Intramedullary melanotic schwannoma

Abstract

Objective To study the clinicopathologic features, diagnosis, differential diagnosis, treatment and prognosis of intramedullary melanotic schwannoma (IMS). Methods and Results A 47-year-old male underwent an excision of thoracic intraspinal space-occupying lesion 6 years ago and was admitted to the hospital with a history of low back pain for one year. Spinal MRI revealed an intramedullary mass at the level of T_4-5. Gross total resection of the tumor was done. Histological findings revealed that spindle or epithelioid cells were arranged in sheets, nests or intersecting bundles. The cytoplasms contained varying amounts of melanin pigments. The nuclei were round to oval with small nucleoli but no mitotic figures. Immunohistochemically, the tumor cells were positive for S-100 protein (S-100), HMB45, Melan-A, and Collagen Ⅳ. They were negative for epithelial membrane antigen (EMA), glial fibrillary acidic protein (GFAP), CD57, progestrone receptor (PR), desmin (Des) and myogen. Ki-67 labeling index was about 10%. Ultrastructural findings revealed that the tumor cells were surrounded by continuous basal lamina, and melanin granules in different stages of maturity were present in the cytoplasms. Final pathological diagnosis was IMS. No recurrence of tumor was found after follow-up for 18 months.  Conclusions Intramedullary melanotic schwannom is a rare neoplasm. The diagnosis relies on its morphological characteristics, immunophenotype and ultra microstructure, and should be differentiated from melanoma, melanocytoma and pigmentary neurofibroma. The biologic behavior of the tumor is difficult to predict. It may occur local recurrence. Therefore, long-term follow-up is required.

DOI: 10.3969/j.issn.1672-6731.2016.09.013