On chest X-ray, which of the following features indicates LEFT atrial enlargement?
- A Bulging of the right heart border
- B Widening of the carinal angle (>70°) with splaying of the main bronchi ✓
- C Right ventricular enlargement causing filling of the retrosternal space
- D Enlargement of the aortic knuckle
Correct answer: B. Widening of the carinal angle (>70°) with splaying of the main bronchi
Explanation
Left atrial enlargement (LAE) is detected on chest X-ray by multiple signs: splaying of the carinal angle >70° (double contour on the right heart border), elevation of the left main bronchus, posterior displacement of the esophagus (on barium swallow), and prominence of the left atrial appendage on the left heart border. Bulging of the right heart border is caused by right atrial enlargement. Filling of the retrosternal space on lateral view is a sign of right ventricular enlargement. Enlargement of the aortic knuckle indicates aortic dilation or prominent aortic arch.
Reference: Grainger & Allison's Diagnostic Radiology, 7th ed.
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