External Branch Of The Superior Laryngeal Nerve Research Articles

Effectiveness and feasibility of nerve real-time monitoring and intermittent monitoring in endoscopic thyroidectomy: A multicenter retrospective cohort study of 1621 patients.

Protecting recurrent laryngeal nerve (RLN) and external branch of the superior laryngeal nerve (EBSLN), a crucial indicator for assessing the quality of thyroid surgery, poses a challenge in endoscopic thyroidectomy. The aim of this study was to investigate the effectiveness and feasibility of nerve real-time monitoring and intermittent monitoring in endoscopic thyroidectomy. In this retrospective cohort study, patients underwent endoscopic thyroidectomy were included, and the characteristics and outcomes of real-time monitoring and intermittent monitoring groups were compared. Thereafter, the outcomes of four surgical types (unilateral lobectomy, total thyroidectomy, unilateral lobectomy + lymph node dissection (LND), and total thyroidectomy + LND) were compared in both groups. A total of 1621 patients were enrolled. Compared to intermittent monitoring group, real-time monitoring group significantly shortened operation durations in the four surgical types (30.8 ± 6.1 min vs. 35.7 ± 5.7 min, 54.7 ± 4.4 min vs. 59.1 ± 5.2 min, 39.3 ± 4.6 min vs. 42.0 ± 4.7 min, 59.1 ± 4.9 min vs. 66.0 ± 5.8 min, respectively). As for surgical complications, compared to intermittent monitoring group, real-time monitoring group had lower rates of transient vocal cord paralysis among the four surgical types (0.0% vs. 3.3%, 0.0% vs. 4.0%, 0.8% vs. 3.2%, 2.8% vs. 6.7%, respectively), and lower rates of EBSLN injury (1.1% vs. 4.4%, 0.0% vs. 12.0%, 0.8% vs. 3.8%, 0.9% vs. 4.8%, respectively). Clinicopathologic characteristics and postoperative inflammatory reactions were similarly paralleled in both groups. Implementation of real-time monitoring in endoscopic thyroidectomy effectively protects the RLN and EBSLN while shortening operation duration, demonstrating its feasibility and efficacy in enhancing nerve protection and surgical efficiency.

갑상선 및 부갑상선 수술 중 신경 모니터링에 대한 가이드라인과 표준 술식

The benefits of intraoperative neuromonitoring (IONM) extend beyond merely reducing the incidence of vocal cord paralysis. Although widely used, a review of various literatures and clinical studies indicates diverse applications of nerve monitoring. To advance and standardize IONM techniques, the International Neural Monitoring Study Group (INMSG) has published guidelines for monitoring the recurrent laryngeal nerve (RLN) and the external branch of the superior laryngeal nerve (EBSLN). While IONM effectively preserves RLN function, application methods vary among surgeons. Implementing standardized setups and guidelines can reduce vocal cord paralysis and facilitate appropriate decisions when loss of signal (LOS) occurs, thereby ensuring the best outcomes for patients. This review aims to synthesize the current INMSG guidelines and summarize standard procedures for RLN monitoring.

Various methods for intraoperative neural monitoring during thyroid surgery

Intraoperative neural monitoring (IONM) during thyroidectomy is an essential technique to safeguard the recurrent laryngeal nerve (RLN) and the external branch of the superior laryngeal nerve (EBSLN), both critical for vocal cord function. Utilizing electromyography (EMG), IONM provides real-time feedback on nerve integrity, significantly reducing the risk of nerve damage during surgery. The primary methods of IONM include endotracheal tube electrodes, surface electrodes, needle electrodes, and continuous monitoring, each with distinct advantages and limitations. Endotracheal tube electrodes offer direct measurements but can be difficult to position, while surface electrodes are non-invasive but may experience signal interference. Needle electrodes provide precise measurements but are invasive, and continuous monitoring offers ongoing feedback but requires advanced equipment. The evolution of IONM began in the mid-20th century and has progressed significantly, leading to its widespread adoption in thyroid surgery by the mid-2000s. Enhanced by recent technological advancements and standardized by professional guidelines, IONM has become integral in reducing postoperative complications. Ongoing research aims to further refine IONM techniques, ensuring optimal patient outcomes and the preservation of nerve function in thyroid surgery.

Current Knowledge on the Use of Neuromonitoring in Thyroid Surgery.

Thyroid surgery rates have tripled over the past three decades, making it one of the most frequently performed procedures within general surgery. Thyroid surgery is associated with the possibility of serious postoperative complications which have a significant impact on the patient's quality of life. Recurrent laryngeal nerve (RLN) palsy and external branch of the superior laryngeal nerve (EBSLN) palsy are, next to hypoparathyroidism and postoperative bleeding, some of the most common complications. The introduction of neuromonitoring into thyroid surgery, which enabled both the confirmation of anatomical integrity and the assessment of laryngeal nerve function, was a milestone that began a new era in thyroid surgery. The International Neural Monitoring Study Group has produced a standardization of the technique of RLN and EBSLN monitoring during thyroid and parathyroid surgery, which in turn increased the prevalence of neural monitoring during thyroidectomy. The current status of IONM and the benefits of its use have been presented in this publication.

Ansa Cervicalis External Branch Anastomosis to Restore High Tone Voice in Thyroid Surgery.

Injury to the external branch of the superior laryngeal nerve (EBSLN) causes low-pitch voice and voice fatigue, particularly in female subjects, and available treatments are limited. Here, we assess a novel surgical procedure to restore a high-tone voice: ansa cervicalis to EBSLN anastomosis (A-E anastomosis). Between November 2012 and April 2022, 13 patients (12 female) underwent unilateral EBSLN resection and A-E anastomosis, while 20 (16 female) underwent EBSLN resection during thyroid surgery. Patients (4494 women and 1025 men) with normal laryngoscopy scheduled for thyroid surgery served as normal controls. Phonatory function was examined using a Phonation Analyzer PA-1000 preoperatively and intermittently postoperatively. In patients who underwent A-E anastomosis, high-tone voice pitch decreased significantly postoperatively (673.9-471.5 Hz, p = 0.047), with restoration achieved within 5 months. The mean voice pitch in female patients who underwent A-E anastomosis, EBSLN resection, and controls were 580.4, 522.8, and 682.0 Hz, respectively, indicating a significant decrease in EBSLN resection patients than controls (p = 0.002). The (mean - 1SD) of high-tone voice pitch in female controls was 497 Hz; exceeding this may indicate recovery to a high-tone voice. Overall, 73% (8/11) of A-E anastomosis patients exceeded this value, which was marginally larger than the 43% (6/14) who underwent EBSLN resection. Data on male subjects are limited. There were no cases of adverse functional or cosmetic events. A-E anastomosis, a novel simple procedure, restored high-tone voice to some extent without any adverse events and thus warrants further investigation. 3 Laryngoscope, 134:3868-3873, 2024.

Key points for protecting the external branch of the superior laryngeal nerve in open thyroidectomy: A possible exploration technique

ObjectiveInjury of the external branch of the superior laryngeal nerve (EBSLN) is easily overlooked in thyroidectomy, and voice changes caused by the injury have a negative effect on an increasing number of patients. This study aimed to reduce the injury rate of EBSLN by expanding the sternothyroid-laryngeal triangle and standardizing the exploration procedure. MethodsA total of 520 patients who had undergone thyroidectomy at the First Affiliated Hospital of Nanchang University between September 2021 and April 2022 were analyzed. During the operation, the exposure rate of the EBSLN before and after sternothyroid-laryngeal triangle expansion was compared, and all EBSLNs were anatomically classified. ResultsThe exposure rate of EBSLN after sternothyroid-laryngeal triangle expansion reached 82.7%, which is much higher than that before sternothyroid-laryngeal triangle expansion (33.7%), and voice change caused by injury of the EBSLN was reported in one case (the injury rate was 0.2%). The classification and proportion of the EBSLN were as follows: Type 1 (55.3%), the nerve ran within 1 cm above the STP, but no coincidence or crossover with blood vessels was observed in this region; Type 2 (14.7%), the nerve travelled within 1 cm above the STP and overlapped or intersected with blood vessels in this region; Type 3 (12.7%), the EBSLN ran below the level of the STP; and Type 4 (17.3%), no EBSLN was observed within 1 cm above the STP. ConclusionIn thyroidectomy, injury to the EBSLN can be effectively reduced by expanding the sternothyroid-laryngeal triangle and exploring the upper pole area of the thyroid as far as possible, which has great clinical significance in reducing postoperative voice box injury.

Noninvasive monitoring of the vagus nerve during thyroid surgery using cutaneous adhesive and needle electrodes: What is the optimal configuration?

Endotracheal tube (ETT) surface electrodes are used to monitor the vagus nerve (VN), recurrent laryngeal nerve (RLN), and external branch of the superior laryngeal nerve (EBSLN) during thyroid and parathyroid surgery. Alternative nerve monitoring methods are desirable when intubation under general anesthesia is not desirable or possible. In this pilot study, we compared the performance of standard ETT electrodes to four different noninvasive cutaneous recording electrode types (two adhesive electrodes and two needle electrodes) in three different orientations. The VN was stimulated directly during thyroid and parathyroid surgery using a Prass stimulator probe. Electromyographic (EMG) responses for each patient were recorded using an ETT plus one of the following four cutaneous electrode types: large-foot adhesive, small-foot adhesive, long-needle and short-needle. Each of the four electrode types was placed in three orientations: (1) bilateral, (2) ipsilateral mediolateral, and (3) ipsilateral craniocaudal. Four surgical cases were utilized for data collection with the repetitive measures obtained in each subject. Bilateral electrode orientation was superior to ipsilateral craniocaudal and ipsilateral mediolateral orientations. Regardless of electrodes type, all amplitudes in the bilateral orientation were >100 μV. When placed bilaterally, the small-foot adhesive and the long-needle electrodes obtained the highest EMG amplitudes as a percentage of ETT amplitudes. Cutaneous electrodes could potentially be used to monitor the VN during thyroid and parathyroid procedures. Different electrode types vary in their ability to record amplitudes and latencies. Bilateral orientation improves EMG responses in all electrode types. Additional validation of cutaneous electrodes as an alternative noninvasive method to monitor the VN is needed.

Intraoperative cricothyroid muscle electromyography may contribute to the monitorization of the external branch of the superior laryngeal nerve during thyroidectomy.

In thyroid surgery, both the recurrent laryngeal nerve (RLN) and external branch of the superior laryngeal nerve (EBSLN) should be preserved for maintaining the vocal cord functions. We aimed to evaluate whether EMG of the CTM applied after the superior pole dissection provided additional informative data to the IONM via ETT or not, regarding the EBSLN function. The prospectively collected data of the patients, who have undergone thyroidectomy with the use of IONM for the exploration of both the RLN and EBSLN between October 2016 and March 2017, were evaluated retrospectively. Patients over 18 years of age with primary thyroid surgery for malignant or benign thyroid disease, and whom were applied CTM EMG with a needle electrode after the completion of thyroidectomy were included in the study. In the study, each neck side was evaluated as a separate entity considering the EBSLN at risk. The data of 41 patients (32 female, 9 male) (mean age, 46.7+9.1; range, 22-71) were evaluated. Sixty seven EBSLNs out of 26 bilateral and 15 unilateral interventions were evaluated. With EBSLN stimulation after the superior pole dissection, positive glottic EMG waveforms via ETT were obtained in 45 (67.2%) out of 67, and the mean glottic amplitude value was 261+191 μV (min-max: 116-1086 μV). Positive EMG responses via the CTM EMG were achieved from all of the 67 EBSLNs (100%) with stimulation using a monopolar probe at the most cranial portion above the area of divided superior pole vessels. The mean value of CTM amplitudes via CTM EMG obtained with EBSLN stimulation was 5268+3916 μV (min-max:1215 -19726 μV). With EBSLN stimulation, the mean CTM EMG amplitude was detected significantly higher than the mean vocal cord amplitude (p<0.0001). The CTM EMG provided more objective quantifiable data regarding the EBSLN function (100% vs 67,2%, p<0.001). In addition to the IONM via ETT, intraoperative post-dissection CTM EMG via needle electrode is a safe, simple and applicable method that may provide significant additional informative data to IONM with ETT by obtaining and recording objective quantitative data related to the EBSLN function.

갑상선 수술중 신경모니터링의 최근 연구

Thyroid surgery is associated with a risk of injury to the recurrent laryngeal nerve(RLN), the external branch of the superior laryngeal nerve(EBSLN), and voice changes. Intraoperative neuromonitoring(IONM) has already gained universal reliability to help in nerve identification, safe nerve dissection, and prediction of postoperative vocal cord function. IONM techniques have evolved over the past decade into intermittent IONM(I-IONM) and continuous IONM(C-IONM) modes of application. Research in the field of IONM continues, exploring new techniques and approaches to further enhance the safety and efficacy of thyroid surgery. In this article, the role of IONM and its recent studies will be reviewed.

Anatomical Variations of the External Branch of the Superior Laryngeal Nerve and its Correlations with the Superior Thyroid Artery and the Upper Pole of the Thyroid Gland: A Review of the Literature

Injury to the external branch of the superior laryngeal nerve (EBSLN) following thyroid or parathyroid surgery often results in devastating voice changes especially noticed by patients who use their voice professionally. The external branch arises from the vagus nerve which provides the motor supply to the cricothyroid muscle, an exclusive tensor of the vocal cords. The course of the EBSLN is subject to great anatomic variability. Damage to the nerve occurs during improper ligation of superior thyroid vessels close to the upper pole of thyroid gland in up to 58% of patients undergoing thyroid surgery. Thus, a thorough knowledge of the anatomy of the EBSLN and its variations, is essential requirement to minimize iatrogenic complications during surgery of the neck. Additionally, nerve monitoring methods have been developed to facilitate the localisation of the nerve, decreasing the possibility of nerve injury during thyroid surgery. The aim of this study is to analyze and review the anatomical variations of the EBSLN and its correlations with the superior thyroid artery and the upper pole of the thyroid gland. The literature search was performed during the period from February 1992 through November 2021. The position of the EBSLN was classified according to the Cernea and Kierner classification. Based on this classification, type 2a variant of EBSLN was the commonest followed by type 1. In addition, neuromonitoring allowed a higher identification rate than the visual identification.

Comparison of intraoperative neural monitoring between endoscopic transoral and bilateral axillo-breast approach thyroidectomy.

The use of intraoperative neuromonitoring (IONM) during endoscopic thyroidectomy has not been fully explored, with limited studies focusing solely on the recurrent laryngeal nerve (RLN) and neglecting the external branch of the superior laryngeal nerve (EBSLN). This study aimed to compare the effectiveness of IONM in two endoscopic thyroidectomy techniques, namely the transoral and bilateral axillo-breast approach (BABA). We retrospectively reviewed patients who underwent endoscopic thyroidectomy with IONM and compared the outcomes between those who underwent different surgical techniques (transoral or BABA). We recorded the detection method and identification rate of the EBSLN and RLN, along with the amplitude and latency of the evoked potential. We monitored 98 nerves at risk (NAR) from 74 patients (60 and 38 in the transoral and BABA groups, respectively). Almost all EBSLNs were identified using electromyography (EMG) signals and/or cricothyroid muscle twitches, except for one patient in the transoral group who developed EBSLN palsy. Patients in the transoral group were more likely to have the sternothyroid muscle divided (75.0% vs. 15.8%, p < 0.001) and had a lower rate of visual recognition of the EBSLN fibers (10.0% vs. 31.6%, p = 0.007) than did those in the BABA group. All RLNs were identified in both groups; however, patients in the BABA group had a relatively higher rate of post-dissection amplitude reduction > 50% (15.8% vs. 5.0%, p = 0.072), and one patient had transient RLN palsy. Both the EBSLN and RLN could be adequately identified and monitored during endoscopic transoral and BABA thyroidectomies using IONM.

Utility of video-assisted method for identifying and preserving the external branch of the superior laryngeal nerve during thyroidectomy.

The EBSLN is vulnerable to damage during thyroidectomy, results in voice related complications, negatively affect patient quality of life, routine identification of the EBSLN prior to surgical manipulation is necessary for a complication-free thyroidectomy. We aimed to validate a video-assisted procedure for identifying and preserving the external branch of the superior laryngeal nerve (EBSLN) during thyroidectomy and analyze the EBSLN Cernea classification and the localization of the nerve entry point (NEP) from the insertion of the sternothyroid muscle. A prospective descriptive study was performed; 134 patients, who scheduled for lobectomy with an intraglandular tumor max diameter ≤ 4 cm and without extrathyroidal extension, were randomly divided into the video-assisted surgery (VAS) and conventional open surgery (COS) groups. We used the video-assisted surgical procedure for visually identifying the EBSLN directly, and compared the differences in the visual identification rate and total identification rate of the two groups. We also measured the localization of the NEP using the insertion of the sternothyroid muscle as a reference. There was no statistically significant difference in clinical characteristics between the two groups. The visual identification rate and total identification rate were significantly higher in the VAS group than the COS group (91.04% vs. 77.61%, 100% vs. 89.6%). The EBSLN injury rate was 0 in both groups. The mean vertical distance (VD) of the NEP from the sternal thyroid insertion was 1.18 mm (SD 1.12 mm, range, 0-5 mm), with approximately 88.97% of the results occurring within the 0-2 mm range. The mean horizontal distance (HD) was 9.33 mm (SD 5.03 mm, range, 0-30 mm), with over 92.13% of the results occurring within the 5-15 mm range. Both the visual and total identification rates of the EBSLN were significantly higher in the VAS group. This method provided a good visual exposure rate of the EBSLN, aiding in identifying and protecting the EBSLN during thyroidectomy.

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

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. 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. 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%). 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.

Effect of mouse nerve growth factor combined with the exposure of the external branch of superior laryngeal nerve on voice changes after thyroidectomy: a prospective non-randomized controlled trial.

The superior laryngeal nerve (SLN) injury may also affect vocal fold function and voice quality. It is efficient yet simple approach to expose the external branch of the superior laryngeal nerve (EBSLN). Neurotrophic agent mouse nerve growth factor (mNGF) to treat patients after thyroid surgery, and found it had significant efficacy in improving the voice of patients. However, the potential effectiveness and safety of mNGF combined with EBSLN were unclear. In this study, 96 patients who suffered from hoarseness after thyroidectomy at Hangzhou First People's Hospital between January 2018 and October 2019 were screened and divided into the control group and the observation group by patients' choice. In the control group, the SLN was not exposed. In the observation group, the SLN was exposed. The mNGF treatment was administered for observation group once a day at 20 µg each time for 4 weeks. The data of acoustic voice indicators was analysis by univariate analyses. Patients in both groups were followed up for more than 6 months. The rate of SLN damage was compared between two groups. The baseline clinical characteristics of the two groups showed no statistic difference. The results showed that the fundamental frequency was significantly lower 1 month after surgery than 3 days after surgery in both groups. The fundamental frequency perturbation, shimmer, maximum phonation time, highest fundamental frequency, and dysphonia severity index in 1 month after surgery were significantly higher than they were 3 days after surgery (all P<0.001). There was no significant difference in the postoperative harmonic-to-noise ratio between the 2 groups (P=0.426). MNGF combined with the exposure and protection of the EBSLN effectively may prevent voice damage after thyroid surgery.

The effect of strap muscle transection on voice and swallowing changes after thyroidectomy in patients without laryngeal nerve injury.

Voice and swallowing symptoms are frequently reported after thyroidectomy even without laryngeal nerve injury. We aimed to evaluate the effect of strap muscle transection on voice and swallowing outcome after thyroidectomy. Group 1 (G1) consisted of 17 patients who had their strap muscles transected during thyroidectomy and group 2 (G2) consisted of 17 patients who had their strap muscles preserved during thyroidectomy. None of the patients had laryngeal nerve injury. Voice impairment scores (VIS) and swallowing impairment scores (SIS) were obtained preoperatively and at 1 week and 1, 3 and 6 months postoperatively. Pre- and postoperative vocal cord examinations were performed for all patients. The external branch of the superior laryngeal nerve (EBSLN) was evaluated by intraoperative cricothyroid muscle electromyography. There was no significant difference in VIS and SIS between the two groups. At postoperative week 1, the VIS and SIS for each group were above preoperative values (G1: p = 0.005 and p = 0.035; G2: p = 0.031, p = 0.346, for VIS and SIS respectively). The VIS and SIS scores at 6 months postoperatively were significantly lower than those of the first week postoperatively (G1: p = 0.04 and p = 0.001; G2: p = 0.022 and p = 0.034 respectively) and similar to preoperative values (G1: p = 0.924 and p = 0.086; G2: p = 0.822 and p = 0.187 respectively). Although voice and swallowing complaints increased in the early postoperative period even without recurrent laryngeal nerve and EBSLN injuries, these symptoms are not related with the strap muscle transection.

Stepwise approach to preserve the external branch of superior laryngeal nerve during thyroidectomy

BackgroundMost of the surgeons tend to avoid exposing and identification the external branch of the superior laryngeal nerve (EBSLN) during thyroidectomy. In this study, our aim is to assess sequential steps to ligate superior thyroid vessels safely away from the External branch of superior laryngeal nerve (EBSLN).MethodsThis prospective case series study was conducted on 60 patients going for either total or hemi thyroidectomy in a tertiary teaching hospital between January 2016 and June 2019. During thyroidectomy, firstly we skeletonized the upper pole of the thyroid gland by its capsular dissection followed by anterolateral down retraction of the superior pole. Then, entry and opening of the cricothyroid space and lastly clamping and ligating superior thyroid pedicle close to the upper pole away from EBSLN.ResultsThis study included 60 cases; 19 total thyroidectomy and 41 hemi thyroidectomy with 79 superior thyroid vessels ligation and EBSLN at risk. In all patients, no evidence of superior laryngeal nerve (SLN) palsy or bleeding was detected. Postoperative video laryngoendoscopy showed apparently normal mobility, length, level, and position of the vocal folds with symmetry of the larynx. The patients’ voice showed no changes from preoperative evaluation in all studied patients at 3 months postoperative evaluation. No patients complained of any changes in their voice or voice activities.ConclusionThe described stepwise approach for preservation of the EBSLN serves to completely remove the superior pole of the thyroid gland and ligate superior thyroid vascular pedicle without risk of SLN injury.

Intraoperative Neuromonitoring: Evaluating the Role of Continuous IONM and IONM Techniques for Emerging Surgical and Percutaneous Procedures.

Continuous and intermittent intraoperative nerve monitoring (IONM) has become an important asset for endocrine surgeons over the past few decades. The ability to determine neurophysiologic integrity of the recurrent laryngeal nerve (RLN) and external branch of the superior laryngeal nerve (EBSLN) on top of identification and meticulous dissection of the nerve in the surgical field, has allowed for advances in technology and improved outcomes when it comes to prevention of vocal fold immobility. This article aims to compare in review continuous and intermittent nerve monitoring (CIONM, IIONM), as well as review the current paradigms of their use. This article will also discuss the future of intraoperative nerve monitoring technologies in scarless thyroid surgery and percutaneous approaches to thyroid pathology in form of radiofrequency ablation (RFA).

Evaluation of the Cricothyroid Muscle Innervation Pattern Through Intraoperative Electromyography

Objectives:We observed significant contractions in the cricothyroid muscle (CTM) after recurrent laryngeal nerve (RLN) stimulation in some patients. We aimed to evaluate whether these contractions resulted from the laryngeal-muscle movement due to the contraction of other intrinsic muscles or actual CTM contraction, with objective real-time intraoperative electromyography (EMG) recordings.Methods:This study was performed prospectively in 106 consecutive patients who underwent intraoperative neural monitoring-guided primary thyroid surgery due to various thyroid diseases between February-2015 and February-2016. After completion of the thyroidectomy procedure; the RLN, vagus nerve (VN), external branch of the superior laryngeal nerve (EBSLN), plexus pharyngeus (PP), and contralateral EBSLN (CEBSLN) were stimulated and the responses from the CTM and CPM were recorded and evaluated by EMG through needle electrodes.Results:182 CTMs of 106 patients, with the mean age of 45, were evaluated regarding their innervation patterns. Positive EMG waveforms were achieved from 181 CTMs with EBSLN stimulation. A total of 132 (74%) positive EMG responses were recorded after the stimulation of 179 RLNs. The mean amplitude obtained with CTM EMG with RLN stimulation was 5.5% of that with EBSLN stimulation. The CTM amplitude was 39% of the vocal cord amplitude with RLN stimulation. Positive EMG responses of 96 CTMs (55%) with VN stimulation were recorded. The mean amplitude through CTM EMG with VN stimulation was 6% of that with EBSLN stimulation. Positive EMG responses were achieved from 10 (0.6%) CTMs with the stimulation of 170 PPs. The mean amplitude obtained from CTMs with PP stimulation was 4.3% of that with EBSLN stimulation. Positive EMG amplitudes of 35 (67%) CTMs were obtained with stimulation of 52 CEBSLN. Temporary vocal cord paralysis was detected in six patients (5% of patients and 3.3% of the nerves) postoperatively.Conclusion:The RLN contributes significantly to the innervation of the CTM. Despite the findings associated with the contribution of the PP and CEBSLN to the CTM innervation, further studies are needed. We are of the opinion that these are among the significant factors that contribute to the differences in clinical findings between patients with EBSLN injuries.

Cernea's classification of the External Branch of the Superior Laryngeal Nerve during Microscopic Thyroidectomy at Gandaki Medical College, Pokhara

Background: Preservation of the external branch of the superior laryngeal nerve (EBSLN) during thyroidectomy is important because its injury may lead to frequent occurrence of vocal fatigue and the inability to perform phonation. The objective of the study was to identify and classify the nerve as per Cernea's classification using operating microscope during thyroidectomy Method: Between January 2017 to December 2019, we evaluated 50 patients for the position of external branch of superior laryngeal nerve, who underwent microscopic thyroid surgeries in the department of ENT- head and neck surgery at Gandaki Medical College. Results: In our study, we dissected a total 59 superior poles of thyroid from 50 patients and identified the nerve in all the cases. Of the total superior poles, 36 (61.01%) had type IIa EBSLN among which 24 was on the right side and 12 on the left followed by 19 (32.20%) patients with type IIb EBSLN among which 8 on right and 11 on left side. There were only 4 poles (6.77%) of type I with 3 on the right and 1 on the left side. Conclusion: The EBSLN can be very efficaciously identified during a microscope assisted thyroidectomy. Cernea type 2a and 2b EBSLNs are in position to be at high risk of injury during ligation of the superior vascular pedicle, which can be avoided by prompt identification through a microscope and a meticulous extra capsular dissection technique.

Anterolateral approach for thyroid swellings: impact on postoperative voice outcomes.

The sternothyroid muscle (ST) is routinely divided during grossly enlarged thyroid surgery to facilitate gland exposure. However, the ST is considered to play a role in controlling of pitch in the human voice. In this prospective cohort study, we described an anterolateral approach (AA) by which it was easy to expose the enlarged gland while preserving the ST, and evaluated the impact of this approach on vocal outcomes after total thyroidectomy. The AA was performed on eligible patients from October 2018 to January 2020 in our department. Consecutive cases hospitalized from March 2020 and followed up to June 2021 who received total thyroidectomy via the midline approach (MA) served as controls. All participants underwent voice analysis before the operation and at 2 weeks and 3 months after the surgery. In 26 patients from AA group, strap muscles were mobilized along the anterior margin of both sternocleidomastoid muscles (SCMs) until 3 cm above the sternal notch followed by thyroidectomy, and their voice outcomes were compared to those of 36 patients from the MA group with a bilateral division of ST. Distribution of age, gender, specimen size, thyroid histopathology and laryngeal nerve identification rates did not differ significantly between groups. At 2 weeks post-surgery, objective assessment of voice change rate indicated no significant difference between groups, whereas the difference appeared to be partially manifest 3 months later. In the single-arm study, the AA group showed a decrease of maximum and fundamental pitch frequency 2 weeks after surgery but showed no difference in fundamental frequency after 3 months. The MA group continued to show a mild decrease in maximum and fundamental frequency at 3 months after surgery. The AA affords sufficient visualization of the superior thyroid vessels and external branch of the superior laryngeal nerve (EBSLN) without sacrificing the integrity of the strap muscles. This approach is a feasible solution for selective difficult thyroid surgery and could reduce the postoperative changes in pitch of voice.