Chest X-ray Signs of Left Atrial Enlargement

The chest radiograph is a classic (if now largely superseded by echocardiography) tool for detecting left atrial (LA) enlargement. The correct answer is 1 and 3 only.

• 1. Straight left heart border — Normally the left heart border shows a gentle concavity below the pulmonary trunk (the "aortopulmonary window/left atrial appendage" segment). As the LA (and often its appendage) enlarges, it bulges outward and fills in this concavity, producing a straight or convex left heart border on the frontal film. Correct — this is a genuine, well-recognised sign of LA enlargement.
• 2. Rounding of the left heart border — A rounded, globular left heart border is the radiological signature of left ventricular dilatation, where the LV apex becomes more spherical and displaces laterally and downward. This is a distinct chamber from the left atrium and is not how LA enlargement presents. Incorrect.
• 3. Double cardiac shadow (double density/double contour sign) — When the LA enlarges, it expands posteriorly and to the right, projecting through the normal right heart border (formed by the right atrium). This creates a second, overlapping density visible within or just beyond the right heart border on the PA film. Correct — this is one of the most specific classic signs of LA enlargement.
• 4. Widening of the angle of carina — Splaying of the carinal angle occurs when the LA becomes markedly and chronically enlarged (as in long-standing mitral stenosis), elevating the left main bronchus and increasing the tracheobronchial angle beyond ~90°. However, this is a late and less specific sign, seen only with gross LA enlargement, and is not included among the core/classic signs expected in this answer code. Not included in the correct combination for this question.

Conclusion: The straight left heart border and the double cardiac shadow (statements 1 and 3) are the direct, specific radiographic hallmarks of left atrial dilatation, making option "1 and 3 only" the correct answer. Rounding of the left heart border reflects left ventricular, not atrial, enlargement, and carinal widening is an inconsistent, late finding rather than a core defining sign.