Uncommon dorsal tributary of the right external iliac vein connecting with venous tributaries derived from intrapelvic organs

The external iliac vein is the direct continuation of the femoral vein and originates at the level of the lower margin of the inguinal ligament. The external iliac vein receives typical venous tributaries, such as the inferior epigastric vein and the deep circumflex iliac vein. Herein, we identified a rare tributary, which joined the dorsal aspect of the right external iliac vein and did not correspond to any of the typical tributaries. It arose from periosteum near the greater sciatic notch, received several venous tributaries, and finally joined the right external iliac vein. Caudally, it communicated with a tributary originated from a venous ring within the pelvic cavity. As it ran cranially, it received an anastomotic vein derived from the right superior vesical vein and the right uterine vein, the right iliolumbar vein, and a venous tributary originated from the right spinal vein. It was noted that, in present case, there are several venous rings in the pelvic cavity. In particular, the venous ring surrounding the right internal pudendal artery received the right obturator vein and the right inferior vesical vein. This venous ring gave off four veins, two of them joined the tributary that we identified in the present study and another two connected to the right internal iliac vein. The present case may be helpful for understanding the variation of the iliac venous system.