[Endocardial myxoma. Current aspects of its histopathogenesis].

Primary tumours of the heart are rare. Among these the myxoma is not only the most common but also the most fascinating neoplasm, because some proponents have argued in favour of a thrombotic rather than a true neoplastic origin. The most compelling arguments against the theory of a thrombotic origin are based on ultrastructural characteristics. Using light-microscopy and immunohistochemistry, the authors attempt to clarify the histogenesis of this peculiar tumour which does not arise from any tissue normally occurring in the heart. It is assumed that the stem cell of the cardiac myxoma is a multipotential mesenchymal cell able to differentiate into fibroblasts, smooth muscle cells and endothelial cells. The most striking feature of the myxoma is excessive production of gelatinous matrix. This abundance of mucoid ground substance is typically observed in embryonic tissue. It is suggested that cardiac myxoma derives from multipotential embryonic remnants of the subendocardium.