Magnetic resonance imaging features of spontaneously regressed thymoma: report of 2 cases.

The authors describe 2 cases in which thymoma spontaneously regressed. The first patient was a 49-year-old woman with myasthenia gravis. A chest radiograph on admission showed an anterior mediastinal mass that spontaneously decreased in size as shown on a radiograph obtained 2 weeks later. Surgical removal of the mass was performed and the histopathologic examination showed a type B2 thymoma with marked coagulation necrosis in the central area. The second patient was a 46-year-old woman who was hospitalized due to chest and back pain. A chest radiograph on admission showed an anterior mediastinal mass and bilateral pleural effusion. The mass decreased in size and the effusion disappeared as shown on a chest radiograph obtained 2 months later. Computed tomography-guided biopsy was performed, and histopathologic examination revealed thymoma with marked necrosis. In both cases, dynamic contrast-enhanced magnetic resonance images showed peripheral ringlike enhancement of the mass. The clinical and radiologic features of spontaneously regressed thymoma may be different from those of common thymoma.