A case of double inferior vena cava with the connection to sacral venous plexus.

Double inferior vena cava (IVC) is known as a variation in which the additional IVC is found on the left side of the abdominal aorta. Their developmental process has been well documented, but the venous development around the lumbosacral region is controversial. In the present double IVC case, the left IVC entered the left renal vein at the L2 level, and the renal veins on each side flowed into the right IVC at the L1 level. The internal and external iliac veins were merged at the S1 level on each side. Besides, a venous communication (3-mm-width) was found horizontally between the internal iliac veins near their origin at the S1 level. It had also an extra narrow branch (1-mm-width), which ran obliquely upward and reached the left IVC at the level of L5. The median sacral artery (MSA) ran at the ventral side of the horizontal communication but at the dorsal side of its extra oblique branch. These results suggest that the oblique branch is a remnant of the anastomosis between the right and left posterior cardinal veins. Furthermore, the horizontal vein corresponds to the sacral venous plexus, suggesting that the anastomosis can be formed between the IVC and sacral venous plexus.