Anatomical variations of recurrent laryngeal nerve: a systematic review and meta-analyses.

PURPOSE: The aim of this systematic review and meta-analysis was to systematically review and perform a meta-analysis on the anatomical variations of the RLN. METHODS: We performed online research for studies that addressed anatomical variations of the RLN and laterality, published between 2015 and 2021. We found 230 articles, and nine were included. RESULTS: Eight variations were found, with Type I prevailing (41.17%; 95% CI 19.44-64.88), extra laryngeal divergence of the RLN. The other types were: II-fan shape; III-distance greater than 5 mm to the cricothyroid joint; IV-thickening and adipopexy in the elderly; V-non-recurrent laryngeal nerve; VI-intracranial branch; VII-tortuous ascending RLN; and VIII-combination between the inferior branch of the NV and the ascending trunk of the RLN. Types I (p = 0) and III (p < 0.01) prevailed on the left and types II (p < 0.01) and V (p < 0.01) on the right. CONCLUSIONS: It was observed that variations occurred due to the path of the RLN to the entrance to the larynx, its shape, and the age of the evaluated individual. The most frequent variation and side were, respectively, Type I, extra laryngeal divergence and left.

Reconstruction of Vocal Fold Medial Surface 3D Trajectories: Effects of Neuromuscular Stimulation and Airflow.

INTRODUCTION: Analysis of medial surface dynamics of the vocal folds (VF) is critical to understanding voice production and treatment of voice disorders. We analyzed VF medial surface vibratory dynamics, evaluating the effects of airflow and nerve stimulation using 3D reconstruction and empirical eigenfunctions (EEF). STUDY DESIGN: In vivo canine hemilarynx phonation. METHODS: An in vivo canine hemilarynx was phonated while graded stimulation of the recurrent and superior laryngeal nerves (RLN and SLN) was performed. For each phonatory condition, vibratory cycles were 3D reconstructed from tattooed landmarks on the VF medial surface at low, medium, and high airflows. Parameters describing medial surface trajectory shape were calculated, and underlying patterns were emphasized using EEFs. Fundamental frequency and smoothed cepstral peak prominence (CPPS) were calculated from acoustic data. RESULTS: Convex-hull area of landmark trajectories increased with increasing flow and decreasing nerve activation level. Trajectory shapes observed included circular, ellipsoid, bent, and figure-eight. They were more circular on the superior and anterior VF, and more elliptical and line-like on the inferior and posterior VF. The EEFs capturing synchronal opening and closing (EEF1) and alternating convergent/divergent (EEF2) glottis shapes were mostly unaffected by flow and nerve stimulation levels. CPPS increased with higher airflow except for low RLN activation and very dominant SLN stimulation. CONCLUSION: We analyzed VF vibration as a function of neuromuscular stimulation and airflow levels. Oscillation patterns such as figure-eight and bent trajectories were linked to high nerve activation and flow. Further studies investigating longer sections of 3D reconstructed oscillations are needed. LEVEL OF EVIDENCE: N/A, Basic Science Laryngoscope, 134:1249-1257, 2024.

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

BACKGROUND: 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). METHODS: 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. RESULTS: 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. CONCLUSIONS: Both the EBSLN and RLN could be adequately identified and monitored during endoscopic transoral and BABA thyroidectomies using IONM.

Safety of continuous intraoperative vagus nerve neuromonitoring during thyroid surgery.

BACKGROUND: Continuous intraoperative neuromonitoring has successfully demonstrated to predict impending damage to the recurrent laryngeal nerve, by detecting changes in electromyographic recordings. Despite the apparent benefits associated with continuous intraoperative neuromonitoring, its safety is still a debate. The aim of this study was to investigate the electrophysiological impact of continuous intraoperative neuromonitoring on the vagus nerve. METHODS: In this prospective study, the amplitude of the electromyographic wave of the vagus nerve-recurrent laryngeal nerve axis was measured both proximally and distally to the stimulation electrode placed upon the vagus nerve. Electromyographic signal amplitudes were collected at three distinct events during the operation: during the dissection of the vagus nerve, before application of the continuous stimulation electrode onto the vagus nerve and after its removal. RESULTS: In total, 169 vagus nerves were analysed, among 108 included patients undergoing continuous intraoperative neuromonitoring-enhanced endocrine neck surgeries. Electrode application resulted in a significant overall decrease in measured proximo-distal amplitudes of -10.94 µV (95 per cent c.i. -17.06 to -4.82 µV) (P < 0.005), corresponding to a mean(s.d.) decrease of -1.4(5.4) per cent. Before the removal of the electrode, the measured proximo-distal difference in amplitudes was -18.58 µV (95 per cent c.i. -28.31 to -8.86 µV) (P < 0.005), corresponding to a mean(s.d.) decrease of -2.50(9.59) per cent. Seven nerves suffered a loss of amplitude greater than 20 per cent of the baseline measurement. CONCLUSION: In addition to supporting claims that continuous intraoperative neuromonitoring exposes the vagus nerve to injury, this study shows a mild electrophysiological impact of continuous intraoperative neuromonitoring electrode placement on the vagus nerve-recurrent laryngeal nerve axis. However, the small observed differences are negligible and were not associated with a clinically relevant outcome, making continuous intraoperative neuromonitoring a safe adjunct in selected thyroid surgeries.

Effectiveness of the recurrent laryngeal nerve monitoring during endoscopic thyroid surgery: systematic review and meta-analysis.

BACKGROUND: Thyroid disease is a common endocrine disorder, and thyroid surgeries and postoperative complications have increased recently. This study aimed to explore the effectiveness of intraoperative nerve monitoring (IONM) in endoscopic thyroid surgery using subgroup analysis and determine confounding factors. MATERIALS AND METHODS: Two researchers individually searched for relevant studies published till November 2022 in the PubMed, Embase, Web of Science and Cochrane Library databases. Eventually, eight studies met the inclusion criteria. Heterogeneity was assessed using the Cochran's Q test, and a funnel plot was implemented to evaluate publication bias. The odds ratio or risk difference were calculated using fixed-effects models. The weighted mean difference of continuous variables was calculated. Subgroup analysis was performed according to the disease type. RESULTS: Eight eligible papers included 915 patients and 1242 exposed nerves. The frequencies of transient, permanent and total recurrent laryngeal nerve (RLN) palsy were 2.64, 0.19 and 2.83%, respectively, in the IONM group and 6.15, 0.75 and 6.90%, respectively, in the conventional exposure group. In addition, analysis of the secondary outcome indicators for the average total length of surgery, localisation time of the RLN, recognition rate of the superior laryngeal nerve and length of incision revealed that IONM reduced the localisation time of the RLN and increased the identification rate of the superior laryngeal nerve. Subgroup analysis showed that IONM significantly reduced the incidence of RLN palsy in patients with malignancies. CONCLUSIONS: The use of IONM significantly reduced the incidence of transient RLN palsy during endoscopic thyroid surgery, but it did not significantly reduce the incidence of permanent RLN palsy. However, the reduction in the total RLN palsy was statistically significant. In addition, IONM can effectively reduce the location time of the RLN and increase the recognition rate of the superior laryngeal nerve. Therefore, the application of IONM for malignant tumours is recommended.

A Prospective Study of Electromyographic Amplitude Changes During Intraoperative Neural Monitoring for Open Thyroidectomy.

BACKGROUND: Intraoperative nerve monitoring (IONM) of the vagus and recurrent laryngeal nerve (RLN) enables prediction of postoperative nerve function. The underlying mechanism for loss of signal (LOS) in a visually intact nerve is poorly understood. The correlation of intraoperative electromyographic amplitude changes (EMG) with surgical manoeuvres could help identify mechanisms of LOS during conventional thyroidectomy. METHODS: A prospective study of consecutive patients undergoing thyroidectomy was performed with intermittent IONM using the NIM Vital nerve monitoring system. The ipsilateral vagus and RLN was stimulated, and vagus nerve signal amplitude recorded at five time points during thyroidectomy (baseline, after mobilisation of superior pole, medialisation of the thyroid lobe, before release at Ligament of Berry, end of case). RLN signal amplitude was recorded at two time points; after medialisation of the thyroid lobe (R1), and end of case (R2). RESULTS: A total of 100 consecutive patients undergoing thyroidectomy were studied with 126 RLN at risk. The overall rate of LOS was 4.0%. Cases without LOS demonstrated a highly significant vagus nerve median percentage amplitude drop at medialisation of the thyroid lobe (- 17.9 ± 53.1%, P < 0.001), and end of case (- 16.0 ± 47.2%, P < 0.001) compared to baseline. RLN had no significant amplitude drop at R2 compared to R1 (P = 0.207). CONCLUSIONS: A significant reduction in vagus nerve EMG amplitude at medialisation of the thyroid and the end of case compared to baseline indicates that stretch injury or traction forces during thyroid mobilisation are the most likely mechanism of RLN impairment during conventional thyroidectomy.

The Utility of Intraoperative Neuromonitoring in Pediatric Surgical Oncology.

BACKGROUND: Intraoperative nerve monitoring (IONM) is a technique used to decrease the possibility of nerve-associated morbidity and damage to nearby neural structures during complex surgical procedures. The use and potential benefits of IONM in pediatric surgical oncology are not well-described. METHODS: An overview of the current literature was performed to elucidate the various techniques that may be useful to pediatric surgeons for resection of solid tumors in children. RESULTS: The physiology and common types of IONM relevant to the pediatric surgeon are described. Important anesthetic considerations are reviewed. Specific applications for IONM that may be useful in pediatric surgical oncology are then summarized, including its use for monitoring the recurrent laryngeal nerve, the facial nerve, the brachial plexus, spinal nerves, and lower extremity nerves. Troubleshooting techniques regarding common pitfalls are then proposed. CONCLUSION: IONM is a technique that may be beneficial in pediatric surgical oncology to minimize nerve injury during extensive tumor resections. This review aimed to elucidate the various techniques available. IONM should be considered as an adjunct for the safe resection of solid tumors in children in the proper setting with the appropriate level of expertise. A multidisciplinary approach is advised. Additional studies are necessary to further clarify the optimal use and outcomes in this patient population. LEVELS OF EVIDENCE: Level III.

Incidence of Vocal Cord Paralysis in Medullary Thyroid Cancer.

OBJECTIVE: Medullary thyroid cancer (MTC) is a neuroendocrine tumor that comprises 3-5% of all thyroid cancers in the United States. Vocal cord paralysis (VCP) may be due to involvement of the recurrent laryngeal nerve (RLN) preoperatively, or nerve sacrifice during surgery. The purpose of this study was to demonstrate the incidence of VCP in MTC and evaluate whether VCP has an impact on overall survival. METHODS: This was a retrospective chart review of patients with MTC treated at Loyola University Medical Center from 2007 to 2021. Information on demographics, cancer diagnosis and treatment, laboratory data, and survival were collected. RESULTS: A total of 79 patients were included in our study. 47 (59.5%) patients were female. The average age at the time of diagnosis was 51.3 years (SD 13.58). VCP was identified in 13 out of 79 (16.5%) patients. There were 71 patients with at least 1-year follow-up with median (Q1, Q3) years of 7.2 (3.9, 11.0). Those with VCP within 1 year had 7.2 (95% CI: 2.3, 22.7) times the risk of death compared to those without (p < 0.001). CONCLUSION: MTC is a rare thyroid cancer, however, its incidence is on the rise. Our study suggests that the incidence of VCP in these patients appears to be higher than seen in other thyroid malignancies, and VCP is associated with a statistically significant negative impact on survival. LEVEL OF EVIDENCE: 3 Laryngoscope, 133:890-894, 2023.

Utility of the continuous intraoperative neuromonitoring in the prevention of the recurrent laryngeal nerve paralysis during thyroid surgery. A prospective observational study.

BACKGROUND: The continuous intraoperative neuromonitoring (C-IONM) of the recurrent laryngeal nerve (RLN) could help reducing the incidence of nerve paralysis after thyroid surgery, in comparison with the mere anatomical visualization of the RLN. The objective is to assess the efficacy and utility of C-IONM as a predictive test for recurrent laryngeal nerve paralysis after thyroidectomy. METHODS: A prospective observational study was performed in 248 patients who underwent thyroid surgery where C-IONM was applied, between September 2018 and December 2019, in a high-volume center. A previous and later laryngoscopy was performed, which allowed to evaluate the reliability of the C-IONM as a predictive test for recurrent paralysis. Sensitivity (SE), specificity (SP), positive predictive value (PPV), negative predictive value (NPV) were studied. RESULTS: A total number of 171 thyroidectomies, 62 hemithyroidectomies, 15 totalization thyroidectomies and 27 thyroidectomy with cervical dissections were performed. Postoperative laryngoscopy was altered in 40 patients (16.12%). The SE, SP, PPV and NPV values ​​were 65%, 94.7%, 70.2% and 93.4% respectively. CONCLUSIONS: C-IONM is a safe technique that provides real-time information about anatomical and functional integrity of the RLN and can improve the results of thyroid surgery.

Preoperative voice analysis and survival outcomes in papillary thyroid cancer with recurrent laryngeal nerve invasion.

Objective: To investigate the clinicopathological characteristics of papillary thyroid cancer (PTC) and identify risk factors for postoperative recurrence of PTC with recurrent laryngeal nerve (RLN) involvement. Methods: In total, 171 patients (112 women and 59 men, age: 18-80 years, and 65 patients aged ≥ 55) with T4a PTC with RLN involvement, treated at Beijing Tongren Hospital, Capital Medical University, from January 2006 to December 2020, were retrospectively examined. Clinicopathological characteristics, including voice analysis results, and survival outcomes were assessed. The Mann-Whitney U and Kruskal-Wallis H tests were used to analyze differences in acoustic parameters. The Kaplan-Meier method was used to calculate the overall survival (OS) and recurrence-free (RFS) rates. Univariate and multivariate Cox regression analyses were performed of the clinical data. Results: The postoperative follow-up period ranged from 12 to 196 months (mean: 66.18 months). Of the 171 patients, 16 had recurrence and 8 died of thyroid-related diseases. The 5-year OS rate was 95.22%. The 5-year RFS rate was 89.38%. Jitter and shimmer were higher and maximum phonation time was shorter in patients with preoperative vocal cord paralysis (VCP) than in those without RLN involvement, and in those with RLN involvement but without preoperative VCP. Acoustic parameters were similar in patients with no preoperative VCP and those without RLN involvement. Voice analysis results did not differ between cases with RLN adhesion and RLN invasion. Univariate analysis showed that age at onset ≥ 55 years, preoperative RLN palsy, and esophageal invasion were risk factors for postoperative recurrence of PTC with RLN involvement. Multivariate analysis showed that onset age ≥ 55 years (OR 4.52, 95% confidence interval: 1.44-14.19, P = 0.010) was an independent risk factor for recurrence. Conclusions: PTC patients with RLN invasion can achieve good outcomes. Preoperative voice analysis may offer insights into RLN function. Age of onset ≥ 55 years is an independent risk factor for postoperative recurrence in T4a PTC patients.

The Importance of Mapping Vagus and Laryngeal Nerves Monitoring During Thyroid Surgery.

OBJECTIVE: To determine the location of thyroid-related nerves by nerve monitoring and demonstrate the usefulness of Nerve Integrity Monitor in thyroid surgery. STUDY DESIGN: Descriptive study. PLACE AND DURATION OF STUDY: Department of General Surgery, University of Health Sciences, Istanbul Training and Research Hospital, Turkey, from February 2017 to January 2020. METHODOLOGY: Patients, who underwent thyroid surgery, were evaluated for age, gender, preoperative diagnosis, type of surgery, histopathological result, postoperative hoarseness, and postoperative vocal cord examinations. The vagus nerve, recurrent laryngeal nerve (RLN), and superior laryngeal nerve (SLN) were mapped by nerve monitoring. RESULTS: A total of 328 patients were included in this study. On both sides, the vagus nerve was most often located in the posterior of the internal carotid artery and internal jugular vein and less frequently anterior to this vein. A total of 303 right RLNs and 305 left RLNs were verified. The SLN was visualised or motor activity was verified by nerve monitoring on the right side in 181 patients and on the left side in 179 patients. The SLN's location was classified most frequently as type I and least frequently as type IIb on the right and left sides. CONCLUSION: The reported variations, the experience of the surgeon, and these anatomical markers cannot be adequate in preventing nerve injuries. Furthermore, the variations can be identified more clearly peroperatively with the use of nerve monitoring. KEY WORDS: Laryngeal nerves, Nerve mapping, Nerve monitoring, Nervus vagus, Thyroid surgery, Zuckerkandl tubercles.

Extracellular matrix deformations of the porcine recurrent laryngeal nerve in response to hydrostatic pressure.

Damage to the recurrent laryngeal nerve (RLN) caused by supraphysiological compression or tension imposed by adjacent tissue structures, such as the aorta, may contribute to onset of idiopathic unilateral vocal fold paralysis (iUVP) resulting in difficulty speaking, breathing, and swallowing. We previously demonstrated in adolescent pigs that the right RLN epineurium exhibits uniform composition of adipose tissue, with larger quantities along its length within the neck region in contrast to the left RLN that shows greater collagen composition in the thoracic region and greater quantities of adipose tissue in the neck region. In contrast, the epineurium in piglets was primarily composed of collagen tissue that remained uniform along the length of the left and right RLNs. Tensile testing of the left and right RLN in piglets and pigs showed associated differences in strain by RLN side and segment by age. The goal of this study was to investigate how external hydrostatic compression of the RLN affects the nerve's connective tissue and microstructure. RLN segments were harvested from the distal (cervical/neck) regions and proximal (subclavian for the right RLN, thoracic for the left RLN) regions from eight adolescent pigs and nine piglets. RLN segments were isolated and assessed under fluid compression to test hypotheses regarding epineurium composition and response to applied forces. Second harmonic generation (SHG) imaging of epineurial collagen was conducted at 0, 40, and 80 mmHg of compression. The cartesian strain tensor, principal strain (Eps1), and principal direction of the RLN collagen fibers were determined at each pressure step. Significantly larger values of the 1st principal strain occurred in the proximal segments of the pig left RLN when compared to the same segment in piglets (p = 0.001, pig = 0.0287 [IQR = 0.0161 - 0.0428], piglet = 0.0061 [IQR = 0.0033 - 0.0156]). Additionally, the median transverse strain Eyy) for the second pressure increment was larger in the right proximal segment of pigs compared to piglets (p < 0.001, pig = 0.0122 [IQR = 0.0033 - 0.0171], piglet = 0.0013 [IQR = 0.00001 - 0.0028]). Eyy values were significantly larger in the right proximal RLN versus the left proximal RLNs in pigs but not in piglets (p < 0.001). In contrast to piglets, histological analysis of pig RLN demonstrated increased axial alignment of epineurial and endoneurial collagen in response to compressive pressure. These findings support the hypothesis that the biomechanical response of the RLN to compressive pressure changed from being similar to being different between the right and left RLNs during development in the porcine model. Further investigation of these findings associated with age-related onset of idiopathic UVP may illuminate underlying etiologic mechanisms. STATEMENT OF SIGNIFICANCE: Damage to the recurrent laryngeal nerve (RLN) caused by compression imposed by the aorta may contribute to the onset of left-sided idiopathic unilateral vocal fold paralysis resulting in difficulty speaking, breathing, and swallowing. The goal of this study was to investigate how compression affects the connective tissue and microstructure of the RLN. We quantified the pressure induced deformation of the RLN using multiphoton imaging as a function of both location (proximal versus distal) and age (piglets, adolescent pigs). Our results demonstrate that the biomechanical response of the RLN to compression changes in the right versus left RLN throughout development, providing further evidence that the the left RLN is exposed to increasing dynamic loads with age.

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).

Pediatric intraoperative nerve monitoring during thyroid surgery: A review from the American Head and Neck Society Endocrine Surgery Section and the International Neural Monitoring Study Group.

Children are more likely to experience recurrent laryngeal nerve (RLN) injury during thyroid surgery. Intraoperative nerve monitoring (IONM) may assist in nerve identification and surgical decision making. A literature review of pediatric IONM was performed and used to inform a monitoring technique guide and expert opinion statements. Pediatric IONM is achieved using a variety of methods. When age-appropriate endotracheal tubes with integrated surface electrodes are not available, an alternative method should be used. Patient age and surgeon experience with laryngoscopy influence technique selection; four techniques are described in detail. Surgeons must be familiar with the nuances of monitoring technique and interpretation; opinion statements address optimizing this technology in children. Adult IONM guidelines may offer strategies for surgical decision making in children. In some cases, delay of second-sided surgery may reduce bilateral RLN injury risk.

Evaluation of Laryngeal Motor Neuropathy Using Transcranial Magnetic Stimulation-Mediated Evoked Potentials.

OBJECTIVES/HYPOTHESIS: Contemporary evaluation of vocal fold motion impairment largely relies on clinical laryngoscopy, with the diagnoses of vocal fold paresis (VFPa) and paralysis (VFP) being based on identification of partial and complete restriction of gross vocal fold motion, respectively. No consensus exists on the diagnostic criteria of VFPa. Laryngeal electromyography does not offer any insight into nerve conduction velocity without the adjunction of nerve conduction studies, which are impractical to perform on laryngeal nerves due to their anatomic location. The present study aims to assess the feasibility of laryngeal nerve conduction studies using transcranial magnetic stimulation (TMS)-mediated myogenic evoked potentials in the evaluation of laryngeal motor nerve function. STUDY DESIGN: Prospective controlled cohort study. METHODS: Enrollment of three groups of subjects defined as healthy volunteers, subjects with clinically diagnosed unilateral VFP, and subjects with clinically diagnosed unilateral VFPa of peripheral etiology. Electrodiagnostic studies consisting of bilateral stimulation of the laryngeal motor cortex, proximal cisternal, and peripheral portions of the vagus nerves were performed using figure-of-eight magnetic stimulation coils, and myogenic evoked potentials recorded from bilateral thyroarytenoid, cricothyroid, and posterior cricoarytenoid muscles using indwelling hook wire electrodes. Conduction latencies were plotted against demographic and anthropometric variables. Values obtained in healthy volunteers were used as normative references and compared to aggregated latencies of VFP and VFPa groups. RESULTS: Enrolled subjects included 19 healthy volunteers, 5 subjects with VFP, and 4 subjects with VFPa. Normative laryngeal nerve conduction latency ranges measured in healthy subjects were comparable to prior published values, and recorded latencies increased in positive correlation with age. VFPa subjects exhibited increased latencies in affected nerve sites, while VFP subjects presented more variability in electrophysiologic manifestations, mostly dependent on their degree of compensatory reinnervation. Aberrant and synkinetic reinnervation patterns were more predominant in the VFP group than the VFPa group. CONCLUSIONS: Laryngeal nerve conduction studies using TMS-mediated myogenic evoked potentials are safely feasible. They may serve as a useful complement to laryngeal electromyography in the evaluation of motor laryngeal neuropathy and represent a promising diagnostic modality in the evaluation of VFPa. Based on the present study's findings, the commonly accepted notion of VFPa as a manifestation of a less severe form of neuropathy than VFP may be unsubstantiated. Aging may contribute to progressive motor nerve dysfunction. Future investigations are needed to ascertain the role of nerve conduction studies in clinical laryngology practice. LEVEL OF EVIDENCE: 3 Laryngoscope, 132:S1-S12, 2022.

The learning curve and safety of continuous intraoperative vagus nerve monitoring in thyroid surgery.

INTRODUCTION: Continuous intraoperative nerve monitoring allows for continuous feedback on the integrity of the recurrent laryngeal nerve (RLN) and the quality of its induced myogenic potential. The aims of this study were to assess the time requirements and risks associated with vagus nerve electrode placement when learning the technique. METHODS: This is a prospective observational study carried out in a single otolaryngology department at the start of a trainee's placement. A total of 40 vagus nerve dissections in 31 consecutive operations (22 hemithyroidectomies, 9 total thyroidectomies) using automatic periodic stimulation (APS, Medtronic) are included. Of the electrode placements, 10 were performed by the trainer and 30 by the trainee. The time required for each surgical step and complications relating to vagus nerve dissection were recorded. RESULTS: The average (median+IQR) total additional time attributable to vagus nerve dissection, electrode placement and baseline electromyogenic assessment was 3.1mins (2.5-3.3) for the trainer and 4.8mins (4.1-5.3) for the trainee (p<0.0001). There was a downward trend in time requirement for the trainee (not statistically significant, p=0.080). Total operative time was 38min (35-45) for hemithyroidectomy and 56min (53-62) for total thyroidectomy. There was a mix of benign (74%) and malignant (26%) histology, no intraoperative complications relating to autonomic dysfunction and one (2.5%) transient nerve palsy. CONCLUSIONS: Operative time attributable to vagus nerve electrode placement is short and the procedure is easy to learn. Appropriate surgical technique and careful anaesthetic considerations allow monitoring to be performed safely, and may reduce the rate of RLN palsy.

Intraoperative Monitoring and Preservation of Anatomic Integrity of Palsied Recurrent Laryngeal Nerve is Extremely Meaningful During Redo Thyroid Surgery.

Redo thyroid surgery on patients with unilateral recurrent laryngeal nerve (RLN) palsy certainly poses a great surgical challenge. We present a case of a patient with unilateral vocal cord (VC) palsy who underwent redo thyroid surgery under intraoperative neuromonitoring. The patient's normal speaking voice was maintained after the primary surgery, even though preoperative laryngoscopy showed an immobile right VC with a normal structure. During reoperation, surgical exploration revealed the anatomical integrity of palsied RLN with extralaryngeal terminal bifurcation. The electrophysiological stimulation of the vagus nerve and palsied RLN generated wave amplitudes (V1: 242, R1: 347, R2: 352 and V2: 152 µV). Despite positive amplitudes, postoperative laryngoscopy confirmed RLN palsy and corresponding VC paralysis but preserved the structure of the immobile VC. Even palsied RLN should be monitored during redo surgery. A positive signal delineates at least partial neural transmission despite VC palsy. The preservation of anatomical integrity of palsied RLN for eventual partial conductivity may be vital in preserving the normal structure of VC and maintaining the patient's voice despite its immobility. Key Words: Surgery, Redo thyroidectomy, Recurrent laryngeal nerve injury, Vocal cord palsy.

How blue lining the recurrent laryngeal nerve can aid in re-operative surgery?

The recurrent laryngeal nerve (RLN), is one of the main structures at risk of injury causing vocal cord paralysis during head and neck surgery, especially during thyroid or parathyroid surgery, central neck dissection and upper oesophageal sphincter surgery. We describe the systematic use of marking of the RLN using non-resorbable blue polypropylene suture after its localisation, just inside its penetration below the cricopharyngeal muscle, to help identify the nerve for cases of re-operative surgery in this area. This specific marking technique could facilitate subsequent preservation of the nerve and reduce nerve injury risk in cases of planned or unexpected future operations, as well as emergency surgery due to postoperative complications. We apply this technique simultaneously with intra-operative laryngeal neuromonitoring. This method is safe and easy to perform.