Portal Vein Thrombosis

Portal vein thrombosis (PVT) is a partial or complete clot within the portal venous system. The obstruction reduces blood flow toward the liver and can increase pressure upstream in the portal circulation. The causes differ between patients. Cirrhosis promotes PVT through slow portal flow, portal hypertension, endothelial dysfunction, and a prothrombotic state. In patients without cirrhosis, precipitating factors may include pancreatitis or inflammatory bowel disease, abdominal infection or surgery, intra-abdominal malignancy, myeloproliferative neoplasms, and inherited or acquired thrombophilia. The extent of the clot matters more than the label alone. If thrombus extends into the superior mesenteric vein, venous drainage from the intestine becomes impaired. The bowel becomes congested, its perfusion deteriorates, and intestinal ischemia, infarction, or necrosis can follow. A chronic occlusion may lead to cavernous transformation: a network of collateral veins develops around the blocked portal vein. These collaterals can restore some portal flow, but they do not remove the consequences of portal hypertension. Ascites, splenomegaly, and gastroesophageal varices may develop, and varices can bleed heavily.