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Keywords:

  • CT;
  • MRI;
  • donor nephrectomy;
  • angiography;
  • renal vascular;
  • anatomy

Abstract

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. SUBJECTS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. CONFLICT OF INTEREST
  8. REFERENCES

OBJECTIVE

To prospectively compare the accuracy of multislice spiral computed tomographic angiography (CTA) and magnetic resonance angiography (MRA) in evaluating the renal vascular anatomy in potential living renal donors.

SUBJECTS AND METHODS

Thirty-one donors underwent multislice spiral CTA and gadolinium-enhanced MRA. In addition to axial images, multiplanar reconstruction and maximum intensity projections were used to display the renal vascular anatomy. Twenty-four donors had a left laparoscopic donor nephrectomy (LDN), whereas seven had right open donor nephrectomy (ODN); LDN was only considered if the renal vascular anatomy was favourable on the left. CTA and MRA images were analysed by two radiologists independently. The radiological and surgical findings were correlated after the surgery.

RESULTS

CTA showed 33 arteries and 32 veins (100% sensitivity) whereas MRA showed 32 arteries and 31 veins (97% sensitivity). CTA detected all five accessory renal arteries whereas MRA only detected one. CTA also identified all three accessory renal veins whereas MRA identified two. CTA had a sensitivity of 97% and 47% for left lumbar and left gonadal veins, whereas MRA had a sensitivity of 74% and 46%, respectively.

CONCLUSION

Multislice spiral CTA with three-dimensional reconstruction was more accurate than MRA for both renal arterial and venous anatomy.


Abbreviations
L(O)DN

laparoscopic (open) donor nephrectomy

MRA

magnetic resonance angiography

CTA

CT angiography

3D

three-dimensional

MIPS

maximum-intensity projections.

INTRODUCTION

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. SUBJECTS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. CONFLICT OF INTEREST
  8. REFERENCES

The number of living donors has increased steadily in the UK in last few years. The optimum evaluation of potential live donors for renal transplantation is crucially important. Conventional intra-arterial angiography and IVU have been the main imaging methods for assessing the donor's renal vascular and structural status, but conventional angiography is invasive, time-consuming and the venous anatomy is not well depicted.

Multislice spiral CT angiography (CTA) and MR angiography (MRA) can be used to show both the arterial and venous anatomy, with multiplanar reconstructions. Both CTA and MRA can also depict the pelvicalyceal anatomy, and both are useful in evaluating living renal donors [1–3]. These two methods can also be used to detect incidental findings, e.g. tumours and cysts. CTA has the advantage of being relatively quick but still requires exposure to radiation, whereas MRA has the advantage of being radiation-free and uses a relatively safe contrast medium, gadolinium [4]. The disadvantages of MRA include failure to detect calcification, and that some people can find it claustrophobic when inside the magnet.

With the introduction of laparoscopic live-donor surgery a thorough understanding of renal vascular anatomy, especially renal venous anatomy, is required. This prospective study was carried out to compare which of the two methods, CTA and MRA, provided the best evaluation of renal vascular anatomy.

SUBJECTS AND METHODS

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. SUBJECTS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. CONFLICT OF INTEREST
  8. REFERENCES

From July 2001 to December 2003, 31 potential living consecutive donors were evaluated with both CTA and MRA to assess their renal vascular and structural anatomy, as part of a more extensive evaluation of prospective donors. Ethical committee approval and informed consent was obtained before imaging. CTA and MRA were used in no particular order, depending on the availability of scanning time. The findings were reported by two radiologists independently, with a consensus view formed if there was any discrepancy between the methods. The two scans were taken and reported at least 2 weeks apart, in an attempt to ensure that the radiologist was unaware of the findings from the other method. Radiological findings were discussed with the surgeon before deciding on the method and side of donor nephrectomy. Left laparoscopic donor nephrectomy (LDN) was used if the vascular anatomy was favourable, and otherwise a right-sided open donor nephrectomy (ODN) was carried out. A correlation of CTA and MRA findings with surgery was available in all 31 patients.

The multislice spiral CT protocol was as follows: images were acquired with a Volume Zoom four-slice system (Siemens, Germany) using 4 × 1.0 mm collimation, a 1.25 mm slice width (5 mm feed), and 1 mm reconstruction, with 100 mL of contrast medium injected at 3 mL/s. Scanning was started 10 s after reaching 140 Hounsfield Units at the level of the coeliac axis, to allow for some enhancement of the renal veins. A 90-s delayed scan was taken at 4 × 2.5 mm collimation, 5 mm slice width (12.5 mm table feed) with 5 mm reconstructions for soft-tissue detail.

Post-processing involved coronal, oblique, axial and sagittal reconstructed thin maximum-intensity projections (MIPS, 3–5 mm) at a workstation by an experienced cross-sectional radiologist, to detect all the relevant anatomy.

The MRA protocol used a Gyroscan Intera 1.5 T system (Philips, Holland), with the donor given 20 mg i.v. of frusemide before scanning. The protocol used included standard renal imaging followed by three-dimensional (3D) gadolinium-enhanced MRA (35 mL of i.v. gadolinium injected at 1.5 mL/s). The T1-weighted gradient-echo angiographic sequence was manually triggered when the contrast medium was visible in the abdominal aorta. The first two scans were run contiguously over 40 s with one breath-hold to obtain both arterial and venous data. A third scan was taken after ≈ 90 s for additional venous images, and then a fourth scan at 5 min for the MR urogram.

Post-processing included coronal, axial and sagittal reconstructed thin MIPS (3–5 mm) at a workstation by an experienced cross-sectional radiologist, to detect all the relevant anatomy.

When vascular anatomy showed a single artery and vein on the left side, the donor had a left LDN, but donors with multiple vessels had ODN on the right side. LDN was via a transperitoneal approach, by one surgeon using four 10-mm ports for access. The technique involved mobilizing the spleen and left colon. The left ureter and gonadal vein were identified and lifted off the psoas muscle. Renal vessels were dissected and any lumbar veins clipped and divided. Dissection of the kidney was completed before the vessels were clamped and divided. The donor kidney was delivered through a 6-cm Pfannenstiel incision. Donor and recipient operations were performed synchronously.

ODN was through a right intercostal incision using an extraperitoneal approach; the vascular anatomy was again displayed clearly and correlated with the radiological findings.

RESULTS

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. SUBJECTS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. CONFLICT OF INTEREST
  8. REFERENCES

Thirty-one potential donors underwent both CTA and MRA, with LDN in 24 and ODN in seven. All of the 31 kidneys were successfully transplanted. There were no open conversions in laparoscopic group (Table 1). Two donors had two renal arteries on each side and one donor had two renal veins on each side, and therefore the total number of main renal arteries and veins was 33 and 32, respectively, on the side of surgery; 33 renal arteries (100%) and 32 renal veins (100%) were detected by CTA, whereas MRA detected 32 arteries (97%) and 31 veins (97%). All five accessory renal arteries were detected by CTA whereas MRA only detected one. All three accessory renal veins were accurately predicted by CTA, whereas MRA detected two. There were 22 left lumbar veins, of which CTA accurately detected 18 (81%), whereas MRA only detected nine (41%); CTA detected 17 of 23 (74%) left gonadal veins whereas MRA detected 11 (46%).

Table 1.  The comparison of CTA and MRA with surgical findings in 31 patients
AnatomySurgeryCTASensitivity, n/N (%)MRASensitivity, n/N (%)
  • *

    P < 0.001,

  • P < 0.01,

  • P < 0.05, Fisher's exact test.

Main renal arteries33331003297
Main renal veins32321003197
Accessory renal arteries 5 5  5/5* 1 1/5*
Accessory renal veins 3 3  3/3* 2 2/3*
Left lumbar vein1918 95* 947
Left gonadal vein2417 71 1146

DISCUSSION

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. SUBJECTS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. CONFLICT OF INTEREST
  8. REFERENCES

Conventional angiography has remained the ‘gold standard’ for evaluating vascular renal anatomy for potential renal donors. Both MRA and CTA have the potential to replace this because both are noninvasive procedures that can be done on an outpatient basis. However, there has been concern about the accuracy of predicting renal vascular anatomy. In the present study we compared the efficacy and sensitivity of MRA and CTA for evaluating potential renal donors. A meticulous evaluation of the donors before renal transplant is essential; an accurate understanding of renal vascular anatomy, especially venous anatomy, has become more important with the emergence of LDN. CTA and MRA have provided a noninvasive opportunity to study the donor's vascular anatomy in more detail, especially with refinements in collimation and spatial resolution, which have improved image quality.

Multiple renal arteries are common; almost 30% of the donors are expected to have two or more renal arteries on one or both sides. Of kidney donors being assessed, 23% have been found to have double renal arteries and 4% to have triple arteries [5]. Renal veins have a more constant anatomy; multiple right renal veins with separate origins from the inferior vena cava are seen in up to 15% of donors, whereas on the left side an additional renal vein is uncommon (1%) [6].

Lumbar veins are also subject to considerable variation; they join the left renal vein in up to 75% of people and the right renal vein in 3%[6,7]. With all of these variations in renal hilar and lumbar vein anatomy, it is obvious that a thorough preoperative donor evaluation for surgical planning is of critical importance.

The role of MRA for evaluating potential renal donors has been studied and comparisons of conventional angiography with MRA have also produced good correlations [2,3,8–10]. However, most of these studies concentrated on detecting renal arteries; none compared MRA with a conventional angiogram for detecting renal veins and their variations. One group found a 22% discrepancy in the first year between MRA and surgical findings. Another group compared 50 consecutive donors who had MRA, with an overall accuracy of 90%[11,12]. Some studies assessed the efficacy of MRA in evaluating renal venous anatomy, with varying success [2,10].

There are similar evaluations of CTA for renal vascular anatomy. One group evaluated spiral CT in 77 donors and compared it with surgical findings; the detection rate for renal arteries was 98%. Another group evaluated 80 donors, of whom 50 had CTA and 30 MRA, and found that CTA had a detection rate 93% and MRA 90% for renal arteries [1,3]. Another study compared 175 donors who had LDN and found a 93% accurate correlation for renal arteries, whereas the accuracy for identifying renal veins was 97%[13]. The results were similar in another study, which found 90.5% accuracy in predicting renal arteries in 199 donors who had CTA, but the sensitivity reduced further when multiple arteries were present [14].

Comparisons of CTA with conventional angiography have shown excellent accuracy for predicting renal arterial and venous anatomy. Some groups compared CTA and MRA, as in the present study, but a surgical correlation is available in very few donors [3,9]. The present CT protocol yielded excellent sensitivity for both arterial and venous anatomy, and achieved a very good surgical correlation, which compares with other studies [15,16]. 3-D reconstruction of spiral CT images was useful for accurately identifying renal arteries and especially veins. The sensitivity of MRA was similar to CTA in detecting renal arteries. CTA was better then MRA for both arterial and venous anatomy, especially in detecting lumbar and accessory renal veins. It was therefore more useful in planning donor surgery, especially LDN (Fig. 1).

image

Figure 1. (A) CTA clearly shows the left gonadal vein (closed arrow) and split retroaortic left renal vein with joining adrenal vein (open arrow). (B) MRA showed the renal vein poorly and failed to detect the superior renal vein branch.

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In patients undergoing LDN an accurate understanding of venous anatomy is critical, especially on the left side. After concluding this study, the investigation of choice at our institution at present is multislice spiral CTA with 3-D reconstruction for evaluating live renal donors.

REFERENCES

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. SUBJECTS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. CONFLICT OF INTEREST
  8. REFERENCES
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