Congenital anomalies of the portal venous system--CT appearances with embryological considerations.

The portal vein is formed by the union of the splenic and superior mesenteric veins behind the neck of the pancreas. This system is derived from the vitelline veins, a component of the extraembryonic venous system. In this paper we report three cases, each of which illustrates a congenital variant of the portal venous system, describe their computed tomography appearances and discuss the embryological processes accounting for these anomalies.