An unusual case of giant mediastinal teratoma with malignant transformation.

Mediastinal teratoma with malignant transformation is extremely rare. It consists of two components: (1) a pre-existing mature teratoma and (2) a nongerm cell malignant tumor. The radiologic appearances are usually straightforward, including a cystic mass and findings suggestive of malignancy. The authors describe an unusual case of giant mediastinal teratoma with malignant transformation in a 59-year-old patient. Radiographically, multiple spherical nodules appeared in the cyst that necessitated differentiation from hydatid disease. Computed tomography, magnetic resonance imaging, and operative and pathologic findings are provided.