Usual and Unexpected Variations in the Veins of the Posterior Abdomen: A Case Study

Abstract

Two venous system components comprise the drainage of the posterior abdominal cavity. One component drains blood from the visceral derivatives of the urogenital ridge (e.g., kidneys, gonads) directly to the inferior vena cava (IVC). The other venous system collects blood from the body wall and drains into the azygos system through the subcostal vein, ascending lumbar vein, and lower posterior intercostal veins. Veins, and especially the azygos system, are notoriously variable. Much of this variability arises from the complex embryological development of the caval venous system in the thoracic and abdominopelvic cavities; but the formation of venous anastomoses representing multiple routes of drainage from a single region also contribute to the variability of veins.During routine dissection of the abdomen of a male cadaver (Caucasian, 67 years), the right testicular vein demonstrated multiple anatomical variations. An anomalous vein arising from several small tributaries at the lateral end of the 11th and 12th ribs was discovered during the dissection. This vein crossed the posterior abdominal wall inferomedially to drain into the right testicular vein. Further exploratory dissection revealed direct communication between the anomalous vein and the right 11th posterior intercostal vein, which could be traced from the origination of the anomalous vein to the connection with the azygos vein at the appropriate vertebral level. The anomalous vein represents an unusual route for collateral venous circulation between the azygos system and the caval system in the abdomen via the right 11th posterior intercostal vein. Additionally, the right testicular vein drained into the right renal vein instead of directly draining into the IVC. No other notable variations were observed in the abdominal vasculature. The left testicular vein, left renal vein, left posterior intercostal veins, and left subcostal vein all demonstrated typical merging patterns. Accompanying renal, testicular, and posterior intercostal arteries on the right side also appeared to have normal branching patterns.