Congenital absence of the horizontal portion of the left portal vein.

Abstract

The adult portal vein and hepatic veins are the descendants of the vitelline and umbilical veins in embryo. Early in intrauterine life there are many anatomic channels between the vitelline and umbilical veins. As the embryo matures, certain channels regress and others become more prominent. The anatomic channels connecting the caudal portion of the right vitelline vein and the left umbilical veins form the horizontal portion of the left portal vein. If this anastomosis fails to develop normally, another venous channel maintains the communication. Clinically, this event is represented by the congenital absence of the horizontal portion of the left portal vein and the development of an aberrant vessel feeding the left lobe. As a result, the left lobe is suffi ciently fed by this aberrant vessel and does not atrophy. US demonstrates this anomaly as an echogenic line in the usual location of the horizontal portion of the left portal vein, the undeveloped horizontal portion, and a large aberrant vessel communicating between the anterior segmental branch of the right portal vein and the vertical portion of the left portal vein. The fl ow direction of the aberrant vessel is always from the former toward the latter. If the entire course of the portal vein is carefully observed with US and color Doppler US, there is very little room for ambiguity in diagnosing this extremely rare congenital anomaly.