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The hepatic venous system extends from the central veins of the hepatic lobule, up to the hepatic vein ostia into the inferior vena cava (IVC). There are numerous hepatic veins. The three major hepatic veins open into the IVC close to the right atrium. The hepatic venous system can be involved in arterio-venous or porto-venous fistulas, mostly of congenital origin, a topic which has been recently reviewed1 and will not be discussed here. Most of the other disorders of the hepatic venous system eventually cause its obstruction. Significant hepatic venous outflow block occurs either from a diffuse involvement in small vein diseases, or from a focal or extensive obstruction in diseases of the largest veins. So-called Budd–Chiari syndrome (BCS) is the liver disease resulting from the hepatic venous outflow block. The hepatic venous system can be invaded or compressed by malignant tumours of the liver, primary leimyosarcoma of the veins, or hepatic echinococcal disease. These diseases cause secondary BCS, which will not be discussed here. Primary BCS relates to the primary venous lesions including phlebitis, thrombosis or fibrosis.
Veno-occlusive disease (VOD) is characterised by particular, non-thrombotic, microvascular lesions without involvement of the large veins, occurring in a particular context of exposure to endothelial toxins. By convention, VOD has been separated from primary BCS, although VOD also causes hepatic outflow blockade, and mimics most clinical and laboratory features of primary BCS. Due to the particularities of VOD, and in order to make the distinction from BCS more clear, it was recently proposed to replace the denomination of VOD by sinusoidal obstruction syndrome (SOS).2
Primary BCS is a rare disease. Accurate estimates of incidence are lacking for western countries. In Japan, in 1989, an incidence estimate derived from a questionnaire survey and an autopsy registry was 0.2 per million inhabitants …
Competing interests: None.
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