The portal vein represents a confluence of the superior mesenteric vein (SMV) and the main splenic vein into which drains the pancreatic vein, left gastroepiploic vein, short gastric vein, and inferior mesenteric vein (IMV) (Fig. 14). The IMV receives its supply from the left colic, sigmoid and superior hemorrhoidal veins. It usually joins the splenic vein prior to the junction of the splenic vein with the SMV. The SMV receives its contribution from the jejunal, ileal, right colic, and middle colic veins. The right and left gastric veins usually drain directly into the portal vein.
The portal vein then divides into the right and left portal branches at the hepatic hilum. Approximately 50% of individuals demonstrate a bifurcation of the portal vein outside the liver capsule. A common anomaly of the portal-venous system is a trifurcation of the main portal vein, which occurs in about 8% of patients. In this case, the main portal vein divides into the right posterior segmental branch, the right anterior segmental branch and the left portal vein [11,19].
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