[Concurrent Thymoma and Mature Teratoma in the Mediastinum].

A 41-year-old asymptomatic male with no significant medical history had a heterogenous cystic tumor with a diameter of 5.1 cm containing fatty density in the anterior mediastinum and a nearby homogeneous enhancing nodule with a diameter of 2.0 cm were observed on chest computed tomography( CT). A malignant teratoma with mediastinal lymph node metastasis was suspected preoperatively. The tumor was completely removed via median sternotomy, with concomitant resection of the lung, pericardium, and right phrenic nerve. Postoperative pathological examination revealed a large mature cystic teratoma, 6.0 cm in diameter, and a small nodule, 3.7 cm in diameter, diagnosed as stageⅠ, type B2 thymoma. The postoperative course was uneventful, with no recurrence 30 months later. The simultaneous occurrence of mature teratoma and stageⅠthymoma is extremely rare. When suspecting a teratoma with small satellite nodules preoperatively, consideration of concurrent small thymoma is suggested.