Objective: To evaluate the mechanisms of recurrent laryngeal nerve (RLN) injury during thyroidectomy and the impact of continuous intraoperative nerve monitoring (C-IONM) on surgical strategy.
Material and Methods: The data of 364 consecutive patients who underwent total or hemithyroidectomy between June 2014 and January 2016 were evaluated prospectively. All patients underwent thyroidectomy by using C-IONM. The mechanisms of RLN injury and the outcomes of the patients with combined events (CE) and loss of signal (LOS) were evaluated.
Results: Combined events (CE) occurred in 6 (1.6%) of these 364 patients. The reduced electromyographic (EMG) amplitude and prolonged latency recovered in all patients intraoperatively by the reversal of the medial traction maneuver. Loss of signal (LOS) occurred in 7(1.9%) patients. The mechanisms of LOS was ligation of the anterior branch of the nerve in 1 (14.3%) patient and traction in 4(57%) patients. The probable mechanism of LOS was traction or transection in 2 (28.6%) patients in whom LOS occurred during the dissection of the intrathoracic portion of large substernal goiter. Of these 7 patients, LOS recovered intraoperatively after 20 minutes of waiting in 1(14.3%) patient. In the remaining 6 (85.7%) patients, unilateral vocal cord paralysis (VCP) was verified on the postoperative laryngoscopic examination. The overall temporary and permanent unilateral VCP rates were 1.6% (n=6) and 0.8% (n=3), respectively in these 364 patients. No bilateral VCP was recorded. Continuous intraoperative nerve monitoring (C-IONM) prevented bilateral VCP in 1 (0.3%) patient.
Conclusion: The major advantage of C-IONM is to alert the surgeon for imminent RLN injury. Combined event (CE) is a pathognomonic sign of impending nerve injury that may progress to LOS. This situation enables the surgeon to adverse (reverse) the surgical maneuver before permanent damage to the nerve sets in. Continuous intraoperative nerve monitoring (C-IONM) can also immediately spot RLN injury during thyroidectomy. This property of C-IONM gives the surgeon the opportunity for an early corrective action to release the affected nerve promptly. In case of permanent LOS, staged thyroidectomy could be planned to prevent bilateral VCP.
Key words: Continuous intraoperative neuromonitoring, Thyroid surgery, IONM, C-IONM, recurrent laryngeal nerve injury, vocal cord palsy, loss of signal
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