Abstract
We encountered a case of thymoma, which showed spontaneous regression after rapid growth. A 25-year-old male was admitted to our hospital because of fever and sudden severe pain in his chest and back. Chest radiograph, CT and MRI showed an anterior mediastinal tumor measuring 9.0×5.5×10.0cm. The histological findings of a CT-guided needle biopsy suggested that the tumor was a thymoma. One week after admission, the fever and pain disappeared and the tumor spontaneously decreased by 30% in maximum diameter. Total thymectomy was performed to confirm the diagnosis. Histopathologically, the tumor was composed of hemorrhagic and necrotic foci and a few viable tumor cells were found in the sub-capsular region which was diagnosed as thymoma, WHO classification type B1. Thymoma should be noted as a differential diagnosis when an anterior mediastinal tumor shows spontaneous regression.
