Imaging assessment of portal venous system: pictorial essay of normal anatomy, anatomic variants and congenital anomalies.

The purpose of this pictorial essay is to describe anatomic variants and congenital anomalies of portal venous system and related liver parenchymal alterations. The imaging findings of some of these entities have been previously described in other articles, however this work encompasses all congenital anomalies of portal venous system with attention to their features on various imaging modalities; in particular we illustrated with detailed pictures all the main portal vein variants, congenital extra- and intra-hepatic porto-systemic venous shunts and portal vein aneurysm. Variants of portal branches and intrahepatic portosystemic shunts are quite uncommon, however, when present, they should be recognized before performing surgery or interventional procedures. Congenital absence of the portal vein is an important finding as the complete loss of portal perfusion predisposes the liver to focal or diffuse hyperplastic or dysplastic changes. Portal vein aneurysm is a rare clinical entity that can affect intra- and extra-hepatic portal branches; although usually asymptomatic, thrombosis can occur. Awareness of congenital variants of portal venous system among radiologists should allow a more confident diagnosis and permit an accurate planning of surgical procedures and percutaneous interventions; identification of portal system anomalies also suggest an accurate evaluation of associated hepatic parenchymal anomalies such as nodular regenerative hyperplasia, focal nodular hyperplasia (FNH), and adenomas with high risk of malignant transformation.