The surface lining cells of cardiac myxoma. Light, electron microscopic and immunohistochemical observation

Morphological, enzymatic and electron microscopic studies have been performed on the surface covering cells of cardiac myxoma (CM) in 4 clinical cases. The superficial layer of CM is composed of mono- or poly-layers of polygonal cells and the superficial cells are connected with the tumor cells within CM. Electron microscopic picture showed many microvilli on the surface of the superficial cells, and the neighboring cells extend extrusions one to another connecting with desmosomes. Formation of incomplete basal membrane was observed in the underlying cells. These cells were morphologically similar to those of the tumor cells in CM. Polygonal superficial cells were shown by scanning electron microscope, and there was no consistent arrangement, which was different from the vascular endothelial cells. Factor VIII-related antigen was proved in the tumor cells having vascular like space in CM, suggesting differentiation of the tumor cells to the vascular endothelial cells. Factor VIII-related antigen was negative in the superficial covering cells. It may be said that the superficial covering cells of CM are premature tumor cells having no character as endothelial cells.