Mediastinal benign epithelioid schwannoma: a rare tumor in an unreported location

Benign epithelioid schwannoma is a very rare variant of schwannoma, that can pose a diagnostic challenge. The reported cases were predominantly located in dermal/subcutaneous tissue. Although conventional schwannoma occurring in the posterior mediastinum was common, to our knowledge, no mediastinal benign epithelioid schwannoma was reported in English literature. Herein, we presented a case of mediastinal benign epithelioid schwannoma in a 50-year-old Chinese male. Histologically, the tumor was well encapsulated and consisted of sheets of epithelioid tumor cells with mild cellular atypia set in fibrous or myxoid stroma. Immunohistochemically, the tumor cells were positive for S-100, GFAP and Vimentin, negative for cytokeratin, EMA, P63, Actin (SM), CD3, CD20, CD30, CD31, CD34, cytokeratin19, HMB45, CD68 and Desmin. Ki-67 proliferation index was approximately 2%. Based on morphologic features and the immunohistochemical staining, the tumor was diagnosed as an epithelioid schwannoma. It should be noted that epithelioid schwannoma may be also an important differential diagnosis in mediastinal tumor.