Electrophysiological neural monitoring of the laryngeal nerves in thyroid surgery: review of the current literature

Comparing Thyroidectomy Techniques, Surgical Loupe and Neuromonitoring Between ENT and Endocrine Surgeons-an Observational Study

Thyroid surgery is performed by ENT head and neck (ENT-HNS), endocrine (ES) and general surgeons (GS). Each modality adopts different surgical techniques causing difference in outcome, operative time and postoperative complication. A retrospective chart review of thyroid surgeries performed by two ENT-HNS, three ES of a single tertiary center was conducted. We compared the use of neuromonitoring and surgical loupe and subsequent patient outcomes between surgeries performed by ENT-HNS versus ES, focusing on parathyroid gland identification, operative duration, vocal cord paralysis and length of hospital stay. A total of 167 patients underwent thyroid surgery. Surgical loupes were used in all the surgeries performed by ENT-HNS vs. 85% by the ES. Parathyroid glands were identified in all the surgeries performed by ENT-HNS versus 95% by ES. Neuromonitoring was used in all the surgeries performed by ENT-HNS, and none by the ES. Vocal cord paralysis developed in two patients of ES versus none in the ENT-HNS. Mean operative duration for total thyroidectomy in ENT-HN surgeries, 183.7 min vs. 151 min in the ES. The mean hospital stay of patients was 3.6 ± 1.6 days for ENT-HNS, and 5.45 ± 3 days for ES. Identification of parathyroid gland and recurrent laryngeal nerve by neuromonitoring and surgical loupes may increase operative time but decrease the rate of vocal cord paralysis and increases the chance of parathyroid gland identification.

Risk Factors That Influence Surgical Decision-Making for Patients with Low-Risk Differentiated Thyroid Cancer with Tumor Diameters of 1-4 cm

Background

There are several controversies between thyroid lobectomy and total thyroidectomy for surgical management of low-risk differentiated thyroid cancer (DTC) with a tumor diameter of 1–4 cm.

Patients and Methods

In this study, we explore the factors related to selection of type of surgical procedure for 103 low-risk DTC patients with a tumor diameter of 1–4 cm.

Results

Among 103 low-risk DTC patients with tumor diameters of 1–4 cm, 43 patients underwent total thyroidectomy and 60 patients underwent thyroid lobectomy based on postoperative pathology. A ROC curve showed that the optimal diagnostic threshold for selecting surgical modality was a tumor diameter of 2.15 cm. For these low-risk DTC patients, the sensitivity and specificity for predicting thyroid lobectomy when tumor diameter <2.15 cm while total thyroidectomy when tumor diameter ≥2.15 cm are 46.5% and 78.3%, respectively. There were significant differences between the selection of type of surgical procedure in patient groups with 1) tumors with multiple foci group vs a single focus (P<0.05), and 2) tumor diameter of ≥2.15 cm vs <2.15 cm (P<0.05). There was no significant difference between gender and age groups (P>0.05). Multivariate analysis confirmed that tumors with multiple foci and diameter ≥2.15 cm were the primary risk factors for implementation of total thyroidectomy (P<0.05).

Conclusion

The diameter and multifocal nature of low-risk DTC tumors are the primary factors related to preferred surgical modality. This study revealed that thyroid lobectomy is more applicable to patients with tumor diameter <2.15 cm and a single focus, whereas, total thyroidectomy was preferred in patients with tumor diameter ≥2.15 cm and/or multiple foci.

Continuous intraoperative neuromonitoring (cIONM) in head and neck surgery-a review

Although the history of intraoperative neuromonitoring (IONM) dates back to the 19th century, the method did not evolve further than the mere differentiation of nerves until recently. Only the development of continuous IONM (cIONM) has allowed for non-stop analysis of excitation amplitude and latency during surgical procedures, which is nowadays integrated into the software of almost all commercially available neuromonitoring devices. The objective of cIONM is real-time monitoring of nerve status in order to recognize and prevent impending nerve injury and predict postoperative nerve function. Despite some drawbacks such as false-positive/negative alarms, technical artefacts, and rare adverse effects, cIONM remains a good instrument which is still under development. Active (acIONM) and passive (pcIONM) methods of cIONM are described in literature. The main fields of cIONM implementation are currently thyroid surgery (in which the vagal nerve is continuously stimulated) and surgery to the cerebellopontine angle (in which the facial nerve is either continuously stimulated or the discharge signal of the nerve is analyzed via pcIONM). In the latter surgery, continuous monitoring of the cochlear nerve is also established.

[Continuous intraoperative neuromonitoring (cIONM) in head and neck surgery-a review. German version]

Obwohl die Geschichte des intraoperativen Neuromonitorings (IONM) bereits in das 19. Jahrhundert zurückdatiert werden kann, hat sich diese Methode bis vor Kurzem nicht von der reinen Differenzierung des Nervs weiterentwickelt. Erst das kontinuierliche IONM (cIONM) ermöglichte die durchgehende Analyse der Reizamplituden und -latenzen, welche mittlerweile ebenfalls in die Software gängiger Monitoringsysteme integriert wurde. Zielsetzung des cIONM ist ein Real-Time-Monitoring des Nervenstatus während des Eingriffs, um so drohende Nervenverletzung erkennen und verhindern zu können und die postoperative Funktion des Nervs vorhersehbar zu erhalten. Trotz einiger Nachteile wie falsch-positiver oder -negativer Alarme, technischer Artefakte und seltener Nebenwirkungen bleibt das cIONM ein gutes Hilfsmittel, das noch weiterentwickelt wird. In der Literatur sind sowohl aktive (acIONM) als auch passive (pcIONM) Reiz- und Ableitmethoden des cIONM beschrieben. Derzeit gängige Anwendungsgebiete des cIONM umfassen die Schilddrüsenchirurgie mit der kontinuierlichen Stimulation des N. vagus sowie die Chirurgie des Kleinhirnbrückenwinkels (KHBW) mit dem Monitoring des N. facialis; hierbei werden neben kontinuierlicher Stimulation auch die Entladungsmuster des Nervs analysiert. Des Weiteren ist in die Chirurgie des KHBW das kontinuierliche Monitoring des Hörnervs etabliert.

Intraoperative nerve monitoring during thyroidectomy: evaluation of signal loss, prognostic value and surgical strategy

INTRODUCTION

Intraoperative neural monitoring of the recurrent laryngeal nerve has been widely used to avoid nerve injury during thyroidectomy. We discuss the results of the change in surgical strategy after unilateral signal loss surgeries using intermittent intraoperative neural monitoring in a high-volume referral centre.

MATERIALS AND METHODS

Details of consecutive patients who underwent thyroidectomy with intermittent intraoperative neural monitoring between January 2014 and December 2017 were prospectively recorded and retrospectively reviewed. Loss of signal was defined as recurrent laryngeal nerve amplitude level lower than 100 μV during surgery. The rate of loss of signal and change in surgical strategy during the operation were evaluated.

RESULTS

Loss of signal was detected in 25 (5.4%) of 456 patients for whom intermittent intraoperative neural monitoring was performed. Four patients had anatomic nerve disruption and surgery was completed by an experienced endocrine surgeon making use of intraoperative neural monitoring with continuous vagal stimulation. Staged thyroidectomy was performed on 16 patients with unilateral loss of signal in whom the nerves were intact visually. Postoperative vocal cord paralysis was encountered in 18 of 21 (85.7%) patients with loss of signal, and 16 of 18 (88.8%) were improved during the follow-up period. Patients' voices were subjectively normal to the surgeon postoperatively in 9 of 21 (42.8%) patients who were found to have loss of signal with intact nerves.

CONCLUSIONS

Intraoperative neural monitoring can be used safely in thyroid surgery to avoid recurrent laryngeal nerve injury. It enables the surgeon to diagnose recurrent laryngeal nerve injury intraoperatively to estimate the postoperative nerve function and to modify the surgical strategy to avoid bilateral vocal cord paralysis.

Intraoperative neuromonitoring versus visual nerve identification for prevention of recurrent laryngeal nerve injury in adults undergoing thyroid surgery

BACKGROUND

Injuries to the recurrent inferior laryngeal nerve (RILN) remain one of the major post-operative complications after thyroid and parathyroid surgery. Damage to this nerve can result in a temporary or permanent palsy, which is associated with vocal cord paresis or paralysis. Visual identification of the RILN is a common procedure to prevent nerve injury during thyroid and parathyroid surgery. Recently, intraoperative neuromonitoring (IONM) has been introduced in order to facilitate the localisation of the nerves and to prevent their injury during surgery. IONM permits nerve identification using an electrode, where, in order to measure the nerve response, the electric field is converted to an acoustic signal.

OBJECTIVES

To assess the effects of IONM versus visual nerve identification for the prevention of RILN injury in adults undergoing thyroid surgery.

SEARCH METHODS

We searched CENTRAL, MEDLINE, Embase, ICTRP Search Portal and ClinicalTrials.gov. The date of the last search of all databases was 21 August 2018. We did not apply any language restrictions.

SELECTION CRITERIA

We included randomised controlled trials (RCTs) comparing IONM nerve identification plus visual nerve identification versus visual nerve identification alone for prevention of RILN injury in adults undergoing thyroid surgery DATA COLLECTION AND ANALYSIS: Two review authors independently screened titles and abstracts for relevance. One review author carried out screening for inclusion, data extraction and 'Risk of bias' assessment and a second review author checked them. For dichotomous outcomes, we calculated risk ratios (RRs) with 95% confidence intervals (CIs). For continuous outcomes, we calculated mean differences (MDs) with 95% CIs. We assessed trials for certainty of the evidence using the GRADE instrument.

MAIN RESULTS

Five RCTs with 1558 participants (781 participants were randomly assigned to IONM and 777 to visual nerve identification only) met the inclusion criteria; two trials were performed in Poland and one trial each was performed in China, Korea and Turkey. Inclusion and exclusion criteria differed among trials: previous thyroid or parathyroid surgery was an exclusion criterion in three trials. In contrast, this was a specific inclusion criterion in another trial. Three trials had central neck compartment dissection or lateral neck dissection and Graves' disease as exclusion criteria. The mean duration of follow-up ranged from 6 to 12 months. The mean age of participants ranged between 41.7 years and 51.9 years.There was no firm evidence of an advantage or disadvantage comparing IONM with visual nerve identification only for permanent RILN palsy (RR 0.77, 95% CI 0.33 to 1.77; P = 0.54; 4 trials; 2895 nerves at risk; very low-certainty evidence) or transient RILN palsy (RR 0.62, 95% CI 0.35 to 1.08; P = 0.09; 4 trials; 2895 nerves at risk; very low-certainty evidence). None of the trials reported health-related quality of life. Transient hypoparathyroidism as an adverse event was not substantially different between intervention and comparator groups (RR 1.25; 95% CI 0.45 to 3.47; P = 0.66; 2 trials; 286 participants; very low-certainty evidence). Operative time was comparable between IONM and visual nerve monitoring alone (MD 5.5 minutes, 95% CI -0.7 to 11.8; P = 0.08; 3 trials; 1251 participants; very low-certainty evidence). Three of five included trials provided data on all-cause mortality: no deaths were reported. None of the trials reported socioeconomic effects. The evidence reported in this review was mostly of very low certainty, particularly because of risk of bias, a high degree of imprecision due to wide confidence intervals and substantial between-study heterogeneity.

AUTHORS' CONCLUSIONS

Results from this systematic review and meta-analysis indicate that there is currently no conclusive evidence for the superiority or inferiority of IONM over visual nerve identification only on any of the outcomes measured. Well-designed, executed, analysed and reported RCTs with a larger number of participants and longer follow-up, employing the latest IONM technology and applying new surgical techniques are needed.

Risk factors for thyroid surgery-related unilateral vocal fold paralysis

Objectives/Hypothesis

We aimed to identify the risk factors for iatrogenic unilateral vocal fold paralysis (UVFP) caused by thyroid surgery, to allow the identification of patients requiring nerve‐protection procedures and monitoring technologies.

Study Design

Retrospective case study in a medical center.

Methods

Patients who underwent thyroid surgery from April 2011 to February 2016 and who were diagnosed with UVFP by laryngoscopy and laryngeal electromyography were included. Patient demographics, types of surgery, and characteristics of the thyroid lesions were analyzed.

Results

Sixty (2.1%) of 2,815 patients who received thyroid surgery developed UVFP. The risk of UVFP was higher in patients over 60 years old (odds ratio, 1.89; 95% confidence interval, 1.01‐3.26; P = .01). Involvement of the external branch of superior laryngeal nerve (EBSLN) occurred in 19 (31.7%) of the 60 UVFP patients, and was more likely to occurr in patients with diabetes mellitus (odds ratio, 14.19; 95% confidence interval, 3.80‐52.94; P < .001). The incidence of UVFP and involvement of the EBSLN differed among surgery types, and was the highest among patients undergoing total thyroidectomy with neck dissection (TTND) (10/158, 6.3% and 5/158, 3.2%, respectively).

Conclusions

The risk of thyroid surgery–related UVFP is higher in older patients. EBSLN involvement is more likely in patients with diabetes mellitus. TTND is associated with higher risks of UVFP and EBSLN injury than other types of surgery, implying the need of intraoperative nerve monitoring in these high‐risk characteristics.

Level of Evidence

4 Laryngoscope, 129:275–283, 2019

Motor Interconnections Between Superior and Inferior Laryngeal Nerves

Introduction Anatomical studies on human cadavers have established anastomoses between laryngeal nerves. However, we need to functionally identify motor communication via these anastomoses between the recurrent laryngeal nerve (RLN) and the external branch of the superior laryngeal nerve (EBSLN) in living bodies. We aim to establish motor interconnections using intraoperative nerve monitoring (IONM). Methods IONM of 112 EBSLNs and RLNs in 62 thyroidectomy cases was used to establish motor functions of laryngeal nerves. Electrophysiological parameters were recorded, and cricothyroid muscle (CTM) contraction was observed after stimulation of laryngeal nerves. Results Eighty (71.4%) EBSLNs were visually identified, and 109 (97.3%) EBSLNs were functionally identified with CTM contraction. Stimulation of 74 (67.9%) EBSLNs induced contraction of laryngeal muscles and generated wave amplitude from intrinsic laryngeal musculature. The stimulation of the RLN induced CTM contraction in 65 (58%) of the 112 muscles. The mean conductivity powers of the EBSLN and of the RLN to intrinsic laryngeal musculature were calculated as 231.3 µV and 1354.5 µV, respectively. Conclusion Recordable waveform amplitude with EBSLN stimulation yielded motor relations between laryngeal nerves. CTM contraction after stimulation of the RLN confirmed these relations. These results of IONM established motor interconnections between superior and inferior laryngeal nerves in the majority of patients. The EBSLN may have an effect on motor innervations for intrinsic laryngeal muscles via motor interconnections.

Opportunities and challenges of intermittent and continuous intraoperative neural monitoring in thyroid surgery

The number of thyroid operations and there radically continues to rise in the western hemisphere, bringing prevention of recurrent laryngeal nerve (RLN) palsy to the fore. Overall, the incidence of RLN palsy is fairly low but continues to prompt litigation for malpractice. In an effort to diminish transient, and more importantly permanent, RLN palsy rates, intraoperative neuromonitoring (IONM) has been advocated as a risk minimization tool. Recent meta-analyses of studies, many of which were limited by poor study design and the sole use of intermittent nerve stimulation, were unable to demonstrate superiority of IONM over mere anatomic RLN dissection. This is where continuous IONM (CIONM) comes into play: this technology enables the surgeon to (I) identify impending nerve injury as it unfolds; (II) release distressed nerves by reversing causative surgical maneuvers; and (III) verify functional nerve recovery after intraoperative loss of the electromyographic signal. Despite this superiority, CIONM is not devoid of methodological limitations, which need to be accounted for. This review summarizes the current key achievements of IONM; outlines opportunities for improvement regarding clinical implementation; and suggests areas of future research in this rapidly evolving field.

Evaluation of collimated polarized light imaging for real-time intraoperative selective nerve identification in the human hand

Intraoperative peripheral nerve lesions are common complications due to misidentification and limitations of surgical nerve identification. This study validates a real-time non-invasive intraoperative method of nerve identification. Long working distance collimated polarized light imaging (CPLi) was used to identify peripheral radial nerve branches in a human cadaver hand by their nerve specific anisotropic optical reflection. Seven ex situ and six in situ samples were examined for nerves, resulting after histological validation, in a 100% positive correct score (CPLi) versus 77% (surgeon). Nerves were visible during a clinical in vivo observation using CPLi. Therefore CPLi is a promising technique for intraoperative nerve identification.

Continuous intraoperative neural monitoring in thyroid surgery: a Mexican experience

Intraoperative continuous neural monitoring (C-IONM) during thyroid surgery has been recognized as a useful tool to identify and confirm recurrent laryngeal nerve integrity. The aim of the present study is to analyze electromyographic features and thresholds for normal vocal fold function in our initial experience with C-IONM in thyroid surgery. C-IONM was utilized in 57 patients who underwent thyroid surgery between July 2012 and December 2015. EMG parameters were analyzed looking for potential predictors of postoperative vocal fold dismotility. There were 54 females (94.7%) and 3 males (5.3%) with a mean age of 46.7 ± 11.6 years. C-IONM was successfully registered in 89 of 107 nerves at risk (83.1%). Mean basal amplitude was 727.31 ± 471.25 μV and mean final amplitude was 650.27 ± 526.87 μV (P = 0.095, CI 95% 13.83-167.91). Mean basal latency was 5.23 ± 1.42 mS and mean final latency was 5.18 ± 1.50 mS (P = 0.594, CI 95% 0.39-0.24). Four patients had transient postoperative vocal fold paresis. None of these four patients had loss of signal (LOS), three had transient decrease in amplitude, and one had a normal registry throughout the operation. C-IONM is a useful tool to identify patients in whom intraoperative RLN is at risk during surgery. Final amplitude above 500 μV and no LOS is associated with RLN integrity and normal postoperative vocal fold function.

Phrenic nerve stimulation during neck dissection for advanced thyroid cancer involving level IV: is it worth doing it?

During thyroidectomy and neck dissection surgery for advanced or recurrent metastatic thyroid cancer under intraoperative monitoring, we used the available technology to assess the feasibility of such an intervention to monitor those patients with phrenic nerves at risk. A retrospective review of patients operated on from January 2009 to December 2015 by a single surgeon (CSD) was conducted. Patients who had neck and mediastinal dissection, with or without total thyroidectomy, due to advanced or recurrent metastatic disease to the neck were selected. The procedures were done under intraoperative nerve monitoring using nerve monitoring systems (NIM 2.0 or 3.0; Medtronic, Jacksonville, FL, USA). A total of 19 patients were included in the study, with a mean age of 57.6 years ± 16.3 and a male/female ratio of 10:9. Overall, all patients had an intact phrenic nerve at the conclusion of the surgery. One patient had an aggressive tumor that precluded sacrifice of the left recurrent laryngeal nerve and ipsilateral thoracic duct. The procedure was complicated by a temporary impairment of the diaphragm contraction with intraoperative nerve monitoring as well as a chyle fistula. This was due to the manipulation of the tissue surrounding the phrenic nerve. Intraoperative nerve monitoring of the phrenic nerve offers the surgeon a "potential" method of ensuring phrenic nerve integrity in cases of advanced thyroid cancers with gross level IV metastatic disease. Further prospective studies are needed to assess the risks of this intervention and evaluate the method of recording diaphragm contraction movement.

Continuous intraoperative neural monitoring of the recurrent nerves in thyroid surgery: a quantum leap in technology

The continuous intraoperative neural monitoring (CIONM) technique is increasingly acknowledged as a useful tool to recognize impending nerve injury and to abort the related manoeuvre to prevent nerve injury during thyroid surgery. CIONM provides valuable real-time information constantly, which is really useful during complex thyroid surgeries especially in the settings of unusual anatomy. Thus, CIONM overcomes the key methodological limitation inherent in intermittent nerve monitoring (IINOM); which is allowing the nerve to be at risk in between the stimulations. The clinically important combined electromyographic (EMG) event, indicative of impending recurrent laryngeal nerve (RLN) injury, prevents the majority of traction related injuries to the anatomically intact RLN enabling modification of the causative surgical manoeuvre in 80% of cases. These EMG changes can progress to loss of EMG signal with postoperative vocal cord palsy (VCP) if corrective action is not taken. As a further extension, CIONM also helps to identify intraoperative functional nerve recovery with restitution of amplitude to ≥50% of initial baseline; this allows continuing of resection of contralateral side. CIONM facilitates for early corrective action before permanent damage to the nerve has been done. CIONM is a recent but rapidly evolving technique, constantly being refined by various studies focusing on improvement in its implementation and interpretation, as well as on the elimination of the technical snags.

Morphology and Functional Anatomy of the Recurrent Laryngeal Nerve with Extralaryngeal Terminal Bifurcation

Anatomical variations of the recurrent laryngeal nerve (RLN), such as an extralaryngeal terminal bifurcation (ETB), threaten the safety of thyroid surgery. Besides the morphology of the nerve branches, intraoperative evaluation of their functional anatomy may be useful to preserve motor activity. We exposed 67 RLNs in 36 patients. The main trunk, bifurcation point, and terminal branches of bifid nerves were macroscopically determined and exposed during thyroid surgery. The functional anatomy of the nerve branches was evaluated by intraoperative nerve monitoring (IONM). Forty-six RLNs with an ETB were intraoperatively exposed. The bifurcation point was located along the prearterial, arterial, and postarterial segments in 11%, 39%, and 50% of bifid RLNs, respectively. Motor activity was determined in all anterior branches. The functional anatomy of terminal branches detected motor activity in 4 (8.7%) posterior branches of 46 bifid RLNs. The motor activity in posterior branches created a wave amplitude at 25–69% of that in the corresponding anterior branches. The functional anatomy of bifid RLNs demonstrated that anterior branches always contained motor fibres while posterior branches seldom contained motor fibres. The motor activity of the posterior branch was weaker than that of the anterior branch. IONM may help to differentiate between motor and sensory functions of nerve branches. The morphology and functional anatomy of all nerve branches must be preserved to ensure a safer surgery.

Minimally invasive thyroidectomy: a ten years experience

BACKGROUND

The conventional thyroidectomy is the most frequent surgical procedure for thyroidal surgical disease. From several years were introduced minimally invasive approaches to thyroid surgery. These new procedures improved the incidence of postoperative pain, cosmetic results, patient's quality of life, postoperative morbidity. The mini invasive video-assisted thyroidectomy (MIVAT) is a minimally invasive procedure that uses a minicervicotomy to treat thyroidal diseases.

METHODS

We present our experience on 497 consecutively treated patients with MIVAT technique. We analyzed the mean age, sex, mean operative time, rate of bleeding, hypocalcemia, transitory and definitive nerve palsy (6 months after the procedure), postoperative pain scale from 0 to 10 at 1 hour and 24 hours after surgery, mean hospital stay.

RESULTS

The indications to treat were related to preoperative diagnosis: 182 THYR 6, 184 THYR 3-4, 27 plummer, 24 basedow, 28 toxic goiter, 52 goiter. On 497 cases we have reported 1 case of bleeding (0,2%), 12 (2,4%) cases of transitory nerve palsy and 4 (0,8%) definitive nerve palsy. The rate of serologic hypocalcemia was 24.9% (124 cases) and clinical in 7.2% (36 cases); 1 case of hypoparathyroidism (0.2%).

CONCLUSIONS

The MIVAT is a safe approach to surgical thyroid disease, the cost are similar to CT as the adverse events. The minicervicotomy is really a minimally invasive tissue dissection.