Fetal mediastinal teratoma: Misinterpretation as congenital cystic lesions of the lung on prenatal ultrasound.

Congenital mediastinal teratoma can lead to development of hydrops fetalis and may be misinterpreted on ultrasound. In this case report, ultrasound revealed severe fetoplacental hydrops, moderate posthemorrhagic hydrocephalus, and multiple pulmonary cysts suggesting cystic adenomatoid malformation and displacement of the heart to the left side. Autopsy of the hydropic 24-weeks male fetus showed a large cystic-solid mediastinal mass that was consistent with nonmetastatic immature teratoma. It also demonstrated thymic, cardiac and pulmonary hypoplasia, and confirmed the germinal matrix-intraventricular hemorrhage. Accurate prenatal diagnosis of mediastinal teratoma may be achieved by a careful Doppler ultrasound assessment that also allows evaluating the fetal outcome.