Objectives: In living renal donors, digital subtraction angiography and intravenous pyelogram techniques developing traditional evaluation before transplant have started to give place to more modern and less-invasive methods such as multidetector computerized tomography angiography, and magnetic resonance angiography via the developments in the imaging technology. We aimed to evaluate the renal arteries of living-renal donors by multidetector computerized tomography angiography and to compare the findings with the surgical results.

Materials and Methods: In our renal transplant center, 286 living-donor candidates to whom multi-detector computerized tomography angiography was applied, were evaluated retrospectively and the findings were compared with the surgical operation notes.

Results: In 180 of 286 living donor candidates to whom computerized tomography angiography was applied, bilateral single renal artery was deter-mined. In 79 renal donor candidates, unilateral multiple renal artery; and in 27 renal donor candidates, bilateral multiple renal artery were found. In 58 renal donor candidates, at least 1 polar artery was specified; in 32 renal donor candidates, a unilateral single renal artery; in 10 renal donor candidates, a bilateral double renal artery was determined. When computerized tomography angiography and operative notes were compared, we observed that the findings in 280 donor candidates were the same. In 6 renal donor candidates, differences in the findings were present. Our accuracy rate was 97% and according to the operative notes, our sensitivity and specificity ratios in determining multiple renal arteries were calculated as 98% and 95%.

Conclusions: Multidetector computerized tomography angiography can be used rapidly and efficiently in living-donor renal candidates with high specificity and sensitivity ratios.

Key words : Kidney transplant, Digital subtraction angiography, Intravenous pyelogram, Renal artery variations

Introduction

Kidney transplant can be performed from a deceased or a living donor. In kidney transplant from a living donor, it is important to protect the donor from postoperative morbidity and mortality. Preoperative imaging is applied as part of a living donor?s anatomic and functional evaluation to select the kidney to be taken and to determine the surgical approach.

In living donors, seeing the renovascular anatomy is important for safe explantation without complications. Renal artery quantity, length, localization and the presence of the accessory artery are among the significant predictive factors in surgical planning.^1,2

Computerized tomography angiography (CTA) is a noninvasive, rapid imaging method used in the evaluation of donor candidates before renal transplant surgery. It evaluates the collecting duct system together with the anatomy and variations of renal arteries and veins. It is a well-accepted and safe method of evaluating incidentally determined extrarenal pathologies that may affect the surgical plan and the results before kidney transplant. Especially after the multidetector computerized tomography devices came into use, it has become a significant step in the algorithmic evaluation of the candidates before transplant surgery.^3,4

This study evaluates the renal arteries of 286 living renal donors by CTA and compares the findings with those found during surgery.

Materials and Methods

Between 2007 and 2009, three hundred forty living-donor candidates to whom CTA was applied in our transplant center (Akdeniz University Hospital, Antalya, Turkey) were evaluated retrospectively. This study was conducted with the approval of the Institutional Review Board. Before performing CTA, renal function tests were evaluated. All of the protocols conformed to the ethical guidelines of the 1975 Helsinki Declaration.

Because 54 living donor candidates evaluated by CTA were excluded from the study, renal CTAs of 286 kidney donor candidates were evaluated. Of 286 donor candidates to whom CTA was applied, 115 were men and 171 were women (mean age, 44; range, 19-78 y).

All information about the patients was obtained retrospectively from the hospital radiology information system, general patient files, and from the patient transplant files and imaging archive systems of tomography units.

Scanning protocol
Multidetector CTA protocol applied to all kidney donor candidates consists of the imaging of renal arteries obtained on the standard arterial phase. In the study, a 64-detector computer tomography (CT) device (Aquilion; Toshiba Medical System, Tokyo, Japan) was used. No oral contrast was used. Scanning started under the diaphragm and continued to the end of the bladder. During the scanning, the donors held their breath. No pre-contrast examination was performed in order to reduce the radiation dose taken. Ninety cc 350 mg/mL nonionic iodized contrast material (iohexol [Omnipaque], GE healthcare [General Electric Company Healthcare, USA]) was given via an automatic pump from the antecubital vein by using No. 20 G at an injection rate of 4.5 mL/sec. For starting the arterial phase, bolus tracking was applied. Automatic scanning of the renal arteries started when the density of the abdominal aorta reached 145 Hounsfield units. As the imaging parameters for the arterial phase, tube voltage was adjusted to 120 kVp (fixed), effective mAs was 64-209 mAs (variable according to the body mass of the patient), detector collimation was 64 ?0.5 mm, rotation time was 0.5 seconds, pitch value was 0.82, and section thickness was 1 mm.

Image analysis
Source images were sent to a separate work station (Vitrea, Vital Images, Minnetonka, MN, USA) and the images formed by maximum intensity projection, multiplanar reformation, and volume rendering methods from 0.625 mm axial images were evaluated. Multidetector CTA images were evaluated at the work station in the CT unit by 2 experienced radiologists.

All the kidney donor candidates were evaluated as randomized and independent from the patient names and information. While the renal vascular structures were being evaluated, renal artery variations and pathologies were separately noted for every donor candidate.

In the evaluation, first renal arteries are divided into 2 groups: single and multiple. Second, multiple renal arteries are categorized according to their calibration as either codominant (the same calibration as the ipsilateral main renal artery) or accessory (the smaller calibration than main renal artery). Codominant arteries are so-called because there are 2, 3, or 4 renal arteries. Then accessory arteries are divided into 2 groups. The polar accessory renal arteries pierce the upper or lower pole of the kidney. Hilar accessory renal arteries enter the kidney at the hilum. Another variant is the perihilar (early) branching pattern.⁵ If the main renal artery divides within 1.5 cm of the renal ostium in the abdominal aorta, it is early branching. Most surgeons want at least a 2-cm length of renal artery before hilar branching to guarantee satisfactory control and anastomosis. We did not evaluate this pattern. Differences of opinions between the radiologists were settled by negotiation.

Results

In 180 of 286 living donor candidates to whom CTA was applied, a unilateral single renal artery was found. In 79 renal donor candidates, unilateral multiple renal arteries were found, and in 27 renal donor candidates, bilateral multiple renal arteries were found. In 58 renal donor candidates, at least 1 accessory artery was specified; in 32 renal donor candidates, unilateral single renal artery; in 10 renal donor candidates, a bilateral double renal artery was determined (Figures 1A and 1B). In 6 renal donor candidates, at least unilateral 3renal arteries, and in 1 renal donor candidate, 4 renal arteries of the right kidney are observed (Table 1).

In 58 kidney donor candidates with polar artery, there were 74 polar arteries. Of these polar arteries, 20 were upper and 54 were lower. Among the kidney donor candidates; 45 had single accessory artery (right, 23; left, 22), 10 had double accessory artery (different kidney, 9; same kidney, 1) and 3 had triple accessory arteries (Figure 2). Four kidney donor candidates had a double polar artery of the same kidney. In 56 kidney donor candidates with accessory arteries, there was a single renal artery. In 8 renal donor candidates, stenosis in the renal artery proximal between 20% and 80% was observed.

Comparison of the multidetector computerized tomography angiography findings and transplant surgery findings
Surgery notes of the donors to whom transplant surgery was applied, were evaluated, and renal artery findings and CTA results were compared. According to the surgical notes, the right kidney was taken from 80 of 286 kidney donors and the left kidney from 206 donors. When the renal arteries of the kidney taken were evaluated by preoperative CTA, 240 kidney donors had a single renal artery and 46 kidney donors had multiple renal arteries. In the operative notes of 240 kidney donors for whom single renal artery is specified by preoperative CTA, 238 had a single renal artery. In the operative notes, 42 of 46 kidney donors had multiple renal arteries. Multiple renal arteries were determined in the operative notes of 2 kidney donors with single renal artery found in the preoperative CTA. In 4 kidney donors, we found that multiple renal arteries specified in the CTA were identified as single renal arteries in the operative notes (Table 2).

The results obtained in 280 cases were the same. There were differences between the renal artery findings of 6 kidney donors obtained by CTA and the operative notes.

In 3 kidney donors with single renal artery and 1 polar accessory artery found in CTA, renal arteries were specified as single renal artery in the transplant surgery notes. In 2 kidney donors, a single renal artery observed in CTA was specified as multiple (single renal artery and 1 hilar accessory, a single renal artery and 1 hilar accessory) renal artery in the surgery notes and in another kidney donor, a double renal artery observed in CTA was specified as a single renal artery in the surgical notes (Table 3).

When we compared the operative results to the CTA findings, we found the CTA to be 97% accurate. According to the operative notes of CTA, sensitivity of determination of multiple renal arteries was 95% and the specificity was 98%. In our study, false positive and false negative values of the CTA were 1% and 0.08%.

We have reevaluated the CTAs of 3 kidney donors for whom a single renal artery and 1 polar accessory artery are observed in CTA and single renal artery is observed in transplant surgery notes. In these kidney donors, the arteries evaluated as thin-calibration arteries in CTA are not indicated as such in the surgical notes. In these cases, we thought that polar arteries had been neglected during operation and thus, were not mentioned in the operative notes because no anastomosis had been applied to the transplanted kidney. In contrast, a thin polar accessory artery that was present surgically was determined in the CTA when the images are reexamined retrospectively.

In 2 other donors with differences in the CTA and surgery notes, we found no difference when we reviewed the CTA findings. None of the cases with different information had serious surgical problems.

Discussion

Surgical and medical evaluation of kidney donor candidates is critical in transplant surgery. Along with functional evaluation, anatomic evaluation has an important place in a transplant decision. Bilateral observation of major arterial variations may cause a contraindication in the kidney donor and the candidate may lose his/her kidney donor candidacy.6 In addition, knowing the vascular anatomy before surgery shortens the operation period and improves the surgical results. Kok and associates have specified that transplant surgery is difficult in donors with multiple renal arteries with no significant increase in the operative period.⁷

In previous periods, digital subtraction angio-graphy (DSA) and intravenous pyelography have been used for the preoperational evaluation of the kidney donor candidates. These are 2 separate imaging modalities. Renal arteries were evaluated by DSA.^7,8 Intravenous pyelography was used to assess the collecting system and nonvascular anatomy. Intravenous pyelography has major disadvantages such as low contrast resolution, superposition, and artifacts (eg, gas). However, with the technological developments in spiral CT, evaluation performed by the CTA is an alternative to DSA and intravenous pyelography because of the 3-dimensional configur-ation of the images and detailed imaging of artery and venous anatomy.^8,9 Using CT alone, we can detect renal calculi, small renal masses, ureteral duplication, and developmental abnormalities such as pelvic and horseshoe kidney.¹⁰ Computed tomography also can show the renal parenchyma, renal function, and collecting system in the late phase.

Several studies have been performed among the donor nephrectomy surgery findings, DSA, CTA, and in the evaluation of renal arteries and variants in living donor candidates. Digital subtraction angiography is now the criterion standard for the evaluation of renal artery anatomy. However, this is an invasive technique that requires injection of iodine-containing contrast material and ionizing radiation.¹¹ Computed tomography angiography is less invasive than conventional angiography. Length of hospital stay and costs in CTA are lower than the traditional algorithm (DSA with intravenous pyelography)⁹ but it use iodinated contrast material and exposes the donor to ionizing radiation.¹¹

In the late 1990s, studies compared CTA and DSA in living donors. Cochran, Alfrey and Slakey found concordant results of 89% to 96% between CTA and DSA.^9,12,13 Yi?t and associates compared CTA and operation findings in living donors; sensitivity, specificity and accuracy values of CTA are specified as 86%, 97% and 93% respectively.¹⁴ Our comparison of CTA and operative notes is 97% accurate. This value is similar to that of other studies in the literature.

Other studies have evaluated living donor candidates by magnetic resonance angiography (MRA). Magnetic resonance angiography has advantages over both conventional angiography and CTA.¹¹ They require injection of iodine-containing contrast material, and the patient is exposed to ionizing radiation on both modalities. In addition, MRI is a noninvasive technique but MRA examination time is longer than with CT. Patients should remain hospitalized for a long time and need to keep breathing. When we observe the studies that compare MRA with DSA and MRA with the operation findings, we see that the accuracy percentages of MRA for showing the renal arteries are over 90%.^5,11,15 False negative results due to the limited spatial resolution are reported in these studies.

However, in studies of both CTA and MRA, there were fewer cases than in our study. General accuracy of Platt and associates with 117 patients is 95%¹⁰ and the study of Bozkurt and associates consists of 60 cases and general accuracy is 94%.⁵ Slakey and associates used 19 cases, and general accuracy is 90%.13 Cochron and associates have reached 90% accuracy with 57 cases, and Patil and associates reached to 97% accuracy with 102 cases.^9,16 Gourlay and associates studied 15 cases and general accuracy is 97%; Nelson and associates studied 50 cases with an accuracy of 90%.^15,17 In the study of Yi?t and associates, there are 48 cases and general accuracy is 93%.¹⁴ Our study is distinguished from the other studies because it has more cases.

Hanninen and associates applied CTA and DSA to the same cases and compared the findings to the operative results. The accuracy of CTA in the evaluation of renal artery and variations was 97%. Laugharne and associates compared the multidetector CTA and surgery results of 156 patients, and found an accuracy of 96%. These 2 studies and ours have similar findings^18,19 (Table 4).

Despite the determination of single renal artery and single polar accessory (1 mm or less than 1 mm) in 3 cases, they are identified as single renal artery in the operative notes. However, when we evaluate these cases again, we thought that the discrepancy was related to the surgical notes and polar accessory arteries had been ignored during operation and thus, were not mentioned in the operative notes because no anastomosis had been applied to the transplanted kidney. Because accessory vessels smaller than 1 mm in diameter supply an insignificant portion of the renal parenchyma, preservation of these during the surgery may not be critical.²⁰

One case with a hilar accessory renal artery is not specified in CTA, but is observed in the operative notes; again, there is 1 case with a polar accessory artery (1 mm) that is not specified in CTA. While the hilar accessory artery is observed in the retrospectively observed images, no polar accessory artery is determined. This makes us think that some arteries cannot be identified by the imaging methods. In a study by Hanninen and associates, there are accessory renal arteries that cannot be scanned by CTA and DSA.¹⁸

There are technical and radiologist-related reasons for the inability to detect small-calibre accessory arteries for CTA. Technical factors include using a thick slice during scanning, motion artifacts, and errors in the timing of contrast. Very small-calibre accessory arteries can be missed by CTA because of contrast and spatial resolution.¹⁸ Computerized tomography angiography could not detect a polar accessory artery that is 0.8 mm. Radiologists? errors can be reduced by using methods like maximum intensity projection, multiplanar reformation, and volume rendering. In our study, a hilar accessory artery was found when examined retrospectively.

As CT technology advances, the results of angiographic evaluation obtained by multidetector CT are similar to DSA or operation results.^18,21,22 However, in the study of Blondin and associates that was performed by 64-detector CTA, all the accessory renal arteries were identified. In an operation performed by Raman and associates with a 16-detector CTA, an accessory renal artery was observed, which had not been detected by CTA.^21,22 In the study by Hanninen and associates, 2 accessory renal arteries observed in the operation could not be identified in the evaluation performed by 4-detector CTA; all the accessory renal arteries are specified in the evaluations performed by a 16-detector CTA.¹⁸ In Platti and associates? study performed with a Helikal CT, 5 accessory renal arteries could not be specified. Considering these results, we can say that the study results performed by 64-detector CTA are much more accurate than the study results performed by helical-, 4-, and 16-detector CTA devices in determining accessory renal arteries. By increasing the number of detectors and the multidetector CT rate; small-calibre arteries can be found.

Another important point in the imaging of renal arteries is to spot possible pathologies in the renal artery. Although pathologies such as slight stenosis and asymptomatic fibromuscular dysplasia do not cause contraindication in transplant surgeries, knowing that the lesions are there affects the surgical plan and changes the transplant period and surgical technique.⁹ In our study, renal artery stenoses that are observed incidentally in 8 donor candidates did not pose an obstacle for kidney transplant, and we can see that the kidneys with stenosis are taken.

Our study has the following limitations: The first limitation is that only the operative notes of the kidney taken were present; there was no information about the other kidney. As a result, comparison was performed only on the operative findings of the kidney taken, the renal artery, and variations. If we consider that the surgical option sides with taking the kidney with few or no variations, we do not have surgical information about the kidneys with more vascular variations. The second limitation was that our study was retrospective. A third limitation of our study was that no evaluation be performed on the renal arteries in terms of early branching. All patients were examined 2 readers so no interindividual reader analysis could be made. Although our routine protocol is 3-phase, we evaluated the single-phase CT angiographic images for renal artery map. In a precontrast series the stones can be evaluated or ruled out. The late images can demonstrate the collecting system in detail and give some idea of renal function. Complicated cysts and solid masses can be evaluated in this phase. As a result, CTA is a quick and safe preoperative evaluation of the living donors and it has become a standard in many transplant centers.

References:

1. Buzzas GR, Shield CF 3rd, Pay NT, Neuman MJ, Smith JL. Use of gadolinium-enhanced, ultrafast, three-dimensional, spoiled gradient-echo magnetic resonance angiography in the preoperative evaluation of living renal allograft donors. Transplantation. 1997;64(12):1734-1737.
   CrossRef - PubMed
2. Bakker J, Ligtenberg G, Beek FJ, van Reedt Dortland RW, Hen?RJ. Preoperative evaluation of living renal donors with gadolinium-enhanced magnetic resonance angiography. Transplantation. 1999;67(8):1167-1172.
   CrossRef - PubMed
3. Kawamoto S, Montgomery RA, Lawler LP, Horton KM, Fishman EK. Multi-detector row CT evaluation of living renal donors prior to laparoscopic nephrectomy. Radiographics. 2004;24(2):453-466.
   CrossRef - PubMed
4. Kim JK, Park SY, Kim HJ, et al. Living donor kidneys: usefulness of multi-detector row CT for comprehensive evaluation. Radiology. 2003;229(3):869-876.
   CrossRef - PubMed
5. Bozkurt FB, A?ldere AM, Tarhan NC, et al. Canl?b?rek vericilerinde renal arterlerin kontrastl?3B-FISP MRA tekni? ile de?rlendirilmesi. Diagn Interv Radiol. 2001;7:201-206.
6. Pollak R, Prusak BF, Mozes MF. Anatomic abnormalities of cadaver kidneys procured for purposes of transplant. Am Surg. 1986;52(5):233-235.
   PubMed
7. Kok NF, Dols LF, Hunink MG, et al. Complex vascular anatomy in live kidney donation: imaging and consequences for clinical outcome. Transplantation. 2008;85(12):1760-1765.
   CrossRef - PubMed
8. Rubin GD, Alfrey EJ, Dake MD, et al. Assessment of living renal donors with spiral CT. Radiology. 1995;195(2):457-462.
   CrossRef - PubMed
9. Cochran ST, Krasny RM, Danovitch GM, et al. Helical CT angiography for examination of living renal donors. AJR Am J Roentgenol. 1997;168(6):1569-1573.
   CrossRef - PubMed
10. Platt JF, Ellis JH, Korobkin M, Reige K. Helical CT evaluation of potential kidney donors: findings in 154 subjects. AJR Am J Roentgenol. 1997;169(5):1325-1330.
    CrossRef - PubMed
11. Firat A, Akin O, Agildere AM, Aytekin C, Haberal M. Contrast-enhanced magnetic resonance angiography: evaluation of renal arteries in living renal transplant donors. Eur J Radiol. 2004;52(1):84-93.
    CrossRef - PubMed
12. Alfrey EJ, Rubin GD, Kuo PC, et al. The use of spiral computed tomography in the evaluation of living donors for kidney transplant. Transplantation. 1995;59(4):643-645.
    CrossRef - PubMed
13. Slakey DP, Florman S, Lovretich J, Zarifian AA, Cheng SS. Utility of CT angiography for evaluation of living kidney donors. Clin Transplant. 1999;13(1 Pt 2):104-107.
    CrossRef - PubMed
14. Yi?t B, Berber ? Kara M, Tellio?u G, Ak?c?O, Titiz ? Use of 3-D spiral computerized tomographic angiography for preoperative assessment of living kidney donors. Official J Turkish Soc Nephrol. 2007;16(2):77-79.
15. Nelson HA, Gilfeather M, Holman JM, Nelson EW, Yoon HC. Gadolinium-enhanced breathhold three-dimensional time-of-flight renal MR angiography in the evaluation of potential renal donors. J Vasc Interv Radiol. 1999;10(2 Pt 1):175-181.
    CrossRef - PubMed
16. Patil UD, Ragavan A, Nadaraj, et al. Helical CT angiography in evaluation of live kidney donors. Nephrol Dial Transplant. 2001;16(9):1900-1904.
    CrossRef - PubMed
17. Gourlay WA, Yucel EK, Hakaim AG, et al. Magnetic resonance angiography in the evaluation of living-related renal donors. Transplantation. 1995;60(11):1363-1366.
    PubMed
18. H?ninen EL, Denecke T, Stelter L, et al. Preoperative evaluation of living kidney donors using multirow detector computed tomography: comparison with digital subtraction angiography and intraoperative findings. Transpl Int. 2005;18(10):1134-41. Erratum in: Transpl Int. 2005;18(12):1390. Tullius, Stefen G [corrected to Tullius, Stefan G].
    CrossRef - PubMed
19. Laugharne M, Haslam E, Archer L, et al. Multidetector CT angiography in live donor renal transplant: experience from 156 consecutive cases at a single centre. Transpl Int. 2007;20(2):156-166.
    CrossRef - PubMed
20. Agildere AM, Tutar NU, Demirag A, Boyvat F, Coskun M, Haberal M. Renal magnetic resonance angiography with Gd-DTPA in living renal transplant donors. Transplant Proc. 1999;31(8):3317-3319.
    CrossRef - PubMed
21. Raman SS, Pojchamarnwiputh S, Muangsomboon K, Schulam PG, Gritsch HA, Lu DS. Utility of 16-MDCT angiography for comprehensive preoperative vascular evaluation of laparoscopic renal donors. AJR Am J Roentgenol. 2006;186(6):1630-1638.
    CrossRef - PubMed
22. Blondin D, Andersen K, Kroepil P, et al. Analysis of 64-row multidetector CT images for preoperative angiographic evaluation of potential living kidney donors [in German]. Radiologe. 2008;48(7):673-680.
    CrossRef - PubMed