[Cardiac myxoma. Ultrastructural and immunohistochemical study of two cases]

Two cases of cardiac myxoma studied by electron microscopy and by immunohistochemical methods are reported. In one case, the initial clinical manifestation was systemic embolization, and histological sections from the arterial deobstruction material set the diagnosis of an embolizing cardiac myxoma. In the second case, the investigations of a post-capillary pulmonary hypertension with echocardiography disclosed a left intraauricular tumor. Ultrastructural studies demonstrated mesenchymal tumor cells of various degrees of differentiation characterized by numerous cytoplasmic microfilaments and intermediate-sized filaments. The most differentiated cells were surrounded by a continuous basement membrane; there were intracellular junctions and microvilli. Furthermore these cells contained numerous micropinocytosis vesicles, several Weibel-Palade bodies and an abundant rough endoplasmic reticulum. Analysis of their cytoskeleton, using indirect immunofluorescnece techniques, showed that these cells were laden with actin and myosin microfilaments; the intermediate filaments were composed of vimentine. Staining with anti-desmin and anti-prekeratin sera remained negative. These results contribute to confirm that cardiac myxomas represent tumors originating from the primitive multipotential mesenchymal cells. An obvious tendency to differentiate into endothelial cells is noted in the two cases studied.