Thymoma with spontaneous regression and disappearance of pleural effusion.

A 31-year-old woman was admitted to our hospital with sudden onset of chest pain. Chest radiography and computed tomography (CT) on admission showed an anterior mediastinal tumor with left pleural effusion, which was diagnosed as an inoperable malignant mediastinal tumor. However, 3 weeks after admission CT showed that the tumor was diminishing and the pleural effusion had disappeared without any treatment. CT-guided needle biopsy was performed, but diagnosis was impossible because most of the specimen was necrotic. A biopsy during video-assisted thoracic surgery was then performed. The intraoperative finding showed that the tumor was round, well mobilized, and did not invade adjacent structures. It was then assumed to be a benign teratoma that had been ruptured into the thoracic cavity. The operation was converted to a thoracotomy to resect it, but it could not be completely resected because of inflammatory adhesions to the mediastinum. Two months later, total thymectomy was performed through a median sternotomy because the tumor was pathologically diagnosed as a thymoma.