'Egg on Side' Appearance is seen in:

Chest Xray in a case of transposition of great aeries shows 1) appearance of an egg on its side because the aoa and pulmonary aery shadows are overlapping producing a narrow pedicle 2)Concave pulmonary aery segment, although vascularity in the lungs is increased unless transposition is associated with pulmonary stenosis. Ref: The Great Ormond Street Colour Handbook of Paediatrics and Child Health By Stephan Strobel, Peter Smith, Page 127; The Chest X-Ray By Francis Burgener, Mati Kormano, Page 16, 23; Pediatric Cardiovascular Medicine By James H. Moller, Page 479