Left atrial myxoma. A morphologic and histogenetic study.

Seven cases of excised left atrial myxoma are described. These are compared with organizing and organized thrombi. The tumors occurred at ages ranging from 13 to 48 years with male preponderance. There were distinct histological and histochemical differences between myxomas and thrombi. Myxomas were lobulated, soft and gelatinous. The cells were arranged singly, in syncytium, or in gland like manner and around blood vessels. Scant to abundant acid mucopolysaccharide rich stroma with strong metachromasia was present. The cells on histochemical staining revealed a wide range of differentiation and contained small amounts of neutral mucopolysaccharides. Thrombi, on the other hand, were firm, laminated, and the cells were arranged in several stratified layers. Metachromasia was absent. Neutral polysaccharides were absent within the cells of thrombi, These features support the concept that cardiac myxoma is a neoplasm and arises possibly from multipotential mesenchymal cells.