Histogenesis,differential diagnosis and prognosis of melanotic schowannoma

Purpose:To study the histogenesis,the differential diagnosis and the prognosis of melanotic schwannoma.Methods:The age of the patients was 4,17,28 years old, respectively.Three cases of melanotic schwannoma were examined using histologic (HE), immunohistochemical (ABC method) and electron microscopic techniques. Results: The diameter of tumor was 2,4,8, respectively. Histological examination showed pigmented spindle cells arranged in interlacing fascicles and occasional nuclear palisading. The pigmented polygonal cells were loosely arranged in sheets. After bleaching, the nuclei were oval and some showed slight pleomoprohism with prominent nucleoli, and nuclear mitoses were found. There was local invasion in two cases. Immunohistochemical stains for S 100 protein, HMB45, Vim, Leu 7, NSE were positive. Ultrastructrual examinations showed a lot of melanosomes in all stages of development and seldom basal lamina. Conclusions:①Melanotic schwannoma usually occurs in young adults. Most of the tumors are benign or only potentially malignant. Malignant MS is rare,and require follow up. ②MS originate from neural crest with a proliferation of the bipotential cell.