(Radiographics. 2001;21:373-386.)
© RSNA, 2001
Three-dimensional Volume-rendered CT Angiography of the Renal Arteries and Veins: Normal Anatomy, Variants, and Clinical Applications1
Bruce A. Urban, MD, 2,
Lloyd E. Ratner, MD and
Elliot K. Fishman, MD
1 From the Russell H. Morgan Department of Radiology and Radiological Science, Johns Hopkins Medical Institutions, 600 N Wolfe St, Baltimore, MD 21287. Presented as a scientific exhibit at the 1999 RSNA scientific assembly. Received March 14, 2000; revision requested April 14; revision received and accepted June 26. Address correspondence to E.K.F. (e-mail: efishman@jhmi.edu).
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Abstract
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Three-dimensional volume-rendered computed tomographic (CT) angiography represents an increasingly important clinical tool that, in many institutions, is replacing conventional angiography in the depiction of normal vascular anatomy and the diagnosis of vascular disorders. Evaluation of conditions affecting the renal vasculature constitutes a major focus of volume-rendered CT angiography, which has documented utility for demonstrating both arterial and venous disease. Arterial disorders include renal artery stenosis, renal artery aneurysms, and dissection. Venous disorders include splenorenal shunts, thrombosis, and intravascular tumor extension. In addition, volume-rendered CT angiography accurately displays the normal and variant renal vascular anatomy, which is crucial to detect before surgery, especially partial nephrectomy and laparoscopic nephrectomy. CT angiography is also useful in the evaluation of the renal vasculature following renal transplantation. Familiarity with proper CT protocols and data acquisition techniques are crucial for accurate diagnosis.
Index Terms: Computed tomography (CT), angiography, 96.12916 • Computed tomography (CT), volume rendering, 96.12916 • Kidney, CT, 81.12916 • Renal angiography, 96.12916
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LEARNING OBJECTIVES FOR TEST 2
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After reading this article and taking the test, the reader will be able to:
- Describe the basic concepts and techniques of 3D volume-rendered CT angiography.
- Recognize the common variants of renal vascular anatomy.
- Identify and discuss the common clinical applications of CT angiography involving the renal vascular pedicle.
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Introduction
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Three-dimensional (3D) volume-rendered computed tomographic (CT) angiography provides a fast, noninvasive modality for the evaluation of the renal vascular pedicle (1)–(14). CT angiography can reliably and accurately depict the renal arteries and veins and approaches the accuracy of conventional angiography in the assessment of most vascular abnormalities (1)–(10). The number, size, course, and relationship of the renal arteries and veins are easily demonstrated by using real-time interactive editing of the images (1)–(5).
This article provides a CT angiographic atlas of normal anatomy and common variants of the renal vasculature. Protocols for image data acquisition, contrast material injection, and 3D postprocessing techniques are also reviewed. In addition, the application of 3D volume-rendered CT angiography to the evaluation of several common pathologic conditions of the renal vasculature is illustrated. Arterial disorders include renal artery stenosis, renal artery aneurysms, and dissection. Venous disorders include splenorenal shunts, thrombosis, and intravascular tumor extension. The role of CT angiography in the vascular evaluation of the renal transplant donor and recipient is also addressed.
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Imaging and Postprocessing Techniques
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Protocol for CT Angiography
The quality and accuracy of any 3D image depend on the quality of the raw data obtained from the original CT study (1)–(4). Attention to proper patient preparation, patient positioning, and contrast material injection technique is paramount. Tailoring the imaging parameters to the clinical region of interest is also crucial for obtaining optimal images. The following paragraphs summarize our recommended protocol for CT angiography of the renal vasculature (1)–(4).
- A large-bore (18-gauge) intravenous line is placed in the antecubital fossa.
- The patient is given water orally. Water is used as a negative contrast agent because a positive orally administered contrast agent would interfere with the 3D rendering to follow.
- The patient is instructed in breath-hold technique. Most CT scanners require a 30- to 40-second breath hold for obtaining optimal images of the renal hilum. Newer multidetector helical CT scanners are much faster, and a breath hold of only 10–20 seconds is needed.
- In select cases, the renal hilum is localized accurately by obtaining a few nonenhanced images. The appropriate table position is calculated for evaluation of the renal hilum. The region of interest for scanning extends from the suprarenal abdominal aorta to the iliac artery bifurcation.
- Helical CT scanning parameters are entered. Use of narrow collimation (1–3 mm) is crucial. A pitch up to 2 is used to ensure adequate coverage and will not substantially decrease image quality. Newer multidetector scanners allow an even greater pitch (up to 8) to be used without incurring image degradation.
- Contrast material is injected at 3–4 mL/sec for a volume of 120–150 mL.
- The helical acquisition of image data is initiated after a preset empiric delay of 20–25 seconds after the start of the contrast material injection. Use of bolus triggering devices should be considered to ensure appropriate timing, especially in examinations of older patients with decreased cardiac output.
- Images are reconstructed equally throughout the data set. For evaluation of the renal hilum, use of 1-mm interscan spacing is ideal (especially for assessing renal artery stenosis). For routine anatomic evaluation, 3-mm interscan spacing is suitable.
- Data are transferred over the network to an imaging workstation. Free-standing workstations (such as Advantage Windows, GE Medical Systems, Milwaukee, Wis; 3D Virtuoso, Siemens Medical Systems, Iselin, NJ) provide the most flexibility and have more capabilities.
3D Postprocessing Principles and Techniques
Once conventional CT data are obtained, 3D postprocessing techniques are employed to produce images that simulate conventional angiograms. Common techniques include surface rendering, maximum intensity projection (MIP), and volume rendering. Of all the reconstruction algorithms available for performing CT angiography, volume rendering has emerged as the postprocessing technique of choice (1)–(4). In volume ren-dering, the entire CT data set is used to create the angiogram, and the contributions of each voxel are summed along a line from the viewer’s eye through the data set. For CT angiography, volume rendering is commonly performed with a window or level transfer function that results in high-density materials (eg, enhanced vessels or vascular calcifications) appearing bright and opaque, whereas less-dense structures appear dim and translucent. Each voxel contributes a brightness, color, and opacity that are used to form the final image. The result is an image that provides a single, comprehensive vascular map of the arteries and veins.
Volume rendering is an extremely user-friendly technique because it eliminates the need for preliminary editing, a cumbersome step that previously hampered the clinical utility of the other 3D reconstruction algorithms (1)–(4). By using volume rendering, one can perform all of the editing manipulations within seconds and view the resultant images in real time. The user actively interacts with the image, editing and modifying the position, orientation, opacity, and brightness of the structures. Overlying structures are easily removed with an interactive clip plane, and the vessels of interest are easily rotated into the best orientation for visualizing the region of interest. For examination of the renal hilum, axial, coronal, and sagittal views are often used in conjunction for optimal evaluation of the number, caliber, and course of the renal arteries and veins. Perspective volume rendering can provide an additional view, which allows the user to see the data set from "within" the vessel. With this technique, the user can produce an angioscopic view that can be helpful for identifying a vascular orifice and vascular stenosis (Fig 1).
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Figure 1a. Normal renal arteries in a 44-year-old man. (a) Anterior volume-rendered image from CT data shows prepolar branching of the left renal artery (arrow). (b) Sagittal angioscopic volume-rendered image from CT data provides a view from "inside" the aorta and clearly depicts the renal ostium (arrowhead). This view can be helpful in the evaluation of dissection flaps and renal artery stenosis.
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Figure 1b. Normal renal arteries in a 44-year-old man. (a) Anterior volume-rendered image from CT data shows prepolar branching of the left renal artery (arrow). (b) Sagittal angioscopic volume-rendered image from CT data provides a view from "inside" the aorta and clearly depicts the renal ostium (arrowhead). This view can be helpful in the evaluation of dissection flaps and renal artery stenosis.
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MIP represents the other common reconstruction algorithm commonly employed in examinations of the renal vasculature (1)–(3). In the MIP technique, each voxel is evaluated from the viewer’s eye through the data set, but only the maximal voxel values are selected and displayed. The image produced lacks depth orientation, but a 3D effect can be produced with rotational viewing of multiple projections. In general, volume-rendered images are better than MIP images at displaying complex anatomy, especially when overlapping vessels are present (Fig 2). MIP images can still provide useful information about atherosclerotic burden, vascular stents, and vascular stenoses, and are therefore often reconstructed and interpreted in conjunction with volume-rendered images.
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Figure 2a. Comparison of MIP versus volume-rendered images. (a) Anterior volume-rendered image from CT data shows an accessory artery (arrow) arising from the left iliac artery in a 49-year-old man undergoing a preoperative renal donor evaluation. (b) Anterior MIP image from the same data also reveals the accessory vessel, but its usefulness is limited because overlying bone obscures the aorta and iliac vessels on the anterior view. MIP images can be rotated about an axis to determine depth and better appreciate vascular relationships, but volume-rendered images are probably less cumbersome and easier to interpret in cases with crossing vessels and overlapping anatomy, as in this case.
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Figure 2b. Comparison of MIP versus volume-rendered images. (a) Anterior volume-rendered image from CT data shows an accessory artery (arrow) arising from the left iliac artery in a 49-year-old man undergoing a preoperative renal donor evaluation. (b) Anterior MIP image from the same data also reveals the accessory vessel, but its usefulness is limited because overlying bone obscures the aorta and iliac vessels on the anterior view. MIP images can be rotated about an axis to determine depth and better appreciate vascular relationships, but volume-rendered images are probably less cumbersome and easier to interpret in cases with crossing vessels and overlapping anatomy, as in this case.
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Normal Renal Vascular Anatomy
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Renal Arteries
In most individuals, each kidney is supplied by a single renal artery that originates from the abdominal aorta (15)–(18). The renal arteries typically arise from the aorta at the level of L2 below the origin of the superior mesenteric artery, with the renal vein being anterior to the renal artery. The renal arteries course anterior to the renal pelvis before they enter the medial aspect of the renal hilum (Fig 3). The right renal artery typically demonstrates a long downward course to the relatively inferior right kidney, traversing behind the inferior vena cava. Conversely, the left renal artery, which arises below the right renal artery and has a more horizontal orientation, has a rather direct upward course to the superiorly positioned left kidney. Both renal arteries usually course in a slightly posterior direction because of the position of the kidneys.
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Figure 3. Normal renal arteries in a 39-year-old woman with longstanding hypertension. Axial MIP image, obtained to evaluate for renal artery stenosis, clearly shows the renal arteries (arrows), which are normal and demonstrate no evidence of stenosis.
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The main renal artery divides into segmental arteries near the renal hilum (15)–(18) (Fig 4). The first division is typically the posterior branch, which arises just before the renal hilum and passes posterior to the renal pelvis to supply a large portion of the blood flow to the posterior portion of the kidney. The main renal artery then continues before dividing into four anterior branches at the renal hilum: the apical, upper, middle, and lower anterior segmental arteries. The apical and lower anterior segmental arteries supply the anterior and posterior surfaces of the upper and lower renal poles, respectively; the upper and middle segmental arteries supply the remainder of the anterior surface. The segmental arteries then course through the renal sinus and branch into the lobar arteries. Further divisions include the interlobar, arcuate, and interlobular arteries. Depiction of the relatively avascular plane between the anterior and posterior arterial divisions of the kidney is important to the surgeon, because the site can be used for a clean incision toward the renal pelvis at the time of surgery (15). The site is usually located posteriorly, one-third of the distance between the posterior and anterior kidney surfaces. A similar avascular plane exists between the posterior renal segment and the polar renal segments.
Renal Veins
The renal cortex is drained sequentially by the arcuate veins and interlobar veins (15)–(18). The lobar veins join to form the main renal vein (Fig 5). The renal vein usually lies anterior to the renal artery at the renal hilum. The left renal vein is almost three times longer than the right renal vein. The left renal vein averages 6–10 cm in length and normally courses anteriorly between the superior mesenteric artery and the aorta before emptying into the medial aspect of the inferior vena cava. The right renal vein averages 2–4 cm in length and joins the lateral aspect of the inferior vena cava. Unlike the right renal vein, the left renal vein receives several tributaries before joining the inferior vena cava. It receives the left adrenal vein superiorly, the left gonadal vein inferiorly, and a lumbar vein posteriorly.
CT Angiography and Normal Anatomy
Use of volume-rendered CT angiography allows a quick, accurate determination of the location and course of the renal vascular anatomy (1)–(5),(7),(10). Angioscopic and MIP views provide additional information about the renal arteries and veins and complement conventional volume-rendered images (Fig 6).
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Figure 6a. Comparison of MIP versus volume-rendered images. (a) Axial MIP image of a 62-year-old woman undergoing a preoperative renal donor evaluation shows a confusing tangle of vessels in the left renal hilum (arrow). MIP images, because they only select the voxel with highest attenuation along a line extended from the viewer’s eye, do not allow overlapping vessels to be differentiated. (b, c) Axial (b) and anterior oblique (c) volume-rendered images use the entire CT data set and enable easy differentiation of arteries (arrows in b) from veins (arrow in c).
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Figure 6b. Comparison of MIP versus volume-rendered images. (a) Axial MIP image of a 62-year-old woman undergoing a preoperative renal donor evaluation shows a confusing tangle of vessels in the left renal hilum (arrow). MIP images, because they only select the voxel with highest attenuation along a line extended from the viewer’s eye, do not allow overlapping vessels to be differentiated. (b, c) Axial (b) and anterior oblique (c) volume-rendered images use the entire CT data set and enable easy differentiation of arteries (arrows in b) from veins (arrow in c).
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Figure 6c. Comparison of MIP versus volume-rendered images. (a) Axial MIP image of a 62-year-old woman undergoing a preoperative renal donor evaluation shows a confusing tangle of vessels in the left renal hilum (arrow). MIP images, because they only select the voxel with highest attenuation along a line extended from the viewer’s eye, do not allow overlapping vessels to be differentiated. (b, c) Axial (b) and anterior oblique (c) volume-rendered images use the entire CT data set and enable easy differentiation of arteries (arrows in b) from veins (arrow in c).
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Typically, arterial branches can be identified to at least the segmental level. Detection of vessels smaller than 2 mm is limited (7). The sensitivity of volume-rendered CT angiography for the demonstration and location of main renal arteries, however, approaches 100% (2),(7),(10). Surgical and CT findings correlate in over 95% of patients (7).
The renal venous anatomy is also well demonstrated with CT angiography and is especially important to document for patients being evaluated for laparoscopic donor nephrectomy (Fig 7) (10). The left renal anatomy is especially critical because it is the preferred side for resecting the donor kidney. Tributaries of the left renal vein are confidently displayed and are of potential surgical importance if noted to be enlarged (10).
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Figure 7. Normal renal veins. Anterior volume-rendered image of a patient undergoing a preoperative renal donor evaluation demonstrates a single left renal vein (arrow) and two renal veins (arrowheads).
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Renal Vascular Variants
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Renal Arteries
Accessory renal arteries constitute the most common, clinically important renal vascular variant and are seen in up to one-third of patients. Multiple renal arteries are unilateral in approximately 30% of patients and bilateral in approximately 10% (16),(19). Accessory arteries usually arise from the aorta or iliac arteries anywhere from the level of T11 to the level of L4. In rare cases, they can arise from the lower thoracic aorta or from lumbar or mesenteric arteries (16). Usually, the accessory artery courses into the renal hilum to perfuse the upper or lower renal poles. Accessory vessels to the polar regions are usually smaller than accessory hilar renal arteries, which are typically equal in size to a single renal artery (16). Prehilar arterial branching is another common variant that must be checked in patients being evaluated for donor nephrectomy.
Volume-rendered images, MIP images, shaded surface display images, and multiplanar reformatted images have all demonstrated a high sensitivity (approaching 100%) in the detection of accessory arteries (Fig 8) (5)–(8),(10). Images must be obtained during the arterial phase of vascular enhancement to obtain such good results (11). Smith et al (10) showed that use of 3D volume-rendered CT angiography enabled correct identification of renal artery anatomy in 41 of 42 prospective patients undergoing preoperative evaluation for laparoscopic nephrectomy. Rubin et al (8) showed 3D CT angiography to be 100% sensitive in the identification of accessory renal arteries. Platt et al (7) found that 3D CT angiography was comparable with conventional angiography in the ability to predict vascular anatomy in 154 patients.
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Figure 8. Accessory renal arteries in a 58-year-old woman scheduled for donor nephrectomy. Posterior volume-rendered image shows two renal arteries (arrows) supplying the left kidney. The inferior artery was not appreciated on initial axial source images.
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Variations in arterial branching patterns, including prehilar branching, are also confidently identified with 3D imaging (Fig 9) (8). In interpreting 3D images, care must be taken not to mistake normal overlapping vessels for accessory renal arteries near the renal hilum (Fig 10).
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Figure 9. Prehilar branching of a renal artery in a 62-year-old man undergoing a preoperative renal donor evaluation. Anterior volume-rendered image demonstrates complex, tortuous prehilar branching of the right renal artery (arrowheads).
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Figure 10. Potential pitfall in assessing an accessory renal artery. Anterior volume-rendered image of a 27-year-old woman obtained before donor nephrectomy shows the superior branch of the inferior mesenteric artery (arrows), which courses toward the left kidney. This vessel can often mimic the appearance of an accessory renal artery on the anterior view. Unlike a true accessory renal artery, however, the mesenteric vessel will not course into the renal hilum.
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Renal Veins
Multiple renal veins constitute the most common venous variant, and are seen in approximately 15%–30% of patients (16). Multiple right renal veins occur in up to 30% of individuals, and sometimes a single vein may divide before joining the inferior vena cava (20).
The most common anomaly of the left renal venous system is the circumaortic renal vein, seen in up to 17% of patients (21). In this anomaly, the left renal vein bifurcates into ventral and dorsal limbs that encircle the abdominal aorta. The posterior limb is usually the smaller of the two, although this is certainly variable. There are two common variants of the circumaortic vein: In the most common variant (approximately 75% of cases), one renal vein at the renal hilum subsequently divides before entering the inferior vena cava; in the less common variant, two distinct veins originate from the renal hilum (Fig 11) (22). In the presence of a circumaortic renal vein, the gonadal vein will typically join the retroaortic limb and the adrenal vein will join the preaortic limb (16).
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Figure 11a. Accessory renal artery and circumaortic renal vein in the same patient. (a) Anterior volume-rendered image of a 58-year-old man being evaluated for donor nephrectomy shows a circumaortic renal vein (arrowheads), which is the most common renal vascular anomaly. (b) Axial volume-rendered image demonstrates an accessory renal artery to the right lower pole (arrow). A significant advantage of volume-rendered CT angiography is the ability to obtain both arterial and venous vascular maps with the same data set, as in this case.
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Figure 11b. Accessory renal artery and circumaortic renal vein in the same patient. (a) Anterior volume-rendered image of a 58-year-old man being evaluated for donor nephrectomy shows a circumaortic renal vein (arrowheads), which is the most common renal vascular anomaly. (b) Axial volume-rendered image demonstrates an accessory renal artery to the right lower pole (arrow). A significant advantage of volume-rendered CT angiography is the ability to obtain both arterial and venous vascular maps with the same data set, as in this case.
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A less common venous anomaly is the completely retroaortic renal vein, seen in 3% of patients (Fig 12) (21). Here, the single left renal vein courses posterior to the aorta and drains into the lower lumbar portion of the inferior vena cava. Alternatively, the retroaortic renal vein can drain into the iliac vein (21).
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Figure 12a. Retroaortic renal vein. Anterior oblique (a) and axial (b) volume-rendered images of a 57-year-old woman undergoing preoperative renal donor evaluation show the renal vein, which courses posterior to the aorta (arrowhead). This represents a not uncommon venous anomaly.
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Figure 12b. Retroaortic renal vein. Anterior oblique (a) and axial (b) volume-rendered images of a 57-year-old woman undergoing preoperative renal donor evaluation show the renal vein, which courses posterior to the aorta (arrowhead). This represents a not uncommon venous anomaly.
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Accurate depiction of venous anomalies is very important in the preoperative evaluation of patients undergoing donor nephrectomy, especially since the newer laparoscopic techniques are now routinely employed for this surgery (2),(14). Unlike conventional open surgery, laparoscopic nephrectomy is performed with a limited view of the venous anatomy. Under these circumstances, all of the venous anomalies listed above constitute a potential surgical nightmare if they are not documented in advance. CT angiography can provide this complete evaluation with an accuracy comparable with that of conventional angiography (2).
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Clinical Applications of CT Angiography
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Renal Artery Disorders
CT angiography is commonly used to evaluate the abdominal aorta and diseases that involve the renal arteries. These disorders include renal artery stenosis, renal artery aneurysms, arteriovenous malformations, dissection, thrombosis, and fibromuscular dysplasia. CT angiography is also valuable in assessing abdominal aortic aneurysms and is very helpful for preoperative evaluation (23). It can accurately depict the extent and location of the aortic abnormality as it relates to the renal arteries. CT angiography demonstrates not only the renal vascular anatomy but also the secondary parenchymal changes, including infarcts and atrophy.
Renal Artery Stenosis.
A diagnosis of renal artery stenosis is important, since the condition represents a potentially reversible cause of hypertension (24). It occurs in fewer than 5% of adult patients with hypertension.
Atherosclerotic disease is the most common cause of renal artery stenosis (25), with the majority of affected individuals being men over 50 years of age. The stenosis typically results from atherosclerotic plaque and calcification located at the proximal renal artery near the orifice. The disease is bilateral in approximately 30% of patients (26).
Fibromuscular dysplasia is the second most common cause of renal artery stenosis and accounts for a significant number of patients with renovascular hypertension (27). The majority of these patients are young or middle-aged women (28). Lesions typically develop in the mid or distal main renal artery, as opposed to the more proximal stenoses seen with atherosclerotic disease. The disease is bilateral in two-thirds of the patients. Fibromuscular dysplasia is classified according to the location of involvement within the vessel wall (28). Medial fibroplasia constitutes the most common type and often demonstrates multiple ridges, which appear as alternating areas of narrowing and dilatation that are often referred to as a "string of beads" (16),(28). In a study of 20 patients, Beregi et al (13) found CT angiography to be 100% sensitive in the diagnosis of fibromuscular dysplasia. Other rare causes of renal artery stenosis include neurofibromatosis, Takayasu arteritis, and congenital stenosis.
CT angiography represents a reliable, noninvasive screening examination for the detection of renal artery stenosis, with reported accuracies in the mid 90th percentile (Fig 13) (5). The examination has nearly 100% specificity in the diagnosis of severe (>50%) stenosis of the renal artery (5),(23). Normal results from CT angiography virtually rule out renal artery stenosis (5). CT angiography is also very sensitive and specific in the demonstration of renal artery occlusion.
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Figure 13. Bilateral renal artery stenosis in a 22-year-old woman with Takayasu arteritis. Anterior volume-rendered image demonstrates bilateral moderate stenosis (arrows) with marked poststenotic dilatation. The patient also had stenosis of the superior mesenteric artery and had developed an extensive collateral network of the inferior mesenteric artery seen on another view (not shown).
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Both MIP and volume rendering techniques are useful and complementary in the CT angiographic evaluation of renal artery stenosis. Axial images alone are not sufficient because the renal arteries often have a tortuous, variable course. The additional views provided by CT angiography allow for display of the renal arteries in multiple planes and projections, which is often necessary for depiction of stenosis (5). In cases with extensive calcification, stenosis can be obscured by MIP rendering techniques, and careful evaluation with volume-rendered images is needed (Fig 14) (29). Angioscopic views often provide the best analysis.
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Figure 14a. Suspected renal artery stenosis in an elderly patient with hypertension. (a) Axial MIP image from a CT angiographic study performed to assess the presence of renal artery stenosis demonstrates extensive calcification near the left renal orifice (arrowhead). However, the calcified plaque obscures the underlying lumen and does not permit appropriate quantification of possible underlying stenosis. (b) Axial volume-rendered image, produced after an interactive clip plane has been used to orient the image through the vessel lumen, reveals no evidence of significant stenosis (arrowhead).
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Figure 14b. Suspected renal artery stenosis in an elderly patient with hypertension. (a) Axial MIP image from a CT angiographic study performed to assess the presence of renal artery stenosis demonstrates extensive calcification near the left renal orifice (arrowhead). However, the calcified plaque obscures the underlying lumen and does not permit appropriate quantification of possible underlying stenosis. (b) Axial volume-rendered image, produced after an interactive clip plane has been used to orient the image through the vessel lumen, reveals no evidence of significant stenosis (arrowhead).
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CT angiography can also depict secondary signs of renal artery stenosis, including poststenotic dilatation (Fig 13) and renal parenchymal changes of atrophy and decreased cortical enhancement. CT angiography is also helpful in the evaluation of renal stent grafts, and the highly attenuating graft material and the intraluminal contrast material can usually be distinguished (Fig 15) (4). Even more complicated postoperative cases can be easily evaluated with CT angiography (Fig 16).
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Figure 15. Follow-up after placement of an endovascular stent for renal artery stenosis in a 54-year-old man with fibromuscular dysplasia. Anterior volume-rendered image shows flow within the left renal artery stent (arrow). The kidney demonstrates a prompt nephrogram.
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Figure 16. Follow-up after placement of an endovascular aortic stent in an 84-year-old man with a history of multiple vascular surgeries including placement of a right iliorenal graft. Anterior volume-rendered image demonstrates that the graft to the right renal artery is patent (white arrows). The right kidney functions well. The aortic graft is clearly seen and is partially thrombosed (black arrow).
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Renal Artery Aneurysms.
Aneurysms of the renal arteries are seen at angiography in approximately 1% of patients (30). Most renal artery aneurysms are detected in the 4th and 5th decades of life. Although many are isolated findings, some reflect a manifestation of a systemic vasculitis or other predisposing cause. Common causes of renal artery aneurysms include atherosclerosis, polyarteritis nodosa, fibromuscular dysplasia, and trauma (16). Atherosclerotic aneurysms can become quite large and often develop rim calcification, although any larger aneurysm can calcify. This calcification can obscure depiction of some aneurysms on MIP images; thus, volume rendering is often the best technique for evaluating these lesions (Fig 17). Polyarteritis nodosa frequently occurs in the renal artery, with aneurysms reported in up to 85% of patients. These inflammatory aneurysms do not calcify and are more prone to rupture (31),(32). Because they are often quite small and peripheral in the distal branches or the interlobar arteries and beyond, these aneurysms may not always be detectable with CT angiography. Aneurysms associated with entities such as fibromuscular dysplasia often involve the main renal artery and proximal branches.
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Figure 17a. Right renal artery aneurysm in a 63-year-old woman with systemic lupus erythematosus. Axial volume-rendered (a) and inverted axial MIP (b) images show a calcified 2-cm renal artery aneurysm deep within the right renal hilum (arrow).
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Figure 17b. Right renal artery aneurysm in a 63-year-old woman with systemic lupus erythematosus. Axial volume-rendered (a) and inverted axial MIP (b) images show a calcified 2-cm renal artery aneurysm deep within the right renal hilum (arrow).
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Other Conditions.
The renal arteries, particularly the left renal artery, are frequently involved in aortic dissection. In such cases, CT angiography demonstrates an intimal flap extending across or into the main renal artery. In rare cases, spontaneous renal artery dissection can complicate fibromuscular dysplasia or trauma (16). Secondary signs of arterial occlusion and infarct are easily seen with CT angiography. Renal arteriovenous malformations and arteriovenous fistulas represent very uncommon arterial conditions that may be seen at CT angiography. Arteriovenous fistulas are often the result of prior trauma or biopsy.
Renal Vein Disorders
Renal Vein Thrombosis.
Suspicion of renal vein thrombosis is an indication for CT angiographic evaluation of the renal pedicle. In children, dehydration and sepsis are common underlying factors for renal vein thrombosis (33). In adults, renal vein thrombosis can result from a variety of disorders, including glomerulonephritis, collagen vascular disease, and diabetes (34). Trauma is another potential cause of renal vein thrombosis.
Arguably, the most important cause of renal vein thrombosis is tumor thrombus from renal cell carcinoma or, in rare cases, adrenal carcinoma. Determining the extent and location of renal vein involvement by tumor is crucial in planning the surgical approach for removing a renal tumor (35). The renal veins are well depicted on the CT angiogram during the early corticomedullary phase of enhancement; thus, this phase is recommended for renal vein evaluation at CT angiography. In the acute state, renal vein thrombosis is seen as a hypoattenuating filling defect within an enlarged renal vein (Fig 18). Over time, thrombus may contract and extensive collateral vessels may develop. CT angiography can also directly demonstrate secondary signs of renal vein thrombosis, including delay in the renal cortical nephrogram and global renal enlargement (35). Thrombus from tumor extension can extend into the inferior vena cava and grow toward the right side of the heart. Complete opacification of the inferior vena cava usually requires a second helical acquisition performed 90–120 seconds after injection of contrast material, and this additional acquisition is recommended in patients with known tumors (35).
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Figure 18. Renal cell carcinoma in the left kidney with renal vein invasion in a 52-year-old man. Anterior volume-rendered image shows a large mass arising from the lower pole of the kidney (curved arrow). Tumor thrombus is demonstrated (straight arrow) extending into the inferior vena cava.
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Other Conditions.
Non–tumor-related renal vein enlargement can result from a variety of causes and is almost always seen on the left side. Left renal vein enlargement from spontaneous splenorenal shunts can be demonstrated in patients with portal hypertension. In these patients, enlarged and tortuous collateral vessels extend inferiorly from the splenic hilum to enter the left renal vein (Fig 19). An isolated renal varix is more rare and has been described as a rare cause of recurrent gross hematuria (36). Alternatively, the left renal vein may be compressed from adjacent lymph nodes and tumors and may dilate secondarily. In rare cases, venous enlargement is a primary condition that results from high-flow states due to tumor shunting. Enlarged left gonadal veins that empty into the inferior left renal vein have been observed and are associated with varicoceles in men (16). In multiparous women, enlarged left gonadal veins are a relatively common benign finding, although it can be associated with chronic pelvic pain (37).
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Figure 19. Spontaneous splenorenal shunt in a 54-year-old man with cirrhosis and portal hypertension. Axial volume-rendered image shows extensive varices from the splenic hilum draining into a massively enlarged left renal vein (arrows).
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Posttransplantion Evaluation
In adults, the renal artery of the transplanted kidney is usually anastomosed in an end-to-end fashion to the internal iliac artery of the recipient. The donor renal vein is most often anastomosed to the recipient’s external iliac vein.
One relatively common complication after renal transplantation is graft renal artery stenosis. This complication has been reported in 3%–15% of patients, usually within the first 3 years after transplantation (38)–(40). Renal artery stenosis can lead to renal insufficiency and failure if it is severe. Focal stenoses typically occur at the anastomosis, either because of technical failure, perioperative trauma during allograft harvesting, or ischemia (16). CT angiography can noninvasively demonstrate the transplant pedicle and document the presence of stenosis (Figs 20, 21) (2),(12). Occasionally, surgical clips can result in artifacts near the transplanted artery and limit evaluation. Venous thrombosis is a less common renal transplant complication.
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Figure 20. Follow-up study to evaluate for renal artery stenosis to the renal transplant in a 43-year-old man. Anterior oblique volume-rendered image shows the renal artery (arrows), which is normal and has no evidence of stenosis.
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Figure 21. Postoperative stenosis in a 42-year-old man who had undergone renal transplantation in the left iliac fossa. Anterior oblique volume-rendered image shows moderate stenosis in the middle segment of the transplanted artery (arrows). This finding was confirmed at angiography.
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Conclusions
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CT angiography has proved useful for many clinical applications involving the renal pedicle, including the assessment of renal artery stenosis, examination of renal arterial disease related to aortic diseases, preoperative evaluation of renal donors, and preoperative evaluation of renal anatomy before surgery. CT angiography provides an accurate assessment of the renal vasculature in a fast and efficient manner, without the risks of more invasive conventional angiography. CT angiography performed with volume rendering is extremely accurate in the preoperative evaluation of renal vascular anatomy, and it has replaced conventional angiography at many institutions. In addition, CT angiography is helpful in the follow-up of postoperative patients, particularly those who have undergone renal transplantation, angioplasty, or stent placement. CT angiography combined with CT is an accurate modality for the staging of renal cell carcinoma.
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Footnotes
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2 Current address: Alexandria Hospital Center, Virginia. 
Abbreviations: MIP = maximum intensity projection, 3D = three-dimensional
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References
|
|---|
-
Kuszyk BS, Heath DG, Ney DR, et al. CT angiography with volume rendering: imaging findings. AJR Am J Roentgenol 1995; 165:445-448.[Free Full Text]
-
Smith PA, Fishman EK. CT angiography: renal applications. In: Ferris EJ, Waltman AC, Fishman EK, Polak JF, Potchen EJ, eds. Syllabus: a categorical course in diagnostic radiology–vascular imaging. Oak Brook, Ill: Radiological Society of North America, 1998; 35-45.
-
Kuszyk BS, Fishman EK. Technical aspects of CT angiography. Semin Ultrasound CT MR 1998; 19:383-393.[Medline]
-
Smith PA, Fishman EK. Three-dimensional CT angiography: renal applications. Semin Ultrasound CT MR 1998; 19:413-424.[Medline]
-
Johnson PT, Halpern EJ, Kuszyk BS, et al. Renal artery stenosis: CT angiography-comparison of real-time volume rendering and maximum intensity projection algorithms. Radiology 1999; 211:337-343.[Abstract/Free Full Text]
-
Kattee R, Beek F, de Lange E, et al. Renal artery stenosis: detection and quantification with spiral CT angiography and optimized digital subtraction angiography. Radiology 1997; 205:121-127.[Abstract/Free Full Text]
-
Platt J, Ellis J, Korobkin M, Reige K. Helical CT evaluation of potential kidney donors: findings in 154 subjects. AJR Am J Roentgenol 1997; 169:1325-1330.[Abstract/Free Full Text]
-
Rubin GD, Alfrey EJ, Dake MD, et al. Assessment of living renal donors with spiral CT. Radiology 1995; 195:457-462.[Abstract/Free Full Text]
-
Rubin GD. Spiral (helical) CT of the renal vasculature. Semin Ultrasound CT MR 1996; 17:374-397.[Medline]
-
Smith PA, Ratner LE, Lynch FC, Corl FM, Fishman EK. Role of CT angiography in the preoperative evaluation for laparoscopic nephrectomy. RadioGraphics 1998; 18:589-601.[Abstract]
-
Herts BR, Coll DM, Lieber ML, Streem SB, Novick AC. Triphasic helical CT of the kidneys: contribution of vascular phase scanning in patients before urologic surgery. AJR Am J Roentgenol 1999; 173:1273-1277.[Abstract/Free Full Text]
-
Hoffman LV, Smith PA, Kuszyk BS, Kraus E, Fishman EK. Three-dimensional helical CT angiography in renal transplant recipients: a new problem solving tool. AJR Am J Roentgenol 1999; 173:1085-1089.[Abstract/Free Full Text]
-
Beregi JP, Louvegny S, Gautier C, et al. Fibromuscular dysplasia of the renal arteries: compari-son of helical CT angiography and arteriography. AJR Am J Roentgenol 1999; 172:27-34.[Abstract/Free Full Text]
-
Dachman AH, Newmark GM, Mitchell MT, Woodle ES. Helical CT examination of potential kidney donors. AJR Am J Roentgenol 1998; 171:193-200.[Abstract/Free Full Text]
-
El-Galley RES, Keane TE. Embryology, anatomy, and surgical applications of the kidney and ureter. Surg Clin North Am 2000; 80:381-401.[Medline]
-
Kadir S. Angiography of the kidneys. In: Kadir S, eds. Diagnostic angiography. Philadelphia, Pa: Saunders, 1986; 445-495.
-
Kadir S. Kidneys. In: Kadir S, eds. Atlas of normal and variant angiographic anatomy. Philadelphia, Pa: Saunders, 1991; 387-428.
-
Dyer R. Renal arteriography. In: Dyer R, eds. Basic vascular and interventional radiology. New York, NY: Churchill Livingstone, 1993; 89-95.
-
Spring DB, Salvatierra O, Jr, Palubinskas AJ, et al. Results and significance of angiography in potential kidney donors. Radiology 1979; 133:45-47.[Abstract]
-
Beckmann CF, Abrams HL. Renal venography: anatomy, technique, applications—analysis of 132 venograms and a review of the literature. Cardiovasc Intervent Radiol 1980; 3:45-70.[Medline]
-
Kahn PC. Selective venography of the branches In:Ferris EJ, Hipona FA, Kahn PC, et al, eds. Venography of the inferior vena cava and its branches. Huntington, NY: Krieger, 1973; 154-224.
-
Beckmann CF, Abrams HL. Circumaortic venous ring: incidence and significance. AJR Am J Roentgenol 1979; 132:561-565.[Abstract]
-
Qanadli SD, Mesurolle B, Coggia M, et al. Abdominal aortic aneurysm: pretherapy assessment with dual-slice helical CT angiography. AJR Am J Roentgenol 2000; 174:181-187.[Abstract/Free Full Text]
-
Thomsen HS, Sos TA, Nielsen S. Renovascular hypertension: diagnosis and intervention. Acta Radiol 1990; 30:113-120.
-
Pickering TG. Renovascular hypertension: etiology and pathophysiology. Semin Nucl Med 1989; 19:79-88.[Medline]
-
Bookstein JJ, Maxwell MH, Abrams HL, et al. Cooperative study of radiologic aspects of renovascular hypertension. JAMA 1977; 237:1706-1709.[Abstract]
-
Youngberg JP, Sheps SG, Strong CG. Fibromuscular disease of the renal arteries. Med Clin North Am 1977; 61:623-641.[Medline]
-
Harrison EG, Jr, Hunt JC, Bernatz PE. Morphology of fibromuscular dysplasia of the renal artery in renovasclar hypertension. Am J Med 1967; 43:97-112.[Medline]
-
Rubin GD, Dake M, Napel S, et al. Helical CT of renal artery stenosis: comparison of three-dimensional rendering techniques. Radiology 1994; 190:181-189.[Abstract/Free Full Text]
-
Tham G, Ekelund L, Herrlin K, et al. Renal artery aneurysms: natural history and prognosis. Ann Surg 1983; 197:348-352.[Medline]
-
Cummings KB, Lecky JW, Kaufman JJ. Renal artery aneurysms and hypertension. J Urol 1973; 109:144-148.[Medline]
-
Capps JH, Klein RM. Polyarteritis nodosa as a cause of perirenal and retroperitoneal hemorrhage. Radiology 1970; 94:143-146.[Medline]
-
Gonzalez R, Schwartz S, Sheldon CA, et al. Bilateral renal vein thrombosis in infancy and childhood. Urol Clin North Am 1982; 9:279-283.[Medline]
-
Clark RA, Wyatt GM, Colley DP. Renal vein thrombosis: an undiagnosed complication of multiple renal abnormalities. Radiology 1979; 132:43-50.[Abstract]
-
Smith PA, Marshall FF, Urban BA, Heath DG, Fishman EK. Three-dimensional CT stereotopic visualization of renal masses: impact on diagnosis and management. AJR Am J Roentgenol 1997; 169:1331-1334.[Abstract/Free Full Text]
-
Mitty HA, Goldman H. Angiography in unilateral renal bleeding with a negative urogram. AJR Am J Roentgenol 1974; 121:508-517.[Abstract]
-
Smith PD. Ovarian syndrome: is it a myth?. Urology 1979; 11:355-364.
-
Baxter G, Ireland H, Moss J, et al. Colour Doppler ultrasound in renal transplant artery stenosis: which Doppler index?. Clin Radiol 1995; 50:618-622.[Medline]
-
Ricotta JJ, Schaff HV, Williams GM, et al. Renal artery stenosis following transplantation: etiology, diagnosis, and prevention. Surgery 1978; 84:595-602.[Medline]
-
Dodd GD, III, Tublin ME, Sha A, Zajko AB. Imaging of vascular complications associated with renal transplants. AJR Am J Roentgenol 1991; 157:449-459.[Abstract/Free Full Text]
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