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1 The Russell H. Morgan Department of Radiology and Radiological Science, Johns
Hopkins Hospital, 601 N. Caroline St., Rm. 3254, Baltimore, MD
21287-0801.
2 Department of Surgery, Johns Hopkins Hospital, 600 N. Wolfe St., Baltimore, MD
21287.
Received July 12, 2002;
accepted after revision November 12, 2002.
Address correspondence to E. K. Fishman.
Abstract
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SUBJECTS AND METHODS. Seventy-four consecutive living kidney donors (30 men, 44 women; mean age, 41.7 years) who underwent MDCT were evaluated. CT examination was performed with 120 mL of IV contrast material at an injection rate of 3 mL/sec and a pitch of 6. In every case, arterial and venous phase volumetric data sets were acquired at 25 and 55 sec, respectively. Scans were reconstructed at 1-mm intervals for three-dimensional (3D) imaging using a volume-rendering technique. Axial CT images and 3D CT angiography were evaluated prospectively by one reviewer and retrospectively by two reviewers who had no knowledge of surgical results. Surgical correlation for the location of primary and accessory renal arteries, early branching of the renal arteries, and renal vein anomalies was made.
RESULTS. Seventy-two subjects underwent left nephrectomy, and two subjects underwent right nephrectomy because supernumerary left renal arteries were detected on preoperative CT angiography. Eighteen supernumerary renal arteries (two arteries to 16 kidneys and three arteries to one kidney) to 74 kidneys underwent nephrectomy. CT and surgical findings agreed in 93% of subjects (the average of three reviewers; range, 89–97%). Two small accessory renal arteries were missed by all three reviewers. Those arteries were diminutive and were thought to be insignificant by the surgeons. Early branching of the renal arteries was shown in 14 arteries, and CT and surgical findings agreed in 96% (the average of three reviewers; range, 93–97%). Renal vein anomalies were present in eight subjects, and CT and surgical findings agreed in 99% of the cases (range, 96–100%).
CONCLUSION. MDCT angiography is highly accurate for detecting vascular anomalies and providing anatomic information for laparoscopic living donor nephrectomy.
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Laparoscopic living donor nephrectomy is a less invasive procedure than open donor nephrectomy and offers numerous advantages over conventional open surgery. The advantages of the laparoscopic approach compared with open nephrectomy are reduction in post-operative pain, a shorter recovery time, reduced length and cost of the hospital stay, and a high degree of patient satisfaction [4, 5, 6]. Several technical challenges are associated with the laparoscopic removal of a kidney [7].
Operative visibility and surgical exposure are limited, so preoperative evaluation of the donor's anatomy is critical. The left kidney is preferred for laparoscopic living donor nephrectomy because it is technically easier to remove and has the longer renal vein [7, 8].
Preoperative radiologic evaluation of kidney donors is used to select the patient and the kidney that is to be harvested. Traditionally, renal angiography and excretory urography have been used to evaluate potential kidney donors. However, several studies have shown that helical CT angiography can replace excretory urography and renal angiography in the evaluation of potential kidney donors [9, 10, 11, 12, 13, 14, 15], and helical CT angiography has become an accepted method for the preoperative evaluation of living donors before they undergo laparoscopic nephrectomy.
Multidetector CT (MDCT) offers shorter image acquisition times, reduction in tube heating, and improved spatial resolution compared with single-detector helical CT. MDCT has been used to evaluate the renal vasculature [16, 17, 18], and promising results have been reported. However, the accuracy of MDCT in preoperative renal vascular evaluation of living donors has not been determined. The purpose of this study is to determine the accuracy of MDCT angiography as the primary imaging technique in the evaluation of living kidney donors.
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MDCT Technique
The MDCT examinations were performed on a Somatom Volume Zoom scanner
(Siemens Medical Solutions, Iselin, NJ) with the following parameters: 120
kVp, 150 mAs, 1.25-mm slice width, beam pitch of 6, 0.5-sec rotation speed,
detector collimation of 4 x 1 mm, and a 1-mm reconstruction increment.
The helical length was approximately 20 sec. All image data were reconstructed
using the body soft-tissue algorithm.
After fasting for at least 2–3 hr, each patient ingested 750 mL of water during a 15- to 20-min period before scanning began. An explanation of the CT angiography procedure and breathing instructions were then offered to each patient. For administration of IV contrast material, a 20-gauge peripheral line was inserted into an antecubital fossa vein. A scout topogram was obtained. Then, in every case, arterial and venous phase volumetric data sets were acquired at 25 and 55 sec, respectively, from the start of the IV injection of 120 mL of iohexol (Omnipaque 350, Amersham Health, Princeton, NJ) at an injection rate of 3 mL/sec. No timing bolus or computer-assisted software was used because we have found that the use of an empiric delay of 25 sec for arterial imaging in the abdomen and of 55 sec for venous imaging is faster and yields excellent results in most patients.
The area scanned extended from above the kidneys to just below the common iliac arteries on the arterial phase and from above the kidneys to the top of the iliac crests on the venous phase. A delayed topogram was routinely obtained 5 min after IV contrast material administration to define the collecting system and ureters.
The volumetric data sets were then transferred to a free-standing Onyx Infinite Reality workstation (Silicon Graphics, Mountain View, CA) that runs 3D Virtuoso software (Siemens Medical Systems) for subsequent review.
Image Analysis
Three independent radiologists reviewed the images from each CT examination
at the workstation, which allows the reviewers to edit CT volume data sets to
create optimal 3D CT angiography images in real time at frame rates of
10–30 frames per second. The reviewers used source images as well as 3D
display images. For 3D CT angiography, volume-rendering techniques were
usually used, but maximum-intensity-projection rendering was also used as an
adjunct display, especially for small vessels. Alternative visualization
techniques included reformatted imaging and stereoscopic display for complex
vascular anatomy. These techniques were primarily relied on by each reviewer,
and the 3D display parameters, including width, level, opacity, and
brightness, were chosen subjectively by the individual reviewer. Renal
arterial and venous anatomy was evaluated primarily on arterial phase images,
but if the renal veins were not enhanced on the arterial phase images, venous
phase images were used.
Images from each CT examination were interpreted by a primary reviewer at the time of the examination before surgery, and were subsequently interpreted by the second and third independent radiologists retrospectively after surgery. Image analyses were performed without knowledge of the interpretations provided by the other reviewers or of the surgical results.
The primary reviewer recorded the number of renal arteries found on each side. Any branch within 2.0 cm from the aorta was classified as early branching. For each artery, other associated findings, including the presence of stenosis and calcifications, were recorded. Renal vein anatomy was evaluated for the number of the renal veins and the presence of accessory veins, retroaortic veins, and circumaortic veins.
The second and third reviewers completed a worksheet independently for each CT examination. The worksheet detailed the numbers of renal arteries, and the presence of early branching was recorded. Renal vein anatomy was also evaluated for the number of renal veins and the presence of accessory veins, retroaortic veins, and circumaortic veins. Retrospective image analysis was limited to one kidney that was surgically removed.
When discrepancies were found between CT and surgical findings, the CT examination was retrospectively analyzed.
Donor Nephrectomy
Laparoscopic surgery was planned by transplantation surgeons after each CT
examination.
Donor nephrectomy was performed from 3 weeks to 13 months (median, 4 months) after CT examinations. The transplantation surgeons completed a surgical record for each patient, which included which kidney was chosen for laparoscopic nephrectomy. If the right kidney was chosen, the record noted the reason the right kidney was selected, the number of renal arteries, the presence of early branching, the number of renal veins, and the presence of renal vein anomalies. Any unexpected surgical findings were also described.
Statistical Evaluation
Surgical correlation for the location of primary and accessory renal
arteries, early branching of the renal arteries, and renal vein anomaly was
made. Sensitivity, specificity, and accuracy for the presence or absence of
supernumerary renal arteries, presence or absence of early branching of the
renal artery, and presence or absence of renal vein anomalies of 74 donor
kidneys were calculated on the basis of each reviewer's evaluation.
Ninety-five percent confidence intervals for each sensitivity and specificity
were obtained. The average sensitivity and specificity of the three reviewers
were also calculated. The degree of interobserver agreement for the presence
of multiple renal arteries, presence of early branching of the renal arteries,
and presence of renal vein anomalies was evaluated using kappa statistics.
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Seventy-two patients underwent left nephrectomy, and two underwent right nephrectomy because supernumerary (three in both patients) left renal arteries (a single right artery in one patient, two right arteries in the other) were detected at preoperative MDCT angiography. For two patients, laparoscopic nephrectomy was initiated, but the procedure was switched to open nephrectomy (in one patient [who had previous right upper quadrant surgery and adhesions] for tear of the inferior vena cava on dissecting out the renal vein during right laparoscopic nephrectomy, and in the other patient for severe adhesion caused by multiple prior surgeries).
Accessory Arteries
Eighteen supernumerary renal arteries (24% of donor kidneys; two arteries
to 16 kidneys and three arteries to one kidney) to 74 donor kidneys were found
at surgery. The primary reviewer agreed on the number of arteries found at
surgery to 69 of 74 donor kidneys (accuracy, 93%). Among those five kidneys
with discrepancy between CT and surgical findings, an additional artery was
suggested for one kidney, and four renal arteries were not identified. None of
the CT errors seriously affected the surgical procedure. The second and third
reviewers agreed on the number of arteries found at surgery to 72 (accuracy,
97%) and 66 (accuracy: 89%) donor kidneys, respectively
(Table 1). The kappa value of
the three reviewers for the presence of multiple renal arteries was 0.78.
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In two patients, a small accessory renal artery to the donor kidney was missed by all three reviewers. Of these two patients, one had two renal arteries to the left kidney with a diminutive left upper pole artery found at surgery. The artery was not seen even in retrospect but was not thought by the surgeon to be significant. The other patient had three renal arteries with a diminutive left upper pole artery. That artery was seen in retrospect as a small artery of less than 2 mm in diameter (Figs. 1A, 1B). It was not thought by the surgeon to be significant.
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The accessory renal artery that was missed by two reviewers was also a diminutive artery to the upper pole. It was seen retrospectively as a small artery of less than 2 mm in diameter (Figs. 2A, 2B).
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Overall, renal artery anatomy was correctly defined in retrospect in all patients except one in whom a diminutive upper pole artery was not seen.
Early Branching of the Renal Arteries
Early branching was shown in 14 renal arteries, all of which were seen in
the left renal artery (Figs.
3A,
3B). Sensitivity and accuracy
of CT were 90% and 96%, respectively (the average of three reviewers; accuracy
range, 93–97%) (Table 2).
The kappa value of the three reviewers for the presence of early branching of
the renal arteries was 0.74.
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In retrospect, two patients in whom early branching was recorded in error may have had a prominent left adrenal artery branching off from the superior aspect of the proximal left renal artery. We defined early branching as a branch within 2.0 cm from the aorta. In three other patients in whom early branching was recorded in error, the average length from the aorta to the renal artery branching was 22.1 mm, and that was probably mistaken for as early branching. In retrospect, early branching of the renal artery was correctly defined in all patients.
Renal Vein Anomalies
Renal vein anomalies were present in eight donor kidneys (11%), all of
which were the left kidney. Sensitivity and accuracy of CT were 92% and 99%,
respectively (the average of three reviewers; accuracy range, 96–100%)
(Table 3). The kappa value of
the three reviewers for the presence of renal vein anomalies was 0.85. Among
these eight donor kidneys with renal vein anomalies, five had circumaortic
renal veins and three had retroaortic renal veins (one of the patients with a
retroaortic renal vein also had duplication of the renal vein [Figs.
4A,
4B]). In retrospect, renal vein
anomalies were correctly defined in all patients.
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TopAbstractIntroductionSubjects and MethodsResultsDiscussionReferences |
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Laparoscopic donor nephrectomy requires precise preoperative vascular mapping [1, 12]. The left kidney is preferred for laparoscopic nephrectomy because it is technically easier to remove. Left kidneys with multiple arteries or anomalous venous drainage are reported to be not problematic, especially when these vascular anomalies are identified with preoperative imaging [8]. Because the operative field of view is limited, surgeons now request more complete information about the renal vein anatomy in addition to the standard mapping of the renal artery anatomy.
The capability of MDCT, including fast data acquisition and narrow collimation, is valuable for angiographic applications because of greater anatomic coverage, increased contrast opacification of the arteries, and higher longitudinal spatial resolution [22, 23]. Several reports have shown the accuracy of one-channel CT angiography in establishing the presence of variations or anomalies of renal arteries and veins. The reported accuracy of one-channel CT angiography in detecting accessory arteries, early branching, and renal venous anatomy is in the range of 78–98%, 89–99%, and 90–99%, respectively [9, 10, 11, 12, 13, 14, 24]. In our study, the accuracy of MDCT angiography in detecting accessory arteries, early branching, and renal vein anomalies was 89–97%, 93–97%, and 96–100%, respectively. These numbers are not significantly different from those for one-channel CT angiography reported previously.
We encountered supernumerary renal arteries in 24%, early branching of the renal artery in 19%, and left renal vein anomalies in 11% of the donor kidneys in this study. Previous studies showed the incidence of accessory renal arteries, early branching, and venous anomalies to be 25–32%, 7–21%, and 7–13%, respectively [9, 10, 11, 25, 26]. The most common venous anomaly in our study was a circumaortic left renal vein. Although the side chosen for nephrectomy was influenced by the results of MDCT angiography in two of 74 patients in our study, we believe that the side chosen did not have a significant effect on the identified anomalies from analysis. In those two patients, three renal arteries to the left kidney were seen on preoperative CT angiography, and one renal artery to the right kidney in one patient and two in the other patient were seen at surgery. Those were the only differences of vascular anatomy between the right and left kidneys, and there was no early branching of the renal arteries or renal vein anomalies to either kidney in these two patients.
We used a fixed delay of 25 sec for arterial imaging and of 55 sec for venous imaging from the start of an IV injection of 120 mL of iohexol. In general, for MDCT angiography, in patients with a known history of cardiac disease or in patients with a large heart on the topogram, we typically add an additional 10 sec to the scanning delay. However, most potential kidney donors did not have a known history of cardiac disease or a large heart on topography, and a fixed delay time yielded excellent image quality for the evaluation of arteries and veins.
Although some authorities recommend performing scanning before contrast administration to exclude nephro- and urolithiasis, we did not perform scanning before contrast administration; we wanted to minimize the dose of ionizing radiation because all patients were healthy donors. In our experience, some nephro- and most urolithiasis can be detected on arterial phase images with careful scrolling of continuous images. In a recent study using MDCT in 65 patients with urinary tract abnormalities, all of five urolithiases (two in renal pelvis, one in distal ureter, one in bladder, one in ileal conduit) were seen on both unenhanced and contrast-enhanced scans [27].
MR angiography is another important modality for the preoperative evaluation of living kidney donors. Recent studies of gadolinium-enhanced MR angiography have shown that it has high rates of accuracy and is comparable to conventional angiography and CT angiography in the evaluation of living kidney donors for nephrectomy. Jha et al. [28] evaluated 64 patients who underwent laparoscopic nephrectomy, and reported that MR angiography for revealing arterial anomalies had a sensitivity of 89%, specificity of 94%, and accuracy of 91%. In other studies, although the study population was relatively small (15–21 donors whose surgical correlation was available), some authors also reported high sensitivity of MR angiography (90–100%) in identifying renal arteries in living kidney donors [25, 29, 30, 31]. MR imaging has the additional advantage of avoiding ionizing radiation and potentially nephrotoxic contrast agents.
Potential complications of our protocol include extravasation of IV contrast material and an increase in creatinine level. However, in our study population, none of the patients had extravasation of IV contrast material or renal dysfunction after the MDCT evaluation.
In conclusion, MDCT angiography is accurate for detecting vascular anomalies and for providing anatomic information necessary for laparoscopic nephrectomy in living donors. Dual-phase MDCT combined with 3D CT angiography can provide a minimally invasive, accurate preoperative evaluation of kidney donor candidates in a single study.
Acknowledgments
We thank John Eng for his kind assistance with statistical analysis.
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