ultrastructure of sinusoidal cells in a benign liver cell adenoma a typical benign liver cell adenoma was removed from a 25yearold female taking an oral contraceptive the biopsy was perfusionfixed allowing good visualization of sinusoids and sinusoidal cells kupffer cells were seldom seen endothelial cells were of irregular thickness most of them had few fenestrae and were attached to each other by well visible junctions normal perisinusoidal cells psc were not seen but were replaced by myofibroblastlike cells with thick subendothelial processes a basement membrane often underlaid endothelial cells and the processes of psc the enlarged disse space with a flattened sinusoidal hepatocyte membrane contained occasional red blood cells and an abundant extracellular matrix but few collagen fibers these sinusoidal abnormalities leading to the capillarization of sinusoids either the cause or the consequence of the disease indicated a loss of normal hepatocyte homeostasis