Question

The 'Egg on side' (egg lying on its side) appearance on a chest radiograph is seen in:

• A. Tricuspid atresia
• B. Tetralogy of Fallot
• C. Total anomalous pulmonary venous connection (TAPVC)
• D. Transposition of the great arteries

Hint:

Think of the great vessels stacked front to back, narrowing the mediastinal pedicle.

Answer 1

The Correct Option is D

Step 1: The question asks about a classic cardiac silhouette sign on chest X-ray in congenital heart disease.
Step 2: In transposition of the great arteries (TGA), the aorta lies directly anterior to the pulmonary artery instead of side by side. This narrows the superior mediastinum because the great vessels overlap on the frontal view. The thymus is also often small.
Step 3: The combination of a narrow vascular pedicle (superior mediastinum) with a globular, enlarged cardiac shadow produces an oval heart shadow that looks like an egg lying on its side, hence 'egg on side' or 'egg on a string'.
Step 4: Why the others are wrong. Tetralogy of Fallot gives the 'boot-shaped' heart (coeur en sabot) from right ventricular hypertrophy and a concave main pulmonary artery segment. TAPVC of the supracardiac type gives the 'snowman' or 'figure of 8' appearance. Tricuspid atresia typically shows a small or normal heart with reduced pulmonary vascularity and left axis deviation, not an egg shape.
Step 5: Therefore the egg on side appearance points to transposition of the great arteries.
Answer: Option D, Transposition of the great arteries.