Melanotic schwannoma arising in association with nevus of Ota: 2 cases suggesting a shared mechanism.

Melanotic schwannoma is a rare markedly pigmented peripheral nerve sheath tumor comprising cells with prominent melanization and schwannian features. The psammomatous variety is associated with Carney complex, a multiple neoplasia syndrome with spotty skin pigmentation. We present the first 2 reported cases of melanotic schwannoma arising in patients with a history of nevus of Ota, a rare dermal melanosis believed to represent a failure of melanocyte migration to the epidermis during embryogenesis. Case 1 involves a 40-year-old woman with a 1.8-cm, deeply pigmented, trigeminal nerve mass and pigmentation of the maxillary sinus mucosa and bone. Case 2 involves a 53-year-old woman with a 1.5-cm mass adjacent to the clavicle. Microscopically, both masses consist of partially encapsulated epithelioid and spindle cells with abundant melanin pigment, arising in association with peripheral nerves. Morphological, immunohistochemical, and ultrastructural features support a diagnosis of melanotic schwannoma. No psammoma bodies are noted, and neither patient exhibits any additional features of Carney complex. Melanotic schwannoma is most often benign but has been associated with malignant behavior in some cases. Distinguishing this nerve sheath tumor from malignant melanoma can be difficult but is of great clinical importance due to differences in prognosis and treatment.