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Precaval Right Renal Arteries: Prevalence and Morphologic Associations at Spiral CT¹

¹ From the Departments of Radiology (B.M.Y., F.V.C., R.S.B.) and Urology (M.V.M., M.L.S.), University of California San Francisco, 505 Parnassus Ave, Box 0628, C-324C, San Francisco, CA 94143-0628. From the 2002 RSNA scientific assembly. Received August 20, 2002; revision requested October 18; final revision received June 2, 2003; accepted June 13. Address correspondence to B.M.Y. (e-mail: benyeh@itsa.ucsf.edu).

	ABSTRACT

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION REFERENCES

 
PURPOSE: To determine the prevalence and morphologic associations of precaval right renal arteries at spiral computed tomography (CT).

MATERIALS AND METHODS: The authors retrospectively reviewed 186 arterial phase contrast material–enhanced spiral CT scans of the abdomen (5.0-mm section thickness in 97 scans, 2.5 mm in 89 scans) obtained during a 2-year period to identify patients with precaval right renal arteries. During routine interpretation of CT scans at daily readout, the authors prospectively identified 39 additional patients with precaval right renal arteries. All cases were evaluated for anatomic variants and associated clinical findings. Fisher exact analysis and ² analysis were performed to compare the frequency of anatomic variants between patients with and those without precaval renal arteries.

RESULTS: Nine of 186 patients had precaval right renal arteries, for a prevalence of 5%. In the 48 patients with precaval renal arteries, 52 precaval arteries were found, of which 48 were accessory and four were dominant. Fourteen patients had right pelviectasis to the level of the precaval artery, and three of these had a clinical diagnosis of right ureteropelvic junction obstruction. Eighteen (35%) of the 52 precaval renal arteries arose from the anterior aspect of the aorta (within 30° of the midline). The lower pole of the right kidney was rotated anteriorly in two (22%) of nine and 13 (33%) of 39 patients with precaval renal arteries in the retrospective and prospective groups, respectively, compared with four (2%) of 177 patients without precaval arteries (P < .05 and P < .001, respectively).

CONCLUSION: On the basis of these results, precaval right renal arteries appear to be more common than previously reported. Anterior rotation of the lower pole of the right kidney should prompt a search for precaval renal arteries.

© RSNA, 2004

Index terms: Hydronephrosis, 81.84, 961.141, 961.762, 961.92 • Kidney, anatomy, 81.92 • Renal arteries, 961.92 • Renal arteries, CT, 961.12915

	INTRODUCTION

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Spiral computed tomography (CT), especially multi–detector row CT, enables accurate noninvasive three-dimensional evaluation of the renal arteries, parenchyma, and collecting system (1–4). Renal arterial variants, including early branching and accessory renal arteries, occur in up to 40% of the population (5). Recognition of these arterial variants is particularly important prior to modern minimally invasive urologic procedures, such as endopyelotomy and laparoscopic radical and donor nephrectomy (6,7). Multiple renal arteries are common anomalies, with a prevalence of 30%–40% (5,8). Right renal arteries are traditionally described as passing posterior to the inferior vena cava, although dominant and accessory right renal arteries that pass anterior to the inferior vena cava have been reported (9,10). Published information regarding the frequency and anatomic relationships of such precaval right renal arteries is minimal. Therefore, we undertook this study to determine the prevalence and morphologic associations of precaval right renal arteries with spiral CT.

	MATERIALS AND METHODS

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Patients
This was a single-center study and was approved by our Committee on Human Research. Written informed consent was not required for any component of our study. To determinethe prevalence of precaval right renal arteries, one author (B.M.Y.) used a computer search to retrospectively identify all contrast material–enhanced multi–detector row CT scans obtained for evaluation of hematuria (105 patients) or suspected aortic dissection (99 patients) between November 1999 and October 2001, because these scans are routinely obtained during the arterial phase of enhancement with intravenous contrast material. Images from only the first CT examination for each patient were included in the review. Eighteen of these 204 patients were excluded by the reader (B.M.Y.) at the time of image interpretation for the following reasons: technically limited examination (10 patients), abdominal aortic dissection or surgery (seven patients), and severe native kidney atrophy (one patient). Patients were excluded for the latter two reasons because accessory renal arteries may be occluded in such patients. The final study group for review consisted of 186 patients (retrospective group), including 94 women (mean age, 61 years; range, 18–95 years) and 92 male patients (mean age, 57 years; range, 13–91 years). There was no statistically significant difference between the mean ages of women and men (P = .15, Student two-sample t test).

An additional 39 patients with precaval renal arteries were prospectively identified during routine CT interpretation by one of three study authors (F.V.C., R.S.B., B.M.Y.) between August 2001 and March 2002, during which time approximately 3,200 CT scans were interpreted by these authors. The 39 patients (prospective group) included 16 women (mean age, 49 years; range, 20–90 years) and 23 men (mean age, 54 years; range, 36–84 years). There was no statistically significant difference between the mean ages of women and men (P = .61, Student two-sample t test). Results for one of these patients were included in a previously published case series on precaval renal arteries (9). Indications for CT in the 39 patients were evaluation of malignancy in nine, abdominal pain in seven, fever in six, elevated liver function test results in five, back pain or hematuria in four, possible aortic aneurysm in three, and miscellaneous in five. One reader (B.M.Y.) reviewed the medical records of all patients with precaval renal arteries for symptoms referable to the genitourinary system, including symptoms of back or flank pain or signs of hematuria or urinary collecting system obstruction.

CT Technique
All 186 patients in the retrospective group underwent multi–detector row CT (LightSpeed; GE Medical Systems, Milwaukee, Wis) and received 150 mL of intravenous iohexol (Omnipaque 350; Nycomed Amersham, Princeton, NJ) at a rate of 3–5 mL/sec. In the 97 patients with hematuria, scans were obtained through the kidneys with 5-mm section thickness, pitch of 1, and scan delay of 45 seconds. Nonenhanced portal venous phase and delayed images were also obtained in patients with hematuria. In the 89 patients suspected of having aortic dissection, arterial phase scans were obtained from the aortic arch to the internal iliac arteries with 2.5-mm section thickness, pitch of 2, and average scan delay of 20 seconds.

The 39 patients in the prospective group had precaval right renal arteries and underwent scanning with spiral CT (LightSpeed QX/I for 16 patients, LightSpeed Plus for 15, HiSpeed CT/i for five, and HiSpeed Advantage for three; GE Medical Systems), with section thickness of 2.5 mm for 18 patients, 3 mm for one, 5 mm for 16, and 7 mm for four. All patients received 150 mL of intravenous iohexol at a rate of 2–5 mL/sec. Twenty-two of the patients imaged with 2.5- or 3.0-mm section thickness and seven of the patients imaged with 5-mm section thickness underwent scanning during the arterial phase of enhancement; 21 of these patients also underwent scanning during the portal venous phase or delayed phase. The remaining 17 patients underwent scanning during the portal venous phase of enhancement.

Image Interpretation
One radiologist with subspecialty training in abdominal imaging (B.M.Y.) independently reviewed all CT images for both the retrospective and prospective groups with a picture archiving and communication system, or PACS, workstation (Agfa, Mortsel, Belgium). For both kidneys, the number, diameter, and course of all renal arteries and veins; the presence of a bifid collecting system; and the presence of pelviectasis were recorded. A precaval renal artery was defined as a tubular structure with attenuation similar to that of and arising from the aorta or iliac artery that passes anterior to the inferior vena cava and terminates in the right kidney (Fig 1). The dominant renal artery was defined as the artery with the largest diameter that extended to a given kidney; all other renal arteries were considered accessory. The origin of precaval right renal arteries that arose from the aorta was classified as anterior or lateral. Arteries that arose ventrally from the aorta within 30° of the midline (between the 11- and 1-o’clock positions on an imaginary clock face superimposed on the aorta) were considered to have an anterior location (Fig 2), while all other arteries were considered to have a lateral location. In patients with pelviectasis, the position of the precaval renal artery relative to the ureteropelvic junction was noted. The rotation of the right kidney upper pole and lower pole was noted in all patients. The upper or lower renal pole was considered to be anteriorly rotated when the corresponding portion of the renal hilum at that level was rotated ventrally more than 45° from the horizontal (Fig 3); otherwise, the lower kidney pole was considered to not be rotated.

View larger version (199K): [in this window] [in a new window] [Download PPT slide]   Figure 1. Transverse CT scan in a 51-year-old woman with abdominal pain. Image demonstrates an accessory precaval right renal artery (arrows) in the lower pole of the right kidney. IVC = inferior vena cava.

View larger version (154K): [in this window] [in a new window] [Download PPT slide]   Figure 2. Transverse CT scan in a 56-year-old man with pancreatitis. Image demonstrates an accessory precaval right renal artery (arrowheads) in the lower pole of the right kidney that originates from the anterior aspect of the aorta (arrow). IVC = inferior vena cava.

View larger version (150K): [in this window] [in a new window] [Download PPT slide]   Figure 3a. Transverse CT scans in a 31-year-old woman with right flank pain and hematuria. (a) Lower pole of the right kidney is rotated anteriorly. Renal hilum at this level is rotated anteriorly more than 45° from the horizontal (angled lines). (b, c) More inferiorly, an accessory precaval renal artery (arrow) arises from the right iliac artery (arrowhead).

View larger version (151K): [in this window] [in a new window] [Download PPT slide]   Figure 3b. Transverse CT scans in a 31-year-old woman with right flank pain and hematuria. (a) Lower pole of the right kidney is rotated anteriorly. Renal hilum at this level is rotated anteriorly more than 45° from the horizontal (angled lines). (b, c) More inferiorly, an accessory precaval renal artery (arrow) arises from the right iliac artery (arrowhead).

View larger version (139K): [in this window] [in a new window] [Download PPT slide]   Figure 3c. Transverse CT scans in a 31-year-old woman with right flank pain and hematuria. (a) Lower pole of the right kidney is rotated anteriorly. Renal hilum at this level is rotated anteriorly more than 45° from the horizontal (angled lines). (b, c) More inferiorly, an accessory precaval renal artery (arrow) arises from the right iliac artery (arrowhead).

	RESULTS

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Anatomy
Nine of the 186 patients in the retrospective group had precaval right renal arteries, for a precaval right renal artery prevalence of 5% (95% CI: 2%, 9%). Of these nine patients, five were women and four were men. Of all 48 patients (nine patients in the retrospective group, 39 patients in the prospective group) with precaval right renal arteries, the precaval artery was single and accessory in 42 patients (eight patients in the retrospective group), single and dominant in two patients (one patient in the retrospective group), double with one dominant and one accessory in two patients, and double and accessory in two patients, for a total of 52 precaval right renal arteries.

The accessory right precaval arteries had a mean diameter of 2.9 mm (range, 1–4 mm) in the nine patients in the retrospective group and a mean diameter of 3.1 mm (range, 1–4 mm) in the 39 patients in the prospective group in comparison to a mean diameter of 5.1 mm (range, 2–7 mm) and 4.8 mm (range, 3–7 mm), respectively, for the dominant right renal artery. The dominant right precaval arteries (four patients) had a mean diameter of 5.2 mm (range, 4–8 mm). All precaval arteries had an origin from the aorta (nine patients in the retrospective group and 40 patients in the prospective group) or right common iliac artery (three patients in the prospective group) (Fig 3) that was separate from the origins of other renal arteries, and in no patient did branches of the same renal artery pass both anteriorly and posteriorly to the inferior vena cava. Eighteen (38%; 95% CI: 24%, 53%) of the 48 precaval renal arteries that arose from the aorta came from the anterior aspect of the aorta (four [44%] of nine patients in the retrospective group and 14 [36%] of 39 patients in the prospective group).

Morphologic Associations
Of the patients with precaval renal arteries, one (11%; 95% CI: 0%, 48%) of nine patients in the retrospective group and 13 (33%; 95% CI: 19%, 50%) of 39 patients in the prospective group had asymmetric dilatation of the right renal pelvis to the level of the precaval crossing artery. Three of the latter patients had a clinical diagnosis of right ureteropelvic junction obstruction (Fig 4). None of the other patients in our study had a diagnosis of right or left ureteropelvic junction obstruction. In patients with a precaval artery, no other clinical symptoms or signs, including flank pain or hematuria, were considered attributable to the precaval artery.

View larger version (169K): [in this window] [in a new window] [Download PPT slide]   Figure 4a. Transverse CT scans obtained at the same level in the lower pole of the right kidney in a 45-year-old woman with the clinical diagnosis of ureteropelvic junction obstruction. (a) Right renal pelvis (arrow) is dilated. (b) Right renal pelvis narrows to normal caliber at the ureteropelvic junction (arrow), and an accessory artery (arrowhead) crosses posterior to the ureter. (c) Accessory artery (arrowheads) is in precaval location.

View larger version (167K): [in this window] [in a new window] [Download PPT slide]   Figure 4b. Transverse CT scans obtained at the same level in the lower pole of the right kidney in a 45-year-old woman with the clinical diagnosis of ureteropelvic junction obstruction. (a) Right renal pelvis (arrow) is dilated. (b) Right renal pelvis narrows to normal caliber at the ureteropelvic junction (arrow), and an accessory artery (arrowhead) crosses posterior to the ureter. (c) Accessory artery (arrowheads) is in precaval location.

View larger version (164K): [in this window] [in a new window] [Download PPT slide]   Figure 4c. Transverse CT scans obtained at the same level in the lower pole of the right kidney in a 45-year-old woman with the clinical diagnosis of ureteropelvic junction obstruction. (a) Right renal pelvis (arrow) is dilated. (b) Right renal pelvis narrows to normal caliber at the ureteropelvic junction (arrow), and an accessory artery (arrowhead) crosses posterior to the ureter. (c) Accessory artery (arrowheads) is in precaval location.

The proportion of patients with precaval right renal arteries who had an anteriorly rotated lower pole of the right kidney (two of nine [22%] patients in the retrospective group and 13 [33%] of 39 patients in the prospective group) was larger than that in patients without precaval renal arteries (four [2%] of 177 patients; P < .05 and P < .001, respectively). One patient with a precaval right renal artery had a horseshoe kidney.

	DISCUSSION

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Familiarity with anatomic variants and their associations contributes to the safety and success of both open and minimally invasive renal surgery. For example, accessory renal arteries may be a contraindication to laparoscopic donor nephrectomy, and injury of a crossing vessel during endopyelotomy for ureteropelvic junction obstruction may result in severe hemorrhage (11). A right renal artery that passes anterior to the inferior vena cava is of particular importance for presurgical planning, because it may be injured inadvertently, especially during the retroperitoneal approach when only the right gonadal vein is expected to lie in the precaval area. Our finding of precaval right renal arteries in 5% in 186 patients suggests that these anomalies are not uncommon. Furthermore, we found that 37% of precaval right renal arteries arose anteriorly from the aorta within 30° of the midline in comparison to findings in a previous report that only 2% of all normal right renal arteries arise from this aspect of the aorta (12). This anterior origin may result in misidentification at laparoscopy of such vessels as the inferior or superior mesenteric or hepatic arteries. Awareness of the possible anterior origin of precaval arteries would also be important during endovascular embolization or stent placement procedures.

It has been suggested that accessory renal arteries in the lower pole of either kidney that cross the ureteropelvic junction contribute to ureteropelvic junction obstruction in up to 11% of children (13) and 52% of adults (14). Case reports show that precaval renal arteries can cause ureteropelvic junction obstruction (15,16). Furthermore, identification of crossing vessels at radiologic imaging is important because they may be a source of massive bleeding during endopyelotomy (11), and the presence of a crossing vessel decreases the success rate of endopyelotomy from 83% to 33% (15). To our knowledge, the frequency with which precaval right renal arteries result in symptomatic ureteropelvic junction obstruction has not been previously reported. We found that 18 of 48 patients with precaval right renal arteries had asymmetric dilatation of the right renal pelvis to the level of the crossing vessel; three of these 18 patients had a clinical diagnosis of right ureteropelvic junction obstruction. This suggests that up to 6% (three of 48) of patients with precaval right renal arteries may develop symptomatic ureteropelvic junction obstruction. Our data are limited by the absence of long-term follow-up in our patients, because, ideally, evaluation of symptoms from infancy to death would help provide more accurate estimation of the frequency of symptomatic ureteropelvic junction obstruction associated with precaval renal arteries.

Case reports of horseshoe kidneys and malrotated right kidneys with associated precaval right renal arteries have been published (17), and findings in our study support the hypothesis that they are related. In particular, we found that 22%–33% of patients with precaval right renal arteries had an anteriorly rotated lower pole of the right kidney in comparison to only 2% of patients without precaval renal arteries. Among the patients in our retrospectively evaluated group, two (33%) of six patients with the lower pole of the right kidney rotated anteriorly had a precaval renal artery. Therefore, the finding of renal anomalies, especially an anteriorly rotated lower pole of the right kidney, should prompt a search for precaval renal arteries.

The prevalence of precaval renal arteries of 5% in patients in our study is much higher than the previously reported prevalence of 0.8% (10) in a series of 380 patients evaluated with sonography and/or contrast-enhanced CT with 6-mm-thick sections. In that study, the authors suggest that the majority of precaval renal arteries were dominant and single (10). In our study, however, the overwhelming majority of precaval renal arteries were accessory lower pole arteries. Our use of multisection CT scanners and arterial phase imaging likely improved accuracy in the current study relative to that in the previous study, which accounts for discrepancies in both the prevalence of precaval renal arteries and the frequency of dominant precaval renal arteries.

Even so, a limitation of our study is the lack of an independent standard of reference for detection of precaval renal arteries. Very small accessory renal arteries less than 1–2 mm in diameter may be missed at CT (18), particularly when thicker sections, suboptimal vascular enhancement, or motion artifact are present. It is unlikely that we falsely overcounted the presence of precaval renal arteries, since few structures could mimic a precaval renal artery, and the arteries included in this study were clearly seen to arise from the aorta, traverse anteriorly to the vena cava, and extend into the right renal parenchyma. Therefore, the 5% prevalence of precaval renal arteries in our study may underestimate the true prevalence. Likewise, selection bias may be present in our study, since the precaval arteries detected at routine CT readout are likely to be skewed toward larger more readily apparent arteries; therefore, evaluation of associations between smaller precaval renal arteries is limited. The lack of a patient denominator for the prospectively identified cases prevented the use of these cases to evaluate prevalence.

In conclusion, on the basis of results in this study, precaval right renal arteries appear to be more common than previously reported and may cause ureteropelvic junction obstruction, be injured during endopyelotomy, or be confused with other vessels such as mesenteric or hepatic arteries at laparoscopy. Identification of certain renal anomalies, particularly anterior rotation of the lower pole of the right kidney, should prompt a search for precaval renal arteries.

	FOOTNOTES

 
Author contributions: Guarantor of integrity of entire study, B.M.Y.; study concepts and design, all authors; literature research, B.M.Y., M.V.M., R.S.B., M.L.S.; clinical studies, all authors; data acquisition, B.M.Y.; data analysis/interpretation, all authors; statistical analysis, B.M.Y.; manuscript preparation, definition of intellectual content and editing, all authors; manuscript revision/review, B.M.Y., F.V.C., R.S.B.; manuscript final version approval, all authors

	REFERENCES

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