Splenic alterations in hairy-cell leukemia: II. An electron microscopic study

Spleen from nine patients with hairy-cell leukemia (HCL) were studied for ultrastructural alterations. In all cases, hairy cells with typical ultrastructural characteristics were observed within splenic cords and sinuses. Hairy cells had numerous cytoplasmic processes that interdigitated with cytoplasmic processes of other hairy cells. Hairy cells also adhered to sinus endothelial cells and ring fibers and protruded into spaces between endothelial cells. Some normal sinuses were filled with aggregated hairy cells. Other sinuses appeared dilated. Many sinuses were lined by hairy cells that covered thinned endothelial cells and ring fibers. In these abnormal sinuses, endothelial cells were decreased and many appeared injured. The splenic cords were expanded by an infiltration of hairy cells and by large blood-filled spaces. These findings suggest that hairy cells adhere to many cell surfaces, produce endothelial cell injury and death, and impede the venous flow of blood in the spleen. All of the factors appear to influence the formation of the abnormal splenic sinuses and the blood-filled spaces that characterize HCL.