The Incidence and Variants of the Reno-Hemiazygos Connection

Background/Objectives: Although common anomalies of the left renal vein (LRV) are pretty well documented in the literature, the drainage of the left renal blood via the hemiazygos vein lacks comprehensive support. We, therefore, aimed to study the incidence of the reno-hemiazygos connection (RHC). Methods: A total of 150 computed tomography scans (85 men and 65 women) were documented for the origin of an RHC from the LRV. Results: RHCs were found in 14/150 cases (9.34%). They were more prevalent in women (71.43%). In 11/14 cases, type 1 RHCs ascended directly along the postero-lateral left side of the aorta (direct hemiazygos flow). In 3/14 cases, type 2 RHCs (indirect hemiazygos flow) had a lumbar segment corresponding to the second lumbar vein and a pretransversary segment corresponding to an ascending lumbar vein. In 9/14 cases (64.29%), the RHC was connected to a typical LRV. In 1/14 cases (7.14%), the RHC was connected to the junction between the LRV and a left retropelvic tributary. In another case (7.14%), the RHC was connected to a retroaortic LRV and, in three cases (21.43%), to a circumaortic LRV. Triple left renal arteries were found in type 1 and, respectively, type 2 cases. The vertebral level of the inferior end of the RHC was variable, from the L1/L2 disc level to the L3 level. Conclusions: When present, the RHC serves to connect the superior and inferior caval systems. This may be physiologically of use or not, but surgically, it is a major anatomical risk factor for bleeding if its presence is not checked preoperatively.