MALIGNANT NERVE SHEATH TUMOR WITH RHABDOMYOBLASTIC DIFFERENTIATION ARISING FROM THE ACOUSTIC NERVE

A case of a malignant nerve sheath tumor with rhabdomyoblastic differe ntiation arising from the acoustic nerve in a 38 year old man is repor ted. At autopsy, the tumor was found to be extensively involved in the right cerebellopontine angle of the brain stem. Histologically, the t umor was composed mainly of spindle-shaped tumor cells proliferating i n hypercellular fascicles scattered with pleomorphic cells. The tumor cells were characterized by high mitotic activity and invasive growth. Occasional tumor cells had eosinophilic cytoplasm, which in a few cas es was cross-striated. Cytoplasmic interdigitations and a thick basal lamina were confirmed ultrastructurally. Immunohistochemical analysis revealed that some tumor cells were positive for myoglobin and desmin, but weakly positive or negative for S-100 protein. The patient did no t have von Recklinghausen's disease.