Primary intracranial malignant schwannoma of trigeminal nerve. A case report with review of the literature.

The authors report a rare case of primary intracranial malignant schwannoma of the trigeminal nerve occuring in a 30-year-old woman without von Recklinghausen's neurofibromatosis (VRNF). The tumour arose from the intracranial part of the left trigeminal nerve, without skull base destruction. The tumour was partially removed operatively, followed by focal 50 Gy irradiation, but unfortunately the tumour showed rapid regrowth. A second operation was attempted, but she died of cerebral infarction soon after operation. Histologically, the original tumour was characterized by the presence of foci of extremely high cellularity, pleomorphism and mitosis in an otherwise typical benign schwannoma. Immunohistochemically, the tumour cells were positive for S-100 protein even in the atypical areas, suggesting the tumour to be of Schwann cell origin. However, the recurrent tumour was composed of undifferentiated spindle cells, which were negative for S-100 protein. Thus, it is possible to consider that the S-100 protein expression could reflect the degree of differentiation of Schwann cells. Furthermore, the postoperative irradiation might have exacerbated the malignant progression in the present case.