A case of middle mediastinal thymoma.

A 56-year-old male was referred to our clinic after an abnormality was found on chest X-ray films during regular health examinations. Middle mediastinal tumor was detected by computed tomography, he was admitted for surgical treatment. The tumor was removed by surgery, and a pathological diagnosis of mixed thymoma (type AB, the World Health Organization Classification) was made by examining the resected specimen. Because the tumor had invaded to its capsule, it was considered to be a stage II thymoma according to the Masaoka staging system. Postoperative radiation therapy (50 Gy) was administered to the mediastinum. The patient has remained disease-free and without any recurrence as of 9 years and 8 months after the operation. We herein present our findings because middle mediastinal thymoma is incredibly rare.