Less commonly they may occur in young adults and also in the older age group. It is difficult to assess the real incidence of rhabdomyosarcoma because of differences in diagnostic criteria. Rhabdomyosarcomas may originate anywhere in the body, most frequently in the head and neck region, the extremeties, the genitourinary tract and the retroperitoneum. Embryonal rhabdomyosarcoma, the most commonly occurring variant, develops mainly in children, rarely in the older age group. By light microscopy rhabdomyosarcomas are poorly differentiated, cellular tumors exhibiting cellular and nuclear pleomorphism and spreading to adjacent tissues.
Mitotic figures are frequent and hemorrhagic areas and necrotic foci are often noticeable.
The tumor cells are elongated, spindle-shaped and are embedded in a loose edematous myxoid stroma. Depending on the extent of differentiation they may resemble striated muscle cells. In many cases scattered cells with hyperchromatic nuclei and acidophilic cytoplasm can be recognized. These cells are regarded as rhabdomyoblasts and their presence can assure the diagnosis. The presence of cross striations in the tumor cell cytoplasm is diagnostic.