Anatomic variation of portal venous anatomy in the porta hepatis: ultrasonographic evaluation.

The appearance of the portal vein as it crosses anterior to the inferior vena cava and enters the liver at the porta hepatis was evaluated on 100 longitudinal and 100 transverse ultrasonograms. Three major variations were noted on the parasagittal scans, while four major variations were evident on the transverse images. These variations were primarily related to the size of the left portal vein and the angle at which the left portal vein coursed away from the main portal vein. The appearance and course of the proximal right portal vein was extremely constant and may therefore be used as a landmark to detect pathologic processes in the porta hepatis. Detection of altered anatomy in this region may be especially helpful in correctly differentiating dilated intrahepatic bile ducts from normal portal veins.