Malignant nerve sheath tumor with rhabdomyoblastic differentiation arising from the acoustic nerve

A case of a malignant nerve sheath tumor with rhabdomyoblastic differentiation arising from the acoustic nerve in a 38 year old man is reported. At autopsy, the tumor was found to be extensively involved in the right cerebellopontine angle of the brain stem. Histologically, the tumor was composed mainly of spindle-shaped tumor cells proliferating in 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 cases 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 not have von Recklinghausen's disease.