A 55-year-old man with a history of hypertension presents with sudden tearing chest pain radiating to the back. CT angiography shows a dissection beginning just distal to the left subclavian artery. Which structure marks the anatomical boundary at this level?

• A Aortic valve
• B Bifurcation of the pulmonary trunk
• C Coronary sinus
• D Ligamentum arteriosum at the aortic isthmus ✓

Explanation

The aortic isthmus is a slight narrowing of the descending thoracic aorta just distal to the origin of the left subclavian artery, at the attachment of the ligamentum arteriosum (remnant of the ductus arteriosus). This is a common site for traumatic aortic injury due to differential deceleration, and for coarctation of the aorta in congenital anomalies. A Type B aortic dissection by the Stanford classification begins distal to the left subclavian origin at this isthmus.

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

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Written and medically reviewed by the StethoPrep medical team.