A case of a resected mediastinal thymoma with spontaneous regression

We report a case of a resected thymoma with preoperative spontaneous regression in a 76-year-old woman. Only 13 cases of spontaneous regression of thymomas have been reported in the English literature, including this one.

During a regular checkup, chest radiography revealed an abnormal shadow in the right hilum of an asymptomatic 76-year-old woman. Chest computed tomography (CT) revealed a 41 × 32 mm anterior mediastinal tumor. Six months later, she presented with sudden anterior chest pain. Chest CT revealed that the tumor had grown slightly to 43 × 42 mm. Chest CT performed one day preoperatively revealed that the tumor had rapidly shrunk in one month (to 26 × 23 mm) and contained areas of necrosis. Surgical resection was performed to obtain a definitive diagnosis. The postoperative diagnosis was a type AB thymoma, classified as pathological stage I (Masaoka's classification) with intratumoral necrosis.

The spontaneous regression in the present case might have been related to the necrosis observed in the tumor. We postulate that vascular occlusion due to minute thromboembolism resulted in tumor necrosis. This might have caused inflammation around the tumor, thereby causing the patient's chest pain.

Thymomas should be included in the differential diagnosis of mediastinal tumors with necrosis that spontaneously regress, and surgical resection is required despite such regression.