Naturally Occurring Mediastinal Teratoma with Malignant Transformation in an Adult Male
A 47-year-old male presented with a mass in the anterior mediastinum. The mass was incidentally detected on a chest X-ray during the evaluation of a minor trauma that he had sustained two months prior to his presentation to Asan Medical Center (). As such, he was referred to our hospital for further evaluation. On his admission, a chest computed tomography (CT) scan was taken, which revealed an 8.9 cm×7.1 cm×8.0 cm heterogeneous mass in the anterior mediastinum. The mass was located anterior to the ascending aorta and the main pulmonary artery in the left hemithorax (). The mass was well demarcated without the overt signs of invasion to the adjacent structures. Also, there was neither pleural effusion nor lymph node enlargement. The differential diagnosis for this tumor based on the radiologic findings indicated a thymoma, a germ cell tumor, or a mediastinal sarcoma. Due to the proximity to the aorta and pulmonary artery, a pre-operative tissue biopsy was not considered. Instead, it was decided that the patient undergo an excision. The procedure was performed via median sternotomy. Intraoperatively, a well-encapsulated mass was identified and noted to arise from the thymus. There was neither adhesion nor invasion to the adjacent structures such as the aorta, pulmonary arteries, or lung parenchyma. The tumor was excised completely with negative margins for a residual tumor. The intraoperative frozen biopsy revealed a rhabdomyosarcoma. The postoperative course did not show any particular issue; the patient was discharged on postoperative day four. The final pathology report identified a mature teratoma with embryonal rhabdomyosarcoma (). Postoperatively, the patient underwent five cycles of chemotherapy and subsequent radiotherapy. However, six months after the primary surgery, the patient was found to have a nodule, which was highly suspected to be a tumor recurrence, in the upper lobe of the left lung. On the serial follow-up CT scans, we learned that the nodule had grown in size up to 17 mm in the 8 months after primary surgery. After discussions with the medical oncology team, we decided to treat him with another cycle of chemotherapy, which shrunk the size of the nodule down to 15 mm (). Eleven months after the primary surgery, the patient underwent wedge resection of the nodule, which turned out to be a metastatic rhabdomyosarcoma from the primary mediastinal mass. As of the writing of this paper, the patient has finished the seventh cycle of chemotherapy and has not shown another tumor recurrence.