Mediastinal teratomas are germ cell tumors composed of tissue arising from more than one of the three primitive germ cell layers. Teratomas can contain teeth, skin, hair, bone, cartilage, or bronchial, intestinal, or pancreatic tissue. Rarely, a mediastinal teratoma contains fetal tissue and is therefore termed "immature." Immature teratomas are considered malignant because of their tendency to metastasize or invade local tissues. Teratomas account for 60-70% of mediastinal germ cell tumors. They are tumors of children or young adults. Unlike the other mediastinal germ cell neoplasms, which are universally malignant and occur almost exclusively in males, teratomas occur with equal frequency in both sexes.

Plain films may demonstrate calcifications in up to 26%, sometimes recognizable as teeth or bones. Teratomas typically manifest on CT as heterogeneous anterior mediastinal masses containing soft tissue, fluid collections, fat, calcification, or any combination of the four. Fat and calcification occur frequently, but lesions without fat or calcium are not uncommon. Fat-fluid levels, considered highly specific for the diagnosis of benign ("mature") teratoma, are uncommon. Surgical excision is curative.

Submitted by Chris Lebrun and Joon Yun, medical students.