[A case of mediastinal seminoma undergoing extremely cystic degeneration].

A-25-year-old male had an abnormal shadow on chest X-ray. CT and MRI films revealed a cystic lesion, with irregular nodules in the right anterior mediastinum. A cystic teratoma was suggested. Antero-axillary thoracotomy revealed a cystic lesion originating from the right lobe of the thymus. The lesion was extirpated, along with the right lobe of the thymus. The cystic part of the lesion, filled with brown fluid, was occupied by several masses originating from the wall of the tumor. Pathologically, the lesion was diagnosed as a seminoma undergoing cystic degeneration. The patient was given post-operative irradiation of 20Gy. No apparent recurrence has been detected 33 months after surgery. Mediastinal seminomas generally occur as a solid tumor consisting of stroma and tumor cells. However, this case report suggests that mediastinal seminomas may undergo extremely cystic degeneration.