Ultrastructure of the cardiac myxoma and the papillary tumour of heart valves.

The ultrastructure of a cardiac myxoma has been studied and compared with that of a papillary tumour of heart'. The histochemistry of the myxoma was studied at the same time. The predominant myxoma cell contains intracytoplasmic fibrils similar to those occurring in cells (myofibroblasts') found in granulation tissue, deep within thrombi, and in the subendocardial layer of the heart. It also contains numerous secretory granules which appear to discharge their contents into the pericellular matrix. The material adjacent to the myxoma cell is shown by histochemistry to contain hyaluronic acid and chondroitin sulphate acidic mucins while the surrounding stroma contains sialomucins. The ultrastructure and histochemistry of the cardiac myxoma are very similar to those of the `papillary tumour of heart' which is widely regarded as non-neoplastic and formed by growth of a Lambl's excrescence. Hence these findings do not resolve the classical controversy as to whether the cardiac myxoma is neoplastic or thrombotic in origin.