Fine Needle Aspiration Cytologic Features of Schwannomas

Kim, Sun Young; Nam, Hae Joo; Kim, Jung Hee; Cho, Young Rok; Kang, Yu Na; Lee, Sang Sook

Abstract

Schwannoma is a benign encapsulated nerve sheath tumor and is histologically characterized by a mixture of Antoni type A and B tissue. A preoperative diagnosis of schwannoma by fine needle aspiration cytology or by any other means is important to preserve clinically important nerves. Therefore, it is necessary to make a specific cytological diagnosis of nerve sheath tumor. However, there are a few reports regarding cytological features of schwannoma in Korea. We experienced seven cases of solitary schwannoma and here we report their characteristic cytological features with a review of literatures. The characteristic features of schwannoma on cytology were the presence of both Antoni type A and B tissue. The cytologic findings common to all cases of schwannoma generally corresponded to the histologic findings of Antoni type A tissue, consisting of fragments of tightly cohesive fascicles with variable cellularity. Dense fibrillary substances were found, along with palisading nuclei and Verocay bodies. Individual tumor cells consisted of cohesive cells having spindle or oval nuclei, with pointed ends and indistinct cell borders. Variation in nuclear size and shape was also present. The Antoni type B consisted of scattered wavy or short spindle cells and some histiocytes and lymphocytes in the abundant myxoid background with formation of microcysts. Immunohistochemistry for S-100 protein revealed a uniformly strong positive reaction and was helpful to make more accurate diagnosis of schwannoma.