Myxoma-like features of organizing thrombi in arteries and veins.

Evidence for the development of the cardiac myxoma from organizing thrombi has been presented previously. In this study, many of the features of the myxoma were observed in organizing thrombi in arteries and veins. Individual undifferentiated mesenchymal cells, cords of similar cells, vascular bud-like cellular aggregates, fibroblasts, well-formed vessels, and multiwalled vessels set within a loose, mucoid ground substance were present in the thrombi. These areas resembled the basilar layer of the cardiac myxoma. Cartilage-like cells, like those in the superficial zone of myxomas, were noted in some thrombi, and ossification had occurred rarely. These observations support a thrombogenic origin of the myxoma. Local physical factors may provide the stimulus for varying differentiation of mesenchymal cells in both the peripheral thrombi and the myxoma.