Hepatic veno-occlusive disease(VOD), also known as sinusoidal obstruction syndrome (SOS), is a process ofcentral venular occlusion characterized by sinusoidal endothelial injury,subendothelial edema, intrahepatic obstruction of blood flow, hepatocellularnecrosis, and intense fibrosis. Its pathophysiology is complex but reflectsa cascade of drug toxicity, cytokine injury, and hypoxic, freeradical-mediated damage to zone 3 of the hepatic acinus. In addition, injuryto the sinusoidal endothelial cells is associated with a procoagulant andhypofibrinolytic state characterized by low plasma levels of antithrombinand protein C, consumption of factor VII, and increased levels ofplasminogen activator inhibitor-1. VOD is reported in 8–14% of patientsafter HSCT. Nevertheless, incidence rates may be as high as 60% in high-riskpatients with underlying liver disease or exposure to drugs such asgemtuzumab ozogamicin and sirolimus. Disease severity ranges from a mildself-limiting illness to a severe disease associated with high mortalityrates (>80%). It generally occurs within the first 30 days ofconditioning, although later onset can occur.

Risk factors

Early identification ofpatients at high risk for VOD is important. In doing so, preventativemeasures (such as reducing sinusoidal toxins) can be implemented.