A branch of the vagus nerve (CN X), the recurrent laryngeal nerve follows an asymmetric course on each side. The right RLN loops under the right subclavian artery and ascends in the right tracheoesophageal groove. The left RLN takes a longer path, looping under the aortic arch at the level of the ligamentum arteriosum before ascending in the left tracheoesophageal groove. Both nerves supply all intrinsic laryngeal muscles except the cricothyroid, and provide sensory innervation below the vocal folds.
The RLN is the most surgically consequential nerve in thyroid and parathyroid surgery. Unilateral injury produces ipsilateral vocal fold paralysis with hoarseness and aspiration risk. Bilateral injury, where both vocal folds assume a paramedian position, causes life-threatening upper airway obstruction requiring emergency tracheostomy. The nerve's position varies: it may be non-recurrent on the right (0.5-1%), usually with an aberrant subclavian artery, making identification during right thyroid surgery critical. Intraoperative neuromonitoring using electromyographic endotracheal tubes is standard practice.
The most feared complication of thyroid surgery, occurring in 0.5-5% of operations, producing hoarseness and aspiration risk with unilateral injury, or airway emergency requiring tracheostomy with bilateral injury; risk is highest for malignant goitre, reoperative thyroid surgery, and substernal extension.
Left RLN palsy from mediastinal pathology (apical lung cancer, aortic aneurysm, mediastinal lymphadenopathy) producing hoarseness is designated Ortner syndrome; chest CT and bronchoscopy are mandatory investigations when no surgical cause is identified.
