Question

The reason for the long left recurrent laryngeal nerve is due to the persistence of which arch artery?

• A. 3^rd arch
• B. 4^th arch
• C. 5^th arch
• D. 2^nd arch

Answer 1

The Correct Option is B

Embryology mnemonic angle. Trace the left recurrent laryngeal nerve and you find it hooking beneath the arch of the aorta. The clue is to remember the fate of each pharyngeal arch artery: the third becomes the carotid, the fourth becomes the aortic arch on the left and the proximal right subclavian, the fifth disappears, and the sixth gives the pulmonary arteries plus the ductus arteriosus. As the heart and great vessels descend into the thorax during development, the left recurrent laryngeal nerve gets caught beneath the persisting left fourth arch, which is the definitive arch of the aorta. That long downward course is why a left aortic arch aneurysm or a mediastinal mass can cause hoarseness (Ortner syndrome). The right nerve loops only around the right subclavian (fourth arch) and stays higher. Hence the answer is the fourth arch. Reference: Langman's Medical Embryology, 13e, pp 88, 239.