A chest x-ray of a child shows Snowman sign. The condition which causes this sign in this child is:

Enlargement of the anomalous channels in Total Anomalous Pulmonary Venous Connection (TAPVC) results in distinct radiological signs. The snowman sign or figure-eight appearance on chest radiography is the classic appearance of supracardiac TAPVC. The upper pa is formed by the dilated left veical vein, innominate vein, and right superior vena cava. The dilated right ventricle and atrium form the lower poion. Ref: Pediatric Cardiovascular Medicine edited by James H. Moller, Julien I. E. Hoffman, 2012, Page 479; Moss and Adams' hea disease in infants, children, and Adolescents: Volume 1, 2007, Page 780.