[Comparative study on ultrastructure of rhabdomyosarcoma and embryonal striated muscle]

Twelve cases of rhabdomyosarcoma identified by electron microscopy were studied. Of them, 6 were diagnosed originally as rhabdomyosarcoma and 6 as other tumors by light microscopy. Five types of tumor cells, primitive mesenchymal cells, undifferentiated myoblasts, poorly differentiated myoblasts, well-differentiated myoblasts and leptomeric fibril myoblasts were observed under electron microscope. Striated muscle tissue from 5 cases of 5-8 week old human embryo was used as control. There was a correlation in differentiation between rhabdomyosarcoma and embryonal striated muscle. Based on their fine features, the diagnosis of rhabdomyosarcoma is discussed.