Abstract
The external branch of the superior laryngeal nerve (EBSLN) provides motor function to the cricothyroid muscle (CTM). EBSLN damage produces changes in voice quality and projection. Intraoperative neuromonitoring (IONM) in thyroid surgery aims to optimize EBSLN control during dissection. We prospectively collected the data of 88 consecutive patients who underwent total thyroidectomy with IONM from July 2019 to December 2019. IONM was offered in the intermittent mode of application. We routinely searched for the EBSLN electromyographic (EMG) signal before (S1) and after (S2) dissection of the superior vascular peduncle. In the absence of the EMG signal, we observed the CTM twitch. We identified 141 (80%) S1 EMG signals, while we recorded the CTM twitch in 15 cases (8.5%). In 20 (11.3%) cases, we were unable to identify the EMG signal. Analysing the S2 results, we found loss of EBSLN signal in 11/141 cases (7.8%) identified with IONM in pre-dissection stimulation. Among the 20 cases without pre-dissection identification (we had not identified the external branch of the superior laryngeal nerve or the muscle twitch), in the post-dissection evaluation, we confirmed the loss of signal in 17 of 20 cases, equal to 85% (p < 0.001). Our data clearly show that intraoperative stimulation and recognition of EBSLN, performed before any dissection manoeuvre to the superior vascular thyroid pole, leads to a much higher rate of nerve conservation.
Highlights
The external branch of the superior laryngeal nerve (EBSLN) provides motor function to the cricothyroid muscle (CTM) [1]
This classification (Fig. 1) is based on the potential risk of nerve injury during thyroid surgery: the EBSLN is surgically relevant because it is in close anatomical proximity to the superior thyroid vessels (STVs), inferior constrictor muscle, CTM and thyroid cartilage
We considered the following prerequisites for definition of loss of EMG EBSLN signal: Vocal cord examination with preoperative laryngoscopy (L1): normal vocal cord (VC) movement
Summary
The external branch of the superior laryngeal nerve (EBSLN) provides motor function to the cricothyroid muscle (CTM) [1]. There are few anatomical classifications of the EBSLN; the most widely adopted is the one proposed in 1992 by Claudio R. Cernea [2, 3] This classification (Fig. 1) is based on the potential risk of nerve injury during thyroid surgery: the EBSLN is surgically relevant because it is in close anatomical proximity to the superior thyroid vessels (STVs), inferior constrictor muscle, CTM and thyroid cartilage. EBSLN dysfunction-related symptoms may, in some cases, deeply and negatively influence the standard quality of life. Of note, these symptoms may be more noticeable with professional speakers (especially true in women)
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