A 3-month-old infant has recurrent choking with feeds and stridor. Barium swallow shows an oblique indentation on the posterior wall of the oesophagus. CT confirms the right subclavian artery arising as the last branch of the aortic arch and passing behind the oesophagus. Embryologically this results from:

• A Persistence of the distal right sixth arch artery
• B Persistence of both fourth arch arteries as double arches
• C Involution of the right fourth aortic arch segment between the right common carotid and right subclavian arteries ✓
• D Failure of involution of the distal portion of the right dorsal aorta

Explanation

Normally the right subclavian artery derives from the right fourth arch plus the right seventh intersegmental artery, with the intervening right dorsal aorta involuting. If the segment of the right fourth arch between the origins of the right common carotid and right subclavian arteries disappears, the right subclavian forms abnormally from the seventh intersegmental artery and distal right dorsal aorta, taking a retro-oesophageal course (dysphagia lusoria). Persistence of both fourth arches gives a double aortic arch ring instead.

Reference: Langman's Medical Embryology, 14th ed.

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Written and medically reviewed by the StethoPrep medical team.