[Mediastinal Thyroid Carcinoma;Report of a Case].

71-year-old woman was pointed out to have an asymptomatic mediastinal tumor. Chest computed tomography(CT) showed a well-demarcated mass measuring 7 cm in diameter in the anterior mediastinum. We resected the mass through a median sternotomy. The tumor had a clear margin without invasion to the surrounding tissue and did not show continuity with the cervical thyroid gland. Histopathologically, the tumor was diagnosed as follicular thyroid carcinoma with capsular invasion. This is an exceptionally rare case.