Endocardial papillary elastofibromas. Histologic, histochemical, and electron microscopical findings.

The organization of cellular and extracellular components appeared similar and was distinctive in three endocardial papillary elastofibromas studied. Each tumor papilla contained (1) a dense, central core of collagen and elastic tissue, (2) a peripheral, myxomatous layer with deposits of acid mucopolysaccharides, and (3) an overlying, hyperplastic layer of endothelial cells. Ultrastructural study of one tumor showed that the cells in all three zones had numerous cytoplasmic filaments, 100 Angstroms in diameter, and dilated cisterns of endoplasmic reticulum; endothelial cells also had intercellular junctions and numerous pinocytotic vesicles. The myxomatous stroma varied from amorphous to fibrillar, and the collagenous cores showed focal degeneration. The name "endocardial papillary elastofibroma" is suggested to emphasize those features which are most conspicuous and which serve to differentiate this tumor from myxoma.