Identification Of External Branch Of The Superior Laryngeal Nerve Research Articles

Success rate and learning curve of intraoperative neural monitoring of the external branch of the superior laryngeal nerve in thyroidectomy.

This study aimed to evaluate the success rate and learning curve of intraoperative neural monitoring (IONM) of the external branch of the superior laryngeal nerve (EBSLN) in thyroidectomy. We studied 130 consecutive patients (200 nerves at risk [NARs]) who had undergone conventional thyroidectomy with IONM of the recurrent laryngeal nerve (RLN) and EBSLN from January 2017 to March 2020. The learning curve was defined as the number of NARs required to achieve an effective and reliable neuromonitoring rate. IONM of the EBSLN was successful in 136/200 (68%) NARs. The cutoff point of the learning curve was 45 NARs (28 patients). The neural identification rate of EBSLN was significantly higher in the post-learning 155 NARs group than the pre-learning group (82.6% vs. 17.8%, p < 0.001). Approximately 45 NAR neuromonitoring attempts were required to reach a significant increase in the EBSLN identification rate and overcome the learning curve.

Visual identification and neuromonitoring vs. no sighting the external branch of the superior laryngeal nerve in thyroid surgery: a randomized clinical trial.

To evaluate the incidence of external branch of the superior laryngeal nerve (EBSLN) injuries after thyroid surgical procedures with or without the functional and visual identification of the EBSLN before ligation at the superior thyroid pole. Patients with papillary thyroid carcinoma (PTC) enrolled from a single tertiary referral academic medical center were assigned to functional and visual identification of EBSLN group (study group) or no identification of EBSLN group (controlled group). The main outcome measures were the incidence of EBSLN injury detected by the intraoperative neuromonitoring and Voice Handicap Index-10 (VHI-10) and Impairment Index-5 (VII-5) valuation questionnaires. Postoperative complications were recorded. A total of 140 (50.4%) patients were enrolled in study group and 138 (49.6%) in controlled group. In the study group, 110 (39.3%) EBSLNs were direct visual recognized and 170 (60.7%) nerves were visually identified with the help of neuromonitoring. Three patients in the study group and two patients in the controlled group were diagnosed with vocal cord paralysis. Six (4.4%) patients in the identification group and 37 (27.2%) patients in the no identification group presented no response from the stimulation of sternothyroid-laryngeal triangle. The VII-5 scores of the study group were significantly higher than those of the controlled group at one and three months postoperatively (P = 0.024 and P = 0.034). With significant lower scores of VII-5 and VHI-10, functional and visual identification of EBSLN might be necessary during thyroid surgery to protect the structural integrity and motor activity of the nerve.

Assessment of nerve stimulation during thyroidectomy for identification of the external branch of superior laryngeal nerve

Background The external branch of the superior laryngeal nerve (EBSLN) injury is an important and not uncommon, though frequently overlooked, complication of thyroid surgery. The rate of EBSLN injury has been reported to vary from 0 to 58%, depending on different postoperative assessment methods. Injury to the EBSLN during thyroid operation can paralyze ipsilateral cricothyroid muscle, and the clinical symptoms mainly include vocal fatigue and diminished vocal frequency range, especially with respect to raising pitch, which may result in decreased quality of life, particularly for voice professionals. Patients and methods This prospective study included 22 patients with goiter. They were divided into two groups: group 1 (G1) included all cases in whom nerve stimulator was used and group 2 (G2) included all cases in whom trial of visual identification of the EBSLN was done. Results It was found that patients with short obese neck, large gland size, large gland weight, and retrosternal extension showed difficulty in EBSLN identification and had high risk of nerve injury (P Conclusion It was concluded that routine use of nerve stimulator in surgical interventions on the thyroid gland will be beneficial for more secure identification and prevention of EBSLN injury and preservation of voice quality postoperatively.

Simple technique to preserve the external branch of the superior laryngeal nerve during thyroidectomy: Clinical practicability of an attachable nerve stimulator

ObjectiveThis study aimed to demonstrate the usefulness of an attachable magnetic nerve stimulator for preservation of the external branch of the superior laryngeal nerve (EBSLN) during thyroidectomy. MethodsWe retrospectively analyzed 120 female patients, of which 60 underwent thyroidectomy with an attachable magnetic nerve stimulator (magnetic group) and the remaining 60 underwent thyroidectomy with a conventional method without EBSLN identification (control group). For both groups, objective and subjective voice parameters were investigated on the day before surgery and at 2 weeks and 2 months after surgery. ResultsIn the magnetic group, a magnetic nerve stimulator was used to ligate only the site without cricothyroid muscle (CTM) twitching, and thyroid surgery was successfully performed without damage to the EBSLN. In the control group, objective voice parameters, including fundamental frequency, voice range profile (VRP), highest VRP (VRP-H), and maximal phonation time, and the subjective thyroidectomy-related voice questionnaire score were significantly decreased at 2 months after surgery compared to preoperative values. Compared to the control group, the magnetic group did not show a significant decrease in the objective VRP and VRP-H at 2 months after surgery. ConclusionThe use of metallic surgical instruments with an attachable magnetic nerve stimulator may provide surgeons with real-time feedback on CTM twitching feedback and EBSLN status. Compared to direct EBSLN identification during thyroidectomy, this is a simple, easy, and noninvasive method for EBSLN preservation that is useful, especially for less-experienced surgeons.

Investigation on EMG Profiles of the Superior Laryngeal Nerve in a In Vivo Porcine Model

Background: The electromyographic (EMG) profiles of external branch of the superior laryngeal nerve (EBSLN) have been defined and the optimal intensity of the stimulation of EBSLN in an in vivo porcine model has been explored. Materials: EMG was simultaneously registered by the surface of endotracheal tube and needle electrodes by applying a monopolar stimulation probe in 12 piglets (22 EBSLNs). Vagal nerve (VN), RLN and EBSLN were excited to record the EMG tracings and cricothyroid muscle twitch (CTM). VN, RLN and EBSLN were stimulated from 0.1 to 1.0 mA. Cmin and Cmax have been defined as the minimum and maximal stimulation to evoke an EMG response. Results: The stimulation resulted in a dose-response curve. Cmin were 0.19 mA (0.04–0.4), 0.19 mA (0.08–0.3) and 0.21 mA (0.1-0.4) for EBSLN, RLN and VN (p > 0.05) respectively. Cmax were 0.6 mA along with an amplitude value of 396 ± 330 μV, 0.5 mA including 1058 ± 382 μV, 0.8 mA coupled with 870 ± 382 μV, equally for EBSLN, RLN and VN (p > 0.05) respectively. No asymmetry of amplitude responses each side for EBSLN, RLN and VN (p = 0.317, p = 0.203 and p = 0.468, respectively) was noted. The amplitudes of EBSLN were significantly lower than RLNs and VN (42% of RLN and 50% of VN amplitude rates). Also, CTM twitch was always detectable with the stimulation of EBSLN. Conclusions: Cmin and Cmax of EBSLN were comparable to RLN and VN standards. The amplitude stimulus-response curves of RLN, VN and EBSLN were highly variable. It has been suggested to apply a stimulation of 1.0 mA and a visual appreciation of CTM twitch for the identification of EBSLN.

Surgical anatomy of the external branch of the superior laryngeal nerve: a systematic review and meta-analysis.

To provide a comprehensive evidence-based assessment of the anatomical characteristics of the external branch of the superior laryngeal nerve (EBSLN). A thorough systematic search was performed on the major electronic databases PubMed, EMBASE, Cochrane library, and ScienceDirect to identify eligible studies. Data were extracted and pooled into a meta-analysis. The primary outcomes were the EBSLN identification rate (total number of EBSLN identified divided by the total number of dissected hemilarynges) and the prevalence of various EBSLN types. A total of 56 studies (n = 13,444 hemilarynges) were included. The overall pooled EBSLN identification rate was 89.24% (95% CI 85.49-92.49). This rate was higher for cadaveric (95.00%; 95% CI 89.73-99.35) compared to that reported in intraoperative studies (86.99%; 95% CI 82.37-91.01). Significantly higher identification rates were reported for studies in which intraoperative nerve monitoring was used (95.90%; 95% CI 94.30-97.25) compared to those which only relied on direct visual identification of the EBSLN (76.56%; 95% CI 69.34-83.08). Overall, Cernea type IIa (nerves crossing the superior thyroid artery less than 1cm above the upper edge of the superior thyroid pole) and Friedman type 1 (nerves running their entire course superficial to the inferior pharyngeal constrictor) were the most prevalent (41.84%; 95% CI 33.28-48.08 and 50%; 95% CI 29.90-65.62, respectively). The combined prevalence of Cernea IIa and IIb (nerves crossing the superior thyroid artery below the upper edge of the superior thyroid pole) was higher in intraoperative studies compared to that in cadaveric studies (64.3% vs 49.4%). The EBSLN coursed medial to the superior thyroid artery in 70.98% (95% CI 55.14-84.68) of all cases. The use of intraoperative nerve monitoring improves EBSLN identification rates. In light of the highly variable anatomical patterns displayed by the EBSLN, thorough pre-operative knowledge of its anatomy can be crucial in minimizing incidences of its iatrogenic injury.

The evolution and progress of intraoperative monitoring of the external branch of the superior laryngeal nerve in thyroid surgery

Hypoparathyroidism and recurrent laryngeal nerve (RLN) damage are the most frequent reported morbidity in thyroid surgery whereas damage of the external branch of the superior laryngeal nerve (EBSLN) has been considered to be the most neglected sequel. EBSLN injury results in subtle changes in voice as a result of dysfunction of the cricothyroid muscle (CTM): changed basic voice frequency, deterioration of voice quality in the production of high frequency sounds and reduced voice projection. Symptoms of this dysfunction are usually more notable for professional voice users and can be difficult to diagnose. EBSLN injury can happen during dissection of the vessels of the upper thyroid pole due to proximity between the nerve and these vessels. Several maneuvers can minimize the risk of injury to the EBSLN including visual identification of the nerve before ligation of the upper thyroid pole vessels and use of either a nerve stimulator or intraoperative neuromonitoring (IONM) for neuromapping and evidence of the EBSLN identification. The EBSLN monitoring is relied on evaluation of CTM twitch (present in all patients) and electromyographic curve traced by the monitor using surface tube electrodes within the vocal folds which present in the majority but not all individuals (70–80% of patients using standard EMG tubes) or approaching to 100% of patients (using NIM TriVantage tubes). IONM has a potential to increase the rate of the EBSLNs identification, diminish prevalence of neural damage, and decrease prevalence of postoperative voice impairment which has been repeatedly supported by recently published data. It is advised that at the end of upper thyroid lobe dissection the EBSLN should be stimulated at the most cranial arc of dissection to confirm not only anatomical but what is even more important functional preservation of intact neural function.

Injury of the external branch of the superior laryngeal nerve in thyroid surgery.

The external branch of the superior laryngeal nerve (EBSLN) innervates the cricothyroid muscle (CTM) to promote lengthening and thinning of the vocal fold, thus increasing voice pitch. The close relation with the superior thyroid vessels (STV) puts the EBSLN in risk every time the superior pole of the thyroid is dissected. It travels downward to innervate the CTM, lateral to the thyroid cartilage and to the inferior pharyngeal constrictor muscle (IPCM), being eventually covered by this muscle fibers as it approaches its entry point. During its descending course, the EBSLN curves and crosses the STV posteriorly. The lower this crossing occurs in the neck, the higher the risk of surgical damage to the nerve by transection, traction, entrapment, thermal damage or disrupted blood supply. The chances of surgical trauma are also increased by size and weight of the specimen, shorter neck length and non-white ethnicity. Voice changes following thyroid surgery are common and multifactorial. The actual rate of vocal impairment due to EBSLN injury is unclear, since changes to the everyday speaking voice can be minimal and laryngeal findings are usually subtle and controversial. CTM electroneuromyography (EMG) is the most accurate tool to diagnose abnormal EBSLN conductivity, but it is technically difficult and barely applicable in routine practice. Recommended approaches to prevent injury include: (I) individual distal ligature of the STV by the thyroid capsule; (II) visual identification of the nerve and its trajectory and (III) electrostimulation with either observation of CTM twitch or intraoperative nerve monitoring (IONM) via dedicated endotracheal tube electrodes. There is accumulating evidence that a combination of visual and standardized electrophysiological EBSLN identification with meticulous division of the STV improves preservation rates. IONM bears the additional benefits of prognostication, quantification and documentation of neural function once it allows intraoperative laryngeal EMG.

International survey on the identification and neural monitoring of the EBSLN during thyroidectomy.

Surgical management of the external branch of the superior laryngeal nerve (EBSLN) during thyroidectomy is complex. We hypothesized that there exist variations in surgical behaviors patterns in the management of the EBSLN during thyroidectomy. A prospective Web-based anonymous survey (www.surveymonkey.com). The survey, consisting of 22 questions including surgeon demographics, laryngeal examination before and after surgery, and utilization of intraoperative neuromonitoring (IONM) for the management of the recurrent laryngeal nerve (RLN) and the EBSLN, was sent to 673 surgeons worldwide with known interest in thyroid surgery. A total of 170/673 (25.3%) surgeons from five continents with low-volume (11.2%), moderate-volume (27.2%), and high-volume practices (61.5%) completed the survey. Laryngeal preoperative examination was performed by 94% of respondents. IONM was utilized in the RLN management by 95% of respondents. IONM was used for identification of the EBSLN by 26.3% of low-volume versus 68.4% of high-volume surgeons (P = .004), and 93% of respondents felt EBSLN identification with IONM as necessary in voice professionals. Staged thyroidectomy was performed for benign disease by 89.5% of low-volume versus 63.2% of high-volume surgeons (P = .031). Post-thyroid surgery laryngeal examination was performed by 36.8% of low-volume versus 64.9% of high-volume surgeons (P = .032). Laryngeal examination and IONM is used frequently. However, the exact pattern of utilization varies notably with demographic information. Generally, high-volume surgeons, those with otolaryngology background, and younger surgeons more commonly utilize IONM according to existing international neural monitoring study group guidelines. Prospective multicenter studies are needed to guide an evidence-based management of the EBSLN during thyroidectomy.

Prospective validation study of Cernea classification for predicting EMG alterations of the external branch of the superior laryngeal nerve.

Cernea classification is applied to describe the external branch of the superior laryngeal nerve (EBSLN). Using intraoperative neural monitoring we evaluated whether or not this classification is useful for predicting which EBSLN subtype has an increased risk of injury. An analysis of 400 EBSLN. The identification of EBSLN was achieved with both cricothyroid muscle twitch and the glottis evoked electromyography response. We defined S1 initial EBSLN stimulation at identification and S2 final nerve stimulation achieved in the most cranial aspect of the nerve exposed above the area of surgical dissection after superior artery ligation. The mean S1 amplitude acquired was 259+/67 (180-421), 321+/79 (192-391), 371+/38 (200-551) μV, respectively, for type 1, 2A, 2B (p=0.08). The S1 and S2 amplitudes were similar in type 1 (p=0.3). The S1 and S2 determinations changed significantly in type 2A and 2B (p=0.04 and 0.03). EBSLN which demonstrated a >25% decreased amplitude in S2 increased significantly from Type 1 (4.9%) to Type 2A (11.2%) and 2B (18%) (p=0.01). None of type 1, 2.8% type 2A and 3% type 2B showed a loss of EBSLN conductivity. The latency determinations did not vary significantly for any parameter compared. The Cernea classification was, therefore, found to predict the risk of EBSLN stress. We identified amplitude differences between S1 and S2 determinations in type 2A and 2B, thus confirming that surgical dissection in these subtypes is, therefore, extremely difficult to perform.

Use of the Nerve Integrity Monitor during Thyroid Surgery Aids Identification of the External Branch of the Superior Laryngeal Nerve

The external branch of the superior laryngeal nerve (EBSLN) is at risk during thyroid surgery. Despite meticulous dissection and visualization, the EBSLN can be mistaken for other structures. The nerve integrity monitor (NIM) allows EBSLN confirmation with cricothyroid twitch on stimulation. The aim of this study was to assess any difference in identification of EBSLN and its anatomical sub-types by dissection alone compared to NIM-aided dissection. Routine intra-operative nerve monitoring (IONM) was used, when available, for 228 consecutive thyroid operations (129 total thyroidectomies, 99 hemi-thyroidectomies) over a 10-month period. EBSLN identification by dissection alone (with NIM confirmation of cricothyroid twitch) and by NIM-assisted dissection was recorded prospectively. Anatomical sub-types were defined by the Cernea classification. Of 357 nerves at risk, 97.2 % EBSLNs (95 % confidence interval [CI], 95.5-98.9) were identified by visualization and NIM-aided dissection compared to 85.7 % (95 % CI, 82.1-89.3) identified by dissection alone (<0.001). EBSLN frequency was 34 % for type 1, 55 % for type 2a, and 11 % for type 2b. All identified EBSLNs were stimulated to confirm a cricothyroid twitch after superior thyroid vessel ligation. Using the NIM and meticulous dissection of the upper thyroid pole improves EBSLN identification. As the EBSLN is at risk during thyroidectomy and can lead to voice morbidity, the NIM can aid identification of the EBSLN and provide a functional assessment of the EBSLN after thyroid resection.

Superior laryngeal nerve quantitative intraoperative monitoring is possible in all thyroid surgeries

To report normative electromyography (EMG) data on the external branch of the superior laryngeal nerve (EBSLN) and to compare this to analogous data of the recurrent laryngeal nerve (RLN) and vagus nerve (VN) during intraoperative neural monitoring (IONM) using both the standard monopolar stimulator probe and a novel bipolar stimulator probe. Prospective multiple tertiary care center study. A prospective study of EBSLN, RLN and VN EMG data in 22 thyroid surgeries was performed. Subjects with preoperative vocal fold paralysis were excluded. Postoperative laryngoscopy was normal in all subjects. Normative EMG data were acquired using both a standard monopolar and a novel bipolar stimulator probe, as well as a novel endotracheal tube. Cricothyroid muscle (CTM) twitch response during EBSLN stimulation was analyzed. In 100% of cases, EBSLN was identified and quantifiable EMG response was observed. EMG amplitude did not change despite extensive nerve dissection and multiple nerve stimulations. EBSLN amplitude was similar for left and right sides for patients under age 50 and aged 50 or older, for both genders, and with monopolar and bipolar stimulators. Intraoperative neural monitoring may be used to safely assist in EBSLN identification during thyroid surgery in 100% of patients. A novel endotracheal tube allows for quantifiable EBSLN EMG activity in 100% of cases. Monopolar and bipolar stimulator probes produce similar EMG data. 4.

Normative Intra‐operative Electrophysiologic Waveform Analysis of Superior Laryngeal Nerve External Branch and Recurrent Laryngeal Nerve in Patients Undergoing Thyroid Surgery

Injury to the external branch of the superior laryngeal nerve (EBSLN) can occur during superior pole dissection in thyroid surgery; the EBSLN injury rate is reported as high as 28 % (Cernea et al., Head Neck 14:380-383, 1992). Injury to the EBSLN leads to variable symptoms that may be overlooked, but that can be significant, especially to professional speakers and singers. Intraoperative nerve monitoring (IONM) is employed widely to aid in nerve identification. We report on normative electroneuromyography (EMG) data on EBSLN-IONM and cricothyroid muscle (CTM) twitch response during stimulation as an aid to EBSLN identification. A prospective study of the SLN and the recurrent laryngeal nerve (RLN) IONM data in 72 consecutive thyroid surgeries was carried out. All patients underwent preoperative and postoperative laryngeal exams, and patients with abnormal preoperative laryngeal function were excluded. Normative EMG data and CTM twitch response during EBSLN stimulation were recorded and analyzed. Stimulation of the EBSLN resulted in a positive CTM twitch response in 100 %, whereas EMG response was recordable in 80 %. Electromyographic amplitude was ~1/3 of ipsilateral RLN amplitude and did not change through the case with multiple stimulations. Stimulation of the EBSLN was similar for men and women and at 1 and 2 mA stimulation levels. Intraoperative nerve monitoring of the EBSLN aids in EBSLN identification and provides electroneuromyographic information in 80 % of cases. The laryngeal head of the sternothyroid muscle is a useful landmark to locate EBSLN.

Identificação do ramo externo do nervo laríngeo superior na tireoidectomia minimamente invasivo vídeo-assistida

A tireoidectomia minimamente invasiva vídeo-assistida (TIMIVA) sem infusão de gás é considerada segura com vantagem estética em relação ao procedimento convencional. OBJETIVO: Apresentar os achados de identificação do ramo externo do nervo laríngeo superior (RELS) durante a TIMIVA. FORMA DE ESTUDO: Estudo de coorte transversal. CASUÍSTICA E MÉTODO: Doze pacientes foram submetidos à hemitireoidectomia por doença nodular tireoidiana. Dissecamos o pedículo vascular tireoidiano superior com o auxílio de endoscópio de cinco milímetros de zero grau visando à identificação do RELS em todos os casos. RESULTADOS: Dos 12 casos, identificamos o RELS em 10 (83,3%), sendo que o trajeto era medial aos ramos da artéria tireoidiana superior em 8 (80%) e cruzava anteriormente tais ramos em 2 (20%). CONCLUSÕES: Identificamos o RELS em 83,3% dos casos, com trajeto medial aos ramos da artéria tireoidiana superior em 80% e cruzando anteriormente tais ramos em 20%. A ligadura do pedículo superior da tireóide pode ser feita com o RELS sob visão direta.

Identification of the external branch of the superior laryngeal nerve during minimally invasive video-assisted thyroidectomy

SummaryThe minimally invasive video-assisted thyroidectomy (MIVAT) without gas infusion is considered safe and has advantages in terms of cosmetic results compared to the conventional approach. Aim: to present our findings regarding the identification of the external branch of the superior laryngeal nerve (EBSLN) during MIVAT. Study design: Transversal cohort study. Material and Method: twelve patients underwent hemithyroidectomy for thyroid nodular disease through MIVAT method. The upper pedicle of the thyroid was dissected under the magnified view at 0-degree five-millimeter endoscope in order to achieve the identification of EBSLN in all cases. Results: We identified 10 (83.3%) EBSLN out of 12 cases. The nerve ran medially to the branches of the superior thyroid artery in 8 cases (80%) and crossed anteriorly in 2 (20%). Conclusions: We identified the EBSLN in 83.3% of the cases, whose course was medial to the branches of the superior thyroid artery in 80% and crossing anteriorly in 20%. The ligation of the upper pedicle of the thyroid can be performed under direct view of the EBSLN.