On a CT cross-section through the upper mediastinum at the level of the manubriosternal junction (sternal angle, T4-T5), which structure bifurcates at this level?
- A Aortic arch
- B Trachea ✓
- C Superior vena cava
- D Pulmonary trunk
Correct answer: B. Trachea
Explanation
The trachea bifurcates at the carina at the level of the sternal angle (angle of Louis, T4-T5 intervertebral disc). The sternal angle is a key anatomical landmark: it marks the upper border of the pericardium, the site of tracheal bifurcation, the level of the aortic arch, the second costal cartilage, and the beginning of the superior mediastinum division. The aortic arch lies at this level but does not bifurcate. The pulmonary trunk bifurcates lower, at the T5-T6 level.
Reference: BD Chaurasia's Human Anatomy, 8th ed.
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