Atypical cellular neurothekeoma

BACKGROUND. Neurothekeoma is a distinctive neoplasm that in the past was often lumped into the broad category of benign peripheral nerve sheath tumors. Atypical cellular neurothekeoma is a rare variant of this neoplasm. This atypical variant is characterized by features that can include the following: large sizes (up to 6 cm), deep penetration extending into skeletal muscle and/or subcutaneous fat, diffusely infiltrative borders, vascular invasion, high mitotic rate, and marked cytologic pleomorphism. METHODS. In this report, we describe the clinical, histopathologic, and immunohistochemical features of a case of atypical cellular neurothekeoma in a 34-year-old woman. RESULTS. This neoplasm demonstrated both the cellular subtype and intermediate subtype. In the cellular area, cells demonstrated rounded or ovoid nucleus with abundant cytoplasm. Mitotic activity ranged from 8 to 12 per 10 high-powered fields, and few individual cell necroses were present. In the intermediate area, cells were arranged as smaller nests with admixed abundant mucin. Mitotic activity ranged from 1 to 2 per 10 high-powered fields. These cells were negative for S100, epithelial membrane antigen, and smooth muscle actin. CONCLUSION. Dermatologists should be aware of the features of atypical cellular neurothekeoma. Although the atypical features raise concern about the malignant potential of this lesion, previous cases show that complete surgical excision of these lesions is curative.