Case report of malignant primary nerve sheath tumor arising in the female pelvis.

This paper reports a malignant primary nerve sheath tumor (MPNST) which originated in the obturator nerve in a 54-year-old woman. That the tumor originated in the nerve sheath is supported by the site of occurrence, which was consistent with the obturator nerve, an arrangement of cells similar to that in schwannoma, and that extracellular basement membrane was noted ultrastructurally. This tumor was classified not as malignant schwannoma but as a nerve sheath fibrosarcoma because the matrix of tumor tissues contained abundant mucinous materials, some tumor cells were fibroblastic, and the clinical change was rapid. In general, with plexiform neurofibroma there is a familial manifestation and it occurs as a complication of von Recklinghausen's disease, associations not demonstrated in this patient. From these findings, this tumor is considered to be an extremely rare nerve sheath fibrosarcoma which originated from a malignant change in a sporadic and solitary plexiform neurofibroma.