The MR images demonstrate the complex nature of the lesion and verify location in the superior aspect of the mediastinum, displacing the heart inferiorly. In addition there is pericardial fluid (arrowhead) and ascites (arrow) on both US and MR imaging.
Mediastinal and pericardial teratomas are uncommon, representing 10% of all teratomas in children. Teratomas are usually benign tumors containing all three germ cells and as a result they appear complex on imaging. The differentiation from a prenatal congenital airway malformation can be difficult but should be suspected when the lesion is centered in the midline of the chest and displaces the heart inferior. Typically lung lesions will result in shift of the heart to the right or left of midline. Identification of calcium in the lesion would also exclude a lung malformation and reinforce the diagnosis of teratoma. These lesions have a more guarded prognosis; therefore, knowledge of this entity is essential for appropriate family counseling and fetal/postnatal therapy.