On a cross-sectional CT at the level of T4, which structure passes from the right side to the left, arching posterior to the left main bronchus before descending on the left side of the vertebral column?

• A Thoracic duct ✓
• B Azygos vein
• C Hemiazygos vein
• D Accessory hemiazygos vein

Explanation

The thoracic duct begins at the cisterna chyli at L2, ascends on the right of the vertebral column, crosses to the left at T4–5 (posterior to the esophagus and left of the aortic arch), then ascends on the left side to drain into the left venous angle. The azygos vein arches over the right main bronchus at T4 to enter the superior vena cava but remains on the right. The hemiazygos and accessory hemiazygos are left-sided and drain into the azygos across the midline at T8–9 and T7–8 respectively.

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

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Written and medically reviewed by the StethoPrep medical team.