Improving classification of the external branch of the superior laryngeal nerve with neural monitoring: a research appraisal and narrative review

Objective: To review the published literature on external branch of superior laryngeal nerve (EBSLN) neural monitoring and propose a new EBSLN classification system using intraoperative neural monitoring (IONM). Background: The injury rate of the external branch of the superior laryngeal nerve (EBSLN) in thyroid surgery is 0-58%. Symptoms of EBSLN injury are not consistent, and patients often complain of modification of the voice timbre with the preservation of vocal cord function. Standards for the diagnosis of EBSLN injury are lacking. Methods: The PubMed database was searched using the terms 'External branch of the superior laryngeal nerve' and 'Intraoperative neuromonitoring' from 2010 through March 2020. Conclusions: This paper reviewed the anatomy of the EBSLN, the diagnosis and treatment of injury, and the application of IONM in the EBSLN. The traditional EBSLN classification method was analyzed and compared with our new classification method. The diagnosis of EBSLN injury is a problem that still needs to be resolved. For anatomic classifications of the EBSLN, we found that the conventional classification systems may not accurately reflect the real status of the EBSLN and the surgical risks that may occur intraoperatively. Using IONM, we developed an EBSLN classification method that was consistent with conventional diagnosis and treatments and can be widely and easily utilized during surgery.