Recurrent laryngeal nerve injury with incomplete loss of electromyography signal during monitored thyroidectomy—evaluation and outcome

Recurrent Laryngeal Nerve with Loss of Signal During Monitored Thyroidectomy: Percentage Reduction in Sum of the Amplitude of Left and Right Channel

PURPOSE

The prognostication for the injured recurrent laryngeal nerve (RLN) with incomplete loss of signal (LOS) and its function outcome have not been well unified. A warning criterion was proposed to predict RLN injury during monitored thyroidectomy.

METHODS

A retrospective review of prospectively collected data from consecutive 357 patients with 560 nerves at risk was conducted. Vocal cords mobility with laryngoscope was performed preoperatively, on the second day, and once a month postoperatively until complete recovery. Different cutoff values of the percentage reduction in sum of the amplitude of left and right channel at the end of the surgery, for postoperative vocal cord paralysis (VCP) prediction were compared.

RESULTS

Percentage reduction in sum of the amplitude of left and right channel at the end of operation ranged from 30.2 to 63.6% in 27 nerves with incomplete LOS (absolute amplitude value of final R₂ > 100 μV with reduction > 50% of R₁). Seven (1.25%) nerves experienced transient postoperative VCP, in which one nerve with postoperative VCP showed no amplitude reduction. The positive predictive value of VCP for the sum amplitude reduction exceeding 30, 40, 50, and 60% was 22.2, 40, 85.7, and 100%, respectively. Accuracy was 96.1, 98.2, 99.6, 99.4%, respectively.

CONCLUSION

Percentage reduction in sum of the amplitude of left and right channel is a meaningful method to improve the accuracy of VCP prediction. When the sum amplitude reduction ≥ 50%, surgeons should consider the possibility of postoperative VCP and correct some surgical maneuvers.

Surgical Significance of Berry’s Posterolateral Ligament and Frequency of Recurrent Laryngeal Nerve Injury into the Last 2 cm of Its Caudal Extralaryngeal Part(P1) during Thyroidectomy

Background and Objectives: Recurrent laryngeal nerve injury is one of the major complications of thyroidectomy, with the lateral thyroid ligament (Berry’s ligament) being the most frequent site of nerve injury. Neuromonitoring during thyroidectomy revealed three possible anatomical regions of the recurrent laryngeal nerve P1, P2, and P3. P1 represents the recurrent laryngeal nerve’s caudal extralaryngeal part and is primarily associated with Berry’s ligament. The aim of this systematic review is to identify the anatomical region with the highest risk of injury of the recurrent laryngeal nerve (detected via neuromonitoring) during thyroidectomy and to demonstrate the significance of Berry’s ligament as an anatomical structure for the perioperative recognition and protection of the nerve. Materials and Methods: This study conducts a systematic review of the literature and adheres to all PRISMA system criteria as well as recommendations for systematic anatomical reviews. Three search engines (PubMed, Scopus, Cochrane) were used, and 18 out of 464 studies from 2003–2018 were finally included in this meta-analysis. All statistical data analyses were performed via SPSS 25 and Microsoft Office XL software. Results: 9191 nerves at risk were identified. In 75% of cases, the recurrent laryngeal nerve is located superficially to the ligament. In 71% of reported cases, the injury occurred in the P1 area, while the P3 zone (below the location where the nerve crosses the inferior thyroid artery) had the lowest risk of injury. Data from P1, P2, and P3 do not present significant heterogeneity. Conclusions: Berry’s ligament constitutes a reliable anatomical structure for recognizing and preserving recurrent laryngeal nerves. P1 is the anatomical area with the greatest risk of recurrent laryngeal nerve damage during thyroidectomy, compared to P2 and P3.

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.

A Surgeon-Centered Neuromuscular Block Protocol Improving Intraoperative Neuromonitoring Outcome of Thyroid Surgery

BACKGROUND

Neuromuscular blocking agents provide muscular relaxation for tracheal intubation and surgery. However, the degree of neuromuscular block may disturb neuromuscular transmission and lead to weak electromyography during intraoperative neuromonitoring. This study aimed to investigate a surgeon-friendly neuromuscular block degree titrated sugammadex protocol to maintain both intraoperative neuromonitoring quality and surgical relaxation during thyroid surgery.

METHODS

A total of 116 patients were enrolled into two groups and underwent elective thyroid surgery with intraoperative neuromonitoring. All patients followed a standardized intraoperative neuromonitoring protocol with continuous neuromuscular transmission monitoring and received 0.6 mg/kg rocuronium for tracheal intubation. Patients were allocated into two groups according to the degree of neuromuscular block when the anterior surface of the thyroid gland was exposed. The neuromuscular block degree was assessed by the train-of-four (TOF) count and ratio. Patients in group I received sugammadex 0.25 mg/kg for non-deep neuromuscular block degree (TOF count = 1~4). Patients in group II were administered sugammadex 0.5 mg/kg for deep neuromuscular block degree (TOF count = 0). The quality of the intraoperative neuromonitoring was measured using the V₁ electromyography (EMG) amplitude. An amplitude less than 500 μV and greater than 500 μV was defined as weak and satisfactory, respectively.

RESULTS

The quality of the intraoperative neuromonitoring was not different between groups I and II (satisfactory/weak: 75/1 vs. 38/2, P = 0.14). The quality of surgical relaxation was acceptable after sugammadex injection and showed no difference between groups [55/76 (72.3%) in group I vs. 33/40 (82.5%) in group II, P = 0.23].

CONCLUSIONS

This surgeon-centered sugammadex protocol guided by neuromuscular block degree (0.5 mg/kg for deep block and 0.25 mg/kg for others) showed comparably high intraoperative neuromonitoring quality and adequate surgical relaxation. The results expanded the practicality of sugammadex for precise neuromuscular block management during monitored thyroidectomy.

Necessity of Routinely Testing the Proximal and Distal Ends of Exposed Recurrent Laryngeal Nerve During Monitored Thyroidectomy

OBJECTIVES

Intraoperative neuromonitoring (IONM) is a useful tool to evaluate the function of recurrent laryngeal nerve (RLN) in thyroid surgery. This study aimed to determine the necessity and value of routinely testing the proximal and distal ends of RLN.

METHODS

In total, 796 patients undergoing monitored thyroidectomies with standardized procedures were enrolled. All 1346 RLNs with visual integrity of anatomical continuity were routinely stimulated at the most proximal (R2p signal) and distal (R2d signal) ends after complete RLN dissection. The EMG amplitudes between R2p and R2d signals were compared. If the amplitude of R2p/R2d ratio reduction (RPDR) was over 10% or loss of signal (LOS) occurred, the exposed RLN was mapped to identify the injured point. Pre- and post-operative vocal cord (VC) mobility was routinely examined with video-laryngofiberscope.

RESULTS

Nerve injuries were detected in 108 (8%) RLNs, including 94 nerves with incomplete LOS (RPDR between 13%-93%) and 14 nerves with complete LOS. The nerve injuries were caused by traction in 80 nerves, dissecting trauma in 23 nerves and lateral heat spread of energy-based devices in 5 nerves. Symmetric VC mobility was found in 72 nerves with RPDR ≤50%. The occurrence of abnormal VC mobility (weak or fixed) was 14%, 67%, 100%, and 100% among the different RPDR stratifications of 51%-60%, 61%-70%, 71%-80%, and 81-93%, respectively. Of the 14 nerves with complete LOS, all showed fixed VC mobility. Permanent VC palsy occurred in 2 nerves with thermal injury.

CONCLUSION

Routinely testing the proximal and distal ends of exposed RLN helps detect unrecognized partial nerve injury, elucidate the injury mechanism and determine injury severity. The procedure provides accurate information for evaluating RLN function after nerve dissection and should be included in the standard IONM procedure.

A comparison between cisatracurium and rocuronium-induced neuromuscular block on laryngeal electromyography recovery after neostigmine reversal in a porcine model

BACKGROUND

Inducing and reversing neuromuscular block is essential to a positive outcome of thyroid surgery, with intraoperative neuromonitoring (IONM) being used to decrease recurrent and superior laryngeal nerve injuries and improve vocal outcome. Neostigmine is a non-specific broad-spectrum and inexpensive reversal agent for neuromuscular blocking agents (NMBAs). The aim of this porcine study was to explore the effect of neostigmine on electromyography (EMG) signal recovery profile following the commonly used NMBAs, cisatracurium and rocuronium.

METHODS

Twelve piglets were allocated into two groups with six piglets in each group. When stable baseline EMG signals were obtained, a neuromuscular block was induced by intravenous cisatracurium 0.2 mg/kg (group C) or rocuronium 0.6 mg/kg (group R) for each piglet. We compared laryngeal EMG tracing with spontaneous recovery (control) and neostigmine (0.04 mg/kg) reversal for each group. The time course of real-time laryngeal EMG signals was observed for 30 min from NMBA injection. Effects of neostigmine on EMG signal were assessed at 50% EMG recovery and by the maximum neuromuscular block recovery degree from the baseline value.

RESULTS

Neostigmine shortened the recovery time to 50% EMG amplitude in both group C (16.5 [2.5] vs. 29.0 [2.0] min, P<0.01) and group R (16.5[2.5] vs. 26.5 [1.5] min, P<0.05) compared to spontaneous recovery, respectively. Neostigmine reversal also enhanced the maximum degree of EMG amplitude recovery in both group C (83.6 [5.1] vs. 47.2 [6.1] %, P<0.01) and group R (85.6 [18.2]vs. 57.1 [6.3] %, P<0.05) compared to spontaneous recovery, respectively. The reversal effect of neostigmine did not differ significantly between cisatracurium and rocuronium.

CONCLUSIONS

This porcine model demonstrated that neostigmine provides an adequate and timely IONM signal suppressed by both cisatracurium and rocuronium. These results can potentially expand the options for precision neuromuscular block management during IONM to improve vocal outcomes in thyroid surgery patients.

Correlation between Electrophysiological Change and Facial Function in Parotid Surgery Patients

This observational study investigated intraoperative electrophysiological changes and their correlation with postoperative facial expressions in parotidectomy patients with visual confirmation of facial nerve (FN) continuity. Maximal electromyography(EMG) amplitudes of the facial muscles corresponding to temporal, zygomatic, buccal and mandibular branches were compared before/after FN dissection, and facial function at four facial regions were evaluated before/after parotidectomy in 112 patients. Comparisons of 448 pairs of EMG signals revealed at least one signal decrease after FN dissection in 75 (67%) patients. Regional facial weakness was only found in 13 of 16 signals with >50% amplitude decreases. All facial dysfunctions completely recovered within 6 months. EMG amplitude decreases often occur after FN dissection. An amplitude decrease >50% in an FN branch is associated with a high incidence of dysfunction in the corresponding facial region. This study tries to establish a standard facial nerve monitoring (FNM) procedure and a proper facial function grading system for parotid surgery that will be useful for the future study of FNM in parotid surgery.

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.

Optimization of electromyographic endotracheal tube electrode position by UEScope for monitored thyroidectomy

OBJECTIVE

Proper position of an electromyographic (EMG) endotracheal tube within the larynx plays a key role in functional electrophysiologic intraoperative neural monitoring (IONM) in thyroid surgery. The purpose of this study was to determine the feasibility of a portable video-assisted intubation device (UEScope) to verify the optimal placement of an EMG tube.

METHODS

A retrospective study enrolled 40 consecutive patients who underwent monitored thyroidectomies. After positioning the patient for surgery, an anesthesiologist performed tracheal intubation with UEScope and checked the position of the tube at the proper depth without rotation to the vocal cords. The main outcome measured was the proper EMG tube position, free from further adjustment. The secondary outcomes assessed were the percentage of available initial vagal stimulation (V1) signals.

RESULTS

All tracheal intubations were successful at first attempt. Proper EMG tube placement without position adjustment was found in 97.5% of the patients. Tube withdrawal was required in a male patient. All patients obtained detectable V1 signals; the lowest and median V1 amplitude was 485 and 767 μV as a reference value, respectively.

CONCLUSION

The UEScope is a valuable and reliable tool for placing an EMG tube and confirming its position during monitored thyroidectomy. In addition, further tube adjustment might be waived in most cases when the anesthesiologist placed the EMG tube after patient positioning for surgery. Routine use of video-assisted intubation devices is highly recommended.

LEVEL OF EVIDENCE

4.

Laryngeal Neural Monitoring during Pediatric Thyroid Cancer Surgery-Is Transcartilage Recording a Preferable Method?

The use of transcartilage (TC) intraoperative neuromonitoring (IONM) in a pediatric population has not been reported. This study evaluated the feasibility and the benefit of using TC-IONM for thyroid cancer surgery in a pediatric population. This retrospective single-center study enrolled 33 pediatric patients who had received an IONM-assisted thyroidectomy. Demographic characteristics, standardized IONM laryngeal examinations and stimulation information (L1-V1-R1-R2-V2-L2) were compared between endotracheal tube (ET) and TC methods. In the 15 cancer patients (30 nerves), TC-IONM provided significant higher electromyography (EMG) amplitude (p < 0.001), signal stability (lower V1/V2 signal correlation, r = 0.955 vs. r = 0.484, p = 0.004), signal quality (higher ratio of V1 or V2 amplitude <500 µV, 0.0% vs. 43.8%, p = 0.005) and lower R1-R2p change (7.1% vs. 37.5%, p = 0.049) compared to ET-IONM. In the 18 benign patients (28 nerves), TC-IONM provided significantly higher EMG amplitude (p < 0.001), signal stability (r = 0.945 vs. r = 0.746, p = 0.0324) and non-significant higher signal quality and R1-R2p change. This report is the first to discuss the use of TC-IONM in pediatric thyroid surgery. In contrast with ET-IONM, TC-IONM had superior amplitude, stability and quality of EMG signals, which greatly facilitates the meticulous recurrent laryngeal nerve dissection in pediatric thyroidectomies. The TC-IONM method can be considered a feasible, effective and preferable method of monitored thyroidectomy in pediatric thyroid cancer.

Intraoperative Posterior Cricoarytenoid Muscle Electromyography May Predict Vocal Cord Function Prognosis after Loss of Signal during Thyroidectomy

PURPOSE

Intraoperative posterior cricoarytenoid muscle (PCAM) electromyography (EMG) may be useful for predicting postoperative vocal cord function (VCF) and prognosis of vocal cord palsy (VCP) in patients with intraoperative loss of signal (LOS).

MATERIALS AND METHODS

Thirty out of 395 patients having LOS detected by intraoperative neural monitoring (IONM), were applied intraoperative PCAM EMG.

RESULTS

VCP was present in all Type 1 injury RLNs (16) (100%) and in 8 (57%) of 14 RLNs with Type 2 injury (p = 0.005). 14 out of 30 LOS patients (47%) had positive PCAM EMG amplitudes. The sensitivity, specificity, positive and negative predictive values and accuracy rates for predicting postoperative VCP via PCAM EMG, were calculated as 66.7%, 100%,100%, 42.86% and 73.33%. The negative PCAM EMG was related to VCP in both Type 1 and Type 2 LOS. VCP recovery time of Type 1 LOS patients was significantly longer than that of Type 2 LOS patients (p = 0.009). In Type 2 LOS, VCP recovery time was significantly longer in negative PCAM EMG patients compared to positive PCAM EMG patients (p = 0.046).

CONCLUSION

Negative PCAM EMG is associated with the postoperative VCP. Type 1 injury results in VCP regardless of PCAM EMG results, and VCF recovers after a longer period compared to Type 2 LOS.In Type 2 LOS, positive PCAM EMG may result in VCP by 40%. However, the presence of negative PCAM EMG is related to the postoperative VCP in all patients and the recovery time is longer compared to positive PCAM EMG patients.

Anatomical, Functional, and Dynamic Evidences Obtained by Intraoperative Neuromonitoring Improving the Standards of Thyroidectomy

The use of intraoperative neuromonitoring (IONM) is getting more common in thyroidectomy. The data obtained by the usage of IONM regarding the laryngeal nerves’ anatomy and function have provided important contributions for improving the standards of the thyroidectomy. These evidences obtained through IONM increase the rate of detection and visual identification of recurrent laryngeal nerve (RLN) as well as the detection rate of extralaryngeal branches which are the most common anatomic variations of RLN. IONM helps early identification and preservation of the non-recurrent laryngeal nerve. Crucial knowledge has been acquired regarding the complex innervation pattern of the larynx. Extralaryngeal branches of the RLN may contribute to the motor innervation of the cricothyroid muscle (CTM). Anterior branch of the extralaryngeal branching RLN has always motor function and gives motor branches both to the abductor and adductor muscles. In addition, up to 18% of posterior branches may have adductor and/or abductor motor fibers. In 70–80% of cases, external branch of superior laryngeal nerve (EBSLN) provides motor innervation to the anterior 1/3 of the thyroarytenoid muscle which is the main adductor of the vocal cord through the human communicating nerve. Furthermore, approximately 1/3 of the cases, EBSLN may contribute to the innervation of posterior cricoarytenoid muscle which is the main abductor of ipsilateral vocal cord. RLN and/or EBSLN together with pharyngeal plexus usually contribute to the motor innervation of cricopharyngeal muscle that is the main component of upper esophageal sphincter. Traction trauma is the most common reason of RLN injuries and constitutes of 67–93% of cases. More than 50% of EBSLN injuries are caused by nerve transection. A specific point of injury on RLN can be detected in Type 1 (segmental) injury, however, Type 2 (global) injury is the loss of signal (LOS) throughout ipsilateral vagus-RLN axis and there is no electrophysiologically detectable point of injury. Vocal cord paralysis (VCP) develops in 70–80% of cases when LOS persists or incomplete recovery of signal occurs after waiting for 20 min. In case of complete recovery of signal, VCP is not expected. VCP is temporary in patients with incomplete recovery of signal and permanent VCP is not anticipated. Visual changes may be seen in only 15% of RLN injuries, on the other hand, IONM detects 100% of RLN injuries. IONM can prevent bilateral VCP. Continuous IONM (C-IONM) is a method in which functional integrity of vagus-RLN axis is evaluated in real time and C-IONM is superior to intermittent IONM (I-IONM). During upper pole dissection, IONM makes significant contributions to the visual and functional identification of EBSLN. Routine use of IONM may minimalize the risk of nerve injury. Reduction of amplitude more than 50% on CTM is related with poor voice outcome.

Warning criterion to predict recurrent laryngeal nerve injury with percentage reduction of the amplitude of V2/R2d in neuromonitoring thyroidectomy

OBJECTIVE

To evaluate the contribution of amplitude reduction compared vagal stimulation at the end of thyroid dissection (V2) to the most distal RLN stimulation during thyroidectomy in predicting postoperative vocal cords paralysis (VCP).

METHODS

Patients with intact preoperative RLN function who underwent monitored thyroidectomy between August 2017 and April 2018 were included. We routinely tested the exposed RLN at the lowest proximal end (R2p signal) and the most distal end near the laryngeal entry point (R2d signal), and then routinely detected the vagal nerve at the horizontal plane of the inferior pole of thyroid with 2mA stimulation current. The cut-off value was calculated with Receiver Operating Characteristic curve. Rates of specificity, sensitivity, negative predictive value, positive predictive value (PPV) for V2/R2d and R2p/R2d were compared.

RESULTS

Percentage reduction of the amplitude of V2/R2d ranged from 34.8% to 76.7%. Twenty-two (1.5%) nerves developed temporary VCP, in which one nerve with VCP showed no significant amplitude reduction at the end of the surgery. There was no permanent or bilateral VCP. Sensitivity, specificity, PPV, NPV, and accuracy for the amplitude reduction of V2/R2d> 60% were 95.5%, 99.8%, 99.9%, 98.2%, respectively, for R2p/R2d were 99.5%, 99.2%, 63.6%, 99.9%, 97.7%, respectively.

CONCLUSION

Percentage reduction of the amplitude of V2/R2d is a reliable and practical warning criterion for RLN injury. When the amplitude reduction> 60% surgeons should consider the possibility of postoperative VCP and correct some surgical maneuvers.

Intraoperative neuromonitoring during prone thoracoscopic esophagectomy for esophageal cancer reduces the incidence of recurrent laryngeal nerve palsy: a single-center study

The incidence of recurrent laryngeal nerve palsy (RLNP) following minimally invasive esophagectomy has yet to be satisfactorily reduced. Use of intraoperative neuromonitoring (IONM), specifically of the RLN, during thyroidectomy has been reported to reduce the incidence of RLN injury. We now apply IONM during curative prone thoracoscopic esophagectomy, and we conducted a retrospective study to evaluate the feasibility and efficacy of intermittent monitoring of the RLN during the surgery. The study involved 32 consecutive patients who underwent esophagectomy with radical lymph node dissection for esophageal cancer. The patients were of two groups: an IONM group (n = 17) and a non-IONM group (n = 15). We chiefly strip around the esophagus preserving the membranous structure, which contains the tracheoesophageal artery, lymph nodes, and RLN. In the IONM group patients, we stimulated the RLN and measured the electromyography (EMG) amplitude after dissection, at the dissection starting point and dissection end point on both sides. For the purpose of the study, we compared outcomes between the two groups of patients. IONM was carried out successfully in all 17 patients in the IONM group. The incidence of RLNP was significantly reduced in this group. We found that both RLNs can be identified by mean of IONM easily, immediately, and safely and that the EMG amplitude attenuation rate is particularly useful for predicting RLNP.

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.

Traction Injury of Recurrent Laryngeal Nerve During Thyroidectomy

BACKGROUND

Loss of the neuromonitoring signal (LOS) during thyroidectomy signifies recurrent laryngeal nerve (RLN) injury, which is one of the common complications, especially by traction injury. Transient intraoperative LOS means spontaneous recovery of nerve function during surgery or within 6-month post-surgery. Few articles discuss intraoperative recovery time and transient LOS, and there is no consensus on the risk factors for RLN traction injury and its recovery course; thus, we wanted to determine the maximum intraoperative recovery time.

MATERIALS AND METHODS

This retrospective study included patients who had undergone thyroidectomies at Tainan National Cheng Kung University Hospital between January 2015 and August 2018. A total of 775 patients (with 1000 nerves at risk) who underwent intermittent intraoperative neuromonitoring during thyroidectomy were included in this study. The LOS nerves were divided into 4 groups based on the LOS subtype and the intraoperative status of the recovery. The postoperative vocal cord function was determined by thyroid ultrasound and/or laryngoscope. All the patients would be followed up postoperatively in 2-3 days, 1 week, 2 weeks, and 4-6 weeks.

RESULTS

LOS occurred in 67 of 775 (8.6%) patients and in 70 of 1000 nerves at risk (7.0%). There were 2 in 70 nerves (2.9%) with LOS type 1 (segmental nerve traction injury) with intraoperative recovery (Group 1), 5 (7.1%) with LOS type 1 without intraoperative recovery (Group 2), 47 (67.1%) with LOS type 2 (global injury) with intraoperative recovery (Group 3), and 16 (22.8%) with LOS type 2 without intraoperative recovery (Group 4). All LOS type 1 (segmental nerve injury) nerves had pathologic lesions near the RLN or vagus nerve, but none had invaded the nerves (p < 0.05). The resolving time intraoperatively in the 2 patients in Group 1 was 5 min and 10 min, respectively. The resolving time intraoperatively in Group 3 was 1-20 min, and the average time was 4.8 min. In Group 2, 3 injured nerves recovered within 6 weeks postoperatively, and 2 nerves in 12 weeks. In Group 4, all the 16 injured nerves recovered within 6 weeks postoperatively.

CONCLUSION

Applying intermittent intraoperative neuromonitoring during thyroidectomy, traction recurrent laryngeal nerve injury still happened in 7.0%. 70% of the injured nerves recovered the function intraoperatively after releasing the traction, and the longest duration of recovery is 20 min.

Intraoperative Neuromonitoring Using a Single Transcartilage Needle Electrode During Thyroidectomy

OBJECTIVES

Application of transcartilage needle electrode for intraoperative neuromonitoring (IONM) during thyroidectomy has been considered an alternative method of electromyography (EMG) tube recording. However, needle electrodes must be inserted into both sides of the thyroid cartilage with exposure of the cartilage lamina. We sought to evaluate the feasibility of applying a single ipsilateral transcartilage needle electrode for IONM during unilateral hemithyroidectomy.

METHODS

Thirty-four patients underwent IONM during unilateral thyroidectomy. A dual disposable needle electrode was inserted obliquely into the inferior lower third of the ipsilateral lamina of the thyroid cartilage. Patients were classified as deep (≥ 5 mm) or superficial (< 5 mm) by the depth of the needle electrode inserted into the thyroid cartilage. Without using an EMG tube, IONM was done according to the standardized procedure using a single needle electrode only.

RESULTS

IONM was successful in all nerves at risk. Amplitude of the EMG signal was stable during the surgery, with no cases presenting loss of signal. Amplitude of the signal from vagal and recurrent laryngeal nerve stimulation was significantly lower when needle insertion was superficial (< 5 mm). None of the patients showed postoperative vocal cord paralysis, and complications related to needle electrode were not identified.

CONCLUSION

IONM using a single ipsilateral transcartilage needle electrode during unilateral hemithyroidectomy was feasible with no significant complications. It may serve as an alternative method of IONM with the advantage of minimal exposure of the thyroid cartilage lamina.

LEVEL OF EVIDENCE

4 Laryngoscope, 131:448-452, 2021.

Correlation Between Electrophysiological Changes and Outcomes of Vocal Cord Function in 1764 Recurrent Laryngeal Nerves with Visual Integrity During Thyroidectomy

Background: The correlation between the injured recurrent laryngeal nerve (RLN) with incomplete loss of signal (LOS) and the outcomes of vocal cord function is still not well understood. This large cohort validation study was aimed to evaluate the effectiveness of the warning criterion, the reduction of the R2p/R2d ratio, in neuromonitoring during thyroidectomy. Methods: A total of 1108 consecutive patients (1764 nerves) with normal vocal cord function undergoing monitored thyroidectomy were included. Standardized intraoperative neuromonitoring procedures were strictly followed, after complete dissection of RLN, the exposed RLN was routinely stimulated at the lowest proximal end (R2p signal) and the most distal end near the laryngeal entry point (R2d signal). If the reduction of the R2p/R2d ratio (([R2d - R2p]/R2d) × 100%) reached >20%, the whole exposed RLN would be checked to pinpoint the injured area of the nerve. Results: Visual anatomical integrity of the RLN was ensured in all 1764 nerves. Eighteen nerves had complete LOS, and the other 97 nerves had incomplete LOS where the reduction of the R2p/R2d ratio ranged from 21% to 84%. Postoperative temporary vocal cord paralysis (VCP) was noted in 11 (61.1%) RLNs with complete LOS and 16 (16.5%) RLNs with incomplete LOS, where the reduction of the R2p/R2d ratio ranged from 63% to 84%. The positive predictive value of a R2p/R2d ratio >63% for postoperative VCP was 79.4%. Conclusions: Testing and comparing the R2p and R2d signals were useful to detect RLN neurophysiologic injury, elucidating the mechanism of nerve injury and predicting vocal cord function. Determining R2p-R2d was found to be essential and can be applied in routine neuromonitoring thyroidectomy.

Neuromuscular blockade management for intraoperative neural monitoring

This article reviews the literature on development of neuromuscular blockade management in thyroid surgery with intraoperative neural monitoring (IONM) in the past decade. Neuromuscular blockade management includes the choice of neuromuscular blocking agents (NMBAs) and reversal of neuromuscular blockade by sugammadex. A series of animal study and clinical trials showed NMBAs effect on IONM in thyroid surgery. We summarized five NMBA regimens for IONM: (a) relaxant-free regimen, (b) depolarizing NMBA-succinylcholine, (c) titration of nondepolarizing NMBA, and (d) rocuronium combined with sugammadex. The proper management of neuromuscular blockade during IONM has greatly developed over the past decade. The misuse of NMBAs is associated with false IONM interpretations to surgeons. A detailed understanding of NMBAs and neuromuscular blockade management by sugammadex may optimize IONM quality in patients receiving monitored thyroid surgery.

Vocal Cord Palsies Missed by Transcutaneous Laryngeal Ultrasound (TLUSG): Do They Experience Worse Outcomes?

INTRODUCTION

Transcutaneous laryngeal ultrasound (TLUSG) is an innovative, non-invasive tool in detecting post-thyroidectomy vocal cord palsy (VCP). However, TLUSG failed to detect about 6-15% laryngoscopic examination (LE)-confirmed VCP. It is unclear whether the outcome of patients with VCP missed by TLUSG [false negative (FN)] is different from those with VCP diagnosed by TLUSG [true positive (TP)]. Therefore, this study aimed to compare the clinical outcome and prognosis between patients with FN results and TP results.

METHODS

Over 46 months, all consecutive patients undergoing thyroidectomy or endocrine-related neck procedure were recruited. They underwent pre-operative and post-operative voice assessments on symptoms, voice-specific questionnaire [voice handicap index questionnaire (VHI-30)], TLUSG and LE. For patients with post-operative vocal cord palsy, reassessment LE would be arranged at second, fourth, sixth and twelfth months post-operatively until VCP recovered.

RESULTS

In total, 1196 patients, including 74 post-thyroidectomy VCP, were recruited. For those with assessable vocal cords (VC), 58 VCP were correctly diagnosed by TLUSG (TP) and 10 VCP were missed by TLUSG (FN). Sensitivity and specificity of detecting a VCP by TLUSG were 85.3% and 94.7%, respectively. VHI-30 score was significantly increased after operation in TP group [31 (range - 6-105), p < 0.001] but not in FN group [20 (14-99), p = 0.089]. Comparing to TP group, VCP recovered earlier (69 vs. 125 days, p < 0.001) and less patients suffered from permanent VCP in patients with FN results. (34.5% vs. 0.0%, p = 0.027).

CONCLUSION

The VCP missed by TLUSG had a milder course of disease. Early recovery of VC function and non-permanent palsy were expected.

Usefulness of intraoperative nerve monitoring in esophageal cancer surgery in predicting recurrent laryngeal nerve palsy and its severity

BACKGROUND

Recurrent laryngeal nerve (RLN) palsy is a critical postoperative complication in esophageal cancer surgery. However, intraoperative prediction of its occurrence and severity is difficult. In this prospective study, we evaluated the usefulness of intraoperative nerve monitoring (IONM) in predicting RLN palsy and its severity.

METHODS

Twenty patients who underwent subtotal esophagectomy with 3-field lymph node dissection were enrolled. Intraoperative electromyography (EMG) amplitudes of the vocal cords were measured by IONM at RLN and vagus nerve (VN) stimulation. Comparison was made between the vocal cords with RLN palsy and those without palsy and additionally between the vocal cords with transient RLN palsy and those with persistent palsy.

RESULTS

Among 40 vocal cords in 20 patients, 26 were intact and 14 were paralyzed. Seven had transient, six had permanent palsy. The mean EMG amplitude of intact vocal cords was significantly larger than that of paralyzed ones at VN (506 ± 498 µV vs. 258 ± 226 µV, p = 0.022) and RLN stimulation (642 ± 530 µV vs. 400 ± 308 µV, p = 0.038). The cut-off value for postoperative palsy were 419 µV [positive predictive value (PPV): 48.0%, negative predictive value (NPV): 84.6%] at VN and 673 µV (PPV: 44.8%, NPV: 90.9%) at RLN stimulation. The mean EMG amplitude of persistently paralyzed vocal cords tended to be small, compared with that of recovered ones at both VN (168 ± 173 µV vs. 336 ± 266 µV, p = 0.11) and RLN (244 ± 223 µV vs. 536 ± 344 µV, p = 0.051) stimulation.

CONCLUSION

The absolute EMG amplitude of IONM might be helpful to predict the occurrence and severity of RLN palsy after esophageal surgery although the predictive value is low.

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.

Two-stage thyroidectomy in the era of intraoperative neuromonitoring

Background

The use of intraoperative neuromonitoring (IONM) provides surgeons with real time information about recurrent laryngeal nerves (RLN) functional integrity. Hence, allowing them to modify the initially scheduled bilateral procedure, to a two-stage thyroidectomy in cases of loss of signal (LOS) on the first side of resection resulting in minimization of bilateral RLN injury. The purpose of our study was to present our results since the implementation of the above mentioned process in both malignant and benign thyroid disease.

Methods

We conducted a retrospective, observational cohort study of prospectively collected data from all patients who underwent a scheduled total thyroidectomy with or without neck dissection in our Department over the last 4 years [2013-2016]. From the 1,138 patients who received surgical treatment during that period, 284 were excluded since they did not meet the criteria. Exclusion criteria involved previous neck operation, parathyroid surgery, pre-existing vocal cord palsy (VCP) and unilateral surgery. A total of 854 patients were eligible for our study. All patients were subjected to pre- and postoperative indirect laryngoscopy by the same experienced ENT specialist team and all the surgeries were performed by the same experienced team. The whole procedure followed the International Neural Monitoring Study Group's (INMSG) Guideline Statement.

Results

We experienced 70 cases (70/854, 8.2%) with postoperative VCP. Two of them (0.23%) had permanent VCP and the rest of those patients (7.97%) experienced transient VCP. Twenty-three (2.7%) patients were candidates for staged thyroidectomy after LOS on the first side of resection, including ten patients with papillary or medullary thyroid carcinoma and one with toxic multinodular goiter (MNG). Of those patients, 22 incidents of VCP (95.7%) have recovered within two months and one of them persisted for more than six months (permanent VCP). We did not experience any permanent bilateral RLN palsy after the implementation of the staged procedure.

Conclusions

Staged thyroidectomy seems a very attractive and promising procedure for both patient and surgeon, since it nearly eliminates one of the most fearful complications in thyroid surgery. We suggest staged thyroidectomy in all cases with first side of resection signal loss, even in malignancies, since the benefits are much more than the disabilities in a patient's morbidity and quality of life.