Rhabdomyoma of larynx:Ultrastructural study and comparison with granular cell tumors (myoblastomas)

The light-and electron-microscopic morphology of a benign skeletal muscle tumor is described and compared with that of a granular cell tumor (myoblastoma). The presence of occasional cross-striations, rod-like cytoplasmic bodies and sarcolemmal sheath serve to differentiate rhabdomyomas from granular cell tumors by light microscopy. Most of the structures normally seen in mature skeletal muscle, especially actin filaments, were present in the rhabdomyoma. These were often in a haphazard arrangement. Abnormally large Z bands, often with crystalline appearance, were present in this tumor. Myosin filaments and hence A bands were absent in all the cells studied. None of these contractile elements were present in the granular cell tumor.