External Branch of the Superior Laryngeal Nerve

ramus externus nervi laryngei superioris

The external branch of the superior laryngeal nerve is the smaller motor branch that descends on the outer surface of the inferior pharyngeal constrictor to supply the cricothyroid muscle, the only intrinsic laryngeal muscle not supplied by the recurrent laryngeal nerve. The cricothyroid is the tensor of the vocal folds and its paralysis reduces high-pitched voice and vocal fold elongation. The nerve runs close to the superior thyroid artery pedicle.

Region: Neck

Clinical Relevance

Clinical Notes

The external SLN is at significant risk during thyroid surgery when the superior thyroid pedicle is ligated near the upper thyroid pole; the nerve runs close to the superior thyroid artery in approximately 20-25% of individuals, where it is most vulnerable. Injury produces a subtle but professionally devastating voice change: loss of high notes and reduced vocal range, particularly significant for singers and voice professionals. The nerve is protected by dissecting and ligating the superior thyroid artery vessels close to the thyroid capsule rather than at the upper pole origin.

Pathology

Common Injuries & Conditions

External SLN Injury in Thyroid Surgery

Ligation of the superior thyroid pedicle close to the upper thyroid pole risks including the external SLN with the artery, producing unilateral cricothyroid paralysis with loss of high-pitched phonation, reduced vocal range, and voice fatigue that is particularly debilitating for professional voice users; protected by meticulous superior pedicle dissection at the thyroid capsule.