Melanotic schwannoma: a case report.

A case of melanotic schwannoma of the sacral region, studied with electron microscopy and immunohistochemistry, is reported. Melanosomes in all stages of formation were ultrastructurally demonstrable in neoplastic cells, which showed prominent basal lamina and interdigitating cytoplasmic processes. These findings support the Schwann cell origin of the tumor and indicate that Schwann cells are capable of melanin production. The immunohistologic examination showed the absence of neoplastic cells for all antigens tested (S-100 protein, glial fibrillary acidic protein, lysozyme, alpha 1-antitrypsin, alpha 1-antichimotrypsin, keratin). Apart from questioning the nature of the tumor, S-100 protein absence could raise doubts on its benign course. In the reported case, no local recurrence or distant metastases have been recorded 2 years after surgery.