Role of intraoperative neuromonitoring in identification of external branch of superior laryngeal nerve during thyroidectomy operation

Thyroidectomy is a common operation performed in otorhinolaryngology. The presence of nodules or tumours on the thyroid gland is the most common reason for thyroid surgery. Nodules can either be benign or malignant. The recurrent laryngeal nerve (RLN) and external branch of superior laryngeal nerve (EBSLN) are the main structures that must be preserved in thyroid surgery to prevent postoperative voice deterioration. One of the most difficult aspects of thyroid surgery is preventing Injury to the external branch of superior laryngeal nerve. EBSLN damage rates have been reported to range from 0 to 58%, depending on different postoperative assessment methods. The EBSLN innervates the cricothyroid muscle (CTM), whose primary function is to raise the tension of the adducted ipsilateral vocal folds during elevation of pitch. Clinical symptoms primarily include: vocal fatigue, reduced vocal frequency range, particularly with regard to raising pitch which may lead to decreased quality of life, especially for those voice professionals. Even in those who are not singers, the injury could result in objective voice quality changes. However EBSLN has received minimal attention, for which Delbridge declared it as the "Neglected nerve in thyroid surgery". Careful anatomic identification during dissection can help prevent injury to the EBSLN during thyroid surgery. Intraoperative neuromonitoring (IONM) has been suggested as an addition to the standard visual identification of both the recurrent laryngeal nerve (RLN) and EBSLN during thyroid surgery, in an effort to aid in the visualisation of and hence reduce the incidence of EBSLN injury during thyroidectomy operation. This study is the first study from our institute whereby we will evaluate the contribution of intraoperative neuromonitoring in identification and preservation of external branch of superior laryngeal nerve during thyroidectomy operation and assess any difficulties and pitfalls during the use of the nerve monitor in such cases.