The superior laryngeal nerve arises from the inferior (nodose) ganglion of the vagus and divides into an internal branch and an external branch at the level of the hyoid bone. The internal branch, the larger of the two, carries sensory fibres to the laryngeal mucosa above the vocal folds and pierces the thyrohyoid membrane alongside the superior laryngeal artery. The external branch, smaller and motor, supplies the cricothyroid muscle and runs closely with the superior thyroid vessels near the superior thyroid pole.
The external branch of the superior laryngeal nerve (EBSLN) is the surgically critical branch, at risk during ligation of the superior thyroid pole vessels in thyroidectomy. EBSLN injury abolishes cricothyroid function, reducing the ability to elevate vocal pitch and project the voice, which is professionally catastrophic for singers and public speakers. Cernea classification describes the EBSLN's variable relationship to the superior thyroid pedicle. Injury to the internal branch impairs laryngeal sensation above the folds, causing silent aspiration without coughing.
Superior pole vessel ligation without identification of the EBSLN injures the nerve in approximately 1-25% of operations depending on technique and anatomy; the result is reduced vocal pitch range and projection, career-ending for professional voice users and detected by voice analysis and laryngoscopy.
Disruption of the internal superior laryngeal nerve reduces supraglottic sensation, producing silent aspiration of liquids and solids particularly in the elderly or post-stroke patients, requiring swallowing rehabilitation and dietary modification.
