Contribution of intraoperative neural monitoring to preservation of the external branch of the superior laryngeal nerve: a randomized prospective clinical trial

Abstract

IONM contributes to visual and functional identification of the EBSLN and decreases the rate of EBSLN injury during superior pole dissection. Routine use of IONM to identify the EBSLN will minimize the risk of injury during thyroidectomy.

Injury of the external branch of the superior laryngeal nerve in thyroid surgery

“…Barczynski et al (20) randomized 210 patients to undergo thyroidectomy without or with nerve monitoring and reported a rate of identification of 34% versus 84% respectively (P<0.01). More recently, Uludag et al (24) documented visual identification-only in 35% of the cases in which EBSLN recognition was attempted in this study, as compared to 65% after searching it with the probe. Hurtado-López et al (71) reported an identification rate of 97% of cases under IONM versus 79% without it.…”

“…This so-called "human communicating nerve" is of special interest in intraoperative nerve monitoring (IONM) of the EBSLN, for it allows the recording of electroneuromyography (EMG) waveforms elicited by electrical stimulation by endotracheal surface electrodes (19). This finding is reinforced by several studies that found clear-cut TAM activity provoked by EBSLN stimulation in 70% to 100% of patients undergoing thyroid surgery (20)(21)(22)(23)(24). Darr et al (22) found that EBSLN-evoked potential of the TAM could be recorded in all cases when a tube with dedicated surface EMG electrodes in contact with the anterior aspect of the vocal cords was employed.…”

“…When laryngoscopy and voice analysis were used, palsy rates ranged from 0 to 6% (7,20,28,29). When the more accurate laryngeal electroneuromyography (LEMG) was included in the analysis, higher rates were reported and reached 58% (1,19,23,24,30,31).…”

“…Hazard can occur by entrapment of the nerve in the ligature of the superior pole vessels, transection, stretching and thermal damage (23,24). Nerve ischemia has also been considered to cause dysfunction (9) and the level of training has been implied by one of the authors (CRC) as one of the factors influencing outcomes (30).…”

“…It is felt that different surgical techniques with different degrees of exposure of the sternothyroid-laryngeal triangle, such as the division of the sternothyroid muscle in Pagedar's series (34), could account for such discrepancy among identification rates (20,24). On the opposite pole of surgical bed exposure, the reports on robotic (72), video-assisted (36), and mini-incision local anesthesia thyroidectomies (37,38) defend that nerve monitoring is feasible and useful in providing, at least, electrophysiological identification of the EBSLN when the field is limited.…”