Diffuse sinusoidal hemangiomatosis of the spleen. A case report with enzyme-histochemical, immunohistochemical, and electron-microscopic findings.

Diffuse hemangiomatosis of the spleen is a very rare benign tumor in which the whole spleen is permeated by neoplastic blood vessels. It is occasionally accompanied by severe disturbances of blood coagulation. The histogenesis of this tumor remains obscure. No systematic investigations of the immunophenotype of the neoplastic endothelium have been published. We describe a case of isolated benign diffuse hemangiomatosis of the spleen in which the enzyme-histochemical and immunohistochemical findings suggested an origin in the splenic sinus endothelial cells. Some of the tumor endothelial cells reacted with UEA-1, BMA 120, antibodies against the von Willebrand factor, CD34, and CD8, an antigen which, in man, is expressed only by suppressor/cytotoxic T cells and the endothelial cells of the splenic sinuses. Enzyme-histochemical investigations revealed reactivity for nonspecific esterase and lack of reactivity for alkaline phosphatase--a pattern typical of the sinus endothelial cells. The tumor could be distinguished from other tumors/tumor-like lesions of the spleen that exhibit endothelium with characteristics typical of the splenic sinuses (peliosis, splenoma, littoral cell angioma) on the basis of its histological features. The lack of expression of histiocytic antigens by the tumor endothelium is also evidence against a diagnosis of littoral cell angioma, which also derives from the sinus endothelium. Thus, this tumor could not be identified as any of the recognized tumors/tumor-like lesions of the spleen and it is therefore proposed that it should be designated diffuse sinusoidal hemangiomatosis.