Mediastinal teratomas are five times more common in adults than in children.
How exactly these lesions originate remains an area of speculation and debate. Cytogenetic studies, however, have confirmed an association with Klinefelter's Disease. In order to be classified as benign, the lesion can show no trace of immature mesenchymal elements. As far as gross and histologic features are concerned, mature cystic teratomas are identical to their gonadal counterparts. Typically these lesions present as large, polypoid masses with focal intimal calcification.