Detecting and identifying nonrecurrent laryngeal nerve with the application of intraoperative neuromonitoring during thyroid and parathyroid operation

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

OBJECTIVE

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.

METHODS

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.

RESULTS

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.

CONCLUSION

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.

Carotid Endarterectomy for a Patient with a Right-sided Aortic Arch and Aberrant Left Subclavian Artery Predicting a Left Non-recurrent Inferior Laryngeal Nerve: A Case Report and Literature Review

Cardiovascular malformations during embryogenesis can lead the inferior laryngeal nerve to branching directly from the cervical vagus nerve and entering the larynx. This rare anatomical variation is known as a non-recurrent inferior laryngeal nerve (NRILN), and increases the risk of accidental injury resulting in postoperative vocal cord paralysis during neck surgery. We report a case of an 83-year-old man who presented with left symptomatic internal carotid artery stenosis with a right-sided aortic arch and aberrant left subclavian artery (ALSCA). We performed carotid endarterectomy (CEA) using intraoperative neuromonitoring to avoid NRILN injury. To the best of our knowledge, this is the first report of searching for a left NRILN by electrophysiology during CEA. Neurovascular surgeons need to understand the variations of the NRILN associated with congenital cardiovascular anomalies and effective use of intraoperative nerve monitoring (IONM). We discuss the embryological origin, IONM, and surgical pitfalls of this case.

Prevention of non-recurrent laryngeal nerve injury in robotic thyroidectomy: imaging and technique

INTRODUCTION

The aim of this report was to summarize observations, evaluate the feasibility, provide detailed information concerning proper techniques, and address limitations for non-recurrent laryngeal nerve (NRLN) dissection and release during the robotic bilateral axillo-breast approach (BABA) for thyroidectomy.

MATERIALS AND METHODS

The BABA approach was used in two cases of thyroidectomy in the setting of NRLN. Preoperative CT imaging findings suggesting the aberrant anatomy are reviewed and technical planning, inclusive of intraoperative nerve monitoring, was employed. Intraoperative videos with narrative discussion of technique for safe dissection are provided, along with supplementary video of additional technical guidance.

RESULTS

In both cases, the NRLNs were identified, dissected, and preserved. We dissected the proximal segment of each NRLN to its origin. We determined that the use of only the NRLN proximal to distal robotic dissection jeopardized the nerve. The BABA approach with the Type I NRLN is similar to the dissection of the recurrent laryngeal nerve (RLN) in transoral thyroidectomy. Due to interference with endoscopic viewing caused by the thyroid cartilage, the Type I NRLN is more challenging to manage both at the laryngeal entry point and its origin from the vagus nerve (VN). For the Type II NRLN, it is essential to identify its point of origin and the reflection of the nerve from the VN. Therefore, modification of nerve dissection to mirror open surgery with bidirectional nerve dissection assisted in avoidance of traction injury to the nerve.

CONCLUSIONS

We presented a video, a detailed description of methods, and discussed limits for NRLN management in robotic BABA. This report included (i) a description of the aberrant anatomy and CT scans to inform surgeons of the possible NRLN locations, (ii) a description of a technique for using the nerve monitor in the robotic surgeries, and (iii) a description of the techniques used to isolate and protect the NRLN during the robotic surgery. In robotic BABA, our NRLN-sparing technique and degree included mainly a multi-directional nerve dissection (i.e., medial-grade, later-grade approach together with proximal to/from distal) using athermal technique. The NRLN-sparing technique is predominantly carried out in an anterior dissection plane.

Correlation Between Objective and Subjective High-Pitched Voice Impairment in Patients After Thyroid Surgery

OBJECTIVES

High-pitched voice impairment (HPVI) is not uncommon in patients without recurrent laryngeal nerve (RLN) or external branch of superior laryngeal nerve (EBSLN) injury after thyroidectomy. This study evaluated the correlation between subjective and objective HPVI in patients after thyroid surgery.

METHODS

This study analyzed 775 patients without preoperative subjective HPVI and underwent neuromonitored thyroidectomy with normal RLN/EBSLN function. Multi-dimensional voice program, voice range profile and Index of voice and swallowing handicap of thyroidectomy (IVST) were performed during the preoperative(I) period and the immediate(II), short-term(III) and long-term(IV) postoperative periods. The severity of objective HPVI was categorized into four groups according to the decrease in maximum frequency (Fmax): <20%, 20-40%, 40-60%, and >60%. Subjective HPVI was evaluated according to the patient's answers on the IVST.

RESULTS

As the severity of objective HPVI increased, patients were significantly more to receive bilateral surgery (p=0.002) and have subjective HPVI (p<0.001), and there was no correlation with IVST scores. Among 211(27.2%) patients with subjective HPVI, patients were significantly more to receive bilateral surgery (p=0.003) and central neck dissection(p<0.001). These patients had very similar trends for Fmax, pitch range, and mean fundamental frequency as patients with 20-40% Fmax decrease (p>0.05) and had higher Jitter, Shimmer, and IVST scores than patients in any of the objective HPVI groups; subjective HPVI lasted until period-IV.

CONCLUSION

The factors that affect a patient's subjective HPVI are complex, and voice stability (Jitter and Shimmer) is no less important than the Fmax level. When patients have subjective HPVI without a significant Fmax decrease after thyroid surgery, abnormal voice stability should be considered and managed. Fmax and IVST scores should be interpreted comprehensively, and surgeons and speech-language pathologists should work together to identify patients with HPVI early and arrange speech therapy for them. Regarding the process of fibrosis formation, anti-adhesive material application and postoperative intervention for HPVI require more future research.

Safety parameters of ferromagnetic device during thyroid surgery: Porcine model using continuous neuromonitoring

BACKGROUND

The ferromagnetic (FM) device is a new surgical energy modality. This study investigated dynamic recurrent laryngeal nerve (RLN) electromyographic (EMG) data to define safety parameters for using FM devices in thyroidectomy.

METHODS

Real-time EMG tracings obtained under continuous neuromonitoring were recorded from 24 RLNs (12 piglets). In the activation study, FM devices were activated at varying distances from the RLN. In the cooling study, FM devices were cooled for varying time intervals, or muscle touch maneuver was performed, before contact with the RLN.

RESULTS

During the FMwand/FMsealer activation, no adverse EMG events occurred at distances of 2 mm or longer. The cooling study revealed no adverse EMG events after 1-second (FMwand) or 3-second (FMsealer) intervals or after muscle touch maneuver.

CONCLUSIONS

An FM device should be activated at a distance of 2 mm from the RLN and should be adequately cooled before further contact with the RLN. Surgeons can avoid RLN injury by observing standard procedures for using FM devices.

THYROID SURGERY, IONM AND SUGAMMADEX SODIUM RELATIONSHIPS: BENEFITS IN SUGAMMADEX SODIUM USE FOR IONM

Background

It is important to protect recurrent laryngeal nerve (RLN) during thyroid surgery. Thus, intra- operative neuromonitoring (IONM) has got popularity. But, the half life of neuromuscular blocking agents used has a reverse correlation with reliability and effectiveness of IONM. This study aimed to research the effect of Sugammadex Sodium, a specific nemuromuscular blocking agent antagonist, on nerve conduction and IONM.

Materials and methods

Twenty patients who underwent thyroidectomy under IONM followed an enhanced NMB recovery protocol-rocuronium 0.6 mg/kg at anesthesia induction and sugammadex 2 mg/kg at the beginning of operation. To prevent laryngeal nerve injury during the surgical procedures, all patients underwent intraoperative monitoring. At the same time, the measurement of TOF-Watch acceleromyograph of the adductor pollicis muscle response to ulnar nerve stimulation was performed; recovery was defined as a train-of-four (TOF) ratio ≥ 0.9. Age, sex, recurrent laryngeal nerve transmission speeds prior to and after operation, BMI, duration of surgery, the change in nerve transmission after drug administration and complications were analyzed.

Results

The mean age and the mean BMI were 47.6±11.82 years and 28.74±3.20, respectively. The mean operation duration was 52.65±5.51 minutes. There was no difference in either right or left RLN monitoring values before and after surgery. Following the drug injection, the TOF guard measurements on the 1^st, 2^nd, 3^rd and 4^th minutes were 23.5±4.90; 69.5±6.86; 88±4.1 and 135.9±10.62, respectively.

Conclusion

Neuromuscular blocking antagonist use and monitoring nerve transmission speed with TOF-guard can provide a safer resection.

Effect of intraoperative neuromonitoring on efficacy and safety using sugammadex in thyroid surgery: randomized clinical trial

Purpose

The use of nondepolarizing neuromuscular blocking agents (NMBAs) may affect intraoperative neuromonitoring (IONM) during anesthesia used during thyroid and parathyroid surgery.

Methods

The use of sugammadex was evaluated in a prospective clinical study during thyroid surgery. Between July 2018 and January 2019, 129 patients were prospectively randomized to either the sugammadex group (group B) or the control group (group A). Group A patients underwent standardized IONM during thyroidectomy, while group B patients used an NMBA-reversal protocol comprised of rocuronium (0.6 mg/kg) in anesthesia induction and sugammadex (2 mg/kg) after first vagal stimulation (V0). A peripheral nerve stimulator was used to monitor the neuromuscular transmission.

Results

In our clinical study, it took 26.07 ± 3.26 and 50.0 ± 8.46 minutes to reach 100% recovery of laryngeal electromyography at injection of the sugammadex group (2 mg/kg) and the control group, respectively (P < 0.001). The train-of-four ratio recovered from 0 to >0.9 within 4 minutes after administering 2 mg/kg of sugammadex at the beginning of resection. Surgery time was significantly shorter in group B than in group A (P < 0.001). Transient recurrent laryngeal nerve (RLN) paralysis was detected in 4 patients from group A and in 3 patients from group B (P = 0.681). There was no permanent RLN paralysis in the 2 groups.

Conclusion

Our clinical study showed that sugammadex effectively and rapidly improved the inhibition of neuromuscular function induced by rocuronium. The implementation of the nondepolarizing neuromuscular block recovery protocol may lead to tracheal intubation as well as favorable conditions for IONM in thyroid surgery.

Usefulness of intraoperative neuromonitoring for preservation of an extralaryngeal bifurcation of the recurrent laryngeal nerve: A case report

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Recurrent laryngeal nerve injury is a major complication of thyroid surgery.

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Use of an electromyography endotracheal tube can prevent this injury.

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We describe a case of extralaryngeal bifurcation of the recurrent laryngeal nerve.

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Intraoperative neuromonitoring could identify and preserve this bifurcation.

Introduction: Recurrent laryngeal nerve injury is a major complication of thyroid surgery. An endotracheal tube with electromyography electrodes attached to it was recently developed for intraoperative neuromonitoring during thyroid surgery. Here we describe the successful identification and preservation of an extralaryngeal bifurcation of the recurrent laryngeal nerve by intraoperative neuromonitoring in a patient undergoing thyroid surgery.

Presentation of case: A 56-year-old woman presented for evaluation of a neck swelling found during a medical examination. Computed tomography (CT) revealed a tumor with a 5-cm diameter in the left thyroid lobe. Fine needle aspiration cytology revealed a Bethesda category III finding. Left thyroid lobe resection was scheduled. During surgery, the left recurrent laryngeal nerve was found to be adhered to the tumor. Careful exploration and intraoperative neuromonitoring allowed us to identify and preserve an extralaryngeal bifurcation of the recurrent laryngeal nerve.

Discussion: The recurrent laryngeal nerve can demonstrate various anomalies and bifurcations. Failure to notice and correctly identify extralaryngeal bifurcation leads to recurrent laryngeal nerve injury. Motor branch injury has a particularly large effect. Intraoperative neuromonitoring has been reported to be useful for identifying and preserving the recurrent laryngeal nerve and its aberrations as well as the external branch of the superior laryngeal nerve during thyroid surgery.

Conclusion: The findings from this case suggest that an extralaryngeal bifurcation of the recurrent laryngeal nerve can be identified and safely preserved by intraoperative neuromonitoring.

Diagnosis, anatomy, and electromyography profiles of 73 nonrecurrent laryngeal nerves

BACKGROUND

The purpose of this work was to compare methods of detecting nonrecurrent laryngeal nerves (NRLNs).

METHODS

Specificity and sensitivity were compared in three NRLN detection methods: CT, electromyography (EMG), and A-B point comparison.

RESULTS

A total of 73 intraoperative pictures and 36 CT details of NRLNs are presented. Incidence of NRLN was 0.39%. Type I NRLN accounted for 50.7%, type IIA 45.2%, type IIB 4.1%. The NRLN median latency was 2.13 ms vs 3.00 ms median in an RLN control group (P < .001). When the threshold was set to 2.5 ms, EMG latency detection had 96.7% sensitivity and 91.6% specificity for detecting NRLN, and the A-B point comparison algrithm had 97.3% sensitivity and 92.5% specificity. Combining EMG latency detection with A-B point comparison achieved 100% sensitivity and specificity for detecting NRLN.

CONCLUSION

This is the largest series of NRLN presented in the literature. Latency shorter than 2.50 ms combined with the A-B point comparison method is the ideal algorithm procedure for early NRLN identification.

Feasibility of Intraoperative Neuromonitoring During Thyroid Surgery Using Transcartilage Surface Recording Electrodes

BACKGROUND

Intraoperative neural monitoring (IONM) has gained widespread acceptance as an adjunct to the gold standard of visual identification of the recurrent laryngeal nerve (RLN) during thyroid surgery. Currently, laryngeal electromyography (EMG) recording during IONM is almost always performed using endotracheal tube (ETT) surface electrodes placed adjacent to vocal folds originating from the inner surface of the thyroid cartilage (TC). Therefore, it was hypothesized that surface recording electrodes placed on the outer surface of the TC should enable access to the EMG response of the vocal folds during IONM. The aim of this experimental study was to evaluate the feasibility of the transcartilage approach for laryngeal EMG recording during IONM.

METHODS

A porcine model (12 pigs and 24 RLN sides) with well established applicability in IONM research was used for the experiments. Both ETT electrodes adjacent to vocal folds and adhesive pre-gelled electrodes on the TC were used for EMG recording during IONM. Electrically evoked EMG signals detected by both electrode types were recorded and analyzed. EMG changes during tracheal displacement and RLN traction injury were compared.

RESULTS

Both the ETT and TC recording electrodes recorded typical laryngeal EMG waveforms evoked by a 1 mA stimulus current applied on both sides of the RLNs and vagus nerves (VNs). Under RLN stimulation, the mean EMG amplitudes recorded with the ETT and TC electrodes were 973 ± 79 μV and 695 ± 150 μV, respectively. Under VN stimulation, the mean amplitudes were 841 ± 163 μV and 607 ± 162 μV, respectively. When upward displacement of the trachea was experimentally induced, the TC electrodes showed less variation in recorded EMG signals compared to ETT electrodes. When RLN traction stress was experimentally induced, both the ETT and TC electrodes accurately recorded the typical EMG pattern of progressively degrading amplitude and gradual recovery after release of traction.

CONCLUSIONS

This study confirms the feasibility of using transcartilage surface electrodes for recording laryngeal EMG signals evoked during IONM in an animal model. However, before practical application of this approach in clinical thyroid surgery, further studies are needed to improve electrode designs by optimizing their shapes and sizes, and increasing their adhesive stability and sensitivity.

A Review of Methods for the Preservation of Laryngeal Nerves During Thyroidectomy

The recurrent laryngeal nerve (RLN) provides motor innervation to the abductor and adductor muscles of the vocal cord, whereas the external branch of the superior laryngeal nerve (EBSLN) provides motor innervation to the cricothyroid muscle, which is the tensor muscle of the vocal cord. Both the RLN and the EBSLN are anatomically close to the thyroid and are therefore at risk of injury during thyroidectomy. These 2 laryngeal nerves must be carefully preserved during surgery to ensure that the function of the vocal cord is not impaired. Currently, complete exposure of the RLN during thyroidectomy is accepted as the gold standard method for the preservation of RLN. Sufficient knowledge of surgical anatomy, clinical experience, and meticulous surgical techniques are key factors in the identification and safe dissection of the RLN. During a thyroidectomy, the RLN can be identified using four different approaches, depending on the type of thyroid growth and choice of the surgeon: There are lateral, inferior, superior, and medial approaches.

The lateral approach is the most commonly used technique in primary thyroid surgery. The RLN is usually found by dissection around the inferior thyroid artery at the level of the middle lobe of the thyroid. RLN is generally found at the site of its entry into the neck region devoid of scar formation when the inferior approach is used especially in cases with secondary surgery. The superior approach is recommended for patients with an huge goiter or large substernal goiter. In this approach, the upper pole of the thyroid is first released and then pulled forward and laterally, and the RLN is exposed on the nerve’s entry point (NEP), into the larynx, under the cricopharyngeus muscle. The medial approach is preferred for patients with substernally or retropharyngeally enlarged goiters. In this approach, the isthmus is first dissected and divided, and then the isthmus and the medial part of the lobe are dissected away from the trachea to reveal the anterolateral part of the trachea. The fibers between the lateral aspect of the second or third tracheal rings and the thyroid, and the fibers of the Berry ligament are gradually dissected cranially, to allow RLN to enter into the field of view lateral to the trachea. The preservation of the anatomical integrity of the RLN does not indicate that its functional integrity is also preserved. IONM is a tool for the functional assessment of RLN, and so this method is an addition to visually identifying RLN, which is the gold standard. IONM significantly contributes to visual identification of the RLN, determination of its anatomical variations, intraoperative recognition of RLN injury, prevention of bilateral vocal cord paralysis, and detection and preservation of electrical activity in the nerve in patients with preoperative vocal cord paralysis.

Although there is no standardized method for the preservation of the EBSLN, 3 methods have been defined during the release of the upper pole of the thyroid. These methods involve dividing the branches of the superior thyroidal artery one by one on the capsule without visually identifying the EBSLN, searching and visually identifying the EBSLN before the dissection of the upper pole vessels, or detecting the EBSLN and dissecting the upper pole under the guidance of IONM. IONM also significantly contributes to the detection and confirmation of the EBSLN and dissection and preservation of the upper pole of the thyroid gland.

Nonrecurrent Laryngeal Nerve: Precise Detection by Electrophysiological Nerve Monitoring

Complication-free thyroid surgery is mainly based on the motor integrity of the recurrent laryngeal nerve (RLN). The nonrecurrent laryngeal nerve (non-RLN) is a rare anatomical variation that may increase the risk of vocal cord palsy. Early identification and exposure of the non-RLN may minimize injury risk. This case report presents functional detection of the non-RLN by intraoperative neuromonitoring (IONM).

Total thyroidectomy was performed under the guidance of IONM on a patient with bulky multinodular goiter. The first step of IONM is pre-dissection stimulation (V1) of the right vagus nerve (VN). V1 at a standard distal point was negative as indicated by the absence of both a sound signal and wave amplitude. The right VN was then followed proximally and dissected under the guidance of IONM. This dissection established a proximal point creating a positive signal that led us to determine the separation point of the non-RLN. The right non-RLN arising from the proximal VN was identified and fully exposed until laryngeal entry. Its motor integrity was confirmed with post-dissection signals. The left RLN was identified at the usual anatomical position that was fully exposed and preserved during thyroid surgery. Total thyroidectomy was then accomplished without complication. The postoperative period was uneventful. Postoperative laryngoscopy confirmed normal vocal cord function.

The non-RLN is accurately identified by IONM during the early part of the thyroid surgery. The absence of a distal VN signal is predictive of the non-RLN. IONM-guided proximal dissection of the right VN leads to the identification of the non-RLN. The prediction of the non-RLN by the absence of a VN signal during an early stage of surgery may prevent or minimize the risk of nerve injury.

The Non-Recurrent Laryngeal Nerve: a meta-analysis and clinical considerations

Background

The Non-Recurrent Laryngeal Nerve (NRLN) is a rare embryologically-derived variant of the Recurrent Laryngeal Nerve (RLN). The presence of an NRLN significantly increases the risk of iatrogenic injury and operative complications. Our aim was to provide a comprehensive meta-analysis of the overall prevalence of the NRLN, its origin, and its association with an aberrant subclavian artery.

Methods

Through March 2016, a database search was performed of PubMed, CNKI, ScienceDirect, EMBASE, BIOSIS, SciELO, and Web of Science. The references in the included articles were also extensively searched. At least two reviewers judged eligibility and assessed and extracted articles. MetaXL was used for analysis, with all pooled prevalence rates calculated using a random effects model. Heterogeneity among the included studies was assessed using the Chi² test and the I² statistic.

Results

Fifty-three studies (33,571 right RLNs) reported data on the prevalence of a right NRLN. The pooled prevalence estimate was 0.7% (95% CI [0.6–0.9]). The NRLN was found to originate from the vagus nerve at or above the laryngotracheal junction in 58.3% and below it in 41.7%. A right NRLN was associated with an aberrant subclavian artery in 86.7% of cases.

Conclusion

The NRLN is a rare yet very clinically relevant structure for surgeons and is associated with increased risk of iatrogenic injury, most often leading to temporary or permanent vocal cord paralysis. A thorough understanding of the prevalence, origin, and associated pathologies is vital for preventing injuries and complications.

Preoperative computed tomography diagnosis of non-recurrent laryngeal nerve in patients with esophageal carcinoma

Background

The non‐recurrent laryngeal nerve (NRLN) is a rare but potentially serious anomaly that is commonly associated with the aberrant right subclavian artery (ARSA). It is easy to damage during surgical resection of esophageal cancer, leading to severe complications.

Methods

Preoperative enhanced thoracic computed tomography (CT) scans of 2697 patients with esophageal carcinoma treated in our hospital between January 2010 and December 2013 were examined. We classified the positional relationship between the right subclavian artery and the membranous wall of the trachea into two types and used this method to predicate NRLN by identifying ARSA.

Results

Twenty‐six patients (0.96%) were identified with ARSA, all of which were cases of NRLN by CT. NRLN was identified during surgery in the 26 patients, and a normal right recurrent laryngeal nerve was observed in 2671 patients. The ARSA was detected on the dorsal side of the membranous wall of the trachea in all 26 NRLN cases, while it was detected on the ventral side in all 2671 recurrent laryngeal nerve cases.

Conclusion

Enhanced CT scanning is a reliable method for predicting NRLN by identifying ARSA. Preoperative recognition of this nerve anomaly allows surgeons to avoid damaging the nerve and abnormal vessels during esophagectomy.

Intraoperative neural monitoring in thyroid surgery: lessons learned from animal studies

Recurrent laryngeal nerve (RLN) injury remains a significant morbidity associated with thyroid and parathyroid surgery. In the past decade, surgeons have increasingly used intraoperative neural monitoring (IONM) as an adjunct technique for localizing and identifying the RLN, detecting RLN injury, and predicting the outcome of vocal cord function. In recent years, many animal studies have investigated common pitfalls and new applications of IONM. For example, the use of IONM technology in animal models has proven valuable in studies of the electrophysiology of RLN injury. The advent of animal studies has substantially improved understanding of IONM technology. Lessons learned from animal studies have immediate clinical applications in establishing reliable strategies for preventing intraoperative RLN injury. This article gives an overview of the research progress on IONM-relevant animal models.

Identifying a Safe Range of Stimulation Current for Intraoperative Neuromonitoring of the Recurrent Laryngeal Nerve: Results from a Canine Model

Background:

Intraoperative neuromonitoring (IONM) of the recurrent laryngeal nerve (RLN) has been widely applied during thyroid surgery. However, the safe range of stimulation intensity for IONM remains undetermined.

Methods:

Total thyroidectomies were performed on twenty dogs, and their RLNs were stimulated with a current of 5–20 mA (step-wise in 5 mA increments) for 1 min. The evoked electromyography (EMG) of vocal muscles before and after supramaximal stimulation were recorded and compared. Acute microstructural morphological changes in the RLNs were observed immediately postoperatively under an electron microscope.

Results:

The average stimulating threshold for RLNs stimulated with 15 mA and 20 mA showed no significant changes compared to the unstimulated RLNs (15 mA group: 0.320 ± 0.123 mA vs. 0.315 ± 0.097 mA, P = 0.847; 20 mA group: 0.305 ± 0.101 mA vs. 0.300 ± 0.103 mA, P = 0.758). Similar outcomes were shown in average evoked EMG amplitude (15 mA group: 1,026 ± 268 μV vs. 1,021 ± 273 μV, P = 0.834; 20 mA group: 1,162 ± 275 μV vs. 1,200 ± 258 μV, P = 0.148). However, obvious acute microstructural morphological changes were observed in the nerves that were stimulated with 20 mA.

Conclusions:

A stimulation intensity less than 15 mA might be safe for IONM of the RLN.

Reversal of rocuronium-induced neuromuscular blockade by sugammadex allows for optimization of neural monitoring of the recurrent laryngeal nerve

OBJECTIVES/HYPOTHESIS

The use of neuromuscular blocking agent may effect intraoperative neuromonitoring (IONM) during thyroid surgery. An enhanced neuromuscular-blockade (NMB) recovery protocol was investigated in a porcine model and subsequently clinically applied during human thyroid neural monitoring surgery.

STUDY DESIGN

Prospective animal and retrospective clinical study.

METHODS

In the animal experiment, 12 piglets were injected with rocuronium 0.6 mg/kg and randomly allocated to receive normal saline, sugammadex 2 mg/kg, or sugammadex 4 mg/kg to compare the recovery of laryngeal electromyography (EMG). In a subsequent clinical application study, 50 patients who underwent thyroidectomy with IONM followed an enhanced NMB recovery protocol-rocuronium 0.6 mg/kg at anesthesia induction and sugammadex 2 mg/kg at the operation start. The train-of-four (TOF) ratio was used for continuous quantitative monitoring of neuromuscular transmission.

RESULTS

In our porcine model, it took 49 ± 15, 13.2 ± 5.6, and 4.2 ± 1.5 minutes for the 80% recovery of laryngeal EMG after injection of saline, sugammadex 2 mg/kg, and sugammadex 4 mg/kg, respectively. In subsequent clinical human application, the TOF ratio recovered from 0 to >0.9 within 5 minutes after administration of sugammadex 2 mg/kg at the operation start. All patients had positive and high EMG amplitude at the early stage of the operation, and intubation was without difficulty in 96% of patients.

CONCLUSIONS

Both porcine modeling and clinical human application demonstrated that sugammadex 2 mg/kg allows effective and rapid restoration of neuromuscular function suppressed by rocuronium. Implementation of this enhanced NMB recovery protocol assures optimal conditions for tracheal intubation as well as IONM in thyroid surgery.

LEVEL OF EVIDENCE

NA.

Nonrecurrent Laryngeal Nerve in the Era of Intraoperative Nerve Monitoring

Nonrecurrent laryngeal nerve (non-RLN) is an anatomical variation increasing the risk of vocal cord palsy. Prediction and early identification of non-RLN may minimize such a risk of injury. This study assessed the effect of intraoperative neuromonitoring (IONM) on the detection of non-RLN. A total of 462 (236 right) nerves in 272 patients were identified and totally exposed, and all intraoperative steps of IONM were sequentially applied on the vagus nerve (VN) and RLN. Right predissection VN stimulation at a distal point did not create a sound signal in three cases (3/236; 1.27%). Proximal dissection of the right VN under IONM guidance established a proximal point, creating a positive signal. The separation point of non-RLN from VN was discovered in all three patients. Non-RLNs were exposed from separation to laryngeal entry. Positive IONM signals were obtained after resection of thyroid lobes, and postoperative period was uneventful in patients with non-RLN. Absence of distal VN signal is a precise predictor of the non-RLN. IONM-guided proximal dissection of the right VN leads to identification of the non-RLN. The prediction of non-RLN by the absence of the VN signal at an early stage of surgery may prevent or minimize the risk of nerve injury.

Efficient, effective, safe procedure to identify nonrecurrent inferior laryngeal nerve during thyroid surgery

BACKGROUND

The nonrecurrent inferior laryngeal nerve (NRILN) is always associated with the aberrant subclavian artery. CT images can detect this vascular anomaly, which predicts an NRILN. The purpose of this study was to report our procedure to identify the NRILN in patients with the aberrant subclavian artery.

METHODS

Four of 730 patients undergoing thyroid operation in our hospital were preoperatively diagnosed with aberrant subclavian artery by CT of the neck. To avoid vocal cord paralysis, we approached the vagal nerve first before dissecting the paratracheal region to discover the separation point of the NRILN from the vagal nerve.

RESULTS

The NRILN was identified without difficulty in all 4 patients. No patients showed vocal cord paralysis.

CONCLUSION

Approaching the vagal nerve first before dissecting the paratracheal region is an efficient, effective, and safe procedure to identify an NRILN in patients who are preoperatively diagnosed as having the aberrant subclavian artery.

Medially placed vagus nerve in relation to common carotid artery: a pointer to a non-recurrent laryngeal nerve

The aim of this study was to highlight a medialized vagus in relation to common carotid artery as an operative marker to a non-recurrent laryngeal nerve during thyroid surgeries. Three patients who underwent thyroidectomy, in who per operative diagnosis of right non-recurrent laryngeal nerve was made and the findings were confirmed radiologically by demonstration of aberrant subclavian artery were included in the study. A medially placed vagus nerve in relation to common carotid artery was the common observation in all the 3 patients. With no operative marker to identify a non-recurrent laryngeal nerve, it is more prone to injury during thyroidectomies. Vagus nerve which was constantly seen medial to the common carotid artery in all our three patients can be used as an operative marker to a non-recurrent laryngeal nerve.

Latencies longer than 3.5 ms after vagus nerve stimulation does not exclude a nonrecurrent inferior laryngeal nerve

Background

It has recently been reported that a signal latency shorter than 3.5 ms after electrical stimulation of the vagus nerve signify a nonrecurrent course of the inferior laryngeal nerve. We present a patient with an ascending nonrecurrent inferior laryngeal nerve. In this patient, the stimulation latency was longer than 3.5 ms.

Case presentation

A 74-years old female underwent redo surgery due to a right-sided recurrent nodular goitre. The signal latency on electrical stimulation of the vagus nerve at the level of the carotid artery bifurcation was 3.75 ms. Further dissection revealed a nonrecurrent but ascending course of the inferior laryngeal nerve. Caused by the recurrent goitre, the nerve was elongated to about 10 cm resulting in this long latency.

Conclusion

This case demonstrates that the formerly proposed “3.5 ms rule” for identifying a nonrecurrent course of the inferior laryngeal nerve has exceptions. A longer latency does not necessarily exclude a nonrecurrent laryngeal nerve.

Increased prediction of right nonrecurrent laryngeal nerve in thyroid surgery using preoperative computed tomography with intraoperative neuromonitoring identification

Background

A nonrecurrent laryngeal nerve (NRLN) is a rare but potentially serious anatomical variant. Although the incidence is reported to be 0.3% to 1.3%, it carries a much higher risk of palsy during thyroid surgery. The objective of this study is to investigate the usefulness of computed tomography (CT) for preoperative identification and intraoperative neuromonitoring identification (IONM) of NRLN in thyroid cancer patients.

Methods

The preoperative neck CT scans from 1,574 patients who needed thyroid surgery were examined. Absence of the brachiocephalic artery (BCA) and the presence of arteria lusoria were defined as positive with NRLN. Systematic intraoperative neuromonitoring (IONM) was also carried out for these 1,574 patients to localize and identify NRLN. A negative electromyography (EMG) response from lower vagal stimulation but a positive EMG response from the upper position indicated the occurrence of an NRLN.

Results

Nine NRLN (0.57%) were intraoperatively identified out of the 1,574 patients, and no patient with a NRLN showed preoperative clinical symptoms related to NRLN. Prior to the operation, surgeons identified only seven suspected NRLN cases based on identification of arteria lusoria. But a review of CT scans revealed that all cases could be identified by vascular anomalies. All patients were successfully detected at an early stage of operation using intraoperative neuromonitoring (IONM). Postoperative vocal cord function was normal in all patients.

Conclusions

CT of the neck is a reliable method for predicting NRLN before thyroid cancer surgery. However, some image features can be easily missed. Neurophysiology helps the surgeon to identify the NRLNs more precisely. Combining the two evaluation methods may decrease the incidence of nerve palsy, especially in cases of NRLN. Considering that CT is expensive, requires an X-ray, and achieves less information than ultrasound (US) concerning thyroid nodules, we suggest that applying US and IONM is more reasonable.

Influence of intravenous anesthetics on neuromonitoring of the recurrent laryngeal nerve during thyroid surgery

Limited reports are available in the literature on the impact of intravenous administration of anesthetics on laryngeal electromyographic (EMG) activity. The purpose of this study was to determine the influence of the two commonly used intravenous anesthetics (propofol and thiamylal) on EMG amplitude evoked from the recurrent laryngeal nerve (RLN) during thyroid surgery. A total of 40 patients were randomized to receive a bolus of propofol (0.5 mg/kg; n = 20) or thiamylal (1.5 mg/kg; n = 20) to increase anesthetic depth when the surgeon found patient movement intraoperatively. Evoked potentials were obtained before and every 1 minute after the administration of each agent for up to 5 minutes by stimulating the RLN. The magnitude of evoked potentials at each time point and hemodynamic response were compared within groups. The mean amplitude of evoked potentials did not change significantly after administration of either propofol or thiamylal (p > 0.05 within groups). Mean arterial pressure measured from 1 minute to 5 minutes was significantly lower in the propofol group than in the thiamylal group (p < 0.05). Heart rate measured within 5 minutes did not differ significantly within groups. Low dose of propofol (0.5 mg/kg) or thiamylal (1.5 mg/kg) did not affect EMG readings during neuromonitoring of the RLN in thyroid surgery. Our results show that thiamylal provides better hemodynamic stability than propofol, and is therefore a preferable agent to increase anesthesia depth and prevent further patient movement during intraoperative neuromonitoring.

Increased detection of non-recurrent inferior laryngeal nerve (NRLN) during thyroid surgery using systematic intraoperative neuromonitoring (IONM)

BACKGROUND

Non-recurrent inferior laryngeal nerve (NRLN) is a rare anatomical variant with a reported incidence of 0.6-1.3 %. It carries a higher risk of palsy during thyroid surgery. Its detection is mandatory in order to avoid such complication.

METHODS

Systematic intraoperative neuromonitoring (IONM) was carried out for 806 consecutive nerve at risk (NAR) patients in two centers (Lille and Varese). In 402 patients surgery to the right side was performed with IONM. The IONM of the inferior laryngeal nerve (ILN) was conducted as recommended by international guidelines (V1/R1/V2/R2).

RESULTS

A NRLN was detected in 11 of 402 NAR (2.7 %). In the first center (Lille) the incidence of NRLN was 6.0 % (7/117). No loss of signal (LOS) was reported in this group of patients. Postoperative laryngoscopy was normal in all patients with NRLN.

CONCLUSIONS

The true incidence of NRLN may be higher than expected. Neurophysiology helps the surgeon to better understand the anatomy and function of nervous structures. Intraoperative neuromonitoring is a useful tool that should be systematically implemented in thyroid surgery to better understand the anatomy and physiology of the inferior laryngeal nerve. Its use may allow the surgeon to decrease the incidence of nerve palsy especially in case of NRLN. The IONM adjunct does not add significantly to the costs for thyroid surgery.

The usefulness of preoperative computed tomography and intraoperative neuromonitoring identification of the nonrecurrent inferior laryngeal nerve

The objective of this study was to avoid the nonrecurrent inferior laryngeal nerve (NRLN) injury during surgery, we performed preoperative CT examinations to determine the variation in abnormal course of the right subclavian artery as an indictor of the presence of the NRLN and used intraoperative neuromonitoring (IONM) to identify nerve. Preoperative thyroid CT examinations were performed in 783 thyroid surgery patients. The imaging characteristics that suggested the presence of the NRLN were the following: (1) the arteria lusoria arising from the dorsal side of the aortic arch and passing through the trachea and esophagus posteriorly, and the CT image showing the characteristic "hook-like" morphology; (2) that the arteria lusoria imaging could be observed posteriorly to the trachea and esophagus; and (3) that the arteria lusoria traveled transversely from the rear of the right common carotid artery to the right subaxillary region. IONM has been applied to localize and identify NRLN. The brachiocephalic trunk was shown in 779 cases and not in the remaining four cases (0.5 %, 4/783), and these four were assumed to have the arteria lusoria. The separation point and path of the NRLNs were localized and identified precisely with IONM. The NRLN was observed during all surgeries. These four cases did not exhibit hoarseness after surgery. In conclusion, understanding of the course variations of the right subclavian artery using a preoperative CT examination provides an indicator of the presence of a NRLN. Combining these evaluation methods with IONM can avoid NRLN injury.

Vagal nerve stimulation without dissecting the carotid sheath during intraoperative neuromonitoring of the recurrent laryngeal nerve in thyroid surgery

BACKGROUND

Vagal nerve stimulation (VNS) has been recommended as a routine procedure during intraoperative neuromonitoring (IONM) of the recurrent laryngeal nerve (RLN). However, many surgeons have been discouraged from performing VNS because of the need for opening the carotid sheath. The purpose of this study was to investigate the feasibility and reliability of VNS without carotid sheath dissection.

METHODS

Two hundred twenty patients with 376 nerves at risk were enrolled in this study. VNS without nerve exposure during IONM was applied by simply pressing a ball-tip stimulator on the space between the carotid artery and jugular vein.

RESULTS

VNS without nerve exposure was feasible in all cases and did not result in any morbidity. All VNS signals were successfully obtained within 30 minutes of the start of the operation and all showed a clear and reliable laryngeal electromyography (EMG) response that was similar to that from the conventional method in which nerve exposure for VNS is applied.

CONCLUSIONS

VNS without dissecting the carotid sheath is feasible and reliable, rendering it a simple, safe, and surgeon-friendly procedure during IONM.