Contrast-enhanced CT scanning has developed to afford excellent noninvasive angiography, and also affords imaging of organs and other structures, unlike conventional angiography.
Atherosclerotic calcium can be a problem.
Knowledge of the range of normal and collateral anatomy is critical.
Noninvasive assessment of carotid artery disease is desirable, as more than half of the permanent morbidity and mortality of the Asymptomatic Carotid Artery Surgery (ACAS) Trial was attributable to catheter-based angiography (1.3% of the 2.3% with permanent morbidity and mortality).
The utility of multidirectional CT (MDCT) for the assessment of cerebrovascular, renal artery, and peripheral arterial disease is less studied and published than is its use for the assessment of coronary disease.
Cerebrovascular and peripheral arterial disease are much less subject to motion, and therefore less taxing of the limited temporal resolution of MDCT, than is coronary artery disease. However, both carotid artery disease and peripheral arterial disease are subject to at least as much calcification as is coronary artery disease. In addition, adjacent bony artifacts (to the popliteal artery from the femur and tibial head) are substantial problems for the MDCT assessment of peripheral arterial disease, and tracking a contrast bolus without getting ahead of it is a protocol challenge for the assessment of peripheral arterial disease.
The renal arteries are subject to motion due to excursion of the adjacent diaphragm, occasionally contributing motion artifacts on MDCT imaging.
Assessment of the functional significance of renal artery disease is not simple, by any modality, given the complex anatomy of renal arteries, their known anatomic variants, the variability of lesion numbers and locations, and the fact that “renal artery disease” is more of a medical (over)-simplification than a single pathologic entity.
The renal arteries arise 1 cm below the origin of the superior mesenteric artery (SMA). The right renal artery is longer than the left renal artery, as the aorta lies to the left side of the spine. The main renal arteries divide into five segmental renal arteries—superior/apical, posterior, anterior superior/upper, anterior inferior/middle, and inferior/lower—which supply the kidney.
When compared with digital subtraction angiography (DSA), neither CT angiography (CTA) nor MR angiography (MRA) appears able to reliably exclude renal artery stenosis ( Table 27-1 ).
Data from Vasbinder GB, Nelemans PJ, Kessels AG, et al. Accuracy of computed tomographic angiography and magnetic resonance angiography for diagnosing renal artery stenosis. Ann Intern Med . 2004;141(9):674-682.
Given the concurrent existence of renal insufficiency in renal artery disease, the nephrotoxicity of CT contrast material is a real concern for the routine use of CTA for the assessment of renal artery disease—a concern that is shared with contrast angiography, but not with MRA or ultrasound.
Approximately one third of the general population demonstrates variability in number, location, and branching patterns of the renal arteries. This is clinically important because renal artery stenosis (RAS) in an accessory renal artery can, even though rarely, be responsible for renovascular hypertension. Lesions causing stenosis of more than 50% of the diameter of the artery are considered significant. Although there are no clear-cut indications for intervention, the following criteria may be used as a guide for renal artery revascularization: recent onset of hypertension, in which the goal is to cure the hypertension; drug-refractory hypertension; intolerance to antihypertensive medications; progressive renal insufficiency/failure; and episodes of flash pulmonary edema.
In addition to atherosclerotic renal artery stenosis, another notable cause of renovascular hypertension is fibromuscualr dysplasia (FMD). FMD is a nonatherosclerotic angiopathy of unknown etiology, although a genetic association with possible autosomal dominant transmission has been suggested.
FMD can involve the intima, media, and adventitia, with medial FMD representing the most common type, and is characterized by the classic “string of beads” appearance. FMD usually affects females between 15 and 50 years of age, frequently involves the mid or distal segments of the renal artery, and is bilateral in two thirds of patients. It is the most common cause of renovascular hypertension in children. Renal artery stenosis secondary to FMD may affect pregnant women and thus remains an important consideration as a cause of secondary hypertension during pregnancy.
For images of renovascular disease, see Figures 27-1 to 27-3 .
A, Renal CT angiogram. Distal “beading” is seen, consistent with renal fibromuscular disease. B, MRA does not depict the same findings as clearly.
A 75-year-old woman with a history of hypertension. A, A heavily calcified abdominal aorta. The right renal artery demonstrates a typical corkscrew appearance, like the one seen in fibromuscular dysplasia. The right kidney is smaller than the contralateral left kidney. B, A curved reformatted image through the right renal artery shows multiple moderate to severe stenoses in the mid-portion of the artery. C and D, Volume-rendered images through the upper abdominal aorta demonstrate a classic beaded appearance of the right renal artery, pathognomonic for fibromuscular dysplasia.
Images from a CT angiogram of the abdomen in a 38-year-old woman with hypertension. The three-dimensional CT volume-rendered view ( A ), maximum intensity projection image ( B ), and volume-rendered image demonstrate mild beading of the proximal right renal artery, with a mild focal area of ectasia. A and B also demonstrate two left-sided renal arteries. The upper, larger renal artery has a moderate to severe renal artery stenosis, which is seen at the origin of the renal artery. Similarly, the smaller, lower-pole left renal artery has a severe proximal stenosis. These findings, confirmed on the conventional angiogram ( C ), are consistent with fibromuscular dysplasia (FMD) of the renal arteries. The patient underwent conventional renal angiography and subsequent balloon angioplasty of the left upper renal artery stenosis ( D ) and the left lower renal artery stenosis ( E, F ). F , An unfortunate, but likely minor, consequence of the balloon angioplasty of the left upper renal artery was segmental renal infarction. G, Image obtained in a parenchymal blush prior to the angioplasty 3 months earlier shows a normal contour to the left upper pole. H, A follow-up CT angiogram study 3 months later demonstrates a focal area of thinning in the medial left upper pole consistent with segmental infarctions from the angioplasty.
Agreement of 16-slice MDCT with DSA is very good (96% sensitive), as is interobserver agreement (κ = 0.84–1.0). However, agreement varies considerably depending on the artery in question. Overestimation in a small percentage (2–3%) of cases occurs more frequently than does underestimation (1%). Anteroposteriorly directed narrowing and extensive calcification are common reasons for disagreement. Older scanners (4-MDCT) were inaccurate.
Confidence with MDCT is similar to that of MR angiography, but is less than with DSA, leading to more testing after CT angiography (35% of cases vs. 14% of cases after DSA).
More studies are needed with current scanners to understand the role of MDCT.
For images of peripheral artery disease, see Figures 27-4 through 27-9 .
Three-dimensional reconstruction and multiplanar imaging of a patient with a thoracic outlet syndrome.