Contribution of intraoperative neuromonitoring to the identification of the external branch of superior laryngeal nerve

Abstract

Objective:We evaluated the contribution of intraoperative neuromonitoring to the visual and functional identification of the external branch of the superior laryngeal nerve. Material and Methods:The prospectively collected data of patients who underwent thyroid surgery with intraoperative neuromonitoring for external branch of the superior laryngeal nerve exploration were assessed retrospectively. The surface endotracheal tube-based Medtronic NIM3 intraoperative neuromonitoring device was used. The external branch of the superior laryngeal nerve function was evaluated by the cricothyroid muscle twitch. In addition, contribution of external branch of the superior laryngeal nerve to the vocal cord adduction was evaluated using electromyographic records. Results:The study included data of 126 (female, 103; male, 23) patients undergoing thyroid surgery, with a mean age of 46.2±12.2 years (range, 18-75 years), and 215 neck sides were assessed. Two hundred and one (93.5%) of 215 external branch of the superior laryngeal nerves were identified, of which 60 (27.9%) were identified visually before being stimulated with a monopolar stimulator probe. Eighty-nine (41.4%) external branch of the superior laryngeal nerves were identified visually after being identified with a probe. Although 52 (24.1%) external branch of the superior laryngeal nerves were identified with a probe, they were not visualized. Intraoperative neuromonitoring provided a significant contribution to visual (p<0.001) and functional (p<0.001) identification of external branch of the superior laryngeal nerves. Additionally, positive electromyographic responses were recorded from 160 external branch of the superior laryngeal nerves (74.4%). Conclusion:Intraoperative neuromonitoring provides an important contribution to visual and functional identification of external branch of the superior laryngeal nerves. We believe that it can not be predicted whether the external branch of the superior laryngeal nerve is at risk or not and the nerve is often invisible; thus, intraoperative neuromonitoring may routinely be used in superior pole dissection. Glottic electromyography response obtained via external branch of the superior laryngeal nerve stimulation provides quantifiable information in addition to the simple visualization of the cricothyroid muscle twitch.

Factors influencing the relationship of the external branch of the superior laryngeal nerve with the superior pole vessels of the thyroid gland

“…IONM-guided superior pole dissection technique has been described in detail in previous studies. [ 1 , 8 , 16 ] During the dissection of the upper pole, each structure thought to be the nerve was stimulated using IONM and EBSLN was confirmed by observing the contraction of the CTM. If EBSLN was not able to be identified visually, it was searched by stimulating the inferior pharyngeal muscle fibers near the laryngeal head of the sternothyroid muscle with a probe.…”

“…If the nerve was not found with the probe, the muscle fibers were not dissected to find EBSLN through or under the inferior pharyngeal constrictor muscle fibers. [ 1 , 16 ] After confirming with EBSLN with IONM, it was categorized according to the Cernea classification[ 9 ] and the data were recorded ( Fig. 1 ).…”

A review of methods for the preservation of laryngeal nerves during thyroidectomy

“…Üst kutup diseksiyonu tamamlandıktan sonra üst kutup damarlarının kesildiği nokta proksimalinden SLSE probla uyarılarak sinir bütünlüğü kontrol edilir. [26,85,86] Daha önce de değinildiği gibi tiroidin büyüklüğüne göre SLSE'nin üst kutup damarları ile ilişkisi de değişmektedir. Üst kutup diseksiyonunda SLSE yaralanması açısından Cernea tip 2b yüksek risk altında olmakla berbaer tip 2a da riskli gruba girmektedir.…”

“…Son İONM çalışmalarında SLSE %28-35 oranında görülebilirken, İONM ile bu oran %83-95'lere çıktığı bildirilmektedir. [26,35,85] Bu çalışmalar İONM ile SL-SE'nin yeri belirlendikten sonra sinirin görsel olarak ortaya konulabilmesini %33-41 oranında arttırdığını göstermek-tedir. Bununla birlikte SLSE'nin IONM ile fonksiyonel olarak saptanmasına karşın yaklaşık %25 olguda kas altında seyrettiğinden görülememektedir.…”

“…Bu verilere göre İONM, SL-SE'nin görsel ve fonksiyonel açıdan belirlenmesine önemli katkılar sağlamaktadır. [26,85] Diğer yandan IONM'nin SLSE yaralanma riskini azaltığını da gösteren iki randomize.e karşılaştırmalı çalışma vardır. SLSE fonksiyonunun intaoperatif veya postoperatif krikotiroit kas EMG'si ile de-ğerlendirildiği bu iki çalışma, SLSE aranmadan yapılan tiroidektomilerde %12-25 olan SLSE yaralanma oranının İONM kullanıldığında anlamlı olarak azaldığını (%0-1,5) ortaya koymuştur.…”