What is the anatomy of the superior laryngeal nerve relevant to thyroid surgery?

Updated: Feb 27, 2020
  • Author: Pramod K Sharma, MD; Chief Editor: Arlen D Meyers, MD, MBA  more...
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The SLN has 2 divisions: internal and external. The internal branch provides sensory innervation to the larynx. It enters the larynx through the thyrohyoid membrane and, therefore, should not be at risk during thyroidectomy. The external branch provides motor function to the cricothyroid muscle and is at risk during thyroidectomy. This muscle is involved in elongation of the vocal folds. Trauma to the nerve results in an inability to lengthen a vocal fold and, thus, an inability to create a high-pitched sound.

The external branch of the SLN is probably the nerve most commonly injured in thyroid surgery. The rate of injury to the external branch of the SLN is estimated at 0-25%. This rate is probably underestimated, because the diagnosis is frequently missed.

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