IMAGING

Evaluation of the renal venous system on late arterial and venous phase images with MDCT angiography in potential living laparoscopic renal donors
Kawamoto S, Lawler LP, Fishman EK
The Russell H. Morgan Department of Radiology and Radiological Science, Johns Hopkins Hospital, Baltimore, MD, USA
AJR Am J Roentgenol. 2005; 184: 539-45

• Objective: The objective of our study was to assess whether both renal arteries and renal veins can be evaluated using single-phase MDCT data sets alone to eliminate the need for both arterial and venous phase data sets.
• Materials and Methods: One hundred consecutive potential living renal donors who underwent 4-MDCT were evaluated. CT was performed with 120 mL of IV contrast material at an injection rate of 3 mL/sec. Both late arterial and venous phase acquisitions were obtained at 25 and 55 sec from the start of IV contrast injection, respectively. The number of the right and left renal veins and its anatomic variations were assessed by two reviewers. Late arterial phase images were evaluated initially, and then venous phase images were analyzed to assess opacification of the renal vein and to see whether venous phase data sets changed or added information about the venous anatomy as seen on late arterial phase images.
• Results: The retroaortic left renal vein was found in two subjects, and the circumaortic left renal vein was detected in three subjects. The renal veins were adequately opacified on late arterial phase images in all subjects. There were six subjects who had a normal left renal vein with a small posterior branch coursing posterior to the aorta and draining into the inferior vena cava, which were difficult to differentiate from the lumbar vein or ascending lumbar vein; in three of these six subjects, the small posterior branch was opacified only on venous phase images.
• Conclusion: Late arterial phase images obtained at 25 sec after the start of contrast injection can reveal the renal vein anatomy except for a small posterior branch of the left renal vein difficult to differentiate from the lumbar or ascending lumbar vein, as seen in three subjects. The data suggest that venous phase imaging is not necessary for the evaluation of renal vein anatomy.
  
  
• Editorial Comment
  Recently, several studies have shown that helical multidetector CT angiography has the potential to replace excretory urography and renal angiography in the evaluation of potential living renal donors. As we know this evaluation should include the assessment of renal arteries, renal parenchyma, collecting system and renal venous system. In order to obtain such complete evaluation several acquisitions should be used (pre-contrast and 25 sec, 70-80 sec, and 180 sec after the start of an intravenous injection of contrast material). It is evident that the radiation dose delivered to living donor will increase with the number of acquisition performed. The purpose of this paper was to assess whether both renal arteries and renal veins can be evaluated using single-phase helical multidetector CT angiography in an attempt to eliminate the need for both arterial and venous phases. The authors concluded the late arterial phase images obtained at 25 sec adequately demonstrated renal arteries and the right and left renal veins in all subjects, but in 7% and 16 % of the patients they could not demonstrate the left adrenal vein and left gonadal vein. This can be considered a relatively limitation of this study since the adrenal vein and gonadal veins are tributary of the left renal vein in almost all individuals. For an adequate and global evaluation of the living donor who is going to be operated by a laparoscopic nephrectomy, some institutions, including ours, prefer the utilization of magnetic resonance imaging. MR-angiography presents 89.4% sensitivity, 94.1 % specificity and 90.6% accuracy for the demonstration of the arterial anomalies. For demonstration of the venous anomalies MR-angiography has 98.3% sensitivity, 100% specificity and 98.4% accuracy. One of the greatest advantages of MR over CT angiography is the fact that MR does no use ionizing radiation. For these reason we can perform, as many acquisition are necessary in order to obtain a complete evaluation of the living donor. However, one of the main limitations of MR imaging is its inability to demonstrate urinary stones particularly those located in the renal parenchyma. This interesting study suggests that venous phase imaging is not necessary for the evaluation of renal vein anatomy. However, a large number of patients need to be studied using this single phase protocol in order to validate this conclusion.

References
1. Jha RC, Korangy SJ, Ascher SM, Takahama J, Kuo PC, Johnson LB: MR Angiography and preoperative evaluation for laparoscopic donor nephrectomy. AJR Am J Roentgenol. 2002; 178: 1489-1495.
2. Low RN, Martinez AG, Steinberg SM: Potential renal transplant donors: evaluation with Gd-enhanced MR angiography and MR urography. Radiology. 1998; 207: 165-172.

Dr. Adilson Prando
Chief, Department of Radiology
Vera Cruz Hospital
Campinas, São Paulo, Brazil