Multimodality imaging of primary extrahepatic portal vein obstruction (EHPVO): what every radiologist should know.

Portal vein thrombosis (PVT) is a frequent complication of liver cirrhosis, but it can also occur as a primary vascular disorder amid absent liver disease. Extrahepatic portal vein obstruction (EHPVO) refers to the obstruction of the extrahepatic portal vein with or without involvement of the intrahepatic portal vein branches, splenic and/or superior mesenteric vein. It is a distinct disorder that excludes PVT occurring in concurrence with liver cirrhosis or hepatocellular carcinoma. The term "EHPVO" implies chronicity and is principally reserved for a long-standing condition characterized by cavernous transformation of the portal vein. The most characteristic imaging manifestation is the formation of portoportal collaterals (via the venous plexi of Petren and Saint) that allow hepatopetal flow. However, this collateral circulation is insufficient resulting in clinically significant pre-hepatic portal hypertension, wherein the liver function and structure remain preserved until late. Although the long-term (more than 10 years) survival with controlled variceal bleeding is up to 100%, affected individuals have an impaired quality of life owing to portal cavernoma cholangiopathy, hypersplenism, neurocognitive dysfunction and growth retardation. Imaging diagnosis is not always straightforward as the collaterals can also present as a tumour-like solid mass that can be inadvertently biopsied. Moreover, EHPVO has its implications for the biliary tree, arterial circulation, liver/splenic volumes and stiffness, which merit proper understanding but have not been so well described in literature. In this review, we present the complete spectrum of the vascular, biliary and visceral changes with a particular emphasis on what our medical/surgical hepatology colleagues need to know from us in the pre-operative and post-operative settings.