How are superior laryngeal nerve (SLN) injuries due to thyroid surgery prevented?

Updated: Feb 27, 2020
  • Author: Pramod K Sharma, MD; Chief Editor: Arlen D Meyers, MD, MBA  more...
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Answer

Answer

The external SLN branch travels inferiorly along the lateral surface of the inferior constrictor until it terminates at the cricothyroid muscle. This branch is intimately related to the superior thyroid artery, though its exact relation to the artery varies.

Data from a recent cadaveric study suggested that the nerve may cross the superior thyroid artery more than 1 cm above the upper pole of the thyroid gland (42%), less than 1 cm above the upper pole (30%), or under the upper pole (14%). In some people, the nerve runs dorsal to the artery and crosses only its terminal branches after the artery has ramified (14%). A critical area 1.5-2 cm from the thyroid capsule is described. In this area, the external branch of the SLN is most intimately involved with the branches of the superior thyroid artery.

Most surgeons agree that identifying the SLN, in contrast to the RLN, is unnecessary. Instead, ligate the terminal branches of the superior thyroid artery as close to the thyroid capsule as possible to avoid damaging the nerve. Electrophysiologic monitoring of the SLN is described, but it is not recommended for routine use.

Direct trauma to the cricothyroid muscle can cause fibrosis and poor muscle function, which may result in a presentation similar to that of a patient with an injury to the external branch of the SLN, even when the nerve is preserved. Therefore, dissect carefully near this muscle and avoid electrocautery damage when possible.


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