A motorcyclist presents with unequal pulses and widened mediastinum on chest X-ray after trauma. CT aortography shows an intimal flap at the aortic isthmus (just distal to the left subclavian artery). This location is the most common site for traumatic aortic injury because:

• A It is the widest part of the aorta
• B Atherosclerotic plaques are most prevalent here
• C It is a point of fixation between the mobile aortic arch and the fixed descending aorta ✓
• D The ductus arteriosus inserts here, creating a wall weakness

Explanation

Traumatic aortic rupture occurs most commonly at the aortic isthmus (approximately 90% of cases), which represents the transition zone between the mobile aortic arch and the tethered descending thoracic aorta. During rapid deceleration, shear forces concentrate at this fixed point, causing intimal tears or pseudoaneurysm formation. The ligamentum arteriosum (not a wall weakness) also tethers this region. It has no specific predilection for atherosclerosis.

Reference: Grainger & Allison's Diagnostic Radiology, 7th ed.

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Written and medically reviewed by the StethoPrep medical team.