[Thymoma showing enlargement and reduction in size with inflammatory events;report of a case]

An 87-year-old male who had gone surgery for bladder cancer in 1994, was pointed out a mass in the anterior mediastinum by follow up in May 2007. Thereafter, no change in size of the mass had been noted. In February 2011, however, enlargement of the tumor with inflammation and right pleural effusion was found. While waiting for surgery, the patient experienced regression of the tumor, and the pleural effusion disappeared. Tumor excision and combined resection of the lung and pericardium were performed. Postoperative histopathological findings showed Masaoka stageI thymoma of type B1 according to the World Health Organization( WHO) Classification. Granulation due to old inflammation, precipitation of cholesterin crystals, hemorrhages, and necrosis were noted in the tumor. In the differential diagnosis of tumors in the anterior mediastinum with spontaneous regression, thymoma should be considered.