Three weeks after total thyroidectomy, a 42-year-old woman reports that her voice sounds flat and she cannot sing or shout at high pitch. Fibreoptic laryngoscopy shows normal cord mobility on abduction and adduction. The structure most likely injured is:

• A Recurrent laryngeal nerve on one side
• B Hypoglossal nerve
• C Internal branch of the superior laryngeal nerve
• D External branch of the superior laryngeal nerve ✓

Explanation

The external branch of the superior laryngeal nerve supplies cricothyroid, the muscle that tenses the cords and produces high-pitched phonation. Its injury causes loss of vocal power and pitch with normal-looking cord movement on laryngoscopy, exactly as described. The nerve courses with the superior thyroid artery, so the artery must be ligated close to the thyroid capsule rather than at the trunk. Unilateral recurrent laryngeal palsy would show a paralysed cord, which excludes option A.

Reference: Sabiston Textbook of Surgery, 21st ed.

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