Laryngeal innervation

The recurrent laryngeal nerve (RLN) and the superior laryngeal nerve (SLN) are branches of the vagus nerve (CN X). Injury to them may occur during thyroid surgeries. The SLN (external branch) innervates the cricothyroid muscle, which tenses and adducts the vocal cords. Injury to the nerve can produce changes in voice quality, but is generally not dangerous. Injury to the RLN is of more consequence, as it innervates all of the intrinsic muscles of the larynx, except for the cricothyroid muscle which is innervated by the SLN. A unilateral RLN injury produces abductor vocal cord paralysis, so the affected cord assumes a paramedian position which causes postoperative hoarseness (may be a delayed presentation of a few weeks). Bilateral vocal cord paralysis, on the other hand, can manifest as partial vs. complete airway obstruction. Symptoms include respiratory distress with stridor. The situation often necessitates emergent reintubation or tracheostomy.