[Electron microscopy in the differential diagnosis and prognostic evaluation of muscle tissue tumors].

The ultrastructure of striated and smooth muscle tumors of man was studied. A set of features indicating the histological origin of these tumors was established. The most informative feature for tumors of both groups is the presence of fragments of specific microfibrillar apparatus. An analysis of the extent of its development in the cell cytoplasm showed that this feature adequately reflects the tumor cataplasia. Thus, for rhabdomyosarcomas it was considered to be expedient to distinguish three groups according to the degree of the involvement of the myofibrillar apparatus (fibrillar, filamentous, and poorly differentiated types) which may be important for the prognostic evaluation of these tumors. Similar relationships were found with smooth muscle tumors. It is concluded that electron microscopy may be used successfully for differential diagnosis and determination of the degree of cataplasia of human muscle neoplasias.