Intraoperative nerve monitoring in thyroid surgery-shifting current paradigms

Abstract

Over the past two decades, intraoperative neural monitoring (IONM) has matured into a powerful risk minimization tool. Meta-analyses of studies, most of which were limited by poor study designs and the sole use of intermittent nerve stimulation, failed to demonstrate superiority of IONM over anatomic recurrent laryngeal nerve (RLN) dissection in the absence of IONM. With the advent of continuous IONM (CIONM), intraoperative nerve electromyographic tracings, registered almost in real time during the operation, accurately predict postoperative vocal fold function when International Neural Monitoring Study Group quality standards are adhered to. CIONM aids in avoiding permanent traction-related nerve injury by urging surgeons to reverse harmful surgical maneuvers. CIONM also forms an integral part in the surgical concept of staged thyroidectomy. Delaying completion surgery on the other side until nerve function has recovered mitigates the risk of bilateral vocal fold palsy. CIONM has greatly furthered our understanding of functional RLN injury, enabling conception of effective risk minimization strategies tailored to the individual patient. The review summarizes the advances of continuous IONM technology that caused a quantum leap in risk minimization for thyroid surgery, shifting current paradigms.

Keywords: Intraoperative neuromonitoring; continuous neuromonitoring; recurrent laryngeal nerve palsy; thyroidectomy; vagus nerve stimulation.

Figure 1

Intraoperative nerve monitoring during thyroidectomy. (A) Intermittent nerve monitoring with recording needle electrodes in a 67-year-old female patient with recurrent follicular thyroid cancer: hand-held monopolar stimulation probe (asterisk) at the right recurrent laryngeal nerve; white recording needle electrode (arrow) inserted through the cricothyroid membrane into the vocal muscle; green grounding needle electrode (hashtag) placed subcutaneously into a skin flap in the left upper corner. (B) Intermittent nerve stimulation with tube surface recording electrodes in a 45-year-old female patient with sporadic medullary thyroid cancer: hand-held blue monopolar probes (asterisk) at the right recurrent laryngeal nerve. (C) Continuous nerve stimulation with tube surface recording electrodes in a 36-year-old female patient with papillary thyroid cancer: Monopolar APS^® circumferential clip electrode mounted on the vagus nerve (encircled); hand-held blue monopolar stimulation probe (asterisk) positioned at the right recurrent laryngeal nerve.

Figure 2

Algorithm of intraoperative management of bilateral thyroid disease after loss of signal on the first side of resection with no, incomplete, or complete recovery.