A ruptured mature teratoma in which follow-up computed tomography observation at short intervals was useful for a definitive diagnosis.

Rupture of mature mediastinal teratomas occasionally occurs, necessitating prompt surgical treatment. However, the clinical presentation of a ruptured teratoma can resemble that of pneumonia and/or pleuritis. We report a case of mediastinal teratoma rupture, in which follow-up computed tomography (CT) a short-interval after the first CT was useful for definitive diagnosis. The patient was a 29-year-old male who presented with chest pain. CT-revealed a fat-containing cystic tumor in the left anterior mediastinum and a small pleural effusion with consolidation of the lower lobe of the left lung. The diagnoses of pneumonia, pleuritis and teratoma rupture were considered, and antibiotic therapy was initiated to begin with. Eighteen hours later, a repeat CT-revealed an increase in the soft tissue area of the chest wall adjacent to the tumor, which led to the definitive diagnosis of ruptured teratoma, and immediate resection was performed. The histological diagnosis was a mature teratoma, and rupture was confirmed by the high lipase level in the pleural fluid. The patient's postoperative course was uneventful.