Recent Developments of Intraoperative Neuromonitoring in Thyroidectomy

At present, intraoperative neuromonitorization (IONM) with surface electrode-based endotracheal tube (ETT) is a standard method in thyroidectomy and can be performed either intermittently IONM (I-IONM) or continuously IONM (C-IONM). Despite the valuable contribution of I-IONM to the thyroidectomy, it still has limitations regarding the recording electrodes and stimulation probe. New approaches for overcoming the limitations of I-IONM and developing the method are taking attention. Most of the technical issues of IONM with surface electrode-based ETT are related with inadequate contact of electrodes to the vocal cords. Nowadays, efficiency of various recording electrodes is under investigation. Recording electrodes such as needle electrodes applied to thyroarytenoid or posterior cricoarytenoid muscle (PCA), surface electrodes applied to the PCA, and needle or adhesive electrodes applied to the tracheal cartilage or skin, can make safe recordings similar to the ETT electrodes. Despite their invasiveness, needle electrodes record higher electromyography (EMG) amplitudes than tube electrodes do. Adhesive surface electrodes make safe EMG recordings, although amplitudes of these electrodes are usually lower than those of the tube electrodes. These different types of electrodes are less affected by tracheal manipulations and amplitude changes are lower compared to the tube electrodes.

During C-IONM, an additional stimulation probe is applied to the vagus nerve after dissecting the nerve circumferentially. Recently, without applying a probe, a new continuous monitorization method called laryngeal adductor reflex CIONM (LAR-CIONM) using sensorial, central, and motor components of LAR arch which is an automatic, primitive brainstem reflex protecting the tracheoesophageal tree from foreign body aspiration, has been implemented. Afferent track of LAR communicates laryngeal mucosa to the brainstem by internal branch of the superior laryngeal nerve and efferent track reaches larynx through recurrent laryngeal nerve. Total outcome of LAR activation is the closure of laryngeal entry by bilateral vocal cord adduction. In LAR-CIONM, a stimulus is given by an electrode from one side of surface electrode-based ETT and amplitude response of the LAR at the vocal cord is followed on the operation side. Recently, it has been reported that real-time EMG response can be obtained with stimulation probe cables applied to dissectors or energy devices during the dissection through I-IONM.

Comparison of Monopolar and Bipolar Stimulator Probes for Intraoperative Nerve Mapping During Thyroidectomy: A Prospective Study

OBJECTIVES/HYPOTHESIS

During intraoperative neuromonitoring in thyroid surgery, two different kinds of stimulator probes, monopolar and bipolar, are commonly used to stimulate the laryngeal nerves. We explore the unique characteristics of both of these probes as they relate to intraoperative laryngeal nerve mapping.

METHODS

Twenty-one patients undergoing neuromonitored thyroidectomy by a single surgeon were enrolled. Electromyography (EMG) amplitude and latency measurements were prospectively recorded concurrently from 1 mA stimulation of vagus nerve (VN) and inferior/superior recurrent laryngeal nerve before (with and without fascia) and after thyroid resection using bipolar and monopolar stimulator probes.

RESULTS

Significantly higher amplitudes were obtained with monopolar stimulator probes as compared to bipolar probes, in several stimulation scenarios such as at right VN pre-resection (carotid sheath intact), right VN pre-resection (carotid sheath dissected), right VN post-resection and left VN (carotid sheath dissected). No significant differences were found between amplitudes and latency values in all other stimulation scenarios.

CONCLUSIONS

According to this study, both probes are reliable and safe for neural mapping. The kind of probe used during neural monitoring is based on surgical situations and surgeon preference.

LEVEL OF EVIDENCE

Level 3 (According to Oxford Centre for Evidence-Based Medicine 2011 Levels of Evidence) Laryngoscope, 2021.

Training Courses in Laryngeal Nerve Monitoring in Thyroid and Parathyroid Surgery- The INMSG Consensus Statement

Intraoperative neural monitoring (IONM) is now an integral aspect of thyroid surgery in many centers. Interest in IONM and the number of institutions that perform monitored thyroidectomies have increased throughout the world in recent years. For surgeons considering the introduction of IONM in their practice, specific training in IONM devices and procedures can substantially shorten the learning curve. The International Neural Monitoring Study Group (INMSG) has been at the forefront of IONM technology and procedural adoption since the introduction of neural monitoring in thyroid and parathyroid surgery. The purpose of this document is to define the INMSG consensus on essential elements of IONM training courses. Specifically, this document describes the minimum training required for teaching practical application of IONM and consensus views on key issues that must be addressed for the safe and reliable introduction of IONM in surgical practice. The intent of this publication is to provide societies, course directors, teaching institutions, and national organizations with a practical reference for developing IONM training programs. With these guidelines, IONM will be implemented optimally, to the ultimate benefit of the thyroid and parathyroid surgical patients.

Informed Consent for Intraoperative Neural Monitoring in Thyroid and Parathyroid Surgery - Consensus Statement of the International Neural Monitoring Study Group

In the past decade, the use of intraoperative neural monitoring (IONM) in thyroid and parathyroid surgery has been widely accepted by surgeons as a useful technology for improving laryngeal nerve identification and voice outcomes, facilitating neurophysiological research, educating and training surgeons, and reducing surgical complications and malpractice litigation. Informing patients about IONM is not only good practice and helpful in promoting the efficient use of IONM resources but is indispensable for effective shared decision making between the patient and surgeon. The International Neural Monitoring Study Group (INMSG) feels complete discussion of IONM in the preoperative planning and patient consent process is important in all patients undergoing thyroid and parathyroid surgery. The purpose of this publication is to evaluate the impact of IONM on the informed consent process before thyroid and parathyroid surgery and to review the current INMSG consensus on evidence-based consent. The objective of this consensus statement, which outlines general and specific considerations as well as recommended criteria for informed consent for the use of IONM, is to assist surgeons and patients in the processes of informed consent and shared decision making before thyroid and parathyroid surgery.