During thyroidectomy, the external branch of the superior laryngeal nerve (EBSLN) is at risk. Damage to this nerve causes which specific functional deficit?

• A Hoarseness and breathy voice due to vocal cord palsy
• B Loss of high-pitch phonation and inability to tense the vocal cord due to cricothyroid muscle paralysis ✓
• C Loss of sensation in the supraglottis, causing aspiration
• D Bilateral vocal cord palsy causing respiratory distress

Explanation

The external branch of the superior laryngeal nerve (EBSLN) innervates the cricothyroid muscle — the only intrinsic laryngeal muscle outside the larynx. The cricothyroid tenses and elongates the vocal cord (increasing pitch), acting as the primary pitch-control muscle for high notes. Injury, which can occur where the EBSLN crosses the superior thyroid artery near the upper thyroid pole, produces loss of high-pitch (falsetto) phonation and subtle voice fatigue — clinically important for professional singers (the 'Amelita Galli-Curci syndrome'). The recurrent laryngeal nerve innervates all other intrinsic laryngeal muscles; its damage causes vocal cord palsy (hoarseness). Sensation above the cords is via the internal branch of the SLN.

Reference: BD Chaurasia's Human Anatomy, 8th ed.

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Written and medically reviewed by the StethoPrep medical team.