Double left renal veins and multiple right renal veins found in Japanese adults.

A case of circumaortic renal venous collar, the first such collar to be observed in a Japanese female cadaver, is presented, and its anatomical organization is compared with that in another case in which four right renal veins accompanied four right and three left renal arteries in a Japanese male cadaver. Double left renal veins are formed by persistence of a more central retroaortic venous anastomosis, in contrast to multiple right renal veins, which are formed by persistence of some embryonic renal veins arranged in ladder-like patterns. In our case, the dorsal limb of the renal collar communicated with the azygos system veins and lumbar veins. The azygos system veins were considered to have atrophied as a result of some persisting retroaortic venous anastomoses located in the thorax. Therefore, we believe that the renal collar was related to the atrophy of the azygos system veins. To determine whether there are racial differences in incidence of renal collar, further studies in Asians are required.