On a CT scan of the thorax at the level of the sternal angle (Louis' angle), which of the following anatomical events occur simultaneously?
- A Bifurcation of the trachea into main bronchi, and junction of superior and inferior mediastinum ✓
- B Origin of the left coronary artery from the ascending aorta
- C Azygous vein arching over the right main bronchus to enter the SVC
- D Crossing of the thoracic duct from left to right behind the esophagus
Correct answer: A. Bifurcation of the trachea into main bronchi, and junction of superior and inferior mediastinum
Explanation
The sternal angle (of Louis) — the articulation between the manubrium and body of sternum at the level of T4/T5 intervertebral disc — marks several key landmarks simultaneously: bifurcation of the trachea (carina), the junction between superior and inferior mediastinum, commencement of the aortic arch, termination of the arch, and entry of the azygous vein. The azygous vein arches at the T4/T5 level but just above the right main bronchus, which itself begins at the carina. The left coronary arises at the level of the aortic sinuses (below the sternal angle).
Reference: BD Chaurasia's Human Anatomy, 8th ed.
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