During thyroid surgery, the external branch of the superior laryngeal nerve (EBSLN) is at risk of injury. What specific voice change would a singer report if this nerve were transected, and which muscle does it innervate?

• A Hoarseness and paralysis of all intrinsic muscles; recurrent laryngeal nerve territory
• B Loss of cough reflex and subglottic sensation; internal branch of SLN
• C Inability to abduct cords; posterior cricoarytenoid muscle
• D Loss of high-pitched singing notes and inability to tense cords; cricothyroid muscle ✓

Explanation

The external branch of the superior laryngeal nerve (EBSLN) exclusively innervates the cricothyroid muscle — the only intrinsic laryngeal muscle supplied by a branch of SLN rather than the recurrent laryngeal nerve. The cricothyroid muscle elongates and tenses the vocal cords to produce high-pitched sounds (increases fundamental frequency). Its injury classically presents as inability to reach high notes, loss of 'head voice,' vocal fatigue, and a slight monotone quality; standard conversational voice may be preserved. This is the 'SLN palsy' well recognized in singers (Amelita Galli-Curci is the classic historical case). The internal branch of SLN provides supraglottic sensation.

Reference: Dhingra Diseases of Ear, Nose and Throat, 7th ed.

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Written and medically reviewed by the StethoPrep medical team.