snowman sign

A rounded, figure-of-eight-like cardiac contour and superior mediastinum seen on a plain anteroposterior chest film of infants with type 1 supracardiac total anomalous drainage of the pulmonary veins accompanied by common pulmonary vein dilatation and supracardiac drainage; the unique contour is produced by the dilated anomalous (vertical) veins, the left innominate vein and superior vena cava which form the head and the right atrium, which forms the body; a similar appearance may be caused by a prominent thymic shadow

snowman sign

Pediatric cardiology A rounded, figure-of-eight-like cardiac contour seen on a plain AP CXR of infants with total anomalous drainage of the pulmonary veins accompanied by common pulmonary.
vein dilatation and supracardiac drainage; the unique contour is produced by the dilated left ventricle and superior vena cava and left innominate vein; a similar appearance may be caused by a prominent thymic shadow