A cyanotic 2-month-old baby has a single loud S2, no murmur, and CXR shows an 'egg on side' cardiac silhouette with narrow mediastinum. ECG shows right-axis deviation and right ventricular hypertrophy. Echocardiography is ordered. Which diagnosis does this presentation most strongly suggest?
- A Tetralogy of Fallot — boot-shaped heart with right ventricular hypertrophy
- B Transposition of the great arteries (TGA) — egg-on-side/egg-on-string cardiac silhouette from narrow vascular pedicle ✓
- C Total anomalous pulmonary venous connection (TAPVC) — figure-of-8 or snowman appearance
- D Truncus arteriosus — plethoric lung fields with cardiomegaly
Explanation
Transposition of the great arteries (d-TGA) classically shows the 'egg-on-side' (or 'egg-on-a-string') CXR appearance: the cardiac silhouette is oval/egg-shaped with a narrow superior mediastinal waist because the aorta (anterior) and main pulmonary artery (posterior) are parallel rather than crossed, creating a narrow vascular pedicle. This is pathognomonic for TGA. ECG shows right ventricular hypertrophy (normal in neonates, persistent in TGA). The single loud S2 is the anteriorly placed aortic valve. TGA requires balloon atrial septostomy (Rashkind) acutely and arterial switch operation (Jatene) within 2 weeks. TOF gives boot-shaped heart. TAPVC (supracardiac) gives snowman/figure-8.
Reference: Ghai Essential Pediatrics, 10th ed.
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Written and medically reviewed by the StethoPrep medical team.