Budd-Chiari syndrome (thrombosis of the hepatic veins) has multiple etiologies, but recently, has been classified into primary and secondary types. The primary type has further been divided into two categories, intrahepatic hepatic vein thrombosis and inferior vena cava thrombosis (hepatic portion). This latter category was previously referred to as membranous obstruction of the inferior vena cava. Recently, researchers have suggested that membranous obstruction of the inferior vena cava is an acquired rather than a congenital phenomenon, thought to be due to the formation of thrombus within the intrahepatic portion of the inferior vena cava. These two categories of Budd-Chiari syndrome are distinctly different from one another. Hepatic vein thrombosis is common in developed Western countries but inferior vena cava thrombosis is more common in underdeveloped countries such as Nepal, China, South Africa, India, and Japan.
