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


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. 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]. 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]. 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].


Renal Failure

Renal Failure. 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. 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- 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. Reprint requests to: publications@acr.org 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]. 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. 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]. 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. 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. MR urography (MRU) is also tailored to improve imaging of the urinary system.


Renal Failure

Renal Failure. 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 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. 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. 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. CT Abdomen There is no relevant literature regarding the use of CT abdomen in the evaluation of AKI. 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. CTU There is no relevant literature regarding the use of CTU in the evaluation of AKI. The requirement for IV contrast limits its utility. 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]. 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]. Unenhanced MRA techniques, such as time-spatial labeling inversion pulse or steady-state free precession, may be considered in AKI.


Renal Failure

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


Renal Failure

Renal Failure. 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. 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. A secondary role of US is the evaluation of renal size, echogenicity, and morphology to differentiate AKI from CKD and allow determination of prognosis.


Renal Failure

Renal Failure. 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 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. 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. 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. 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].


Renal Failure

Renal Failure. 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. 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. 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]. 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. There is no relevant literature regarding the use of CT abdomen and pelvis without and with IV contrast for initial evaluation of CKD.


Renal Failure

Renal Failure. 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. There is no relevant literature regarding the use of CT abdomen and pelvis with IV contrast for initial evaluation of CKD. CT Abdomen There is no relevant literature regarding the use of CT abdomen in the initial evaluation of CKD. 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 CT Urography There is no relevant literature regarding the use of CTU in the initial evaluation of CKD. 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]. 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]. 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. MRI Abdomen Unenhanced MRI may be used for characterization of level and cause of obstruction or evaluation of renal morphologic abnormalities.


Renal Failure

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


Renal Failure

Renal Failure. It should be emphasized that normal-sized kidneys do not exclude CKD as renal size is initially preserved in diabetic nephropathy or infiltrative disorders. 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 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]. 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. For renovascular disease, US is a low-yield test unless the patient has a history of renal artery stenosis [39]. 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.


Renal Failure

Renal Failure. More frequent measurement of serum creatinine will detect the more rapid deterioration of AKI. The imaging workup is similar to patients with AKI. 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. 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. 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. CT Abdomen There is no relevant literature regarding the use of CT abdomen in the initial evaluation of renal failure of unknown duration. 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].


Renal Failure

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


Renal Failure

Renal Failure. 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]. 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. 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]. 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. 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. 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].


Renal Failure

Renal Failure. 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. 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 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. 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. 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. Variant 4: Renal failure. Neurogenic bladder. Initial imaging.


Renal Failure

Renal Failure. 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]. 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]. 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. 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.


Renal Failure

Renal Failure. Other options that do not use iodinated contrast are available. 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 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. CTA Abdomen and Pelvis There is no role for CTA in the initial evaluation of renal failure associated with neurogenic bladder. CT Urography There is no relevant literature for CTU in the initial evaluation of renal failure associated with neurogenic bladder. Fluoroscopy Cystography There is no role for cystography in the evaluation of neurogenic bladder other than as a method of visualization during video urodynamics. 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. 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].


Renal Failure

Renal Failure. 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. 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. 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. 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]. 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. 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]. 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].


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


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]. 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]. 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].


Thoracoabdominal Aneurysm or Dissection Treatment Planning and Follow Up. 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. 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]. 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. 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 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. 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. 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. 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. 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.


Thoracoabdominal Aneurysm or Dissection Treatment Planning and Follow Up. 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]. 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]. 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. 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]. 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]. 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]. MRA Chest, Abdomen, and Pelvis Without IV Contrast Multiple unenhanced MRA techniques such as time-of-flight, phase-contrast imaging, and steady-state free precision (SSFP) have been developed that allow for the evaluation of aortic dissection and aneurysm [44,45]. Even without IV contrast, MRA can be used to precisely evaluate the thoracoabdominal aorta size, as well as for access vessel size, intraluminal thrombus, and branch vessel involvement [37,39]. A 2017 observational study comparing AAA measurements in CTA and noncontrast MRA showed strong agreement, with intraclass coefficient >0.99 and interobserver reproducibility >0.99 for both CTA and MRA [45]. This study also noted a potential benefit of noncontrast MRA allowing evaluation of the composition of intraluminal thrombus, potentially allowing for risk quantification for disease progression [45]. This finding was also supported by a follow-up 2019 article [52]. Although some studies have shown more accurate measurements with contrast-enhanced MRA compared with noncontrast MRA, other studies have shown an equal ability to detect aortic pathology and to measure aortic size [44,50,51].


Thoracoabdominal Aneurysm or Dissection Treatment Planning and Follow Up. A 2014 study comparing thoracic aortic measurements and pathology in 76 patients undergoing both contrast- and noncontrast-enhanced MRA showed high agreement between study types, with low intra- and interobserver dependency (intraclass correlation coefficient 0.99) [51]. A similar 2017 study comparing thoracic aorta measurements/findings on contrast- and noncontrast-enhanced MRA performed on a group of 50 patients favored noncontrast-enhanced MRA over contrast-enhanced MRA as the technique of choice because of superior image quality and better vessel sharpness in the ascending aorta [44]. Although these existing studies focus on the thoracic or abdominal segments of the aorta rather than the thoracoabdominal aorta, findings can likely be extrapolated to the thoracoabdominal aorta. MRA Chest and Abdomen Without and With IV Contrast Compared with MRA of the chest, abdomen, and pelvis, exclusion of the pelvis carries the benefit of faster acquisition time. However, extension to the abdomen without the pelvis involved, results in limited evaluation of the iliofemoral vessels to evaluate suitability for possible endovascular intervention or for aneurysm dilation/dissection of the iliac or femoral arteries if pathology extends to the bifurcation. Thoracoabdominal Aortic Aneurysm or Dissection MRA Chest and Abdomen Without IV Contrast Compared with MRA of the chest, abdomen, and pelvis, exclusion of the pelvis carries the benefit of faster acquisition time. However, extension to the abdomen without inclusion of the pelvis involved results in limited evaluation of the iliofemoral vessels to evaluate suitability for possible endovascular intervention or for aneurysm dilation/dissection of the iliac or femoral arteries if pathology extends to the bifurcation. Radiography Chest Chest radiographs demonstrate abnormalities in a large percentage of patients with acute thoracoabdominal pathology.


Thoracoabdominal Aneurysm or Dissection Treatment Planning and Follow Up. Most commonly, a widened mediastinum is appreciated in patients with pathology extending to the proximal to mid thoracic aorta, and a posteroanterior (PA) projection is found to be significantly more accurate than an anteroposterior (AP) projection [53]. Other studies have found that a chest radiograph is not sensitive (64%) or specific (87%) for thoracic aortic disease [54,55]. Given the relatively low sensitivity and specificity, chest radiography should not substitute for cross-sectional imaging. Furthermore, the role of chest radiography in the follow-up of known thoracoabdominal disease is limited because radiographs would be unlikely to appreciate subtle changes in aortic size. Radiography Chest, Abdomen, and Pelvis There is no relevant literature for chest, abdomen, and pelvis radiographs for the follow-up of thoracoabdominal aortic dissection or aneurysm. Chest radiographs demonstrate abnormalities in a large percentage of patients with acute thoracoabdominal pathology. Most commonly, a widened mediastinum is appreciated in patients with pathology extending to the proximal to mid thoracic aorta, and a PA projection is found to be significantly more accurate than an AP projection [53]. Other studies have found that a chest radiograph is not sensitive (64%) or specific (87%) for thoracic aortic disease [54,55]. Given the relatively low sensitivity and specificity, chest radiography should not substitute for cross-sectional imaging. Furthermore, the role of chest radiography in the follow-up of known thoracoabdominal disease is limited because radiographs would be unlikely to appreciate subtle changes in aortic size. US Duplex Doppler Aorta Abdomen Duplex ultrasound (US) of the abdominal aorta is an option for evaluation of the thoracoabdominal aorta, although the ability to evaluate the aorta above the diaphragm may be markedly limited by acoustic windows.


Thoracoabdominal Aneurysm or Dissection Treatment Planning and Follow Up. Prior studies comparing US, CT, and MRI of the abdominal aorta found that US is a reliable method to diagnose and follow AAAs [56]. In the evaluation of thoracoabdominal aortic dissection, US can also be used to evaluate blood flow in the true and false lumens and to directly and dynamically monitor the motion of dissection flaps [43]. As such, abdomen US can be performed serially to evaluate for aortic size changes or dissection hemodynamic changes. However, a limited ability to evaluate the thoracic aorta due to difficult acoustic windows could result in poor image quality or the inability to view changes to the aorta. US Echocardiography Transthoracic Resting Transthoracic echocardiogram (TTE) allows visualization of the heart and portions of the thoracic aorta. TTE can be used to evaluate the heart for complications such as pericardial effusion in patients with new symptoms [57]. However, portions of the proximal descending thoracic aorta may be poorly visualized with TTE because of patient acoustic windows and habitus, creating the possibility of false-negative examinations in patients with new symptoms [58]. These characteristics have resulted in a low sensitivity of 31% to 55% for the diagnosis of acute type B aortic dissection on TTE [33]. TTE is also limited by the ability to visualize the abdominal aorta to determine the extent of thoracoabdominal aortic pathology. Variant 2: Planning for endovascular or open repair of thoracoabdominal aorta aneurysm or dissection. Aortography Chest Abdomen Pelvis There is no relevant literature regarding aortography for the planning of thoracoabdominal aortic endovascular or open repair. Aortogram with DSA for evaluation of the thoracic and abdominal aorta has a sensitivity of up to 90% and a specificity of 95% for acute aortic syndrome [27]. The role of aortography before endovascular or open repair is limited to noninvasive modalities such as CTA and MRA.


Thoracoabdominal Aneurysm or Dissection Treatment Planning and Follow Up. Furthermore, the projectional nature of catheter angiograms limits its ability to evaluate the 3-D configuration of vessels, increasing the risk of error if procedures are planned based on angiogram [59]. Thoracoabdominal Aortic Aneurysm or Dissection CT Chest, Abdomen, and Pelvis With IV Contrast There is no relevant literature for venous phase CT chest, abdomen, and pelvis for the planning of thoracoabdominal aortic endovascular or open repair. Most preprocedural CT imaging for thoracoabdominal pathology uses an arterially timed contrast bolus in the form of a CTA (discussed below). Although typically not performed for the purpose of procedural planning, contrast-enhanced CT performed to evaluate for extravascular pathology can often assess for acute changes in thoracoabdominal dissection or aneurysm. If venous phase or unenhanced CT has already been performed, additional imaging with CTA may not be required in some patients but may be needed for preprocedure sizing and evaluation of pathology. CT Chest, Abdomen, and Pelvis Without and With IV Contrast There is no relevant literature for venous phase CT chest, abdomen, and pelvis with noncontrast phase for the planning of thoracoabdominal aortic endovascular or open repair. Most preprocedural CT imaging for thoracoabdominal pathology uses an arterially timed contrast bolus in the form of a CTA (discussed below). Although typically not performed for the purpose of procedural planning, contrast-enhanced CT performed to evaluate for extravascular pathology can often assess for acute changes in thoracoabdominal dissection or aneurysm. If venous phase or unenhanced CT has already been performed, additional imaging with CTA may not be required in some patients but may be needed for preprocedure sizing and evaluation of pathology.


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 IV contrast for the planning of thoracoabdominal aortic endovascular or open repair. CT without IV contrast would likely be able to assess aortic size and for nonvascular findings, but utility for preprocedure planning would be markedly limited in the absence of IV contrast. If venous phase or unenhanced CT has already been performed, additional imaging with CTA may not be required in some patients but may be needed for preprocedure sizing and evaluation of pathology. CT Chest and Abdomen With IV Contrast There is no relevant literature for venous phase CT chest and abdomen for the planning of thoracoabdominal aortic endovascular or open repair. Compared with CT of the chest, abdomen, and pelvis, exclusion of the pelvis from the field of view carries the drawback of precluding evaluation of the iliofemoral access vessels if endovascular repair is considered. Furthermore, if the thoracoabdominal dissection or aneurysm extends into the pelvis, a lack of pelvis evaluation could result in incomplete evaluation of the aortic pathology. In select cases with recent imaging of the pelvis or in cases of planned open repair without extension into the pelvic vasculature, further imaging of the pelvis vasculature may not be needed. If venous phase or unenhanced CT has already been performed, additional imaging with CTA may not be required in some patients but may be needed for preprocedure sizing and evaluation of pathology. CT Chest and Abdomen Without and With IV Contrast There is no relevant literature for venous phase CT chest and abdomen with noncontrast phase for the planning of thoracoabdominal aortic endovascular or open repair. Most preprocedural CT imaging for thoracoabdominal pathology uses an arterially timed contrast bolus in the form of a CTA (discussed below).


Thoracoabdominal Aneurysm or Dissection Treatment Planning and Follow Up. Although typically not performed for the purpose of procedural planning, contrast-enhanced CT performed to evaluate for extravascular pathology can often assess for acute changes in thoracoabdominal dissection or aneurysm. However, exclusion of the pelvis from the field of view carries the drawback of precluding evaluation of the iliofemoral access vessels if endovascular repair is considered. Furthermore, if the thoracoabdominal dissection or aneurysm extends into the pelvis, lack of pelvis evaluation could result in incomplete evaluation of the aortic pathology. In select cases with recent imaging of the pelvis or in cases of planned open repair without extension into the pelvic vasculature, further imaging of the pelvis vasculature may not be needed. If venous phase or unenhanced CT has already been performed, additional imaging with CTA may not be required in some patients but may be needed for preprocedure sizing and evaluation of pathology. CT Chest and Abdomen Without IV Contrast There is no relevant literature CT chest and abdomen without contrast for the planning of thoracoabdominal aortic endovascular or open repair. Compared with CT of the chest, abdomen, and pelvis, exclusion of the pelvis from the field of view carries the drawback of precluding evaluation of the iliofemoral access vessels if endovascular repair is considered. If venous phase or unenhanced CT has already been performed, additional imaging with CTA may not be required in some patients but may be needed for preprocedure sizing and evaluation of pathology. Thoracoabdominal Aortic Aneurysm or Dissection CTA Chest, Abdomen, and Pelvis With IV Contrast The high spatial resolution and profound, homogenous enhancement of the aorta and branch vessels in CTA allows for excellent preoperative assessment.


Thoracoabdominal Aneurysm or Dissection Treatment Planning and Follow Up. Prior studies dating back to the 2000s have shown CTA to be a valuable tool to evaluate anatomic suitability for endovascular repair of the thoracic or abdominal aorta [31,60-63]. With anatomic coverage from the aortic root to the superficial femoral arteries, CTA can rapidly evaluate the extent of thoracoabdominal aneurysm or dissection as well as provide information valuable for preoperative planning such as aortic tortuosity, branch vessel location and patency, and suitability of femoral access vessels for endovascular repair. CTA can also readily evaluate for complications related to aortic pathology that could affect surgical or procedural plan including aortic rupture, dissection extension, or malperfusion syndrome. Although TAAA is traditionally treated with open repair, hybrid and endovascular repair of TAAA or dissections have increasingly been used over the past decade [14,64]. Techniques including snorkels/periscopes to allow perfusion of aortic branches, fenestrated EVAR, and branched EVAR have been used for thoracoabdominal aneurysms, and fenestration, branch vessel stenting, and true lumen stenting have progressively been used for thoracoabdominal dissection [9,14,64,65]. Many of these are complex procedures, and precise measurements of the aortic aneurysm or dissection before the procedure facilitates planning and ensures appropriate device availability at the time of procedure [9,65]. The thin slices, high spatial resolution, and isotropic data acquired with CTA permits advanced reconstruction techniques such as centerline measurements and double orthogonal measurements, permitting precise assessment of the aortic and branch vessel anatomy and detailed procedure planning [60- 62,66,67]. Inclusion of the pelvis in the study also aids in procedure planning by allowing evaluation of the iliofemoral access vessels.


Thoracoabdominal Aneurysm or Dissection Treatment Planning and Follow Up. Femoral access is typically preferred for endovascular repair, although access vessels must typically be suitable in size, tortuosity, and calcification of the iliac vessels to permit device delivery to the aorta. In patients with inappropriate iliofemoral vessels, groin cutdown with conduit, direct aortoiliac access, or brachial access can be used. Before open or endovascular repair of a thoracoabdominal aneurysm or dissection, some authors have advocated for imaging for identification of the artery of Adamkiewicz, because preoperative identification could potentially reduce the risk of spinal cord ischemia [68,69]. Given the variability of the origin of this artery, preoperative identification of the origin of this vessel allows for operative planning that minimizes the risk of damage and can reduce surgical times [69]. Multiple studies evaluating the ability of CT and MRI to identify the artery of Adamkiewicz show that the artery can be identified and traced in >75% of patients, with some studies finding >90% identification [68,70-72]. CTA Chest and Abdomen With IV Contrast Compared with CTA of the chest, abdomen, and pelvis, exclusion of the pelvis carries the drawback of precluding evaluation of the iliofemoral access vessels if endovascular repair is considered. Furthermore, if the thoracoabdominal dissection or aneurysm extends into the pelvis, a lack of pelvis evaluation could result in incomplete evaluation of the aortic pathology. In select cases with recent imaging of the pelvis or in cases of planned open repair without extension into the pelvic vasculature, further imaging of the pelvis vasculature may not be needed. MRA Chest, Abdomen, and Pelvis Without and With IV Contrast Although the spatial resolution of MRA without and with IV contrast is less than the spatial resolution of CTA with IV contrast, MRA provides good evaluation of the aorta and branch vessels to allow for procedural or operative planning [38,62,67].


Thoracoabdominal Aneurysm or Dissection Treatment Planning and Follow Up. A 2011 study compared image quality, vessel measurements, and proposed endograft selection among MRA and CTA in 30 patients scheduled for EVAR [67]. This analysis found small differences in measured aortic diameter at multiple locations, all <1 mm between MRA and CTA [67]. Ultimately, this study concluded that the image quality for both CTA and MRA was, in general, adequate and that differences were not clinically relevant because all 30 patients had the same endograft components selected based on measurements [67]. Although the study was focused on AAA, the result is likely applicable to measurements of thoracoabdominal aneurysm or dissection, with the caveat that the complexity of endovascular thoracoabdominal repair may place a higher value on precise measurements. MRA is thus able to evaluate the extent of thoracoabdominal aneurysm or dissection as well as to provide information valuable for preoperative planning such as aortic tortuosity, branch vessel location and patency, and suitability of femoral access vessels for endovascular repair. MRA can also evaluate for complications related to aortic pathology that could affect surgical or procedural plan including aortic rupture, dissection extension, or malperfusion syndrome. Thoracoabdominal Aortic Aneurysm or Dissection Although TAAA is traditionally treated with open repair, hybrid and endovascular repair of TAAA or dissections have increasingly been used over the past decade [14,64]. Techniques including snorkels/periscopes to allow perfusion of aortic branches, fenestrated EVAR, and branched EVAR have been used for thoracoabdominal aneurysms, and fenestration, branch vessel stenting, and true lumen stenting have progressively been used for thoracoabdominal dissection [9,14,64,65].


Thoracoabdominal Aneurysm or Dissection Treatment Planning and Follow Up. Many of these are complex procedures, and precise measurements of the aortic aneurysm or dissection before procedure facilitates planning and ensures appropriate device availability at the time of procedure [9,65] Inclusion of the pelvis in the study also aids in procedure planning by allowing evaluation of the iliofemoral access vessels. Femoral access is typically preferred for endovascular repair, although access vessels must typically be suitable in size, tortuosity, and calcification of the iliac vessels to permit device delivery to the aorta. In patients with inappropriate iliofemoral vessels, groin cutdown with conduit, direct aortoiliac access, or brachial access can be used. Before open or endovascular repair of a thoracoabdominal aneurysm or dissection, some authors have advocated for imaging for identification of the artery of Adamkiewicz because preoperative identification could potentially reduce the risk of spinal cord ischemia [68]. Given the variability of the origin of this artery, preoperative identification of the origin of this vessel allows for operative planning that minimizes risk of damage. Multiple studies evaluating the ability of CT and MRI to identify the artery of Adamkiewicz show that the artery can be identified and traced in >75% of patients, with identification rates typically higher in MRA compared with CTA [68,70-73]. MRA Chest, Abdomen, and Pelvis Without IV Contrast A 2012 study by Shaida et al [63] compared aortic measurements in 20 patients undergoing both CTA and noncontrast MRI before EVAR. The study measured vessel diameter at multiple points as well as several vessel lengths and found small discrepancies between MRI and CTA, typically <1 mm for diameters or 5 mm for lengths [63]. The authors concluded such measurements were unlikely to alter planning of the repair but favored CTA in most patients [63].


Thoracoabdominal Aneurysm or Dissection Treatment Planning and Follow Up. Although this study focused on AAA, the result is likely applicable to measurements of thoracoabdominal aneurysm or dissection, with the caveat that the complexity of endovascular thoracoabdominal repair may place a higher value on precise measurements. Similar conclusions were reached by a 2013 study comparing pre-EVAR MRI without IV contrast and CTA [61,74]. MRA Chest and Abdomen Without and With IV Contrast Compared with MRA of the chest, abdomen, and pelvis, exclusion of the pelvis carries the drawback of precluding evaluation of the iliofemoral access vessels if endovascular repair is considered. Furthermore, if the thoracoabdominal dissection or aneurysm extends into the pelvis, a lack of pelvis evaluation could result in incomplete evaluation of the aortic pathology. In select cases with recent imaging of the pelvis or in cases of planned open repair without extension into the pelvic vasculature, further imaging of the pelvis vasculature may not be needed. MRA Chest and Abdomen Without IV Contrast Compared with MRA of the chest, abdomen, and pelvis, exclusion of the pelvis carries the drawback of precluding evaluation of the iliofemoral access vessels if endovascular repair is considered. Furthermore, if the thoracoabdominal dissection or aneurysm extends into the pelvis, a lack of pelvis evaluation could result in incomplete evaluation of the aortic pathology. In select cases with recent imaging of the pelvis or in cases of planned open repair without extension into the pelvic vasculature, further imaging of the pelvis vasculature may not be needed. Radiography Chest There is no relevant literature regarding the use of radiography for planning thoracoabdominal aortic endovascular or open repair. Radiography Chest Abdomen Pelvis There is no relevant literature regarding the use of radiography for planning thoracoabdominal aortic endovascular or open repair.


Thoracoabdominal Aneurysm or Dissection Treatment Planning and Follow Up. US Duplex Doppler Aorta Abdomen There is no relevant literature regarding the use of duplex US for planning thoracoabdominal aortic endovascular or open repair. Although US can be used to evaluate the abdominal aorta for dissection or aneurysm, limitations to Thoracoabdominal Aortic Aneurysm or Dissection the evaluation of the spatial relationship of the aorta to branch vessels and the inability to visualize portions of the aorta limit its utility as a sole modality for procedural planning. US Echocardiography Transthoracic Resting There is no relevant literature regarding the use of TTE for planning thoracoabdominal aortic endovascular or open repair. Although TTE can evaluate for cardiac complications such as aortic valve regurgitation [33] and evaluate portions of the thoracic aorta, limitations to the evaluation of the spatial relationship of the aorta to branch vessels, the inability to visualize portions of the aorta, and a dependence on operator and patient characteristics limit its utility as a sole modality for procedural planning. Variant 3: Follow-up after endovascular repair of thoracoabdominal aortic aneurysm or dissection. Aortography Chest Abdomen Pelvis Aortogram with DSA for evaluation of the thoracic and abdominal aorta has a sensitivity of up to 90% and a specificity of 95% for acute aortic syndrome [27]. The role of aortography for routine follow-up after endovascular repair is limited in favor of noninvasive modalities such as CTA and MRA, and CTA has been found to have a higher sensitivity than angiogram [75,76]. In cases of increasing aneurysm sac size likely to require treatment of endoleak, aortogram could be considered because it would allow rapid transition from diagnosis to treatment. Additional benefits of angiogram include the ability to evaluate directionality of endoleaks, which can be difficult on CTA [76].


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 endovascular repair of thoracoabdominal aneurysm or dissection because most follow-up imaging uses an arterially timed contrast bolus in the form of a CTA (discussed below). However, contrast-enhanced CT can provide similar information as CTA in evaluating the size and extent of aortic pathology, although with a reduced sensitivity to delineating endoleak and subtle changes to aorta and branch artery diameter. Although typically not performed for the purpose of follow-up of thoracoabdominal aortic pathology, contrast-enhanced CT performed to evaluate for extravascular pathology can often assess for acute changes after endovascular repair including endoprosthesis migration or aortic rupture. If venous phase or unenhanced CT has already been performed, additional imaging with CTA may not be required in some patients. CT Chest, Abdomen, and Pelvis Without and With IV Contrast There is no relevant literature for venous and unenhanced CT chest, abdomen, and pelvis without an arterial phase for follow-up after thoracoabdominal endovascular repair. However, contrast-enhanced CT can provide similar information as CTA in evaluating the size and extent of aortic pathology, although with a reduced sensitivity to delineating endoleak and subtle changes to aorta and branch artery diameter. Although typically not performed for the purpose of follow-up of thoracoabdominal aortic pathology, contrast-enhanced CT performed to evaluate for extravascular pathology can often assess for acute changes after endovascular repair including endoprosthesis migration or aortic rupture. The addition of a noncontrast phase would be expected to aid in identifying endoleak and distinguishing endoleak from other sources of sac/false lumen opacification, although a lack of an arterial phase limits sensitivity.


Thoracoabdominal Aneurysm or Dissection Treatment Planning and Follow Up. If venous phase or unenhanced CT has already been performed, additional imaging with CTA may not be required in some patients. CT Chest, Abdomen, and Pelvis Without IV Contrast Typical CT follow-up after endovascular thoracoabdominal aortic repair incorporates arterial and delayed venous phases to evaluate for endoleak [77]. However, unenhanced CT can be used to evaluate aortic caliber to detect changes to a thoracoabdominal aneurysm or aneurysmal degeneration of a thoracoabdominal dissection. Drawbacks of unenhanced imaging include an inability to identify endoleak, evaluate branch vessel patency, or evaluate for false lumen thrombosis in aortic dissection. Nonetheless, some authors have advocated for routine use of noncontrast-enhanced CT over contrast-enhanced CT in patients after EVAR with stable aneurysm sac size, with contrast-enhanced CTA used for evaluation if aortic sac size changes [32,76]. If venous phase or unenhanced CT has already been performed, additional imaging with CTA may not be required in some patients. CT Chest and Abdomen With IV Contrast There is no relevant literature regarding venous phase CT chest and abdomen for the follow-up of endovascular repair of thoracoabdominal aneurysm or dissection. Compared with CT of the chest, abdomen, and pelvis, evaluation of the chest and abdomen only without imaging of the pelvis may fail to detect changing or new Thoracoabdominal Aortic Aneurysm or Dissection pathology in the pelvic vasculature. If venous phase or unenhanced CT has already been performed, additional imaging with CTA may not be required in some patients. CT Chest and Abdomen Without and With IV Contrast There is no relevant literature for venous and unenhanced CT without an arterial phase for follow-up after thoracoabdominal endovascular repair.


Thoracoabdominal Aneurysm or Dissection Treatment Planning and Follow Up. Compared with CT of the chest, abdomen, and pelvis, evaluation of the chest and abdomen only without imaging of the pelvis may fail to detect changing or new pathology in the pelvic vasculature. If venous phase or unenhanced CT has already been performed, additional imaging with CTA may not be required in some patients. CT Chest and Abdomen Without IV Contrast Compared with CT of the chest, abdomen, and pelvis, evaluation of the chest and abdomen only without imaging of the pelvis may fail to detect changing or new pathology in the pelvic vasculature. If venous phase or unenhanced CT has already been performed, additional imaging with CTA may not be required in some patients. CTA Chest, Abdomen, and Pelvis With IV Contrast CTA is ideal for evaluation after endovascular repair because of its sensitivity in detecting endoleaks, ability to detect changes in aortic diameter, evaluation of false lumen thrombosis, endograft infection, and assessment of branch vessel/stent patency [1,2,77-79]. Because most endovascular repairs of TAAA or dissection are complex, the need for routine surveillance after treatment is crucial, and often, lifelong follow-up is recommended. A 2016 study of 354 patients undergoing endovascular repair for thoracoabdominal aortic pathology underscores the need for close follow-up, because 36% of patients required further intervention within 36 months, most commonly for endoleak [14]. Typically, follow-up imaging is obtained at 1, 3, and 6 months after intervention to evaluate for endoleak, increase in aortic diameter, incomplete false lumen thrombosis (in dissection), and other procedure complications, and prior studies have shown poor compliance with follow-up and increased risk of aortic rupture in these patients with limited imaging follow-up [17,80]. After 6 months, individualized imaging follow-up may be planned based on personal risk factors, with imaging typically at 6- to 12-month intervals.


Thoracoabdominal Aneurysm or Dissection Treatment Planning and Follow Up. Although direct evidence comparing CTA to other modalities in endoleak identification after endovascular thoracoabdominal aneurysm repair is lacking, multiple studies and meta-analyses have compared CTA with MRI and US for endoleak identification after EVAR for AAA [78,79,82,83]. A meta-analysis by Guo et al [82] in 2016 evaluated 3,853 patients after EVAR with paired scans of different modalities (CTA, MRA, US) within a 1-month period. In 2,346 paired CTA and duplex US scans, CTA identified 214 additional endoleaks not seen on duplex US (including 26 type I or type III endoleaks), whereas duplex US identified 77 additional endoleaks not seen on CTA (no type I or III endoleaks) [82]. In 1,694 paired CTA and MRA scans, CTA identified 2 additional endoleaks, whereas MRA identified 42 additional endoleaks [82]. A subsequent meta-analysis in 2018 by Zaiem et al [84] also noted that MRI identified more endoleaks than CTA. These findings suggest higher sensitivity of MRI to detect endoleaks, although the authors caution that the increased endoleaks identified could represent false-positive findings or endoleaks that are not clinically important [84]. CTA Chest and Abdomen With IV Contrast Compared with CTA of the chest, abdomen, and pelvis, evaluation of the chest and abdomen only without imaging of the pelvis may fail to detect changing or new pathology in the pelvic vasculature that could require additional intervention. MRA Chest, Abdomen, and Pelvis Without and With IV Contrast The spatial resolution of MRA is less than that of CTA, but the ability to detect branch vessel complications, endoleaks, stent graft complication, or infection has established MRA as an effective modality for imaging after endovascular repair, particularly for nitinol stent grafts, which have reduced susceptibility artifact.


Thoracoabdominal Aneurysm or Dissection Treatment Planning and Follow Up. Because most thoracoabdominal aortic repairs are complex, the need for routine surveillance after treatment is crucial, and often, lifelong follow-up is recommended. A 2016 study of 354 patients undergoing endovascular repair for Thoracoabdominal Aortic Aneurysm or Dissection thoracoabdominal aortic pathology underscores the need for close follow-up, because 36% of patients required further intervention within 36 months, most commonly for endoleak [14]. Typically, follow-up imaging is obtained at 1, 3, and 6 months after intervention to evaluate for endoleak, increase in aortic diameter, incomplete false lumen thrombosis (in dissection), and other procedure complications, and prior studies have shown poor compliance with follow-up with increased risk of aortic rupture in patients with poor follow-up [17,80]. After 6 months, individualized imaging follow-up may be planned based on personal risk factors, with imaging typically at 6 to 12 month intervals. Early studies evaluating the ability of MRA to evaluate for endoleak or other complication after EVAR established MRI as a suitable alternative to CTA [78,85,86]. Direct evidence comparing MRA with IV contrast to other modalities in endoleak identification after endovascular thoracoabdominal aneurysm repair is lacking, but multiple additional studies and meta-analyses have compared MRA with CTA in identifying endoleaks after EVAR [78,79,82,83,85,86]. A meta-analysis by Guo et al [82] in 2016 evaluated 3,853 patients after EVAR with paired scans of different modalities (CTA, MRA, US) obtained within a 1-month period. In 1,694 paired CTA and MRA scans, CTA identified 2 additional endoleaks, whereas MRA identified 42 additional endoleaks [82]. A subsequent meta-analysis in 2018 by Zaiem et al also noted that MRI identified more endoleaks than CTA [84].


Thoracoabdominal Aneurysm or Dissection Treatment Planning and Follow Up. These findings suggest a higher sensitivity of MRI in identification of endoleak compared with CTA, although the authors caution that the increased endoleaks identified could represent false-positive findings or endoleaks that are not clinically important [84]. MRA with IV contrast also allows superior evaluation of flow dynamics compared with CTA. Time resolved and 4-D flow MRA can be used to improve detection and classification of endoleaks [76,87,88]. Use of multiple phases of contrast can be used in 4-D flow MRA to ascertain not only the presence of endoleak but also the endoleak type [88]. MRA with IV contrast has also shown value in predicting the persistence of type II endoleak. A retrospective review of MRAs with type II endoleak performed by Katahashi et al determined that the use of flow quantification could be used to accurately predict persistence or resolution of type II endoleak after EVAR, although this algorithm has not been applied prospectively [20]. MRA Chest, Abdomen, and Pelvis Without IV Contrast Literature supporting the use of MRA without IV contrast for evaluation after endovascular thoracoabdominal aortic repair is limited compared with evidence of MRA with IV contrast. A 2019 study evaluating 8 patients used a noncontrast MRI protocol to assess for endoleak after EVAR [89]. This study compared noncontrast MRA with contrast-enhanced CTA and angiogram and found the MRAs had comparable ability to detect endoleaks and assess aneurysm size [89]. The applicability of these findings to imaging post-thoracoabdominal endovascular intervention is unknown, although applicability may be incomplete because of multiple stents within the aorta and branch vessels. Additionally, the ability of this sequence to obtain widespread use is unclear. As such, noncontrast MRA would generally be expected to have a lower sensitivity for endoleak, false lumen thrombosis, or branch vessel patency, although evidence is lacking.


Thoracoabdominal Aneurysm or Dissection Treatment Planning and Follow Up. MRA Chest and Abdomen Without and With IV Contrast Compared with MRA of the chest, abdomen, and pelvis, evaluation of the chest and abdomen only without imaging of the pelvis carries the advantage of reduced imaging time although may fail to detect changing or new pathology in the pelvic vasculature that could require further intervention. MRA Chest and Abdomen Without IV Contrast Compared with MRA of the chest, abdomen, and pelvis, evaluation of the chest and abdomen only without imaging of the pelvis carries the advantage of reduced imaging time although may fail to detect changing or new pathology in the pelvic vasculature that could require further intervention. Radiography Chest Postintervention radiography can be used to monitor endograft position and integrity, with location relative to bony landmarks used to infer possible stent migration [76]. Additionally, prior studies have reported the value of radiography to evaluate for endograft fracture and kinking [76,90]. However, the low incidence of stent fracture and the inability of radiography to evaluate for increasing aneurysm sac size, branch occlusion, and many other complications limits value in routine use. Additionally, a radiograph of the chest only is likely to include only a portion of the repaired aorta within the field of view. Thoracoabdominal Aortic Aneurysm or Dissection Radiography Chest Abdomen Pelvis Postintervention radiography can be used to monitor endograft position and integrity, with location relative to bony landmarks used to infer possible stent migration [76]. Additionally, prior studies have reported the value of radiography to evaluate for endograft fracture and kinking [76,90]. However, the low incidence of stent fracture and the inability of radiography to evaluate for increasing aneurysm sac size, branch occlusion, and many other complications limits value in routine use.


Thoracoabdominal Aneurysm or Dissection Treatment Planning and Follow Up. US Duplex Doppler Aorta Abdomen Duplex US of the abdominal aorta carries the advantages of being a readily obtainable bedside examination for evaluation of the distal thoracic and abdominal aorta. After EVAR, duplex US can be used to evaluate aortic diameter and presence of endoleak, with a good correlation of aortic size with CTA in most patients [76,91]. US Echocardiography Transthoracic Resting TTE allows visualization of the heart and portions of the thoracic aorta. However, portions of the proximal descending thoracic aorta may be poorly visualized with TTE, and examination may be limited by poor acoustic windows, creating the possibility of false-negative examinations in following patients after endovascular thoracoabdominal aortic repair [58]. These characteristics have resulted in a low sensitivity of 31% to 55% for diagnosis of acute type B aortic dissection on TTE [33]. TTE is also limited by the ability to visualize the abdominal aorta to determine the extent of thoracoabdominal aortic pathology. Variant 4: Follow-up after open repair of thoracoabdominal aortic aneurysm or dissection. Aortography Chest Abdomen Pelvis There is no relevant literature regarding the use of aortography in the evaluation of follow-up of open repair of TAAA or dissection. Aortogram with DSA for evaluation of the thoracic and abdominal aorta has a sensitivity of up to 90% and a specificity of 95% for acute aortic syndrome [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. 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 open repair of TAAA or dissection because most follow-up imaging uses an arterially timed contrast bolus in the form of a CTA (discussed below).


Thoracoabdominal Aneurysm or Dissection Treatment Planning and Follow Up. However, contrast-enhanced CT can provide similar information as CTA in evaluating the size and extent of aortic pathology and in identifying postsurgical complications. If venous phase or unenhanced CT has already been performed, additional imaging with CTA may not be required in some patients. CT Chest, Abdomen, and Pelvis Without and With IV Contrast There is no relevant literature regarding venous phase CT chest, abdomen, and pelvis with noncontrast phase for the follow-up of open repair of TAAA or dissection because most follow-up imaging uses an arterially timed contrast bolus in the form of a CTA (discussed below). However, contrast-enhanced CT can provide similar information as CTA in evaluating the size and extent of aortic pathology and in identifying postsurgical complications. If venous phase or unenhanced CT has already been performed, additional imaging with CTA may not be required in some patients. CT Chest, Abdomen, and Pelvis Without IV Contrast There is no relevant literature for CT chest, abdomen, and pelvis without IV contrast in the evaluation of follow-up of open repair of TAAA or dissection. Although most follow-up after open thoracoabdominal aortic repair is performed with IV contrast [29-31], select groups of patients may be monitored with noncontrast CT to evaluate measurements of aortic size and for surrounding changes that could suggest inflammation or infection. If venous phase or unenhanced CT has already been performed, additional imaging with CTA may not be required in some patients. Thoracoabdominal Aortic Aneurysm or Dissection CT Chest and Abdomen With IV Contrast There is no relevant literature regarding venous phase CT chest and abdomen for the follow-up of open repair of TAAA or dissection. Compared with CT of the chest, abdomen, and pelvis, exclusion of the pelvis may fail to detect changing or new pathology in the pelvic vasculature.