Anatomical variations of recurrent laryngeal nerve during thyroid surgery: how to identify and handle the variations with intraoperative neuromonitoring

The relation of recurrent laryngeal nerve to inferior thyroid artery and extralaryngeal nerve branching may increase the risk of vocal cord paralysis in thyroidectomy

PURPOSE

The anatomical variations of the recurrent laryngeal nerve (RLN) are common during thyroidectomy. We aimed to evaluate the risk of RLN paralysis in case of its anatomical variations, retrospectively.

METHODS

The patients with primary thyroidectomy between January 2016 and December 2019 were enrolled. The effect of age, gender, surgical intervention, neuromonitorisation type, central neck dissection, postoperative diagnosis, neck side, extralaryngeal branching, non-RLN, relation of RLN to inferior thyroid artery (ITA), grade of Zuckerkandl tubercle on vocal cord paralysis (VCP) were investigated.

RESULTS

This study enrolled 1070 neck sides. The extralaryngeal branching rate was 35.5%. 45.9% of RLNs were anterior and 44.5% were posterior to the ITA, and 9.6% were crossing between the branches of the ITA. The rate of total VCP was 4.8% (transient:4.5%, permanent: 0.3%). The rates of total and transient VCP were significantly higher in extralaryngeal branching nerves compared to nonbranching nerves (6.8% vs. 3.6%, p = 0.018; 6.8% vs. 3.2%, p = 0.006, respectively). Total VCP rates were 7.2%, 2.5%, and 2.9% in case of the RLN crossing anterior, posterior and between the branches of ITA, respectively (p = 0.003). The difference was also significant regarding the transient VCP rates (p = 0.004). Anterior crossing pattern increased the total and transient VCP rates 2.8 and 2.9 times, respectively.

CONCLUSION

RLN crossing ITA anteriorly and RLN branching are frequent anatomical variations increasing the risk of VCP in thyroidectomy that cannot be predicted preoperatively. This study is the first one reporting that the relationship between RLN and ITA increased the risk of VCP.

Variant anatomy of non-recurrent laryngeal nerve: when and how should it be taught in surgical residency?

INTRODUCTION

While the performance of a thyroidectomy is generally associated with a low risk of injury to the recurrent laryngeal nerve (RLN), the presence of a non-recurrent nerve (NRLN) increases the risk of this complication. Generally, the intraoperative detection via visual appreciation of variant anatomy of the RLN has been regarded as poor, possibly due to a lack of knowledge of both the normal and aberrant anatomy of the RLN.

MATERIALS AND METHODS

Articles for the review were searched through PubMed using the search terms and their combinations: "non-recurrent laryngeal nerve," "thyroidectomy," "injury," "palsy," "variant anatomy," and "residency," from January 1, 2000, to December 2022. Papers considered for the review were the articles published in English, with additional classic and articles of surgical importance retrieved from the reference list of papers. Only papers relevant to the scope of the review were considered for this review.

FINDINGS

The NRLN has been found to be associated with concurrent vascular abnormalities, such as the presence of an aberrant right subclavian artery (ARSA) or an arteria lusoria originating from the aortic arch. However, it seems that both the normal as well as aberrant anatomy of the RLN is currently not emphasized enough during postgraduate surgical training. With the increased use of intraoperative neuromonitoring (IONM), detection of NRLN has become possible through appropriate neural mapping during thyroid surgery, besides other pointers such as visualization during surgery, computerised tomography, and duplex ultrasound scans to visualize the variant vascular anatomy. There is also a possible role for cadaveric courses, either during medical school or in a post-graduate setting-adapted to the student's level to teach the variant anatomy. With the development of newer techniques such as artificial intelligence, there are potential new options for teaching and training anatomy in the near future.

CONCLUSIONS AND RELEVANCE

Adequate knowledge of the normal and aberrant anatomy of the RLN remains essential for the best outcomes in thyroid surgery, even in the era of the IONM. Moving forward, the knowledge of (aberrant) anatomy should be made an integral part of the core competencies of both medical students and surgical trainees. It is imperative that leaders of the different field work closely together to combine their knowledge towards providing their trainees with the best possible training options.

Systematic Review and Meta-Analysis: Recurrent Laryngeal Nerve Variants and Their Implication in Surgery and Neck Pathologies, Using the Anatomical Quality Assurance (AQUA) Checklist

INTRODUCTION

The recurrent laryngeal nerve (RLN) is the structure responsible for sensory and motor innervation of the larynx, and it has been shown that its lesion due to a lack of surgical rigor led to alterations such as respiratory obstruction due to vocal cords paralysis and permanent phonation impairment. The objectives of this review were to know the variants of the RLN and its clinical relevance in the neck region.

METHODS

This review considered specific scientific articles that were written in Spanish or English and published between 1960 and 2022. A systematic search was carried out in the electronic databases MEDLINE, WOS, CINAHL, SCOPUS, SCIELO, and Latin American and Caribbean Center for Information on Health Sciences to compile the available literature on the subject to be treated and was enrolled in PROSPERO. The included articles were studies that had a sample of RLN dissections or imaging, intervention group to look for RLN variants, or the comparison of the non-recurrent laryngeal nerve (NRLN) variants, and finally, its clinical correlations. Review articles and letters to the editor were excluded. All included articles were evaluated through quality assessment and risk of bias analysis using the methodological quality assurance tool for anatomical studies (AQUA). The extracted data in the meta-analysis were interpreted to calculate the prevalence of the RLN variants and their comparison and the relationship between the RLN and NRLN. The heterogeneity degree between included studies was assessed.

RESULTS

The included studies that showed variants of the RLN included in this review were 41, a total of 29,218. For the statistical analysis of the prevalence of the RLN variant, a forest plot was performed with 15 studies that met the condition of having a prevalence of less than 100%. As a result, the prevalence was shown to be 12% (95% CI, SD 0.11 to 0.14). Limitations that were present in this review were the publication bias of the included studies, the probability of not having carried out the most sensitive and specific search, and finally, the authors' personal inclinations in selecting the articles.

DISCUSSION

This meta-analysis can be considered based on an update of the prevalence of RLN variants, in addition to considering that the results show some clinical correlations such as intra-surgical complications and with some pathologies and aspects function of the vocal cords, which could be a guideline in management prior to surgery or of interest for the diagnostic.

Near-Infrared Spectral Similarity between Ex Vivo Porcine and In Vivo Human Tissue

BACKGROUND

In vivo diffuse reflectance spectroscopy provides additional contrast in discriminating nerves embedded in adipose tissue during surgery. However, large datasets are required to achieve clinically acceptable classification levels. This study assesses the spectral similarity between ex vivo porcine and in vivo human spectral data of nerve and adipose tissue, as porcine tissue could contribute to generate large datasets.

METHODS

Porcine diffuse reflectance spectra were measured at 124 nerve and 151 adipose locations. A previously recorded dataset of 32 in vivo human nerve and 23 adipose tissue locations was used for comparison. In total, 36 features were extracted from the raw porcine to generate binary logistic regression models for all combinations of two, three, four and five features. Feature selection was performed by assessing similar means between normalized features of nerve and of adipose tissue (Kruskal-Wallis test, p < 0.05) and for models performing best on the porcine cross validation set. The human test set was used to assess classification performance.

RESULTS

The binary logistic regression models with selected features showed an accuracy of 60% on the test set.

CONCLUSIONS

Spectral similarity between ex vivo porcine and in vivo human adipose and nerve tissue was present, but further research is required.

Clinical and Anatomical Factors Affecting Recurrent Laryngeal Nerve Paralysis During Thyroidectomy via Intraoperative Nerve Monitorization

Background

Despite all the technical developments in thyroidectomy and the use of intraoperative nerve monitorization (IONM), recurrent laryngeal nerve (RLN) paralysis may still occur. We aimed to evaluate the effects of anatomical variations, clinical features, and intervention type on RLN paralysis.

Method

The RLNs identified till the laryngeal entry point, between January 2016 and September 2021 were included in the study. The effects of RLN anatomical features considering the International RLN Anatomical Classification System, intervention and monitoring types on RLN paralysis were evaluated.

Results

A total of 1,412 neck sides of 871 patients (672 F, 199 M) with a mean age of 49.17 + 13.42 years (range, 18–99) were evaluated. Eighty-three nerves (5.9%) including 78 nerves with transient (5.5%) and 5 (0.4%) with permanent vocal cord paralysis (VCP) were detected. The factors that may increase the risk of VCP were evaluated with binary logistic regression analysis. While the secondary thyroidectomy (OR: 2.809, 95%CI: 1.302–6.061, p = 0.008) and Berry entrapment of RLN (OR: 2.347, 95%CI: 1.425–3.876, p = 0.001) were detected as the independent risk factors for total VCP, the use of intermittent-IONM (OR: 2.217, 95% CI: 1.299–3.788, 0.004), secondary thyroidectomy (OR: 3.257, 95%CI: 1.340–7.937, p = 0.009), and nerve branching (OR: 1.739, 95%CI: 1.049–2.882, p = 0.032) were detected as independent risk factors for transient VCP.

Conclusion

Preference of continuous-IONM particularly in secondary thyroidectomies would reduce the risk of VCP. Anatomical variations of the RLN cannot be predicted preoperatively. Revealing anatomical features with careful dissection may contribute to risk reduction by minimizing actions causing traction trauma or compression on the nerve.

Seeing Is Not Believing: Intraoperative Nerve Monitoring (IONM) in the Thyroid Surgery

Ensuring the integrity of the recurrent laryngeal nerve (RLN), the external branch of superior laryngeal nerve (EBSLN) and preservation of normal voice are the prime 'functional' goals of thyroid surgery. More in-depth knowledge of neuronal mechanisms has revealed that anatomical integrity does not always translate into functional integrity. Despite meticulous dissection, neural injuries are not always predictable or visually evident. Intraoperative nerve monitoring (IONM) is designed to aid in nerve identification and early detection of functional impairment. With the evolution of technique, intermittent monitoring has given way to continuous-IONM. Over the years, IONM gathered both support and flak. Despite numerous randomised studies, systematic reviews, and meta-analyses, there still prevails a state of clinical equipoise concerning the utility of IONM and its cost-effectiveness. This article inspects the true usefulness of IONM, elaborates on the optimal way to practice it, and presents a critical literature review.

Intraoperative EMG recovery patterns and outcomes after RLN traction-related amplitude decrease during monitored thyroidectomy

OBJECTIVES

Traction injury is the most common type of recurrent laryngeal nerve (RLN) injury in thyroid surgery. Intraoperative neuromonitoring (IONM) facilitates early detection of adverse electromyography (EMG) effect, and this corrective maneuver can reduce severe and repeated nerve injury. This study aimed to evaluate intraoperative patterns and outcomes of EMG decrease and recovery by traction injury.

METHODS

644 patients received nerve monitored thyroidectomy with 1142 RLNs at risk were enrolled. Intermittent IONM with stimulating dissecting instrument (real-time during surgical procedure) and trans-thyroid cartilage EMG recording method (without electrode malpositioning issue) were used for nerve stimulation and signal recording. When an EMG amplitude showed a decrease of >50% during RLN dissection, the surgical maneuver was paused immediately. Nerve dissection was restarted when the EMG amplitude was stable.

RESULTS

44/1142 (3.9%) RLNs exhibited a >50% EMG amplitude decrease during RLN dissection and all (100%) showed gradual progressive amplitude recovery within a few minutes after releasing thyroid traction (10 recovered from LOS; 34 recovered from a 51-90% amplitude decrease). Three EMG recovery patterns were noted, A-complete EMG recovery (n=14, 32%); B-incomplete EMG recovery with an injury point (n=16, 36%); C-incomplete EMG recovery without an injury point (n=14, 32%). Patients with postoperative weak or fixed vocal cord mobility in A, B, and C were 0(0%), 7(44%), and 2(14%), respectively. Complete EMG recovery was found in 14 nerves, and incomplete recovery was found in another 30 nerves. Temporary vocal cord palsy was found in 6 nerves due to unavoidable repeated traction.

CONCLUSION

Early detection of traction-related RLN amplitude decrease allows monitoring of intraoperative EMG signal recovery during thyroid surgery. Different recovery patterns show different vocal cord function outcomes. To elucidate the recovery patterns can assist surgeons in the intraoperative decision making and postoperative management.

Recurrent Laryngeal Nerve Injury Near the Nerve Entry Point in Total Endoscopic Thyroidectomy: A Retrospective Cohort Study

Background

Recurrent laryngeal nerve injury (RLNI) still occurs in total endoscopic thyroidectomy (TET) by using intraoperative neuromonitoring (IONM). As the region where most injuries occur, more attention should be paid to RLNI near the nerve entry point (NEP) in TET.

Materials and Methods

This cohort study collected retrospectively data from 415 patients who underwent TET between February 2012 and December 2019. The functions of the recurrent laryngeal nerve (RLN) in TET were recorded by IONM. The patients with RLNI near the NEP were followed up by laryngoscopies. The demographic and clinical characteristics, the mechanisms of RLNI, and the outcomes of RLNI were recorded and analyzed.

Results

There were a total of 444 at-risk nerves in 405 patients were analyzed. The incidence of RLNI near the NEP was 7.9%. RLNs with extralaryngeal branches were more likely to be injured near the NEP (P = 0.037). The incidences of different types of RLNI, in order of frequency, were 68.8% for thermal injury (n = 22), 28.1% for traction/compression injury (n = 9), and 3.1% for transverse injury (n = 1). A total of 93.8% (n = 30) of RLNI patients had complete recovery of vocal cord activity function.

Conclusion

The extralaryngeal branch was a risk factor for RLNI near the NEP in TET. Thermal injury caused by an ultrasonic scalpel was the most common cause of RLNI near the NEP. Most RLNIs near the NEP would eventually recover.

Varied Recurrent Laryngeal Nerve Course Is Associated with Increased Risk of Nerve Dysfunction During Thyroidectomy: Results of the Surgical Anatomy of the Recurrent Laryngeal Nerve in Thyroid Surgery Study, an International Multicenter Prospective Anatomic and Electrophysiologic Study of 1000 Monitored Nerves at Risk from the International Neural Monitoring Study Group

Background: The recurrent laryngeal nerve (RLN) can be injured during thyroid surgery, which can negatively affect a patient's quality of life. The impact of intraoperative anatomic variations of the RLN on nerve injury remains unclear. Objectives of this study were to (1) better understand the detailed surgical anatomic variability of the RLN with a worldwide perspective; (2) establish potential correlates between intraoperative RLN anatomy and electrophysiologic responses; and (3) use the information to minimize complications and assure accurate and safe intraoperative neuromonitoring (IONM). Methods: A large international registry database study with prospectively collected data was conducted through the International Neural Monitoring Study Group (INMSG) evaluating 1000 RLNs at risk during thyroid surgery using a specially designed online data repository. Monitored thyroid surgeries following standardized IONM guidelines were included. Cases with bulky lymphadenopathy, IONM failure, and failed RLN visualization were excluded. Systematic evaluation of the surgical anatomy of the RLN was performed using the International RLN Anatomic Classification System. In cases of loss of signal (LOS), the mechanism of neural injury was identified, and functional evaluation of the vocal cord was performed. Results: A total of 1000 nerves at risk (NARs) were evaluated from 574 patients undergoing thyroid surgery at 17 centers from 12 countries and 5 continents. A higher than expected percentage of nerves followed an abnormal intraoperative trajectory (23%). LOS was identified in 3.5% of NARs, with 34% of LOS nerves following an abnormal intraoperative trajectory. LOS was more likely in cases of abnormal nerve trajectory, fixed splayed or entrapped nerves (including at the ligament of Berry), extensive neural dissection, cases of cancer invasion, or when lateral lymph node dissection was needed. Traction injury was found to be the most common form of RLN injury and to be less recoverable than previous reports. Conclusions: Multicenter international studies enrolling diverse patient populations can help reshape our understanding of surgical anatomy during thyroid surgery. There can be significant variability in the anatomic and intraoperative characteristics of the RLN, which can impact the risk of neural injury.

The Most Common Anatomical Variation of Recurrent Laryngeal Nerve: Extralaryngeal Branching

Objective:

Extralaryngeal branching of recurrent laryngeal nerve (RLN) is frequent. In various studies, detection rate of extralaryngeal nerve branching was increased by intraoperative neuromonitorization (IONM). Our aim was evaluation of the relationship between the features of extralaryngeal branching of RLN and other anatomic variations in thyroidectomy patients under the guidance of IONM.

Methods:

Patients underwent thyroidectomy using IONM between January 2016 and December 2019 and whose RLNs were fully explored till the nerve’s entry point to the larynx, were enrolled to the study. Extralaryngeal branching of RLN was accepted as branching of the nerve at a ≥5 mm distance from its laryngeal entry point and having its all branches entering the larynx. Entrapment of RLN at the region of ligament of Berry (BL) by a vascular structure or posterior BL and relationship between RLN and inferior thyroid artery (ITA) was evaluated.

Results:

Out of 696 patients meeting the inclusion criteria, 1127 neck sides (536F and 160M) were evaluated. Mean age was 49.1±13.4 (range; 18–89). Nerve branching ratio was 35.3% and was higher in females than males (38.2%vs.25.8%, p<0.0001, respectively). Extralaryngeal branching of RLN was detected in 398 (35.3%) out of 1127 nerves. A total of 368 (92.5%) RLNs had two, 27 (6.8%) nerves had three, and 3 (0.7%) had multiple branches. RLN crossed anterior to and between branches of ITA more frequently in branching nerves than non-branching nerves (47.7 vs. 44.4% and 12.8% vs. 7.6%, respectively) but crossed posterior to ITA less frequently in branching nerves (38.5% vs. 48%, respectively, p=0.001). Entrapment of RLN at the region of BL was higher in branched nerves (25.9% vs. 17.5%, respectively, p=0.001). Entrapment of RLN wasmore frequent at the right side than left side both in branching (31.5% vs.19.4%, respectively, p=0.008) and non-branching nerves (20.6% vs. 14.4%, respectively).

Conclusion:

Extralaryngeal branching of RLN is not rare and mostly divided into two branches. Branching ratio is higher in females than males. In branching nerves, rate of crossing anterior to and between branches of ITA was higher, in non-branching nerves, rate of crossing posterior to ITA was higher. In branching nerves, possibility of entrapment of RLN at the region of BL was higher. Both in branching and non-branching nerves, entrapment of RLN at the region of BL was higher at the right side. Extralaryngeal branching, relationship between RLN and ITA, and entrapment of RLN at the region of BL are frequently seen and variable anatomic variations and cannot be foreseen preoperatively. Most of the extralaryngeal branches and their relationship with other variations can be detected by finding RLN at the level of ITA and following RLN until its entry point to the larynx.

How the Severity and Mechanism of Recurrent Laryngeal Nerve Dysfunction during Monitored Thyroidectomy Impact on Postoperative Voice

Simple Summary

Recurrent laryngeal nerve (RLN) dysfunction remains a major source of morbidity after thyroid surgery. Intraoperative neuromonitoring can qualify and quantify RLN function according to the laryngeal electromyography (EMG) response evoked by electrical stimulation of the RLN. To the best of our knowledge, this is the first report to discuss the severity and mechanism of RLN dysfunction and postoperative voice in patients who have received monitored thyroidectomy. For optimal voice and swallowing outcomes after thyroid surgery, thermal injury must be avoided, especially when using energy-based devices, and mechanical injury must be identified early to avoid a more severe dysfunction. Adherence to standard intraoperative neuromonitoring (IONM) procedures for thyroid surgery is suggested, including standard procedures for acquiring and interpreting intraoperative RLN signals, for identifying and classifying RLN injury mechanisms, for performing laryngeal examinations and comprehensive voice assessments (subjective and objective voice analysis) before and after surgery, and for performing standard follow-up procedures.

Abstract

Intraoperative neuromonitoring can qualify and quantify RLN function during thyroid surgery. This study investigated how the severity and mechanism of RLN dysfunction during monitored thyroid surgery affected postoperative voice. This retrospective study analyzed 1021 patients that received standardized monitored thyroidectomy. Patients had post-dissection RLN(R2) signal <50%, 50–90% and >90% decrease from pre-dissection RLN(R1) signal were classified into Group A-no/mild, B-moderate, and C-severe RLN dysfunction, respectively. Demographic characteristics, RLN injury mechanisms(mechanical/thermal) and voice analysis parameters were recorded. More patients in the group with higher severity of RLN dysfunction had malignant pathology results (A/B/C = 35%/48%/55%, p = 0.017), received neck dissection (A/B/C = 17%/31%/55%, p < 0.001), had thermal injury (p = 0.006), and had asymmetric vocal fold motion in long-term postoperative periods (A/B/C = 0%/8%/62%, p < 0.001). In postoperative periods, Group C patients had significantly worse voice outcomes in several voice parameters in comparison to Group A/B. Thermal injury was associated with larger voice impairments compared to mechanical injury. This report is the first to discuss the severity and mechanism of RLN dysfunction and postoperative voice in patients who received monitored thyroidectomy. To optimize voice and swallowing outcomes after thyroidectomy, avoiding thermal injury is mandatory, and mechanical injury must be identified early to avoid a more severe dysfunction.

Artificial intelligence-augmented, label-free molecular imaging method for tissue identification, cancer diagnosis, and cancer margin detection

Label-free high-resolution molecular and cellular imaging strategies for intraoperative use are much needed, but not yet available. To fill this void, we developed an artificial intelligence-augmented molecular vibrational imaging method that integrates label-free and subcellular-resolution coherent anti-stokes Raman scattering (CARS) imaging with real-time quantitative image analysis via deep learning (artificial intelligence-augmented CARS or iCARS). The aim of this study was to evaluate the capability of the iCARS system to identify and differentiate the parathyroid gland and recurrent laryngeal nerve (RLN) from surrounding tissues and detect cancer margins. This goal was successfully met.

Bilateral axillo-breast approach robotic thyroidectomy: review of a single surgeon's consecutive 317 cases

Background

Bilateral axillo-breast approach robotic thyroidectomy (BABA RT) is one of the most popular remote-access approaches for thyroid surgery. This study aimed to evaluate the surgical outcomes of BABA RT.

Methods

Medical records of patients who underwent BABA RT between July 2008 and July 2016 were retrospectively reviewed. Surgeries were performed by one surgeon at one institution. Clinicopathological features and postoperative surgical outcomes were evaluated.

Results

A total of 317 patients were enrolled. The mean age was 40.0±9.7 years, and 287 (90.5%) were female. The mean tumor size was 1.02 cm. Papillary thyroid carcinoma (PTC) was most commonly seen (n=282, 88.8%), followed by benign nodules (n=33, 10.5%) and follicular thyroid carcinoma (n=2, 0.6%). Total thyroidectomy was performed in 202 (63.7%) patients, while unilateral lobectomy was performed in 113 (35.6%). Two patients (0.6%) had transient vocal cord palsy, but none showed permanent vocal cord palsy. Thirty-four (16.8%) patients developed hypoparathyroidism, 33 (16.3%) were transient and 1 (0.5%) was permanent. The mean operation time for total thyroidectomy and lobectomy was 264.9±52.4 and 203.4±47.6 min, respectively. A decrease in operation time in total thyroidectomy was observed in 49-51 cases (P=0.015). Four patients (1.4%) had local recurrence during the median follow-up of 61±23 months.

Conclusions

BABA RT can be performed safely in selected patients with thyroid nodules. The learning curve duration for BABA RT was 49-51 cases of total thyroidectomy.

Prognostic Indicators of Non-Transection Nerve Injury and Vocal Fold Motion Impairment After Thyroid Surgery - Correlation Between Intraoperative Neuromonitoring Findings and Perioperative Voice Parameters

OBJECTIVES

In patients with recurrent laryngeal nerve (RLN) injury after thyroid surgery, unrecovered vocal fold motion (VFM) and subjective voice impairment cause extreme distress. For surgeons, treating these poor outcomes is extremely challenging. To enable early treatment of VFM impairment, this study evaluated prognostic indicators of non-transection RLN injury and VFM impairment after thyroid surgery and evaluated correlations between intraoperative neuromonitoring (IONM) findings and perioperative voice parameters.

METHODS

82 adult patients had postoperative VFM impairment after thyroidectomy were enrolled. Demographic characteristics, RLN electromyography (EMG), and RLN injury mechanism were compared. Multi-dimensional voice program, voice range profile and Index of voice and swallowing handicap of thyroidectomy (IVST) were administered during I-preoperative; II-immediate, III-short-term and IV-long-term postoperative periods. The patients were divided into R/U Group according to the VFM was recovered/unrecovered 3 months after surgery. The patients in U Group were divided into U1/U2 Group according to total IVST score change was <4 and ≥4 during period-IV.

RESULTS

Compared to R Group (42 patients), U Group (38 patients) had significantly more patients with EMG >90% decrease in the injured RLN (p<0.001) and thermal injury as the RLN injury mechanism (p=0.002). Voice parameter impairments were more severe in U Group compared to R Group. Compared to U1 group (19 patients), U2 Group (19 patients) had a significantly larger proportion of patients with EMG decrease >90% in the injured RLN (p=0.022) and thermal injury as the RLN injury mechanism (p=0.017). A large pitch range decrease in period-II was a prognostic indicator of a moderate/severe long-term postoperative subjective voice impairment.

CONCLUSION

This study is the first to evaluate correlations between IONM findings and voice outcomes in patients with VFM impairment after thyroid surgery. Thyroid surgeons should make every effort to avoid severe type RLN injury (e.g., thermal injury or injury causing EMG decrease >90%), which raises the risk of unrecovered VFM and moderate/severe long-term postoperative subjective voice impairment. Using objective voice parameters (e.g., pitch range) as prognostic indicators not only enables surgeons to earlier identify patients with low voice satisfaction after surgery, and also enable implementation of interventions sufficiently early to maintain quality of life.

The intracranial branch; A rare anatomical variation of the recurrent laryngeal nerve; Case report

INTRODUCTION

The recurrent laryngeal nerve (RLN) originates from the Vagus nerve intrathoracically. It passes through the tracheoesophageal groove (TEG) in the neck and different variations in this section were observed. The RLN is at highest risk for injury during the thyroid surgery. Therefore, it is important to know variations to decrease the injury effectively.

PRESENTATION OF CASE

A 50 years-old woman with no thyroid related complaints except for enlargement of the thyroid gland in recent 12-months that annoyed her during neck movement and for aesthetic features. Medical, surgical, drugs, irradiation history, laboratory data, and physical examination was unremarkable except for multi-lobulated enlarged thyroid gland. The CT scanning study revealed intrathoracic extension of the gland. Patient underwent total thyroidectomy with suspicious diagnosis of multinodular goiter which was confirmed later by pathologic study. Intraoperative exploration of the right RLN discovered an intracranial branch originating from the recurrent laryngeal trunk just beneath the inferior thyroid artery (ITA) at the level of the nerve intersection. The branch then passed laterally about 1 cm and penetrated in ipsilateral carotid sheath.

DISCUSSION

The RLN has different anatomical variations in either the right or the left side of the neck. However extra-laryngeal nerve branching is the most common variation but other seldom variations including the non-RLN, and intracranial branch should be mentioned by surgeon intraoperatively.

CONCLUSION

To decrease iatrogenic injuries to RLN and its associated nerve branches knowledge of the nerve anatomy is mandatory for surgeon to prevent morbid side effects.

Mechanisms of recurrent laryngeal nerve injury near the nerve entry point during thyroid surgery: A retrospective cohort study

BACKGROUND

The use of intraoperative neuromonitoring (IONM) for visual identification of recurrent laryngeal nerve (RLN) has decreased the rates of RLN injury (RLNI) during thyroid surgery. However, little attention has been paid to RLNI near the nerve entry point (NEP), where most injuries occur. The aim of this study was to determine the mechanism of RLNI near the NEP and to describe the recovery of nerve function.

METHODS

Patients undergoing thyroid surgery were analyzed to identify true loss of signal (LOS) by IONM. Follow-up for vocal cord palsy (VCP) was confirmed by a postoperative laryngoscopy. The risk factors for RLNI, the type of RLNI, the prevalence of VCP and the time for VCP recovery were all recorded and analyzed.

RESULTS

We analyzed 3582 at-risk nerves in 2257 surgical patients. The overall rate of RLNI near the NEP in at-risk nerves was 3.2%. RLNI was more likely to occur in nerves with extralaryngeal bifurcation (p = 0.013). The distribution of RLNI types, in order of frequency, was traction (52.6%; n = 61), compression (38.8%; n = 45), thermal (7.8%; n = 9), and nerve transection (0.9%; n = 1). Complete recovery from VCP was documented in 93.1% (n = 108) of RLNI.

CONCLUSION

Patients with a bifurcated RLN were at a higher risk of RLNI near the NEP than those without bifurcation. Traction and compression injuries occurred most frequently, but would eventually recover. Excessive stretching of the thyroid lobe played a role in RLNIs near the NEP.

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.

Efficacy of Transcartilaginous Electrodes for Intraoperative Neural Monitoring During Thyroid Surgery

Objectives.

This study was conducted evaluate the efficacy of electromyography (EMG) using transcartilaginous (TC) electrodes through the thyroid cartilage and perichondrium.

Methods.

We prospectively collected EMG data from intraoperative neuromonitoring (IONM) of 54 nerves at risk in 38 patients during thyroidectomy. We followed standardized IONM procedures in all operations. EMG signals from both endotracheal tube (ET) electrodes and TC needle electrodes were recorded simultaneously. We compared the characteristics of the EMG signals and the efficacy of both methods.

Results.

Significantly higher mean EMG amplitudes were recorded by TC electrodes than by ET electrodes in all four-step procedures (V1-R1-R2-V2, P<0.001). Loss of signal (LOS) occurred in five patients in ET electrodes, but in only two patients in TC electrodes. Postoperative laryngoscopy revealed recurrent laryngeal nerve palsy in the two patients who showed LOS from both the ET and TC electrodes, and vocal cord movement was intact in the other three patients. Therefore, the positive predictive values of LOS in ET and TC electrodes were 40% and 100%, respectively.

Conclusion.

EMG recording using TC needle electrodes is feasible and effective, making it a good alternative technique for IONM.

A Surgical Mouse Model for Advancing Laryngeal Nerve Regeneration Strategies

Iatrogenic recurrent laryngeal nerve (RLN) injury is a morbid complication of anterior neck surgical procedures. Existing treatments are predominantly symptomatic, ranging from behavioral therapy to a variety of surgical approaches. Though laryngeal reinnervation strategies often provide muscle tone to the paralyzed vocal fold (VF), which may improve outcomes, there is no clinical intervention that reliably restores true physiologic VF movement. Moreover, existing interventions neglect the full cascade of molecular events that affect the entire neuromuscular pathway after RLN injury, including the intrinsic laryngeal muscles, synaptic connections within the central nervous system, and laryngeal nerve anastomoses. Systematic investigations of this pathway are essential to develop better RLN regenerative strategies. Our aim was to develop a translational mouse model for this purpose, which will permit longitudinal investigations of the pathophysiology of iatrogenic RLN injury and potential therapeutic interventions. C57BL/6J mice were divided into four surgical transection groups (unilateral RLN, n = 10; bilateral RLN, n = 2; unilateral SLN, n = 10; bilateral SLN, n = 10) and a sham surgical group (n = 10). Miniaturized transoral laryngoscopy was used to assess VF mobility over time, and swallowing was assessed using serial videofluoroscopy. Histological assays were conducted 3 months post-surgery for anatomical investigation of the larynx and laryngeal nerves. Eight additional mice underwent unilateral RLN crush injury, half of which received intraoperative vagal nerve stimulation (iVNS). These 8 mice underwent weekly transoral laryngoscopy to investigate VF recovery patterns. Unilateral RLN injury resulted in chronic VF immobility but only acute dysphagia. Bilateral RLN injury caused intraoperative asphyxiation and death. VF mobility was unaffected by SLN transection (unilateral or bilateral), and dysphagia (transient) was evident only after bilateral SLN transection. The sham surgery group retained normal VF mobility and swallow function. Mice that underwent RLN crush injury and iVNS treatment demonstrated accelerated and improved VF recovery. We successfully developed a mouse model of iatrogenic RLN injury with impaired VF mobility and swallowing function that can serve as a clinically relevant platform to develop translational neuroregenerative strategies for RLN injury.

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.

Bilateral patterns and motor function of the extralaryngeal branching of the recurrent laryngeal nerve

PURPOSE

To evaluate the bilateral patterns and motor function of the extralaryngeal branches (ELB) of the recurrent laryngeal nerve(RLN).

METHODS

This study included 500 consecutive patients who underwent total thyroidectomy. Intraoperative nerve monitoring (IONM) was used in 230 patients. Demographic data, indications for surgery, the bilateral patterns of ELB of the RLN, electromyographic activity of the ELB, distance between the branching point to the entrance into the larynx, and the rate of postoperative morbidity were analyzed.

RESULTS

The overall rate of ELB was 27.6% (276/1000). A single trunk of the RLN on both sides was found in 269 (54%) patients, whereas ELB on both sides was observed in 45 (9%) patients. The rates of ELB on the left and right sides were 26.6 and 28.6%, respectively. Of the 89 branched nerves which were dissected using IONM, an evoked motor response was present in 100% of the anterior branches and 5.6% of the posterior branches. The mean branching distance of the RLN was significantly greater in female patients than in male patients on the left side (p = 0.031). The patterns of ELB showed no significant difference in male and female patients. The rates of postoperative transient and permanent hypoparathyroidism and unilateral RLN palsy were 21.6 and 2.8%, and 3.2 and 0.8%, respectively. The rate of RLN palsy was higher in branched nerves compared to those with a single trunk (0.75 vs 0.3%; p = 0.2).

CONCLUSION

Unilateral ELB of the RLN might be observed in approximately 1/4 of the patients, while bilateral branching is rare. A few number of posterior branches of the RLN can have motor function. The RLN's with ELB might have a higher risk of injury compared to those with a single trunk.

Unintentional recurrent laryngeal nerve injuries following thyroidectomy: Is it the surgeon who pays the bill?

BACKGROUND

Thyroidectomy is one of the most common intervention in general surgery and, after the turn of the century, its rate has sharply increased, along with a worldwide increased incidence of differentiated thyroid cancers. Therefore, injuries of the recurrent laryngeal nerve have become one of the most frequent cause of surgical malpractice claims, mostly following surgery for benign pathology.

MAIN BODY

Even if the incidence of definitive paralysis is generally lower than 3%, during the last 20 years in Italy, the number of claims for damages has sharply raised. As a consequence, a lot of defensive medicine has been caused by this issue, and a witch-hunt has been accordingly triggered, so determining mostly a painful and lasting frustration for the surgeons, who sometimes are compelled to pay a lot of money for increasing insurance premiums and lawyers fees. Recurrent laryngeal nerve injury should be considered as a potentially catastrophic predictable but not preventable event, rather than the result of a surgical mistake.

CONCLUSION

Purposes of the Authors are analyzing incidence, conditions of risk, and mechanisms of recurrent laryngeal nerve injuries, underlining notes of surgical technique and defining medical practice recommendations useful to reduce the risk of malpractice lawsuits and judgments against surgeons.

Thyroid reoperation using intraoperative neuromonitoring

PURPOSE

Thyroid reoperations are at a high risk of recurrent laryngeal nerve (RLN) injury. The aim of the study was to investigate whether the use of intraoperative neuromonitoring (IONM) can aid in the RLN identification and minimize the risk of its injury, in comparison with visual RLN identification.

METHODS

This was a retrospective cohort study of patients who underwent thyroid reoperations with and without the use of IONM. Primary endpoint was the RLN identification rate; secondary: the prevalence of RLN injury, the frequency of total thyroidectomies, and the course of the RLN.

RESULTS

The study involved 61 patients undergoing thyroid reoperation among whom 24 were operated on with visual RLN identification only, while 37 procedures used IONM. In the non-monitored reoperations, 44.4% of the RLN were visually identified, as opposed to 91.6% in the IONM group (p < 0.001). Transient paresis occurred in three nerves with visualization (6.6%), and in one in IONM group 1.6% (p = 0.185). Permanent paresis occurred in the group with visualization (6.6%), as opposed to none with neuromonitoring. The extent of resection in both groups was significantly different (p = 0.043). Total, near-total thyroidectomies, Dunhill operations and subtotal thyroidectomies were performed in 71, 17, 4, and 8% in the visualization group, and in 94, 0, 3, and 3%, respectively, in the IONM group. A non-anatomical RLN course was observed in 80% of the reoperations with IONM.

CONCLUSIONS

Thyroid reoperation should be performed using IONM, because it allows for a significantly improved RLN identification rate and a significantly more radical resection.

Preoperative, intraoperative and postoperative anesthetic prospective for thyroid surgery: what's new

The aim of this review is to analyze what's new on anesthetic prospective to perioperative management for thyroid surgery. For recent decades intraoperative neuromonitoring (IONM) during thyroid and parathyroid surgery has obtained more and more popularity. New modality of anesthetic technique was also developed to incorporate into surgical teamwork. For example, the precise position of EMG tube and optimal use of neuromuscular blocking agents (NMBAs) play key roles in successful IONM system. Special focus is paid to following issues: (I) preoperative airway evaluation and pre-op preparation; (II) anesthetic managements including advanced intubation tools, NMBAs and sugammadex; and (III) post-op adverse events such as pain and postoperative nausea vomiting.

Extralaryngeal division of the recurrent laryngeal nerve: A common and asymmetric anatomical variant

OBJECTIVE

Recognition of extralaryngeal branching of the recurrent laryngeal nerve is crucial because prevention of vocal cord paralysis requires preservation of all branches of the recurrent laryngeal nerve. We assessed the prevalence of extralaryngeal branching of the recurrent laryngeal nerve and the median branching distance from the point of bifurcation to the entry point of the nerve into the larynx.

MATERIAL AND METHODS

Prospective operative data on recurrent laryngeal nerve branching were collected from 94 patients who underwent thyroid or parathyroid surgery between September 2011 and May 2012.

RESULTS

A total of 161 recurrent laryngeal nerves were examined (82 right, 79 left). Overall, 77 (47.8%) of 161 recurrent laryngeal nerves were bifurcated before entering the larynx. There were 36 (43.9%) branching nerves on the right and 41 (51.9%) branching nerves on the left, and there was no significant difference between the sides in terms of branching (p=0.471). Among 67 patients who underwent bilateral exploration, 28.4% were found to have bilateral branching, 40.3% had unilateral branching, and the remaining 31.3% had no branching. The median branching distance was 15 mm (5-60mm).

CONCLUSION

Extralaryngeal division of recurrent laryngeal nerve is a common and asymmetric anatomical variant. These variations can be easily recognized if the recurrent laryngeal nerve is identified at the level of the inferior thyroid artery and then dissected totally to the entry point of the larynx. Inadvertent division of a branch may lead to vocal cord palsy postoperatively, even when the surgeon believes the integrity of the nerve has been preserved.

A novel variation of the recurrent laryngeal nerve

BACKGROUND

Injury to the recurrent laryngeal nerve is one of the most severe complications of thyroid surgery. Several anatomic variations of the nerve increase the likelihood of iatrogenic damage.

CASE PRESENTATION

A 50-year-old woman was presented to our department with a nodule in the right thyroid lobe, and she reported no voice changes. She had no history of surgery or radiation to the head or neck. Fine-needle aspiration was recorded as papillary thyroid carcinoma. The preoperative laryngoscopy revealed left vocal cord paralysis. Right thyroid lobectomy was performed. A scarce course of the left recurrent laryngeal nerve was found during the operation that ascended along the medial edge of the superior thyroid pole and finally disappeared beneath the superior cornu of the thyroid cartilage without any tracheal, esophageal, or laryngeal branches. The patient was discharged on the third postoperative day with the diagnoses of papillary thyroid carcinoma and congenital left vocal cord paralysis.

CONCLUSIONS

The novel variation of the recurrent laryngeal nerve may challenge the current concept of the anatomy of the nerve. The vocal folds mobility should be examined routinely before surgery in patients undergoing thyroid operation.

Intermittent neural monitoring of the recurrent laryngeal nerve in surgery for recurrent goiter

Reoperative thyroid surgery is still challenging even for skilled surgeons, and is associated with a higher incidence of complications, such as hypoparathyroidism and recurrent laryngeal nerve (RLN) palsy. Displacement of the RLN, scar tissue from previous neck surgery and difficulty in maintaining good hemostasis are risk factors in reoperations. The prevalence of RLN injury in reoperative thyroid surgery ranges as high as 12.5% for transient injury and up to 3.8% for permanent injury. Bilateral paresis can also occur during reoperations, and is a dangerous complication influencing the quality of life, sometimes requiring tracheostomy. RLN identification is the gold standard during thyroidectomy, and the use of intraoperative neuromonitoring (IONM) can be a valuable adjunct to visual identification. This technique can be used to identify the RLN and the external branch of the superior laryngeal nerve (EBSLN), both of which are standardized procedures. The aim of this review was to evaluate the use of intermittent neural monitoring of the RLN in surgery for recurrent goiter, and to assess the prevalence of RLN injury while using IONM reported in the current literature.

Electrophysiological identification of nonrecurrent laryngeal nerves

OBJECTIVES/HYPOTHESIS

The nonrecurrent laryngeal nerve (NRLN) is a common anatomic variation of the right recurrent laryngeal nerve (RLN), which has been associated with an increased risk of injury during thyroid and parathyroid surgery. We suggest that early successful identification using intraoperative nerve monitoring (IONM) and preservation of this variant will help the surgeon to avoid injury to this nerve. Our objective was to examine the electrophysiological parameters of the NRLN and the efficacy of IONM for successful identification of the NRLN.

STUDY DESIGN

Retrospective database analysis.

METHODS

This is a retrospective study of a prospectively collected database of all patients who underwent thyroid and parathyroid surgeries by a single surgeon at a tertiary care center over 3 years (n = 481). Patients' demographic data and operative reports, including the IONM reports, were reviewed. Average stimulation thresholds with resulting amplitudes and latencies were compared. Preoperative and postoperative laryngoscopy were performed in all cases.

RESULTS

We identified 15 NRLNs (2.2%) in a total 682 laryngeal nerves. No left-sided NRLNs were observed. The average right vagus latency in the NRLN group was shorter than that of the RLN group (2.40 ms ± 0.49 ms vs. 3.43 ms ± 1.03 ms; P < .001). No statistically significant difference was observed between the initial amplitudes of the right vagus nerves in the two groups (713.67 μV ± 208.71 μV vs. 816.22 μV ± 470.45 μV; P = .14). All NRLN cases exhibited normal functioning of vocal cords on postoperative laryngoscopy.

CONCLUSIONS

IONM is highly effective in the identification of the NRLN. Right vagus nerve latency in the NRLN group was found to be significantly shorter than in the RLN group. Early identification of the NRLN allowed cautious preservation of the NRLN, resulting in excellent postoperative outcomes. The rate of NRLN identification may be improved by routine use of IONM.

LEVEL OF EVIDENCE

4 Laryngoscope, 127:2189-2193, 2017.

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.

A Closer Look at the Recurrent Laryngeal Nerve Focusing on Branches & Diameters: A Prospective Cohort Study

AIM

We aimed to investigate the anatomical characteristics of the recurrent laryngeal nerve (RLN) highlighting on its diameter and branching pattern.

MATERIALS AND METHODS

We prospectively collected 215 patients (178 female, 37 male) who underwent thyroid/parathyroid surgery during over a 2-year period. Apart from demographic features and surgical data, diameter of RLNs, and their branches and as well as branching distance (distance between the point of bifurcation and the laryngeal entry of RLN) were recorded.

RESULTS

In 215 patients, 378 RLNs were assessed and 42% (n = 159) bifurcated RLNs were observed. The bifurcation rate was similar on the right and left side(s) of the neck (40% and 44%, respectively; p = 0.47). In those, who underwent bilateral exploration, in the case of bifurcation on the first side of the neck, the possibility of contralateral bifurcation was approximately 50%, whereas this rate was found to be only 30% in those with nonbranching RLNs. Mean branching distance was 18 ± 9 mm, and it was similar on the right and left sides (17 and 19 mm, respectively). Approximately 80% of bifurcations were observed within 5-24 mm of the RLN. Mean diameter of the anterior branches was found to be significantly larger compared to posterior branches (1.09 ± 0.35 and 0.82 ± 0.36 mm, respectively; p < 0.01).

CONCLUSIONS

There is great variability in RLN branching. We observed that approximately two out of three bifurcations were unilateral and anterior branches were thicker compared to posterior branches. These findings should be taken into consideration to avoid any damage to the RLN during thyroid and parathyroid surgery.

Motor function of the recurrent laryngeal nerve: Sometimes motor fibers are also located in the posterior branch

BACKGROUND

The function of the extralaryngeal branches of the recurrent laryngeal nerve (RLN) has yet to be described precisely. The goal of this study was to evaluate the incidence and motor function of the extralaryngeal branches of the RLN.

METHODS

Our study group consisted of 335 consecutive patients undergoing thyroid and parathyroid operations in whom the branches of the RLNs (n = 200) were evaluated with intraoperative nerve monitoring and by measuring the distance from the point of branching of the RLN into anterior and posterior branches and the entry of the individual branches into the larynx-defined as the branching distance. Anterior and posterior branches of the RLN were assessed separately by electromyography (using a standard electromyography endotracheal tube) for adduction and by finger palpation for abduction. The RLNs were classified as having motor function only in the anterior branches (Group 1) or function both in the anterior and posterior branches (Group 2).

RESULTS

There were 185 RLNs in Group 1 and 15 RLNs in Group 2, assessed by intraoperative nerve monitoring. Motor function was detected in all anterior branches of the RLN (100%) and in 8% of the posterior branches. The mean branching distance was greater in Group 2 compared with Group 1 (24.1 ± 13.6 mm, 17.3 ± 8.5 mm, respectively, P = .045).

CONCLUSION

Although the anterior branch of RLN always has motor function, the posterior branch also has motor function in about 8% of patients. The probability of detecting motor function in the posterior branch was greater among early branching RLNs, which have a greater branching distance. The surgeon should remember that posterior branches may contain motor fibers and protect these branches to avoid postoperative vocal cord dysfunction.

Location of motor fibers within branches of the recurrent laryngeal nerve with extralaryngeal terminal bifurcation; Functional identification by intraoperative neuromonitoring

BACKGROUND

Extralaryngeal terminal bifurcation (ETB) of the recurrent laryngeal nerve (RLN) is an anatomic variation that threatens the safety of thyroid operation. Therefore, it is important to identify motor function in nerve branches to preserve appropriate motor activity. Intraoperative neuromonitoring (IONM) is an accepted procedure to identify motor function of the RLN.

METHODS

We established the operative anatomy of RLNs with ETB in 47 patients. The main trunk, bifurcation point, and the branches were identified and exposed completely during thyroid operation. The location of motor fibers within nerve branches was investigated by identifying motor function via IONM. Wave amplitudes were recorded after electrophysiologic stimulation.

RESULTS

A total of 61 RLNs had ETBs with anterior and posterior branches. Bifurcation occurred early along the pre-arterial (proximal) segment in 13% of bifid RLNs. IONM showed motor function in all anterior branches. IONM identified motor activity in 4 (18%) posterior branches of 22 right, 3 (8%) posterior branches of 39 left, and 7 (12%) posterior branches of all 61 RLNs with ETB. The rate of recorded wave amplitudes of motor function in seven posterior branches was between 14 and 78% of those of corresponding anterior branches.

CONCLUSION

In the RLN, the anterior branch always and the posterior branch uncommonly contain motor fibers. Wave amplitude analysis showed that motor function in the posterior branch is weaker than that in the anterior branch. On the basis of the location of motor fibers in both branches, total exposure and preservation of anatomy and function of all branches of the RLN is mandatory for complication-free thyroid surgery. Electrophysiologic testing may be as an important adjunct to visualization of the nerve with anatomic variation.

Thyroid surgery and the usefulness of intraoperative neuromonitoring, a single center study

Purpose/Aim of study: To compare the use of intraoperative neuromonitoring (IONM) versus visualization of the recurrent laryngeal nerve (RLN) alone in thyroid surgery with regard to incidence in postoperative RLN injury and operation time.

MATERIALS AND METHODS

This retrospective cohort study was performed in the Amphia Hospital, the Netherlands. All thyroid gland operations were collected from September 2009 to October 2012. For each case we recorded the patient characteristics, indication for surgery, intraoperative data, complications, results of pathological evaluation, and consultation of a ENT-surgeon. Research of current literature and statistical analysis was performed.

RESULTS

In total, 147 patients were included and classified into an IONM and non-IONM group. Both groups were similar in demographical aspects and indications for surgery. In total, we had 170 nerves at risk (NAR). In both groups, there were 85 (50%) NAR. Overall injury to the RLN was 6%. A statistical significant decrease of permanent RLN injuries was noticed in the IONM group compared to the non-IONM group (n = 0 vs n = 6; p = .044). In transient RLN injury, no difference was noticed (n = 2 vs n = 2). Operation time with or without IONM was not significantly different for hemithyroidectomies, neither for total thyroidectomies.

CONCLUSION

IONM is a useful tool as an adjunct in thyroid surgery to prevent RLN injury. A statistical significant decrease in permanent RLN injury with the use of IONM was found, but it did not significantly decrease time of operation.

Surgical anatomy of bilateral extralaryngeal bifurcation of the recurrent laryngeal nerve: similarities and differences between both sides

Background:

Anatomical variations of the recurrent laryngeal nerve (RLN) such as extralaryngeal terminal bifurcation is an important risk for its motor function.

Aims:

The objective is to study surgical anatomy of bilateral bifurcation of the RLNs in order to decrease risk of vocal cord palsy in patients with bifurcated nerves.

Materials and Methods:

Surgical anatomy including terminal bifurcation was established in 292 RLNs of 146 patients. We included patients with bilateral bifurcation of RLN in this study. Based on two anatomical landmarks (nerve-artery crossing and laryngeal entry), the cervical course of RLN was classified in four segments: Pre-arterial, arterial, post-arterial and pre-laryngeal. According to these segments, bifurcation point locations along the cervical course of RLNs were compared between both sides in bilateral cases.

Results:

RLNs were exposed throughout their entire courses. Seventy (48%) patients had bifurcated RLNs. We identified terminal bifurcation in 90 (31%) of 292 RLNs along the cervical course. Bilateral bifurcation was observed in 20 (28.6%) patients with bifurcated RLNs. Bifurcation points were located on arterial and post-arterial segments in 37.5% and 32.5% of cases, respectively. Pre-arterial and pre-laryngeal segments contained bifurcations in 15% of cases. Comparison of both sides indicated that bifurcation points were similar in 5 (25%) and different in 15 (75%) patients with bilateral bifurcation. Permanent nerve injury did not occur in this series.

Conclusion:

Bilateral bifurcation of both RLNs was observed in approximately 30% of patients with extralaryngeal bifurcation which is a common anatomical variation. Bifurcation occurred in different segments along cervical course of RLN. Bifurcation point locations differed between both sides in the majority of bilateral cases. Increasing surgeons’ awareness of this variation may lead to safely exposing bifurcated nerves and prevent the injury to extralaryngeal terminal branches of RLN.

The nonrecurrent laryngeal nerve: anatomic and electrophysiologic algorithm for reliable identification

OBJECTIVES/HYPOTHESIS

The recurrent laryngeal nerve (RLN) intraoperative monitoring (IONM) provides a new functional dynamic that adds to visual identification of the RLN to optimize its intraoperative management. Intraoperative monitoring has been applied to the initial identification of the RLN. We now apply IONM to the identification of the nonrecurrent laryngeal nerve (NRLN) and provide electrophysiologic and anatomic parameters to facilitate this technique of neural identification for the NRLN, which is at increased risk of injury during thyroid surgery.

STUDY DESIGN

Retrospective.

METHODS

A study of cases of the NRLN from consecutive thyroid surgeries with IONM was conducted. Preoperative and postoperative laryngoscopy was documented in all cases.

RESULTS

Ten right-sided nerves (0.6%) were identified as NRLN. One hundred percent of NRLNs had documented normal preoperative and postoperative laryngeal function. Distal and proximal vagal nerve stimulation points that allowed for the electrophysiologic prediction of a nonrecurrence in all patients were identified. Electrophysiological normative parameters of NRLN were compared to those of the normal right RLN and right vagus nerves.

CONCLUSION

Nonrecurrent laryngeal nerve is present in 0.6% of patients undergoing thyroid surgery. Intraoperative monitoring involving vagal stimulation at the defined distal and proximal points provides reliable electrophysiologic intraoperative verification of the presence of the NRLN. Three anatomical subtypes of right NRLN are noted that enable early identification of the NRLN. In conjunction with detailed knowledge of the NRLN anatomic pathways, they also may be helpful in preventing injury to the NRLN, which has been shown to be at higher risk during thyroid surgery. We provide an anatomic and electrophysiologic algorithm for reliable identification of the NRLN.

LEVEL OF EVIDENCE

4.