A case report of sclerosing thymoma of the anterior mediastinum: an exceedingly rare morphology.

The morphology of thymoma is diverse, although 5 basic subtypes are recognized in the World Health Organization classification system. Sclerosing thymoma was first documented in 1994 and to date only 13 cases have been reported. Sclerosis itself is considered to be an ancient change and can occur in various histological subtypes. Herein, we present a case of a 62-year-old woman incidentally found to have an anterior mediastinal mass, 31 × 24 × 17 mm in size, without an associated autoimmune disease such as myasthenia gravis. The mass was finally diagnosed as sclerosing thymoma derived from type A thymoma. Intraoperative pathological examination using a limited amount of sample did not allow a definitive diagnosis of thymoma in this case. When dealing with fibrous lesions observed in limited samples such as biopsy and intraoperative frozen specimens, recognizing sclerosing thymoma is important since there are several disease entities accompanying fibrosis in the anterior mediastinum.