Embryological consideration of drainage of the left testicular vein into the ipsilateral renal vein: analysis of cases of a double inferior vena cava

The right gonadal vein (GV = testicular vein in men, ovarian vein in women) usually drains into the inferior vena cava (IVC) while the left gonadal ve in drains into the left renal vein (RV). This anatomical difference induces relatively weak haemodynamics in the left testicular vein (TV) and is cons idered to be a cause of a left varicocele. In textbooks on embryology, it h as been documented that bilateral supracardinal veins ( = origin of right a nd left IVC) and the subcardinal sinus ( = origin of RVs and GVs) symmetric ally develop during early embryogenesis. However, persistence and regressio n of the right and left supracardinal veins, respectively, results in drain age of the left GV into the ipsilateral RV. A double IVC (DIVC) commonly or iginates from a failure of disappearance of the left supracardinal vein. Al though there have been a considerable number of case reports on DIVC, littl e attention has been paid to the anatomy of the left GV in such cases. We r eport here an autopsy case, a 72-year-old Japanese man, with a DIVC. This c ase belongs to type BC of McClure and Butler's classification. In this case , it was observed that the right TV drained into the confluence of the righ t IVC with the ipsilateral RV, while the left TV drained into the left RV i n spite of the presence of the left IVC. This case indicates that the embry onic anastomosis point between the subcardinal sinus and the supracardinal vein on the left side is different from that on the right side. Statistical analysis of many case reports of DIVC also suggests that the bilateral sup racardinal veins tend to asymmetrically anastomose with the subcardinal sin us during embryogenesis. These data imply that drainage of the left GV into the ipsilateral RV leads to regression of the left supracardinal vein but also to asymmetrical anastomosis between the supracardinal veins and the su bcardinal sinus.