Methods of Recurrent Laryngeal Nerve Monitoring

One of the major risks of endocrine neck surgery is injury to the recurrent laryngeal nerve, which can lead to significant functional impairments, both temporary and permanent. The standard of care for prevention of nerve injury involves routine preoperative laryngoscopy followed by intraoperative identification and preservation of the recurrent laryngeal nerve as described in the 2015 ATA guidelines. However, a visually intact nerve does not always correlate with intact function. Therefore, the need for a method to prognosticate nerve function at the time of surgery resulted in the development of intraoperative nerve monitoring (IONM). The purposes of IONM include identifying the recurrent laryngeal nerve and/or its derivative, the vagus nerve, as well as obtaining accurate intraoperative functional assessment and to allow for postoperative prediction of function. To date, the most widely accepted and employed technique is the EMG-based nerve monitoring system, which involves stimulation of the nerve to produce measurable evoked muscle responses. Although data on reduction of nerve injury by intraoperative nerve monitoring versus visualization alone is equivocal, IONM remains a useful tool for decision-making in thyroid and parathyroid surgery. It allows for interrogation of tissue to be divided or excised, it allows for mapping of the course of the nerve during dissection, and it confirms electrical conductive integrity at the conclusion of dissection.