On a standard PA chest radiograph, which structures form the left cardiac border from above downward?

• A Aortic knuckle, pulmonary trunk, left auricle, left ventricle ✓
• B Superior vena cava, right atrium, inferior vena cava
• C Left ventricle, left atrium, pulmonary trunk, aortic arch
• D Pulmonary trunk, ascending aorta, right ventricle

Explanation

From above downward the left border shows the aortic knuckle (arch), then the pulmonary trunk, then a small segment formed by the left auricle, and finally the large convexity of the left ventricle extending to the apex. The right atrium forms the right border, not the left. Recognising these four segments allows localisation of pathology such as left atrial appendage enlargement in mitral stenosis.

Reference: Gray's Anatomy for Students, 4th ed.

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