Intraoral malignant melanotic schwannoma. Ultrastructural evidence for melanogenesis by Schwann's cells.

Clinical and light and electron microscopic findings of one case of malignant melanotic schwannoma of the oral cavity are presented. The tumor recurred four times and developed submandibular metastasis. At autopsy, 24 months after manifestation of the initial symptoms, a hematogenous metastatic nodule was present in the liver. Peripheral melanotic schwannomas show a more malignant behavior than intraspinal examples. The Schwann's cell character of the individual tumor cells is demonstrated ultrastructurally by the presence of a prominent basal lamina, desmosomelike junctions between interdigitated elongated cell processes, and melanosomes in all stages of formation. These findings support the concept that neoplastic human Schwann's cells are capable of melanogenesis.