[An autopsy case of extraskeletal osteosarcoma arising in the mediastinum].

A 90-year-old woman was admitted to our hospital with dyspnea and palpitation. A chest X-ray film showed an enlarged cardiac outline. An enhanced chest CT scan showed a 35-mm tumor in the superior portion of the mediastinum, a large amount of pericardial effusion, and bilateral lung nodules. She showed progressive deterioration and died 2 weeks after admission. At autopsy, there was a solid tumor measuring 35 mm in the anterior mediastinum between the aortic arch and trachea. The tumor invaded the left subclavian artery. The pathological autopsy finding was extraskeletal osteosarcoma arising from the mediastinum. Although extraskeletal osteosarcoma is uncommon and rarely develops in the mediastinum, it should be included in the differential diagnosis of a mediastinal mass.