The ultrastructure of smooth muscle tumors with a consideration of the possible relationship of glomangiomas, hemangiopericytomas, and cardiac myxomas.

Tumors classified as being of smooth muscle origin by light microscopy were studied with the electron microscope. Their ultrastructure verified the diagnosis in all of the seven leiomyomas but in only eight of the twelve (66 percent) tumors that were finally classified as leiomyosarcoma. The discrepancy of the light microscopic and ultrastructural findings in these four sarcomas may be due to sampling problems likely to be encountered in poorly differentiated tumors or simply the failure of development of specific ultrastructural features in the face of a characteristic growth pattern at the light microscopic level. Among other tumors that have been considered to be of smooth muscle origin--hemangiopericytoma, glomangioma, and cardiac myxoma--only the glomangioma showed ultrastructure features identical to those of smooth muscle.