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

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          Abstract

          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.

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          Complications to thyroid surgery: results as reported in a database from a multicenter audit comprising 3,660 patients.

          During recent years, more radical surgery for thyroid disease, i.e., total instead of subtotal resection, has been evident. Results following this strategy on national levels are scarce. From 2004 to 2006, 26 Scandinavian Departments registered 3,660 thyroid operations in a database. Risk factors for complications were analyzed with multiple logistic regression. After thyroidectomy, re-bleeding occurred in 2.1% and was associated with older age (OR 1.04; p < 0.0001) and male gender (OR 1.90; p = 0.014). Postoperative infection occurred in 1.6% and associated with lymph node operation (OR 8.18; p < 0.0001). Postoperative unilateral paresis of the recurrent laryngeal nerve was diagnosed 3.9% and bilateral paresis in 0.2%. Unilateral paresis was associated with older age, intrathoracic goiter, thyreotoxicosis, and if routine laryngoscopy was practiced (OR 1.92; p = 0.0002). After 6 months, the incidence of nerve paresis was 0.97%. After bilateral thyroid surgery (n = 1,648), hypocalcaemia treated with vitamin D analogue occurred in 9.9% of the patients at the first follow-up and in 4.4% after 6 months. Complications to thyroid surgery are not uncommon. The high frequency of hypocalcaemia treated with vitamin D after 6 months is a cause of concern.
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            The mechanism of recurrent laryngeal nerve injury during thyroid surgery--the application of intraoperative neuromonitoring.

            Identification of recurrent laryngeal nerve (RLN) has decreased the rates of permanent RLN palsy during thyroid operations; however, unexpected RLN palsy still occurs, even though the visual integrity was assured and most nerve injuries were not recognized intraoperatively. The aim of this study is to determine the causes of RLN palsy and to identify potentially reversible causes of RLN injury during the operation with the application of intraoperative neuromonitoring (IONM). One hundred and thirteen patients with 173 nerves at risk were enrolled in this study. All operations were performed by the same surgeon. The 4-step procedure of IONM was designed to obtain electromagnetic (EMG) signals from the vagus nerve and RLN before and after resection of thyroid lobe. Sixteen nerves had loss of EMG signals after thyroid dissection, and the causes of nerve injuries were well elucidated with the application of IONM. One nerve injury was caused by inadvertent transection, which led to permanent RLN palsy. Among the remaining 15 nerves, 1 injury was caused by a constricting band of connective tissue, which was detected precisely and released intraoperatively, 2 by inadvertent clamping of the nerve, and 12 by apparent overstretching at the region of Berry's ligament. (Five nerves regained signals before closing the wound, but 1 showed impaired cord movement. Another 7 nerves did not regain signals before closing the wound, and all developed temporary RLN palsy.) Our 4-step procedure of IONM is useful and helpful in elucidating the potential operative pitfalls during dissection near the RLN. Although the rates of RLN palsy were not decreased in this study, the use of neuromonitoring provided instructive information for future operations by ascertaining where and how the RLN has been injured.
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              External branch of the superior laryngeal nerve monitoring during thyroid and parathyroid surgery: International Neural Monitoring Study Group standards guideline statement.

              Intraoperative neural monitoring (IONM) during thyroid surgery has gained widespread acceptance as an adjunct to the gold standard of visual identification of the recurrent laryngeal nerve (RLN). Contrary to routine dissection of the RLN, most surgeons tend to avoid rather than routinely expose and identify the external branch of the superior laryngeal nerve (EBSLN) during thyroidectomy or parathyroidectomy. IONM has the potential to be utilized for identification of the EBSLN and functional assessment of its integrity; therefore, IONM might contribute to voice preservation following thyroidectomy or parathyroidectomy. We reviewed the literature and the cumulative experience of the multidisciplinary International Neural Monitoring Study Group (INMSG) with IONM of the EBSLN. A systematic search of the MEDLINE database (from 1950 to the present) with predefined search terms (EBSLN, superior laryngeal nerve, stimulation, neuromonitoring, identification) was undertaken and supplemented by personal communication between members of the INMSG to identify relevant publications in the field. The hypothesis explored in this review is that the use of a standardized approach to the functional preservation of the EBSLN can be facilitated by application of IONM resulting in improved preservation of voice following thyroidectomy or parathyroidectomy. These guidelines are intended to improve the practice of neural monitoring of the EBSLN during thyroidectomy or parathyroidectomy and to optimize clinical utility of this technique based on available evidence and consensus of experts. 5 Copyright © 2013 The American Laryngological, Rhinological and Otological Society, Inc.
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                Author and article information

                Journal
                Sisli Etfal Hastan Tip Bul
                Sisli Etfal Hastan Tip Bul
                The Medical Bulletin of Sisli Etfal Hospital
                Kare Publishing (Turkey )
                1302-7123
                1308-5123
                2021
                02 July 2021
                : 55
                : 2
                : 146-155
                Affiliations
                [1 ]Department of General Surgery, University of Health Sciences Turkey, Sisli Hamidiye Etfal Teaching and Research Hospital, Istanbul, Turkey
                [2 ]Department of General Surgery, Bahcesehir University Faculty of Medicine, Istanbul; Sisli Memorial Hospital, Istanbul, Turkey
                Author notes
                Address for correspondence: Mehmet Kostek, MD. Saglik Bilimleri Universitesi, Sisli Hamidiye Etfal Egitim ve Arastirma Hastanesi, Genel Cerrahi Anabilim Dali, Istanbul, Turkey Phone: +90 542 391 00 56 E-mail: dr.mkostek@ 123456gmail.com
                Article
                MBSEH-55-146
                10.14744/SEMB.2021.45548
                8298074
                34349588
                95526e9e-1943-41cd-80c8-e52a08fc4f87
                Copyright: © 2021 by The Medical Bulletin of Sisli Etfal Hospital

                This is an open access article under the CC BY-NC license ( http://creativecommons.org/licenses/by-nc/4.0/).

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