The embryology of the portal venous system is extremely complex and yet major congenital malformations of the system have been rarely described. However, the increased use of sophisticated ultrasound techniques and the increase in liver transplantation have resulted in an increase in the number of reports of these abnormalities during the past 15 years. There is also an increased awareness of associated complications from these abnormalities including late onset encephalopathy.

The systemic venous system develops from the intra-embryonic anterior and posterior cardinal veins, whereas the portal venous system develops from the extra-embryonic vitelline and umbilical veins which provide drainage from the yolk sac and placenta, respectively.1 The vitelline veins are paired vessels which drain into the primitive sinus venosus and by the end of the fourth week of gestation, three cross communications have developed between them in subhepatic, retroduodenal and subdiaphragmatic positions.2

The portal vein in the embryo is derived from the inferior section of the left vitelline vein, the retroduodenal communication, and the superior section of the right vitelline vein, and so forms the S-shaped configuration of the mature portal vein. The inferior vena cava is also formed from the amalgamation of several venous channels in the embryo including the right end of the sinus venosus and the right end of the subdiaphragmatic anastomosis of the vitelline veins. Early in development blood …