[Cardiac myxoma--light, electron microscopic and immunocytochemical assessment of histogenesis]

Fourteen cardiac myxomas exhibiting a variety of histologic patterns were examined by light microscopy and the peroxidase anti peroxidase technic using factor VIII relating antigen. Four were also studied by election microscopy. Tumor cells showed variable cellular arrangements, e.g. cord clusters of rounded cells, network-like arrangement, concentric myxoma cell layers and vascular-like structures. Electron microscopically, these myxoma cells revealed smooth muscle-like cells, fibroblast-like cells and endothelial cells. Factor VIII-related antigen was found in some of the single tumor cells, in endothelial-like cells of the vascular-like structures and in cells on the inner side of the concentric cell layers. Cardiac myxoma arises from multipotential mesenchymal cells in the endocardium of the atrial septum which may develop into smooth muscle cells, fibroblasts, cartilage cells and endotherial cells.