In severe cases, venoocclusive disease is characterized by marked congestion in the sinusoids and can be accompanied by areas of hemorrhage 
.
Endothelial injury in sinusoids and small hepatic veins leads to venous outflow obstruction that manifests as sinusoidal dilatation, congestion, and hepatic plate atrophy.
Endothelial swelling with subendothelial edema and fibrosis
leads to partial occlusion of the lumen of a small hepatic vein in venoocclusive disease. These characteristic lesions may not be evident in biopsies.
Sinusoidal obstruction caused by occlusion of hepatic sinusoids by sickled red blood cells
in hepatic sickle cell crisis is shown. This is a rare phenomenon but can cause sinusoidal obstruction syndrome and present in an acute fashion.
