Scanning electron microscopic features of Kaposi's sarcoma.

In order to clarify the three-dimensional structure of Kaposi's sarcoma (KS) five cases of KS of the skin were observed with a scanning electron microscope (SEM). KS lesions were investigated both in vascular and spindle cell areas and were compared with similar areas observed by light microscopy. KS appears as a spongelike neoplasm consisting of irregular vascular channels lacking endothelial cells and well-developed basement membranes. Vascular spaces and vascular slits are packed with numerous red blood cells (RBCs). SEM features of KS share some similarities with those of hemangiopericytoma, a vascular tumor composed of mature endothelial cells surrounded by pericytes. These findings are consistent with the hypothesis according to which the proliferating cells of KS are viewed as immature endothelial cells with partial differentiation into pericytes.