Endoscopic thyroidectomy versus traditional open thyroidectomy for identification of the external branch of the superior laryngeal nerve.

AIM: To explore the anatomical features of the external branch of the superior laryngeal nerve (EBSLN) and determine an effective approach for its preservation during endoscopic thyroidectomy (ET). METHODS: From January 2017 to December 2018, a total of 405 consecutive patients with thyroid disease were retrospectively analyzed. These patients were divided into the ET group and the open thyroidectomy (OT) group according to the surgical approaches. There were 195 cases in the ET group including 43 males and 152 females, and 210 cases in the OT group including 65 males and 145 females. The dissection process of EBSLN, detection rate, distribution of identification methods of the EBSLN and rate of voice change were recorded. RESULTS: There were 205 EBSLNs detected under direct vision in ET group for a detection rate of 88.0%, while 158 EBSLNs were detected under direct vision in OT group for a detection rate of 58.1%. But with the assistant of intraoperative neuromonitoring (IONM), the number of EBSLNs detected visually reached up to 220 in ET group and 226 in OT group, respectively, for a visual detection rate of 94.4% and 83.1%, respectively. There were significant difference in the rate of direct visual identification, total visual identification with IONM. Stratified risk estimation indicated that the tumor size and location were risk factors for the direct visual dissection of EBSLN. Stratified analysis by tumor size indicated that when tumor diameter was ≤ 4 cm, the incidence of vocal cord fatigue and total vocal changes in ET group was significantly lower than that in OT group. CONCLUSIONS: Recognition and exposure of the EBSLN can be facilitated by the magnification and focusing function of high-definition endoscopy and the advantage of a 30° variable angle. Full exposure of the sternothyroid-laryngeal triangle and fine dissection along the superior thyroid vessels is beneficial for recognizing the EBSLN.

Assessment of different classification systems for predicting the risk of superior laryngeal nerve injury during thyroid surgery: a prospective cohort study.

Background: A multitude of anatomical variations have been noted in the external branch of the superior laryngeal nerve (EBSLN). In this study, intraoperative neuromonitoring (IONM) was used to assess the potential value of the different classical EBSLN classifications for predicting the risk of EBSLN injury. Methods: In total, 136 patients with thyroid nodules were included in this prospective cohort study, covering 242 nerves at risk (NAR). The EBSLN was identified by observing the cricothyroid muscle twitch and/or typical electromyography (EMG) biphasic waveform. The EBSLNs were classified by Cernea classification, Kierner classification, and Friedman classification, respectively. The EMG parameters and outcomes of vocal acoustic assessment were recorded. Results: The distribution of Cernea, Kiernea, and Friedman subtypes were, respectively, Cernea 1 (40.9%), Cernea 2A (45.5%), Cernea 2B (10.7%), Kierner 1 (40.9%), Kierner 2 (45.5%), Kierner 3 (10.7%), Kierner 4 (2.9%) and Friedman 1 (15.7%), Friedman 2 (33.9%), Friedman 3 (50.4%). The amplitudes of EBSLN decreased significantly after superior thyroid pole operation, respectively, in Cernea 2A (193.7 vs. 226.6µV, P=0.019), Cernea 2B (185.8 vs. 221.3µV, P=0.039), Kierner 2 (193.7vs. 226.6µV, P=0.019), Kierner 3 (185.8 vs. 221.3µV, P=0.039), Kierner 4 (126.8vs. 226.0µV, P=0.015) and Friedman type 2 (184.8 vs. 221.6µV, P=0.030). There were significant differences in Fmax and Frange for Cernea 2A (P=0.001, P=0.001), 2B (P=0.001, P=0.038), Kierner 2 (P=0.001), Kierner 3 (P=0.001, P=0.038), and Friedman 2 (P=0.004, P=0.014). In the predictive efficacy of EBSLN injury, the Friedman classification showed higher accuracy (69.8% vs. 44.3% vs. 45.0%), sensitivity (19.5% vs. 11.0% vs. 14.0%), and specificity (95.6% vs. 89.9% vs. 89.9%) than the Cernea and Kierner classifications. However, the false negative rate of Friedman classification was significantly higher than other subtypes (19.5% vs. 11.0% vs. 14.0%). Conclusion: Cernea 2A and 2B; Kierner 2, 3, and 4; and Friedman 2 were defined as the high-risk subtypes of EBSLN. The risk prediction ability of the Friedman classification was found to be superior compared to other classifications.

Intraoperative Neuromonitoring in Thyroid and Parathyroid Surgery.

Background: It has been reported that the incidence of recurrent laryngeal nerve (RLN) injury is higher in an operational procedure in the thyroid and parathyroid region. Elevating voice pitch is achieved by the cricothyroid contraction, which in turn is innervated by the external branch of the superior laryngeal nerve (EBSLN). Due to the subtle nature and clinical variability of EBSLN damage, diagnosis may be difficult. The use of intraoperative neuromonitoring (IONM) as a supplement to enhance surgical identification in thyroid and parathyroid operation appeared to have collected momentum with operators. Methods: IONM clinical usage rationale, efficiency, and safety profile are discussed in this overview in thyroid and parathyroid surgery. Results: IONM usage incurred numerous skepticisms in decreasing the frequency of EBSLN or RLN injury. However, a recent article has shown the efficacy and benefits of using IONM in thyroid and parathyroid procedures. IONM facilitates the recognition of RLN and EBSLN, verifies its functional integrity, localizes the site of a nerve injury, and gives postsurgical function feedback. This technique has been successful in reducing rates of bilateral laryngeal paralysis, with the elevated safety profile for surgical patients. Conclusions: It is recommended using IONM in all thyroidectomies and in high-risk parathyroidectomies.

Can we routinely identify the external branch of the superior laryngeal nerves with neural monitoring?: a prospective report on 176 consecutive nerves at risk.

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.