Electrophysiological neuromonitoring of the laryngeal nerves in thyroid and parathyroid surgery: A review

The Effect of Patient Positioning on Intraoperative Neuromonitoring During Thyroid and Parathyroid Surgery

BACKGROUND

Intraoperative neuromonitoring (IONM) has been accepted as a routine adjunct among surgeons who perform thyroid and parathyroid surgeries. Thyroid and parathyroid surgeries use various patient positioning strategies that have poorly understood effects on IONM. The aim of this study was to compare IONM signals between the transaxillary and transcervical approaches.

METHODS

In this retrospective cohort study, we evaluated 463 adult patients who underwent a total of 502 procedures. The procedures performed included total thyroidectomy, right or left hemithyroidectomy, and parathyroidectomy. Vagus nerve and recurrent laryngeal nerve (RLN) latency and amplitude measurements were analyzed intra-operatively. The distances between the vagus nerve and the trachea were measured via ultrasound during transaxillary procedures.

RESULTS

Compared to the transcervical approach, the right vagus nerve latency was significantly decreased in the transaxillary approach. Transaxillary surgery was not associated with increased latency or decreased amplitude on IONM. The distance between the vagus nerve and trachea was significantly decreased post-positioning during transaxillary approaches.

DISCUSSION

Despite differences in patient positioning, a transaxillary approach was not associated with increased stress on the vagus nerve or RLN, according to IONM data. The decreased right vagus nerve latency associated with a transaxillary approach highlights the importance of considering patient positioning and laterality while interpreting IONM data.

Transoral Endoscopic Thyroidectomy Vestibular Approach Versus Endoscopic Thyroidectomy Via Areola Approach for Patients With Unilateral Papillary Thyroid Carcinoma: A Retrospective Study

BACKGROUND

Endoscopic thyroidectomy via areola approach (ETA) has been widely used in thyroidectomy for many years as it can effectively avoid a scar in the neck. Transoral endoscopic thyroidectomy vestibular approach (TOETVA) is newly applied and has gained popularity quickly. This study is to compare the safety and effectiveness of TOETVA and ETA.

MATERIALS AND METHODS

A total of 95 patients who underwent TOETVA or ETA with unilateral papillary thyroid carcinoma were enrolled in this study from March 2019 to February 2020. The basic information (such as gender, age), intraoperative hemorrhage, postoperative drainage volume, hospital durations, intraoperative and postoperative complications, operative time, central lymph node dissection time, total number of central lymph nodes, and number of metastatic central lymph nodes were compared.

RESULTS

The operative time of the TOETVA group was significantly longer than the ETA group (148.11±19.78 vs. 135.90±12.77 min, P<0.05). However, the result was opposite when central lymph node dissection time was compared (10.31±2.93 vs. 12.48±3.55, P<0.05). TOETVA had an advantage on total number of central lymph nodes over ETA (7.82±3.35 vs. 5.26±2.45, P<0.05). No differences were found between the 2 groups on other data.

CONCLUSION

TOETVA and ETA have the similarity on surgical safety and effectiveness. TOETVA has its advantage on central lymph node dissection and might be a reasonable alternative for ETA and open surgery in the future.

Comparison of quality of life between patients undergoing trans-oral endoscopic thyroid surgery and conventional open surgery

Background

Trans-oral endoscopic thyroidectomy allows obviating scar of the neck that expects to gain quality of life (QOL). However, the benefit of the QOL from this technique has not been adequately investigated, therefore, this study compared the QOL outcomes, including cosmetic outcomes, between thyroidectomy by trans-oral endoscopy and conventional open surgery.

Methods

A study was conducted from January 30, 2017 to November 10, 2018. Thirty-two and 38 patients underwent trans-oral endoscopic thyroid surgery and conventional open surgery, respectively. Their quality of life was evaluated at 2, 6, and 12 weeks postoperatively using a thyroid surgery-specific questionnaire and a 36-item short-form questionnaire.

Results

Trans-oral endoscopic group, patients were younger and presented with smaller thyroid nodules (p < 0.05). Regarding surgical outcomes, there were no statistically significant differences between the two groups. Mean operative time was significantly longer in the trans-oral endoscopic group (p < 0.05). The quality of life parameters in the trans-oral endoscopic group was significantly better than in the conventional surgery group (p < 0.05). These parameters included reduction of physical activity, psychosocial impairment, the role of physic, and emotion at 2 weeks after surgery; swallowing impairment, psychosocial impairment, the role of physic, social function and mental health 6 weeks after surgery; tingling and feeling of vitality at 12 weeks after surgery. Cosmetic outcomes and overall satisfaction were significantly better in the trans-oral endoscopic group than in the conventional surgery group at all of our follow up times (p < 0.05).

Conclusions

The trans-oral endoscopic approach allows real scarless on the skin with better cosmetic and QOL outcomes.

Trial registration

This trial was retrospectively registered at the ClinicalTrial.gov (NCT03048539), registered on 4 March 2017.

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.

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.

Intraoperative neuromonitoring in thyroid surgery: Is the two-staged thyroidectomy justified?

BACKGROUND

The aim of this study was to evaluate the diagnostic accuracy of intraoperative neuromonitoring (IONM) in predicting postoperative nerve function during thyroid surgery and its consequent ability to assist the surgeon in intraoperative decision making.

MATERIALS AND METHODS

A total of 2365 consecutive patients were submitted to thyroidectomy by the same surgical team. Group A included 1356 patients (2712 nerves at risk) in whom IONM was utilized, and Group B included 1009 patients (2018 nerves at risk) in whom IONM was not utilized.

RESULTS

In Group A, loss of signal (LOS) was observed in 37 patients; there were 29 true positive, 1317 true negative, 8 false positive, and 2 false negative cases. Accuracy was 99.3%, positive predictive value was 78.4%, negative predictive value was 99.8%, sensitivity was 93.6%, and specificity was 99.4%. A total of 29 (2.1%) cases of unilateral paralysis were observed, 23 (1.7%) of which were transient and 6 (0.4%) of which were permanent. Bilateral palsy was observed in two (0.1%) cases requiring a tracheostomy. In Group A, 31 (2.3%) injuries were observed, 25 (1.8%) of which were transient and 6 (0.4%) of which were permanent. In Group B, 26 (2.6%) unilateral paralysis cases were observed, 20 (2%) of which were transient and 6 (0.6%) of which were permanent; bilateral palsy was observed in 2 (0.2%) cases. In Group B, 28 (2.8%) injuries were observed, 21 (2.1%) of which were transient and 7 (0.7%) of which were permanent. Differences between the two groups were not statistically significant.

CONCLUSIONS

Our results show that IONM has a very high sensitivity and negative predictive value, but also good specificity and positive predictive value. For these reasons, in selected patients with LOS, the surgical strategy should be reconsidered. However, patients need to be informed preoperatively about potential strategy changes during the planned bilateral surgery. Future larger and multicenter studies are needed to confirm the benefits of this therapeutic strategy.

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.

Implementation of Intraoperative Neuromonitoring for Transoral Endoscopic Thyroid Surgery: A Preliminary Report

BACKGROUND

Transoral endoscopic approach is the natural orifice surgery applied in thyroidectomy to achieve an excellent cosmetic result. Recurrent laryngeal nerve (RLN) injury is the most common complication and little advancement was achieved in the previous clinical studies of transoral thyroid surgery. Herein, we introduced the method of intraoperative neuromonitoring (IONM) for transoral endoscopic thyroid surgery.

MATERIALS AND METHODS

Patients with thyroid carcinoma received transoral endoscopic thyroid surgery through vestibular approach (TOETVA) for thyroidectomy and central node dissection (CND). IONM was implemented to identify whether the RLN benefited from oral tracheal intubation. The laryngeal electromyography (EMG) response, operation time, number of CND, drainage volume, hospital duration, surgical complications, and cosmetic results were evaluated.

RESULTS

From August to October 2015, 10 cases were performed with TOETVA and IONM. All EMG responses were recorded intraoperatively, and no case experienced transient or permanent RLN palsy. The operation time ranged from 130 to 215 minutes in ipsilateral lobectomy with CND, whereas bilateral lobectomy with ipsilateral CND lasted 345 minutes. The number of CNDs ranged from three to eight. The average time of drainage extubation and discharge was 4 days (3-5 days) postoperatively. All patients were satisfied with the cosmetic results, and no infection was observed at lip wound or in the anterior neck region.

CONCLUSION

IONM system implemented in transoral thyroid surgery was feasible and serviceable in preventing RLN injury. The method of TOETVA shows promise for thyroidectomy with CND due its ideal cosmetic results.

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.