Multi-detector CT Imaging of Double Left Renal Veins.

Advance awareness of the renal vascular anatomy, including variants of the left renal vein, is important for abdominal and renal surgery. The migratory nature ofrenal embryology and significant transformation of precursors of the inferior vena cava and renal veins can make the final configuration of these structures complex. Two uncommon instances of dual left renal vein with orthotopic left common iliac vein and ectopic caval drainage are presented with multi-detector CT imaging.

Introduction

Anatomic variants of the left renal vein are frequently seen and well-assessed by cross-sectional imaging, especially with the advent of multi-detector computed tomography (CT). The size, number, and location of left renal veins and their anatomic relationship with the surrounding retroperitoneal structures are related to the migration and final location of the left kidney, the embryogenesis of the inferior vena cava and the evolution of the primitive venous renal collar. The most common variants of the left renal vein are the retro-aortic and circum-aortic forms. The presence of additional left renal veins with connection to either distal inferior vena cava or proximal left common iliac vein are rarely seen.

Case Report

Case 1

A 67-year-old woman underwent cross-sectional imaging for non-specific abdominal pain. Intravenous contrast-enhanced multi-detector CT study showed an uncommon pattern of left renal veins. Multiplanar reformations confirmed two left renal arteries and two left renal veins (LRV). The first left renal artery and vein were at normal anatomic locations. The additional left renal artery arose from the lower abdominal aorta just proximal to the aortic bifurcation. The additional LRV, with a distinct renal hilar origin with regard to the first LRV, drained to the left common iliac vein (LCIV) after a course posterior to the left common iliac artery (Fig. 1A, B & C). There was normal drainage of the left ovarian vein and left supra-renal vein to the first LRV.

Figure 1. Case 1

(A) Contrast-enhanced axial CT shows the first LRV (arrow) with a normal course between the abdominal aorta and superior mesenteric artery. (B) At a lower abdominal level, the second LRV (arrow) joins the left common iliac vein posterior to the left common iliac artery. (C) Coronally reformatted CT image shows the double LRV: the first one at a normal anatomic location (yellow arrow) and the second one (green arrow) coursing posterior to the left common iliac artery before its connection to the left common iliac vein (orange arrow). [Powerpoint Slide].

Case 2

A 70-year-old woman was evaluated at our institution for chronic abdominal pain. The contrast-enhanced multi-detector CT examination showed, in addition to colonic diverticulosis, two LRV and two left renal arteries. CT multiplanar reformations demonstrated well the two LRV with two distinct origins from the left renal hilum and two separate connections to the inferior vena cava (IVC): one at the normal location and one at the distal IVC (Fig. 2A & B).

Figure 2. Case 2

(A) Coronally reformatted CT image shows a double LRV with two distinct origins at the left renal hilum. The first LRV (yellow arrow) has a normal anatomic location. The second LRV (orange arrow) has an inferior course draining to the distal IVC. (B) Axial CT image of the lower abdomen shows the connection of the additional LRV (arrow) to the distal IVC. [Powerpoint Slide]

Discussion

Anatomic variants of the LRV have been described in detail by several authors [1, 2, 3]. The LRV originates from the primitive renal venous collar, which is formed by the eighth week of embryogenesis after regression of the paired post-cardinal veins. The renal venous collar is constituted laterally by the paired dorsal and ventral primitive renal veins on each side linked to the centrally paired ventral subcardinal and dorsal supracardinal veins, and anastomoses of these four cranio-caudally oriented subcardinal-supracardinal vessels. Depending on the persistence or regression of different components of this primitive circumaortic venous network, different anatomic presentations of the LRV are encountered. Classically, there are five possibilities encompassing the normal adult LRV configuration: a single renal vein crossing in front of the aorta to drain into the IVC (normal), acircumaortic LRV, a retroaortic LRV, duplication of the IVC or transposition of the IVC [1, 2, 3]. These four anatomic variations are seen respectively in up to 8.7%, 3.2%, 3% and .5% of cases [4]. Two instances of single LRV with ectopic drainage to the left common iliac vein have been previously reported [5, 6]. This uncommon LRV anatomy may represent a variant of the retroaortic LRV category with a possible low implantation to the IVC at the L4-L5 level, which has been described in detail by Hoeltl and collaborators [3]. Our two cases, one with two LRV's draining to two different sites of the IVC and one with orthotopic IVC and ectopic LCIV connection, probably represent a rare combination of the normal LRV configuration and low-positioned variant of the retroaortic LRV.

An additional renal vein has been defined as a supernumerary vessel with distinct emergence from the renal hilum and separate drainage pattern to the IVC [7]. A single additional renal vein is seen on the right side with a frequency of 15-27%. Occurrence of a single left additional renal vein is uncommon (2.6%). A second additional renal vein on the right side is rare (2-3.3%) with none so far reported on the left side [7]. Variations of the LRV are usually asymptomatic and, in the past, carried a high potential for mortality and morbidity when they were unexpectedly discovered during retroperitoneal surgery or abdominal interventional procedures [8]. These variations are more frequently detected and better assessed with the advent of multi-detector CT as well as imaging screening of potential renal transplantation donors. Thus, uncommon variants of the LRV, as seen in our two patients, are expected to be more often imaged, diagnosed and reported in the medical imaging literature in the future.