True congenital mediastinal thymic cyst.
D000790:Angiocardiography; D002675:Child, Preschool; D003560:Cysts; D005260:Female; D006801:Humans; D008476:Mediastinal Cyst / Q000151:congenital*; D013902:Radiography, Thoracic; D013950:Thymus Gland