Etiology and Clinical Outcome of Budd-Chiari Syndrome and Portal Vein Thrombosis

The liver receives approximately one-third of the resting cardiac output. Blood flow to the liver is supplied by both an arterial (hepatic artery) and a venous (portal vein) system and three hepatic veins provide drainage of blood from the liver to the inferior vena cava. The hepatic vascular system is quite dynamic and has the ability to function as a reservoir for blood within the general circulation. Different conditions can interfere with hepatic blood flow and cause disease. The most important clinical syndrome affected by obstruction within the liver vasculature is portal hypertension. Portal hypertension is defined by an increase in the pressure of the portal venous system which results from a disruption of normal blood flow at either a prehepatic, intrahepatic or posthepatic level. The most common cause of portal hypertension in the Western world is liver cirrhosis, leading to an elevated portal pressure due to an increased resistance to intrahepatic blood flow as a result of architectural distortion of the liver. In the absence of liver cirrhosis, numerous less common disorders are known to cause, socalled, non-cirrhotic portal hypertension. Two rare diseases, characterized by thrombosis of the large hepatic vessels are Budd-Chiari syndrome (BCS) and portal vein thrombosis (PVT). Both these disorders share certain features, such as etiologic factors causing thrombosis and the development of portal hypertension, but are considered as separate disease entities based on the location of venous obstruction and their variable clinical presentation. BCS is defined as an obstruction of the hepatic venous outflow tract, ranging from the level of the small hepatic veins up to the junction of the inferior vena cava with the right atrium. Most cases of BCS in the Western world are caused by thrombosis of the hepatic veins, sometimes in combination with thrombosis of the inferior vena cava. The exact incidence of BCS is unknown but is estimated around 1 per million. Thrombotic occlusion of the portal vein is somewhat more common, especially as a complication in patients with liver cirrhosis. Noncirrhotic PVT has a diverse etiology but a significantly better outcome than in patients with underlying liver cirrhosis or hepatobiliary malignancies.

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