Randomized Controlled Trial of Visualization versus Neuromonitoring of the External Branch of the Superior Laryngeal Nerve during Thyroidectomy

Abstract

BackgroundInjury to the external branch of the superior laryngeal nerve (EBSLN) during thyroidectomy results in a lowered fundamental frequency of the voice and deteriorated voice performance in producing high-frequency sounds. It remains unclear if the use of intraoperative nerve monitoring (IONM) can improve the clinical outcome of thyroidectomy in terms of preserved individual voice performance. This study was designed to test that hypothesis.MethodsA total of 210 consenting female patients planned for total thyroidectomy were randomly assigned to two groups equal in size (n = 105): visual inspection of the EBSLN and RLN vs. this plus additional EBSLN and RLN monitoring. The primary outcome was the identification rate of the EBSLN. The secondary outcomes included: anatomical variability of the EBSLN according to the Cernea classification and changes in postoperative voice performance. Voice assessment included pre- and postoperative videostrobolaryngoscopy and an analysis of maximum phonation time (MPT), voice level (VL), fundamental frequency (Fo), and voice quality rating on the GRBAS scale.ResultsThe following differences were found for operations without vs. with IONM: identification rate of the EBSLN was 34.3 % vs. 83.8 % (p < 0.001), whereas a 10 % or higher decrease in phonation parameters was found in 10 % vs. 2 % patients for MPT (p = 0.018), 13 % vs. 2 % for VL (p = 0.003), and 9 % vs. 1 % for Fo (p = 0.03), a change in the GRBAS scale > 4 points in 7 % vs. 1 % (p = 0.03), and temporary RLN injury was found in 2 % vs. 1 % (p = 0.56), respectively.ConclusionsThe use of IONM significantly improved the identification rate of the EBSLN during thyroidectomy, as well as reduced the risk of early phonation changes after thyroidectomy.

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

“…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.…”

“…The rates of reported surgical damage vary depending on the methods relied on to diagnose injury. 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).…”

“…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.…”

“…However, voice anomalies following thyroid surgery are somewhat common, multifactorial and may reflect not only laryngeal nerves injury, but also arytenoid trauma, cricothyroid dysfunction, strap muscle malfunction, lesion of the perithyroidal neural complex, laryngeal fixation and even psychological reaction (20). Lifante et al (37) reported on thyroidectomies under minimal dissection and regional anesthesia, thus putting aside the possible interference of intubation and damage to the strap muscles on the postoperative voice.…”

Contribution of intraoperative neuromonitoring to the identification of the external branch of superior laryngeal nerve

“…Routine identification of EBSLN was thought to be almost impossible and harmful to the nerve previously. However, IONM has recently been reported to be helpful and less invasive for identifying EBSLN (8)(9)(10)(11). As these findings increased the surgical interest in using neuromonitoring for the identification of EBSLN, the rate of neuromonitoring use has increased over time.…”