding the use of CT abdomen and pelvis with IV contrast for initial evaluation of CKD.


Renal Failure

Renal Failure. CT Abdomen There is no relevant literature regarding the use of CT abdomen in the initial evaluation of CKD.


Renal Failure

Renal Failure. CTA Abdomen and Pelvis In CKD, contrast-enhanced CTA might be carefully considered for vascular thrombosis or stenosis depending on the GFR and risk-benefit ratio. In one study of 1,007 patients with CKD undergoing US, renal artery stenosis was found in 4.3% of patients [39]. There is no relevant literature regarding the use of CTA abdomen and pelvis for initial evaluation of CKD.


Renal Failure

Renal Failure. CT Urography There is no relevant literature regarding the use of CTU in the initial evaluation of CKD.


Renal Failure

Renal Failure. MRA Abdomen MRA is indicated when there is a high suspicion of a renovascular cause of CKD, which is rare. In one study of 1,007 patients with CKD undergoing US, renal artery stenosis was found in 4.3% of patients [39]. Unenhanced MRA techniques may be an option. When compared with contrast-enhanced CTA in the detection of <50% or >50% renal artery stenosis, an unenhanced MRA was reported to have a sensitivity, specificity, and accuracy of 74%, 93%, and 90%, respectively [19].


Renal Failure

Renal Failure. For contrast-enhanced MRA, a group II contrast agent using lowest dose that obtains a diagnostic study should be used [9]. In the detection o f >60% renal artery stenosis, c ontrast-enhanced MRA has a sensitivity of 93% and specificity of 93% compared to 85% and 84%, respectively, for Doppler US [18].


Renal Failure

Renal Failure. MRI Abdomen and Pelvis There is no relevant literature regarding the use of MRI abdomen and pelvis without and with IV contrast in the initial evaluation of CKD.


Renal Failure

Renal Failure. MRI Abdomen Unenhanced MRI may be used for characterization of level and cause of obstruction or evaluation of renal morphologic abnormalities. Functional MRI techniques such as BOLD, ASL, DWI, and DKI that provide information on renal perfusion, oxygenation, and diffusion are still the subject of active research [21,22].


Renal Failure

Renal Failure. The use of contrast should be considered only after evaluation of the risk-benefit ratio and degree of renal function [9]. There is no literature to support any added diagnostic value of the use of IV contrast and its attendant risks, and it is not appropriate for the diagnosis of and determination of the cause of CKD.


Renal Failure

Renal Failure. There is no relevant literature regarding the use of MRI abdomen without and with IV contrast in the initial evaluation of CKD.


Renal Failure

Renal Failure. MR Urography There is no relevant literature regarding the use of MRU in the initial evaluation of CKD.


Renal Failure

Renal Failure. Radiography Abdomen and Pelvis The role of abdominal radiography in CKD is limited to evaluation of renal stone disease, which acknowledges that radiography is less sensitive than CT for stone disease [24]. Signs of renal osteodystrophy confirm the presence of CKD.


Renal Failure

Renal Failure. DMSA Renal Scan Tc-99m DMSA scintigraphy is ideal for functional renal cortical imaging and is most useful for detection of focal renal parenchymal abnormalities and scars in the setting of acute or chronic pyelonephritis or for differential renal function. Serial imaging may be useful for monitoring renal cortical scarring.


Renal Failure

Renal Failure. The literature search did not identify any studies regarding the use of Tc-99m DMSA as a first-line test in the evaluation of CKD.


Renal Failure

Renal Failure. MAG3 Renal Scan The literature search did not identify any studies regarding the use of Tc-99m MAG3 as a first-line test in the evaluation of CKD.


Renal Failure

Renal Failure. US Kidneys Retroperitoneum US can differentiate AKI from CKD by determining renal size and volume. Renal length correlates with renal function in CKD [30,40-42]. Renal volume may be less useful given the contribution of renal sinus fat. In CKD, the kidneys are typically small with loss of global parenchymal and cortical thickness [42,43]. Renal length <9 cm in an adult is definitely abnormal [44]. It should be emphasized that normal-sized kidneys do not exclude CKD as renal size is initially preserved in diabetic nephropathy or infiltrative disorders.


Renal Failure

Renal Failure. Increase in renal echogenicity is a nonspecific subjective manifestation of renal disease. In a series of 1,007 patients with CKD, abnormalities were detected in 26.8% of patients at initial US evaluation [39]. The most common US findings were increased echogenicity in 10.3%, cortical t hinning in 4 .3%, renal artery stenosis in 4. 3%, and hydronephrosis in 1.9% of patients [39]. However, these findings contributed to the diagnosis in only 5 .9% o f patients and affected management in 3.3% of patients [39].


Renal Failure

Renal Failure

Renal Failure. Renal Failure


Renal Failure

Renal Failure. The low impact on management does not support the use of US for routine surveillance of CKD. US may be indicated when there is a prior history of stones or obstruction, renal artery stenosis, frequent urinary tract infections, or family history of autosomal dominant polycystic kidney disease [39]. In patients with CKD and diabetes or hypertension, US has minimal impact on diagnosis and management [6,8].


Renal Failure

Renal Failure. US Duplex Doppler Kidneys Retroperitoneal A high RI can be a predictor of progression of CKD, but an elevated RI is not specific to renal disease [37], and threshold values vary in the literature. The literature search did not identify any studies regarding the use of RIs US in the initial evaluation of CKD.


Renal Failure

Renal Failure. For renovascular disease, US is a low-yield test unless the patient has a history of renal artery stenosis [39].


Renal Failure

Renal Failure. Variant 3: Renal failure. Kidney disease of unknown duration. Initial imaging. Some patients will present without prior laboratory results and cannot be definitively categorized into AKI or CKD. In these patients, a detailed history, physical examination, and laboratory analysis of blood (for serum creatinine, blood urea nitrogen, complete blood count, and differential) and urine (microscopy for casts and epithelial cells, chemistry, and biomarkers) will be obtained in addition to imaging. More frequent measurement of serum creatinine will detect the more rapid deterioration of AKI. The imaging workup is similar to patients with AKI.


Renal Failure

Renal Failure. Arteriography Kidney Arteriography is reserved for intervention rather than for the initial diagnosis of renal failure. Renal revascularization may be considered in a very select group of patients with AKI. There is no relevant literature regarding the use of arteriography in the evaluation of renal failure of unknown duration.


Renal Failure

Renal Failure. CT Abdomen and Pelvis Unenhanced CT of the abdomen and pelvis is useful for characterization of US-detected hydronephrosis by determining level and cause of obstruction. CT is the most sensitive modality for urinary tract calculi and more sensitive than US for retroperitoneal pathology [15]. Although CT can determine whether there is hydronephrosis and measure renal size/volume, it is generally not considered a first-line imaging modality [16]. CT may be considered if US is not feasible or is nondiagnostic because body habitus.


Renal Failure

Renal Failure. There is no relevant literature regarding the use of CT abdomen and pelvis without and with IV contrast in the evaluation of renal failure of unknown duration. Iodinated contrast may be administered to patients established on dialysis without residual renal function. However, CT with IV contrast is not appropriate for the diagnosis of and determination of the cause of kidney failure.


Renal Failure

Renal Failure. CT Abdomen There is no relevant literature regarding the use of CT abdomen in the initial evaluation of renal failure of unknown duration.


Renal Failure

Renal Failure. CTA Abdomen and Pelvis Contrast-enhanced CTA abdomen and pelvis is very rarely indicated in these patients, given the potential nephrotoxicity. The risk-benefit ratio should be carefully evaluated if CTA is necessary to diagnose vascular thrombosis or stenosis. The lowest dose of contrast needed for a diagnostic study should be used and supplemented with adequate volume expansion [9]. There is no relevant literature regarding the use of CTA abdomen and pelvis in the evaluation of renal failure of unknown duration.


Renal Failure

Renal Failure. CT Urography There is no relevant literature regarding the use of CTU in the evaluation of renal failure of unknown duration and the requirement for IV contrast limits its applicability.


Renal Failure

Renal Failure. MRA Abdomen and Pelvis There is no relevant literature regarding the use of MRA abdomen and pelvis without and with IV contrast in the evaluation of renal failure of unknown duration.


Renal Failure

Renal Failure. MRA may be indicated when there is a high suspicion of a renovascular cause of AKI/CKD, such as renal artery stenosis, thrombosis, or arterial injury after trauma, all of which are rare [4,17]. Unenhanced MRA techniques, such as time-spatial labeling inversion pulse or steady-state free precession, have a sensitivity of 73% to 100%, specificity of 82% to 99%, and negative predictive value of 88% to 100% in the diagnosis of >50% renal artery stenosis [19,20].


Renal Failure

Renal Failure. Renal Failure There is no relevant literature regarding the use of MRA abdomen without IV contrast in the evaluation of renal failure of unknown duration.


Renal Failure

Renal Failure. For contrast-enhanced MRA, a group II contrast agent should be used [9]. For the detection of >60% renal artery stenosis, an contrast-enhanced MRA has a sensitivity of 93% and a specificity of 93% compared with 85% and 84%, respectively, for Doppler US [18].


Renal Failure

Renal Failure. MRI Abdomen and Pelvis Unenhanced MRI of the abdomen and pelvis may be used to evaluate extent and cause of suspected urinary tract obstruction. However, there is no relevant literature regarding the use of MRI abdomen and pelvis in the initial evaluation of renal failure of unknown duration.


Renal Failure

Renal Failure. MRI Abdomen There is no relevant literature regarding the use of MRI abdomen without and with IV contrast in the initial evaluation of renal failure of unknown duration.


Renal Failure

Renal Failure. MRI performed without IV contrast can be used for further characterization of the cause and level of obstruction and for evaluation of some renal morphologic abnormalities. Alterations in corticomedullary differentiation are recognized but are nonspecific. Acute cortical necrosis can be specifically diagnosed when there is a low T2 signal rim at the corticomedullary junction and absence of cortical enhancement following contrast administration [23]. Functional MRI techniques , such as BOLD, AS L, DWI , and DKI that p rovide information on renal p erfusion, oxygenation, and diffusion are still the subject of active research [21,22].


Renal Failure

Renal Failure. MR Urography There is no relevant literature regarding the use of MRU in the initial evaluation of renal failure of unknown duration. However, nonenhanced contrast MRU may provide additional information in patients with renal failure secondary to obstruction.


Renal Failure

Renal Failure. Radiography Abdomen and Pelvis There is no role for radiography in AKI/CKD other than for evaluation of renal stone disease, which acknowledges that radiography is less sensitive than CT for stone disease [24].


Renal Failure

Renal Failure. DMSA Renal Scan Tc-99m DMSA scintigraphy is ideal for functional renal cortical imaging and is most useful for detection of focal renal parenchymal abnormalities and scars in the setting of acute or chronic pyelonephritis or for differential renal function. The literature search did not identify any studies regarding the use of Tc-99m DMSA as a first-line test in the evaluation of renal failure of unknown duration.


Renal Failure

Renal Failure. MAG3 Renal Scan The literature search did not identify any studies regarding the use of Tc-99m MAG3 as a first-line test in the evaluation of renal failure of unknown duration.


Renal Failure

Renal Failure. US Kidneys Retroperitoneum US has greatest diagnostic value in the detection of hydronephrosis associated with urinary tract obstruction [4] with a sensitivity >90% for hydronephrosis and bladder distension [26]. However, even in hospitalized patients with AKI, the prevalence of hydronephrosis is low, ranging from 5% to 10%, with obstruction the cause of AKI in <45.2% of patients with hydronephrosis [4,27-29]. The highest yield for US is in patients with risk factors for urinary obstruction, such as pelvic tumors, bladder disorders, prostate hypertrophy, stone disease, and pelvic surgery. In patients without risk factors for obstruction, <1% of patients had US-detected obstruction [4]. Hydronephrosis does not necessarily indicate obstruction; a distended bladder, reflux, pregnancy, postobstructive dilation, or diuresis may cause ureteral and collecting system dilatation. A distended bladder should be decompressed, and the patient should be revaluated. False-negative US studies may be secondary to suboptimal quality, dehydration, early obstruction, or compression of the renal pelvis or ureters by tumors or fibrosis.


Renal Failure

Renal Failure. A secondary role of US is the evaluation of renal size, echogenicity, and morphology to differentiate AKI from CKD and allow determination of prognosis. Normal renal length is >10 cm in the third decade, but renal length correlates with height, sex, age (negative correlation), and weight in normal patients and varies with the state of hydration or presence of an obstruction [3]. Renal size/volume correlates with creatinine clearance [30]. Both kidney size and parenchymal thickness decrease in CKD [31]. Therefore, a normal kidney size suggests AKI rather than CKD. However, infiltrative and inflammatory diseases, as well as renal vein thrombosis, may increase kidney size


Renal Failure

Renal Failure

Renal Failure. Renal Failure


Renal Failure

Renal Failure. and parenchymal thickness in AKI or CKD. Increased renal echogenicity is associated with acute and chronic medical renal disease, but this is nonspecific and does not correlate well with renal function. Patients with AKI have only a 30% to 40% chance of increased echogenicity [4,28]. Alternatively, small echogenic kidneys are diagnostic of CKD.


Renal Failure

Renal Failure. Color Doppler is routinely used to assess global perfusion and confirm arterial and venous patency. Color Doppler will differentiate a dilated pelvis from prominent renal veins in the renal sinus and can confirm presence or absence of ureteral jets in the bladder.


Renal Failure

Renal Failure. US Duplex Doppler Kidneys Retroperitoneal Renovascular causes of AKI/CKD are rare; renal artery stenosis was found in 1.5% of cases with AKI even when not the cause of AKI [4]. In an older series of intensive care patients, AKI was attributed to renal artery thrombosis, stenosis, or trauma in 1% [17]. The diagnosis of significant renal artery stenosis can be made by obtaining angle- corrected measurements of the peak systolic velocities in the aorta and main renal arteries. Using a cutoff value of 285 cm/s achieved sensitivity, specificity, and overall accuracy of 67%, 90%, and 81%, respectively, for >60% stenosis [32]. In a smaller series, using a cutoff value of 180 cm/s, the sensitivity and specificity of US were 85% and 84%, respectively, for >60% stenosis [18]. Renal artery duplex Doppler studies may be appropriate in selected patients with a high clinical suspicion of renal artery stenosis.


Renal Failure

Renal Failure. RI has been studied in patients with AKI as a means to detect intrarenal vasoconstriction and differentiate renal from prerenal AKI. An elevated RI has been reported to be an early predictor of early or persistent postoperative AKI after cardiac or hip surgery [33,34], or persistent AKI in critically ill patients [35], and is associated with intensive care unit mortality [36]. An elevated RI can predict progression to CKD [37]. However, an elevated intrarenal RI is not specific to the cause of AKI, as RI depends on multiple physiologic and pathologic factors; including vascular compliance, age, atherosclerosis, renal damage, hypertension, heart rate, as well as intrinsic renal disease [33,37]. Serial RI measurement is largely a research tool at this time.


Renal Failure

Renal Failure. Variant 4: Renal failure. Neurogenic bladder. Initial imaging. Patients with neurogenic bladder due to disorders affecting the central nervous system typically present with signs of urinary frequency, urgency, and bladder overactivity, but there is little recent peer-reviewed original research on the initial imaging of this condition associated with renal failure. Underactivity of the bladder is less common, and it is characterized by prolonged voiding with a sensation of incomplete emptying and hesitancy; however, imaging is not generally part of the evaluation of underactive bladder [45]. Approximately 26% of patients with neurogenic bladder from spina bifida will develop renal failure, but <2% progress to end-stage renal disease [46].


Renal Failure

Renal Failure. Nearly all patients with spinal cord injury have historically developed renal dysfunction, which has been a major cause of death until more recent advances in diagnosis and care [47]. Patients with spinal cord injury have a 7% risk of stone development within 10 years, and this can contribute to renal insufficiency [47]. Review of clinical history, physical examination, US and urodynamic studies are the key components of an initial diagnosis of neurogenic bladder in Europe [48], but recommendations vary by country. For example, urodynamic evaluation is not recommended in British guidelines [49].


Renal Failure

Renal Failure. CT Abdomen and Pelvis Unenhanced CT is useful for characterization of US-detected hydronephrosis by determining the level and cause of obstruction. CT can determine if there is hydronephrosis, measure renal size/volume, and assess urinary bladder distension and wall thickening but it is generally not considered a first-line imaging modality [16]. CT may be considered if US is not feasible or is nondiagnostic because of body habitus.


Renal Failure

Renal Failure. There is no relevant literature regarding the use of CT abdomen and pelvis without and with IV contrast in the evaluation of renal failure associated with neurogenic bladder, but CT with IV contrast is not a first-line test for evaluation of kidney failure due to neurogenic bladder. Other options that do not use iodinated contrast are available.


Renal Failure

Renal Failure. CT Abdomen Unenhanced CT is useful for characterization of US-detected hydronephrosis by determining the level and cause of obstruction if the pelvis is included. CT can determine if there is hydronephrosis and measure renal size/volume, but it is generally not considered a first-line imaging modality [16].


Renal Failure

Renal Failure. There is no relevant literature regarding the use of CT abdomen without and with IV contrast in the evaluation of renal failure associated with neurogenic bladder, but CT with IV contrast is not a first-line test for evaluation of kidney failure due to neurogenic bladder. Other options that do not use iodinated contrast are available.


Renal Failure

Renal Failure. CTA Abdomen and Pelvis There is no role for CTA in the initial evaluation of renal failure associated with neurogenic bladder.


Renal Failure

Renal Failure. CT Urography There is no relevant literature for CTU in the initial evaluation of renal failure associated with neurogenic bladder.


Renal Failure

Renal Failure. Fluoroscopy Cystography There is no role for cystography in the evaluation of neurogenic bladder other than as a method of visualization during video urodynamics.


Renal Failure

Renal Failure. Fluoroscopy Voiding Cystourethrography Voiding cystourethrography is used to image the bladder wall and urethra and evaluate for vesicoureteral reflux but is not part of the evaluation of renal failure. There is no relevant literature regarding the use of voiding cystourethrography in the initial renal failure in a patient with neurogenic bladder.


Renal Failure

Renal Failure. MRI Abdomen and Pelvis MRI can show the urinary system well, and T2-weighted imaging can demonstrate hydronephrosis and hydroureter as well as US. Likewise, the urinary bladder can be well-visualized. In one review from Asia, MRI was favored above US for better evaluation of the collecting systems and ureters, which were shown in the coronal plane [50]. However, MRI of the abdomen and pelvis is not routinely used in the evaluation of renal failure associated with neurogenic bladder regardless of whether or not IV contrast is administered.


Renal Failure

Renal Failure. MRI Abdomen There is no relevant literature for MRI abdomen in the initial evaluation of renal failure associated with neurogenic bladder, regardless of whether or not IV contrasted series are included.


Renal Failure

Renal Failure. MR Urography There is no relevant literature for MRU in the initial evaluation of renal failure associated with neurogenic bladder. However, contrast-enhanced MRU is not routinely performed in this setting, and the majority of the information is obtained by unenhanced MRI sequences.


Renal Failure

Renal Failure. Radiography Abdomen and Pelvis There is no role for radiography in initial evaluation of neurogenic bladder. However, it may be used in the long- term surveillance for development of renal stone disease, acknowledging that radiography is less sensitive than CT for detection of stone disease [24].


Renal Failure

Renal Failure. MAG3 Renal Scan There is no relevant literature regarding the use of Tc-99m MAG3 as a first-line test in the evaluation of renal failure associated with neurogenic bladder.


Renal Failure

Renal Failure. US Kidneys Retroperitoneum The American Urological Association supports clinical evaluation and measurement of postvoid residual but does not specifically endorse US for this measurement. However, US is routinely used by urologists in the initial workup because it can easily measure bladder volume. In patients with neurogenic bladder and lower urinary tract symptoms, US and postvoid residual measurement is also supported by international guidelines [48,49,53].


Renal Failure

Renal Failure. In a study of 60 patients with neurogenic lower urinary tract dysfunction after spinal cord injury, a distended bladder anterior wall detrusor (hypoechoic layer) with a thickness <0.97 mm on US was 92% sensitive and 63% specific for risk assessment of renal damage [54]. Although bladder wall thickness can be characterized by US, this aspect of the examination is not supported as part of any current guideline recommendations [49].


Renal Failure

Renal Failure

Renal Failure. Renal Failure


Renal Failure

Renal Failure. In patients at high risk for upper tract disease, US should include the kidneys to evaluate for hydronephrosis, parenchymal scarring, and stones [49] because it has high sensitivity for upper tract dilatation [55]. The bladder should also be evaluated, for trabeculations, wall thickness, and shape. Sensitivity of US for renal scarring in spinal dysraphism patients is variable, and in one study was unacceptably low relative to scintigraphy (negative predictive value, 0.6) [52]. Predictors of positive US in these patients include time since injury, previous stone removal, nontraumatic spinal cord injury, and previous bladder surgery [56].


Renal Failure

Renal Failure. US Duplex Doppler Kidneys Retroperitoneal Although US has been widely accepted as a first-line imaging modality for neurogenic bladder, there is not any literature to support a role for Doppler.


Renal Failure

Renal Failure. Supporting Documents The evidence table, literature search, and appendix for this topic are available at https://acsearch.acr.org/list. The appendix includes the strength of evidence assessment and the final rating round tabulations for each recommendation.


Renal Failure

Renal Failure. For additional information on the Appropriateness Criteria methodology and other supporting documents go to www.acr.org/ac.


Thoracoabdominal Aneurysm or Dissection Treatment Planning and Follow Up. Aortic dissections are the results of a disruption in the aortic wall with blood flow into the media resulting in a true and false lumen, which may propagate antegrade or retrograde. Aortic dissections are classified by acuity, anatomic location of entry tear, extent of false lumen, and presence or absence of complicating features. The Stanford classification is commonly used to categorize aortic dissections. Type A dissection involves the ascending aorta (and may extend distally), and type B dissection is limited to the aortic arch and descending thoracic aorta. Complicating features include cerebral, coronary, and/or visceral malperfusion syndrome as well as rupture. Aortic dissections may require emergent surgical repair, thoracic endovascular aortic repair (EVAR), or other endovascular interventions to treat malperfusion syndromes following initial medical therapies. Aneurysmal expansion of the false lumen occurs in up to 50% of patients requiring follow-up imaging.


Thoracoabdominal Aneurysm or Dissection Treatment Planning and Follow Up. Traditionally, treatment for thoracoabdominal aneurysm or dissection has been surgical. Although surgical repair demonstrated a survival benefit over medical management, open TAAA repair carries high mortality and morbidity risks [3-5]. A 2016 analysis of outcomes of more than 3,000 TAAA repairs reports an operative mortality rate of 7.5%, with permanent paraplegia in 2.9%, permanent renal failure in 5.7%, and stroke in 2.2% for a total composite rate of an adverse event of 14.4% [3]. Over the past 10 to 20 years, alternative treatment regimens have been


Thoracoabdominal Aneurysm or Dissection Treatment Planning and Follow Up. The American College of Radiology seeks and encourages collaboration with other organizations on the development of the ACR Appropriateness Criteria through representation of such organizations on expert panels. Participation on the expert panel does not necessarily imply endorsement of the final document by individual contributors or their respective organization.


Thoracoabdominal Aneurysm or Dissection Treatment Planning and Follow Up. Reprint requests to: publications@acr.org


Thoracoabdominal Aneurysm or Dissection Treatment Planning and Follow Up. Thoracoabdominal Aortic Aneurysm or Dissection developed for some patient groups including hybrid repair and entirely endovascular repair. In hybrid repair, a combination of surgical and endovascular techniques is used, often in a staged format, with techniques including abdominal debranching followed by thoracic endovascular repair. Hybrid repairs showed favorable results in several series, although with aortic related mortality rates of 9%, 14%, and 14% at 1, 2, and 5 years, respectively, in one study [6-8].


Thoracoabdominal Aneurysm or Dissection Treatment Planning and Follow Up. More recently, a number of endovascular techniques have been used for repair, including thoracic EVAR, EVAR with parallel (eg, chimney/snorkel) stents into the branch artery, fenestrated EVAR, and branched EVAR [9-12]. Multiple studies have found encouraging results in terms of technical success, intraprocedural mortality, and branch vessel patency, although with high rates of reintervention for endoleaks [10,13-16]. Similarly, techniques for endovascular treatment of type B dissection have also been refined over the past decades, with new innovations in treating type A dissection emerging as well. The decision of surgical versus hybrid or endovascular repair is based on the characteristics of the aneurysm or dissection, along with factors such as suitability for surgery and patient preference. Regardless of type of treatment, postprocedural surveillance is important because patients with poor compliance with follow-up imaging are found to have higher rates of aortic rupture [17].


Thoracoabdominal Aneurysm or Dissection Treatment Planning and Follow Up. Special Imaging Considerations As MRI technology and sequences have continued to improve, multiple new sequences and protocols have been developed for assessment of the aorta. In particular, sequences aimed at evaluating flow dynamics and aortic wall stress have been used to predict aneurysm growth [19-24]. Other authors have advocated for the use of superparamagnetic iron oxide given intravenously to assess for inflammatory changes in the aortic wall [25,26]. Continued innovation has allowed advancement in sequences and techniques such as 4-D MRI for evaluation of TAAA or dissection, most commonly used at academic institutions.


Thoracoabdominal Aneurysm or Dissection Treatment Planning and Follow Up. Discussion of Procedures by Variant Variant 1: Follow-up of known thoracoabdominal aortic aneurysm or dissection without repair. Without or with new symptoms. Aortography Chest Abdomen Pelvis Aortogram with digital subtraction angiography (DSA) for evaluation of the thoracic and abdominal aorta has a sensitivity of up to 90% and a specificity of 95% for acute aortic pathology [27]. Although it has the advantage of allowing immediate intervention if an abnormality is identified, aortography is an invasive procedure that is now typically performed for treatment after diagnosis of a new or worsening aortic pathology. Additionally, a 2003 study comparing MR angiography (MRA) with angiography suggested increased accuracy of MRA in assessing vessel diameter: a key component of follow-up for TAAA or dissection [28].


Thoracoabdominal Aneurysm or Dissection Treatment Planning and Follow Up. CT Chest, Abdomen, and Pelvis With IV Contrast There is no relevant literature regarding venous phase CT chest, abdomen, and pelvis for the follow-up of known thoracoabdominal aneurysm or dissection, because most follow-up imaging for known dissection or aneurysm uses an arterially timed contrast bolus in the form of a CT angiography (CTA) (discussed below). However, contrast- enhanced CT can provide information regarding the size and extent of aortic pathology as well as evaluate for extravascular pathology. If venous phase or unenhanced CT has already been performed, additional imaging with CTA may not be required in some patients.


Thoracoabdominal Aneurysm or Dissection Treatment Planning and Follow Up. CT Chest, Abdomen, and Pelvis Without and With IV Contrast There is no relevant literature regarding venous phase CT chest, abdomen, and pelvis for the follow-up of known thoracoabdominal aneurysm or dissection because most follow-up imaging for known dissection or aneurysm uses an arterially timed contrast bolus in the form of a CTA (discussed below). However, contrast-enhanced CT can provide information regarding the size and extent of aortic pathology as well as evaluate for extravascular pathology.


Thoracoabdominal Aneurysm or Dissection Treatment Planning and Follow Up. Although typically not performed for the purpose of follow-up of thoracoabdominal aortic pathology, multiphase CT performed to evaluate for extravascular pathology can often assess for acute changes in thoracoabdominal


Thoracoabdominal Aneurysm or Dissection Treatment Planning and Follow Up. Thoracoabdominal Aortic Aneurysm or Dissection dissection or aneurysm, such as intramural hematoma. Unenhanced CT may be able to delineate extravascular complications such as hemorrhage or rupture. If venous phase or unenhanced CT has already been performed, additional imaging with CTA may not be required in some patients.


Thoracoabdominal Aneurysm or Dissection Treatment Planning and Follow Up. CT Chest, Abdomen, and Pelvis Without IV Contrast There is no relevant literature for CT chest, abdomen, and pelvis without intravenous (IV) contrast for the follow- up of known thoracoabdominal aneurysm or dissection. Although most follow-up of known aortic disease is performed with IV contrast [29-31], select groups of patients may be monitored with unenhanced CT to evaluate measurements of aortic size, which may guide further management [32]. Unenhanced CT may be able to delineate extravascular complications such as hemorrhage or rupture [32]. If venous phase or unenhanced CT has already been performed, additional imaging with CTA may not be required in some patients.


Thoracoabdominal Aneurysm or Dissection Treatment Planning and Follow Up. CT Chest and Abdomen With IV Contrast There is no relevant literature regarding venous phase CT chest and abdomen for the follow-up of known thoracoabdominal aneurysm or dissection because most follow-up imaging uses an arterially timed contrast bolus in the form of a CTA (discussed below). Compared with CT of the chest, abdomen, and pelvis, exclusion of the pelvis may result in incomplete evaluation of the extent of aortic pathology. If venous phase or unenhanced CT has already been performed, additional imaging with CTA may not be required in some patients.


Thoracoabdominal Aneurysm or Dissection Treatment Planning and Follow Up. CT Chest and Abdomen Without and With IV Contrast There is no relevant literature regarding CT chest and abdomen without and with IV contrast for the follow-up of known thoracoabdominal aneurysm or dissection because most follow-up imaging uses an arterially timed contrast bolus in the form of a CTA (discussed below). Compared with CT of the chest, abdomen, and pelvis, exclusion of the pelvis may result in incomplete evaluation of the extent of aortic pathology. If venous phase or unenhanced CT has already been performed, additional imaging with CTA may not be required in some patients.


Thoracoabdominal Aneurysm or Dissection Treatment Planning and Follow Up. CT Chest and Abdomen Without IV Contrast There is no relevant literature regarding CT chest and abdomen without IV contrast for the follow-up of known thoracoabdominal aneurysm or dissection because most follow-up imaging uses an arterially timed contrast bolus in the form of a CTA. Compared with CT of the chest, abdomen, and pelvis, exclusion of the pelvis may result in incomplete evaluation of the extent of aortic pathology. If venous phase or unenhanced CT has already been performed, additional imaging with CTA may not be required in some patients.


Thoracoabdominal Aneurysm or Dissection Treatment Planning and Follow Up. CTA Chest, Abdomen, and Pelvis With IV Contrast CTA of the chest, abdomen, and pelvis with IV contrast uses fast acquisition times to allow for rapid evaluation of the aorta and diagnosis of pathology. Fast acquisition times are particularly valuable in patients with known TAAA or dissection with new symptoms, given the high acuity of these conditions in the event of disease extension or worsening. The precise and reproducible measurements of the aorta with CTA are valuable for monitoring aortic growth and interval changes [33,34]. Electrocardiographically (ECG)-gated or triggered CTA is an additional option that can be used to evaluate the ascending aorta in patients with concern for conversion of a dissection into a type A dissection or for aneurysmal enlargement of the ascending aorta. With ECG gating, artifact from aortic pulsation is reduced and maximum interobserver variability of 1.2 mm in the ascending aorta has been reported, emphasizing the reproducibility of CTA [31,34].


Thoracoabdominal Aneurysm or Dissection Treatment Planning and Follow Up. Acquisition of thin axial slices with subsequent 3-D reconstruction along with homogenous luminal opacification allows for precise measurements and assessment of aortic anatomy, using postprocessing software for vessel analysis. Along with low interobserver variability, this allows for an excellent ability to detect changes in the aortic diameter or extent of dissection [31,33,34]. Furthermore, CTA can readily detect complications including thoracoabdominal aneurysm rupture or dissection extension causing malperfusion of the supra-aortic branch vessels, mesenteric arteries, renal arteries, lower extremities, or coronary arteries [31,35]. CTA has also been used in certain situations to predict enlargement of saccular aneurysms using flow dynamics [36].


Thoracoabdominal Aneurysm or Dissection Treatment Planning and Follow Up. Compared with CTA of the chest and abdomen, imaging of the pelvis carries the benefit of evaluation of the iliofemoral vessels to evaluate the extent of dissection or aneurysmal dilatation and suitability for possible endovascular intervention.


Thoracoabdominal Aneurysm or Dissection Treatment Planning and Follow Up. Thoracoabdominal Aortic Aneurysm or Dissection CTA Chest and Abdomen With IV Contrast Compared with CTA of the chest, abdomen, and pelvis, the lack of visualization of the iliofemoral vessels precludes evaluation for suitability for possible endovascular intervention or for aneurysm dilation/dissection of the iliac or femoral arteries if pathology extends to the bifurcation.


Thoracoabdominal Aneurysm or Dissection Treatment Planning and Follow Up. MRA Chest, Abdomen, and Pelvis Without and With IV Contrast Similar to CTA, MRA of the thoracoabdominal aorta allows for precise and reproducible assessment or aortic sac size in aneurysm or extent of dissection in thoracoabdominal aortic dissection [33,37-39]. In patients with new symptoms, MRI has conventionally been used as a secondary imaging modality because of relatively long imaging times [40]. However, MRI can be used to accurately assess for acute aortic pathology in this clinical setting [40- 42].


Thoracoabdominal Aneurysm or Dissection Treatment Planning and Follow Up. Use of a contrast agent in MRA allows for 4-D evaluation of flow dynamics, with acquisition of multiple time- points allowing for detailed evaluation of flow dynamics associated with aortic aneurysm or dissection [43]. This can be used with a variety of unenhanced MRA techniques such as time-of-flight and phase-contrast imaging that can also allow for evaluation of aortic dissection and aneurysm [44,45]. Similar to CTA, ECG gating can be used for a more accurate assessment of the ascending thoracic aorta if concern exists for retrograde extension of pathology [46,47]. MRA can allow for the evaluation of aortic valve dysfunction associated with ascending aortic dilation or dissection, which cannot typically be identified on CTA [33,46,47].


Thoracoabdominal Aneurysm or Dissection Treatment Planning and Follow Up. MRI also allows evaluation for extravascular pathology. In a 2014 study, more than 80% of patients had at least one extravascular finding, with 6.4% found to have a major extravascular finding including neoplasm, spine infection, or pericardial effusion [48].


Thoracoabdominal Aneurysm or Dissection Treatment Planning and Follow Up. A 2018 comparative study with 45 patients divided into noncontrast-enhanced and blood pool contrast groups was performed to qualitatively and quantitatively evaluate image quality as well as reproducibility [47]. This study concluded that IV contrast allows for higher quality imaging with more reproducible and accurate vessel measurements [47]. The findings were consistent with a 2010 study supporting the use of IV contrast for vascular detail [49]. In contrast to these findings, however, multiple other studies have found similar accuracy and reproducibility in assessing vessel diameter between contrast- and noncontrast-enhanced MRI studies [44,50,51].