Congenital thymic cyst: prenatal sonographic and postnatal magnetic resonance findings

A case of congenital thymic cyst was investigated by prenatal sonography and studied after birth by magnetic resonance imaging (MRI), computerized tomography (CT) and sonography. Prenatal sonography showed a unilocular cyst approximately 3 cm in diameter in the left hemithorax. The cyst size remained unchanged over the course of gestation. Postnatal sonography and CT showed a cyst in the anterior mediastenum adjacent to the left thymic lobe. With MRI, the cyst was hypointense on T1-weighted images and hyperintense on T2-weighted images, clearly localized within the left thymic lobe. The size of the cyst gradually diminished on a follow-up sonography.