The posterior renal vein (new definition), together with its morphological significance.

A particular branch of the renal vein, which is detected behind the renal pelvis at the hilum at the rate of ca. 80%, and which is proposed as the posterior renal vein (PRV), may be remarked as morphologically significant. PRV may be divided into the typical and non-typical categories. But, in accordance with the bilateral asymmetry of the renal vein, PRV differs between the two sides. Thus on the right (82/270 = 30%), the first category of PRV directly joins the inferior vena cava (IVC) 1-3cm lower than the ordinary or anterior renal vein (ARV), and on the left (90/270 = 33%), it joins ARV after receiving the second lumbar vein in most of the examples. The other category of PRV (99/221 = 45%), which joins ARV near the hilum, is morphologically regarded to represent the former, which is degenerated to a certain extent. By considering the characteristics above and below the renal vein, the flowing level of PRV into IVC on the right will, above all, indicate the point of transition of the constituent portions of the developing IVC. In the meantime, in view of the assessment that the final portion of the left PRV represents IVC, PRV will afford a logical clue to understand the bilateral symmetry. The posterior veins as observed in the upper retroperitoneal cavity such as the suprarenal gland and diaphragm will constitute the posterior venous system related to PRV.