Membranous obstruction of the inferior vena cava (obliterative hepatocavopathy, Okuda).
Confusion prevails throughout the world regarding the definition and classification of the Budd-Chiari syndrome. The original patients (Budd and Chiari) described had hepatic vein thrombosis, but this syndrome now encompasses various hepatic venous outflow blocks, of which membranous obstruction of the inferior vena cava (IVC) is the most common. This author has been suggesting that the classical Budd-Chiari syndrome or hepatic vein thrombosis and membranous obstruction of IVC or primary thrombosis of IVC at its hepatic portion are epidemiologically, pathologically and clinically different, and that they should be treated as two clinical entities that are not to be mixed. The two diseases have a different onset, different clinical manifestations and a different natural history. Whereas hepatic vein thrombosis is a severe disease with an acute onset, IVC thrombosis presents mildly at onset, but it recurs and eventually turns into a fibrous occlusion of IVC of varying thickness or stenosis of a various degree. The fibrous IVC occlusion is found as a mysterious thin membrane, but is more often much thicker than a membrane, and therefore 'membrane' is a misnomer. Although the genesis is not established, formation of a thin membrane may be an outcome of recurrent thrombosis. The past congenital vascular malformation theory no longer holds, because the disease occurs mostly in adulthood, and transformation of thrombosis into a membrane has now been well documented pathologically as well as clinically. This author suggests that a term 'obliterative hepatocavopathy' replace membranous obstruction of IVC, the term 'Budd-Chiari syndrome' be abandoned, and that primary hepatic venous outflow block be divided into primary hepatic vein thrombosis and primary IVC thrombosis (obliterative hepatocavopathy).