Teaching Case

A 33-year-old male patient with a history of chronic alcohol use presented to the emergency department after he was involved in a motor vehicle accident. The patient presented with altered mental status and subsequently received a total body CT as per trauma protocol.

A contrast-enhanced CT abdomen was performed. While there was no evidence of any intraabdominal traumatic injury, an incidental finding of a retro-aortic left renal vein was made. The CT demonstrates a fenestration-like appearance of the left renal vein with a superior and inferior branch draining into the IVC through a retroaortic course. The left renal vein is single and prior to its entrance into the IVC, it splits into two branches craniocaudally. Specifically, the superior branch traverses horizontally posterior to the aorta, draining into the IVC, near the L2 level, with the inferior branch passing obliquely posterior to the aorta, joining the IVC, near L4 vertebral level.

During normal embryological development, the bilateral supracardinal veins and bilateral subcardinal veins, which drain the upper and lower half of the body respectively, coalesce to form what is called the renal collar. Eventually, the dorsal aspect of this renal collar is resorbed, leaving the ventral aspect to mature into the renal vein [1]. Retroaortic renal veins, or renal veins that lay posterior to the abdominal aorta, occur when the dorsal aspect of the renal collar persists and the ventral aspect is resorbed [1, 2].

The incidence of retroaortic left renal veins (RLRV) is between 0.5% and 3.7% [2, 3]. There has been only one other case of a duplicated RLRV [4]. We report the second case in literature for a duplicated RLRV. Despite the relatively low incidence of RLRV, which are usually found incidentally on CT imaging, RLRV has serious implications for aortic, renal, and retroperitoneal surgeries, including abdominal aortic aneurysm repair and renal transplants [4, 5]. Failure to recognize existing RLRV prior to these surgeries can lead to haemorrhage, nephrectomy, or in severe cases, death [4, 5, 6]. Additionally, this variation is crucial for IVC filter placement, as complications such as venous infarction of the left kidney in case of acute IVC thrombosis can result. Thus, with a RLRV, the IVC filter should be positioned caudal to the inferior branch of the duplicated RLRV.

Although RLRV are frequently asymptomatic findings, they can be associated with haematuria and flank pain, known as posterior nutcracker phenomenon. This condition occurs when the RLRV gets compressed between the aorta and lumbar vertebrae, causing hypertension in the renal vein leading to breakdown of the vessel [6]. Other symptoms include varicoceles, orthostatic hypotension, or in women, pelvic congestion syndrome, which is characterized by dysmenorrhoea, dyspareunia, lower abdominal pain, and lower extremity varices [3, 7]. Therefore, RLRV and anatomic variations of the left renal vein should be considered in the differential diagnosis of haematuria, left flank pain, inguinal pain and pelvic congestion syndrome.

Although most RLRV are incidental findings, given their serious implications during aortoiliac surgeries, accurate imaging is essential in detecting any abnormal vasculature prior to surgery. These anomalies can be identified most effectively by abdominal CT scans with IV contrast [3]. In patients who are believed to have nutcracker phenomenon, multiphase CT urography is appropriate. In asymptomatic patients, no treatment is recommended. However, in patients with severe symptoms, numerous surgical options ranging from stenting to nephrectomy are available [7].