A method for intraoperative identification of the recurrent laryngeal nerve

Intraoperative monitoring of the recurrent laryngeal nerve by vagal nerve stimulation in thyroid surgery

The aim of the present study was to evaluate the thyroarytenoid muscle response during bilateral thyroid surgery using vagal nerve stimulation. 195 patients (390 nerves at risk) underwent a total thyroidectomy. The recurrent laryngeal nerve's function was checked by analyzing the amplitude and the latency of the thyroarytenoid muscle's responses after a vagal nerve's stimulation (0.5 and 1 mA) using the NIM3 Medtronic system. All patients were submitted to preoperative and postoperative laryngoscopy. 20 patients get no thyroarytenoid muscle response to the vagal nerve stimulation, and 14 postoperative recurrent laryngeal nerve palsies were confirmed (3.8 %). Two palsies were present after 6 months (0.51 %). All the patients with muscle's response have normal mobility vocal fold. The test sensitivity was 100 % and the test specificity was 98 %. Physiologically, the mean latencies of the muscular potentials for the right RLN were, respectively, 3.89 and 3.83 ms (p > 0.05) for the stimulation at 0.5 and 1 mA. The mean latencies for the left RLN were, respectively, 6.25 and 6.22 ms for the stimulation at 0.5 and 1 mA (p > 0.05). The difference of the latencies between the right and the left nerve was 2.30 ms (1.75-3.25 ms) with a stimulation of 0.5 or 1 mA (p < 0.05). Thyroarytenoid muscle's response via a vagal nerve stimulation showed a functional asymmetry of the laryngeal adduction with a faster right response. Surgically, this method can predict accurately an immediate postoperative vocal folds function in patients undergoing a bilateral thyroid surgery.

Neuromonitoring in thyroid surgery

PURPOSE OF REVIEW

Laryngeal nerve injuries are among the most important complications of thyroidectomy. Recently, the use of neuromonitoring has been increasingly employed in order to predict and document nerve function at the end of thyroidectomy.

RECENT FINDINGS

There is much controversy in recent studies concerning neuromonitoring in thyroid surgery. Some authors believe that the method does not bring any additional reduction in the paralysis rate of the laryngeal nerves. Other researchers defend its use only in selected cases and in very specific situations. Finally, some much respected surgeons advocate the routine use of neuromonitoring in all thyroidectomies.

SUMMARY

In this review, we try to present relevant recent publications dealing with this still controversial subject, emphasizing the advantages and disadvantages of neuromonitoring in thyroidectomy.

Electrophysiologic recurrent laryngeal nerve monitoring during thyroid and parathyroid surgery: international standards guideline statement

Intraoperative neural monitoring (IONM) during thyroid and parathyroid surgery has gained widespread acceptance as an adjunct to the gold standard of visual nerve identification. Despite the increasing use of IONM, review of the literature and clinical experience confirms there is little uniformity in application of and results from nerve monitoring across different centers. We provide a review of the literature and cumulative experience of the multidisciplinary International Neural Monitoring Study Group with IONM spanning nearly 15 years. The study group focused its initial work on formulation of standards in IONM as it relates to important areas: 1) standards of equipment setup/endotracheal tube placement and 2) standards of loss of signal evaluation/intraoperative problem-solving algorithm. The use of standardized methods and reporting will provide greater uniformity in application of IONM. In addition, this report clarifies the limitations of IONM and helps identify areas where additional research is necessary. This guideline is, at its forefront, quality driven; it is intended to improve the quality of neural monitoring, to translate the best available evidence into clinical practice to promote best practices. We hope this work will minimize inappropriate variations in monitoring rather than to dictate practice options.

Use of a single bipolar electrode in the posterior arytenoid muscles for bilateral monitoring of the recurrent laryngeal nerves in thyroid surgery

The aims were to assess the technical feasibility of using a single electrode in the posterior arytenoid muscles (PAM) for intraoperative monitoring of the recurrent laryngeal nerve (RLN) in thyroid surgery, to validate the new method against the insertion of electrodes placed in the vocal cord muscle, and to report the results of the clinical application of the new concept. A total of 52 patients were enrolled. The handling and safety of RLN monitoring was tested by simultaneous registration of the EMG response from vocal fold electrodes and PAM electrodes. Acoustically and electromyographically we found nearly the same values for the arytenoid muscles as for the vocal folds, although the signals taken from the vocal folds were slightly stronger. PAM recording using a single bipolar electrode is technically feasible and as reliable compared to the standard vocal cord monitoring.

Total thyroidectomy is improved by loupe magnification

With this study, we verified if a microsurgical approach with magnification could improve the outcome of total thyroidectomy. Ninety-seven patients were consecutively randomized into group A (surgery with x 2.5 magnification and microsurgical instruments, n = 47) or group B (surgery with no magnification, n = 50). The mean operative time was 125 +/- 4.0 min in group A, and 150 +/- 4.0 min in group B (P = 0.00012). The recurrent laryngeal nerve was identified in all patients of group A, and in 96.8% of group B. The overall morbidity rate was 4.0% in group A and 25.5% in group B (P = 0.0038). This study indicates that a microsurgical approach with magnification is feasible, reduces surgical time, and improves the outcome in total thyroidectomy.

Recurrent laryngeal nerve monitoring in thyroid and parathyroid surgery: the University of Michigan experience

OBJECTIVES/HYPOTHESIS

Intraoperative monitoring of the recurrent laryngeal nerve (RLN) is finding increasing acceptance during thyroidectomy. Recently, a laryngeal surface electrode was introduced to enable another form of noninvasive monitoring of the RLN. The present report examines the University of Michigan experience with RLN monitoring using the postcricoid surface electrode.

STUDY DESIGN

All patients undergoing partial or total thyroidectomy or parathyroidectomy from January 1999 to July 2001 were considered candidates for the study. Audiologists trained in intraoperative electrophysiological techniques performed all of the monitoring.

METHODS

Data collected on each patient included 1) stimulation threshold for a laryngeal compound muscle action potential on initial RLN identification, 2) stimulation threshold of the laryngeal compound muscle action potential on completion of the procedure, and 3) flexible fiberoptic evaluation of the larynx at the initial postoperative visit and at the 3-month follow-up visit. The average duration of follow-up was 9.8 months with a range of 3 to 60 months.

RESULTS

The average minimum current required for stimulation on first identification of all nerves was 0.57 mA (+/-0.48 mA). After completion of the procedure a mean threshold level of 0.42 mA (+/-0.55 mA) was obtained during direct RLN stimulation. Post-dissection stimulation of the RLN on the side of tumor dissection was 0.92 mA (+/-0.65 mA) compared with a stimulation threshold of 0.76 mA (+/-0.57 mA) for the nontumor side.

CONCLUSIONS

Electromyographic monitoring of the RLN using a postcricoid surface electrode provides a safe, simple, and effective method for intraoperative monitoring during thyroid or parathyroid surgery. Further, evoked electromyography confirms RLN integrity at the conclusion of surgery.

Intra-operative electromyographic monitoring of the lower cranial motor nerves (LCN IX-XII) in skull base surgery

The functional preservation of lower (motor) cranial nerves (LCN) is endangered during skull base surgery. Intra-operative EMG monitoring of the LCN IX-XII was investigated in 78 patients undergoing 80 operations on various skull base tumors with regard to technical feasibility and clinical efficacy. Ongoing 'spontaneous muscle activity' (SMA) and 'compound muscle action potentials' (CMAP) following supramaximal bipolar stimulation were intra-operatively recorded applying needle electrodes into the soft palate (CN IX: n=76), the vocal cord (CN X: n=72), the trapezius muscle (CN XI: n=18), and the tongue (CN XII: n=71). From 24/22/8 cases with LCN IX/X/XII deficits (despite monitoring) only 5/6/4 remained unchanged (3-6 months postoperative). An irreversible plegia of the LCN IX/X/XII occurred in three (1/1/1) patients. In 7/6/1 patients postoperative (3-6 months) LCN IX/X/XII function was better than preoperatively. In all patients accessory nerve function remained unchanged. 'Pathological' SMA of the LCN IX/X/XII occurred in 12/16/8 cases, but in only 6/5/3 cases corresponded to postoperative LCN deficits. Corresponding 'pathological' SMA patterns were found in 18/17/5 out of 24/22/8 cases with postoperative LCN IX/X/XII dysfunction. Reproducible CMAP of LCN IX/X/XI/XII could be recorded in 59/56/11/32 patients. Approximate 'normal' values were calculated and compared to (very few) data so far given in the literature. Electromyographic monitoring proved to be a safe tool for the intra-operative identification and localization of the LCN contributing to their anatomical and functional preservation. The predictive value of standard neurophysiological parameters for functional outcome, however, is limited.

Use of a disposable electrode for recurrent laryngeal nerve monitoring

Our experience with a non-invasive, disposable electrode for intra-operative identification and monitoring of the recurrent laryngeal nerve is described. The electrode system, while simply attached to the endotracheal tube, acts as a laryngeal surface electrode and detects electromyographic activity of the intrinsic laryngeal muscles when the recurrent laryngeal nerve is stimulated. We have successfully used this electrode to monitor 19 recurrent laryngeal nerves in 15 patients who have undergone partial or total thyroidectomy. We feel that this device can be useful particularly in cases of re-exploration and malignancies of the thyroid gland.

Recurrent laryngeal nerve palsy after thyroid gland surgery

Risk factors for recurrent laryngeal nerve (RLN) lesions after thyroid gland surgery were evaluated retrospectively in 1026 patients. RLN palsy occurred in 5.9 per cent; the incidence of permanent palsy was 2.4 per cent as 59 per cent of paralyses were transient. For euthyroid nodular goitre, Graves' disease, chronic lymphocytic thyroiditis, recurrent goitre and thyroid carcinoma, permanent nerve damage occurred in 1.7, 4, 5, 3.8 and 8 per cent of patients respectively. In relation to the number of nerves at risk, the incidence of permanent RLN palsy was 1.1 per cent for subtotal lobectomy and 4.0 per cent for total lobectomy. The overall incidence of permanent RLN palsy was 1.8 per cent of nerves at risk. There was no statistically significant difference between the number of RLN paralyses occurring after nerve exposure and that occurring after non-exposure in subtotal lobectomy, but in total lobectomy the permanent palsy rate increased from 3.8 to 7 per cent when the nerve was not exposed or identified (P < 0.01). Underlying thyroid disease, the extent of resection and exposure of the nerve in total lobectomy are risk factors for both transient and permanent RLN palsy.

A device for the intraoperative identification of the recurrent laryngeal nerve in piglets

The recurrent laryngeal nerve (RLN) is one of the most frequently injured nerves in head and neck surgery. Routine identification of the RLN during thyroid surgery has reduced the injury rate from 10% to less than 4%. Difficulty in identification of the RLN contributes to this surgical morbidity. Devices previously used for intraoperative identification of the RLN have failed to achieve the simplicity and reliability necessary for clinical use. This animal study uses a simple double-ballooned endotracheal tube and pressure transducer system, which assists intraoperative RLN identification through nerve stimulation and graphic documentation of vocal fold (VF) motion. Iatrogenic injury is demonstrated by a dampened stimulation-pressure tracing. The RLNs of three piglets were injured and examined, and the degree of injury was correlated with perioperative nerve stimulation patterns. The piglet proved to be an adequate model for laryngeal research. An FDA-approved multi-institutional prospective human study using this system of identification of the RLN is in progress.