During thyroidectomy, a surgeon finds that the right recurrent laryngeal nerve cannot be identified in its usual position in the tracheo-oesophageal groove. A nerve is eventually found entering the larynx directly from a more horizontal, almost transverse course. Which vascular anomaly explains this operative finding?

• A Coarctation of the aorta with enlarged intercostal collaterals
• B Right-sided aortic arch with mirror-image branching
• C Persistent left superior vena cava
• D Aberrant right subclavian artery arising distal to the left subclavian artery ✓

Explanation

When the right subclavian artery arises abnormally as the last branch of the arch, passing behind the oesophagus, the embryological ligamentum arteriosum does not drag the right recurrent laryngeal nerve down into the chest. The nerve then runs directly from the vagus to the larynx as a non-recurrent right laryngeal nerve, taking a transverse course at the level of the thyroid. This anomaly occurs in about 0.5 to 1 percent of patients and increases the risk of inadvertent nerve injury.

Reference: Gray's Anatomy, 42nd ed.

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Written and medically reviewed by the StethoPrep medical team.