Which thoracic structure lies immediately posterior to the tracheal bifurcation (carina) at the level of the sternal angle (T4–T5)?

• A Left atrium ✓
• B Esophagus
• C Descending thoracic aorta
• D Thoracic duct

Explanation

The left atrium is the most posterior chamber of the heart and lies directly anterior to the esophagus and posterior to the tracheal bifurcation. Left atrial enlargement (e.g., in mitral stenosis) displaces and compresses the esophagus posteriorly (barium swallow shows posterior indentation) and can widen the carinal angle (Gothic arch / carinal angle >70 degrees indicates LA enlargement on chest X-ray). The esophagus lies posterior to the left atrium.

Reference: BD Chaurasia's Human Anatomy, 8th ed.

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Written and medically reviewed by the StethoPrep medical team.