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Research Article: Intraoperative neuromonitoring for preservation of the external branch of the superior laryngeal nerve in transoral endoscopic thyroidectomy: initial experience from Vietnam

Date Published: 2026-08-03

Abstract:
To evaluate the feasibility of intraoperative neuromonitoring (IONM) in identifying the external branch of the superior laryngeal nerve (EBSLN), classifying its anatomical variations, and to evaluate short-term vocal function in patients undergoing transoral endoscopic thyroidectomy vestibular approach (TOETVA). A prospective descriptive study was conducted on 30 patients with thyroid nodules who underwent TOETVA with IONM using the NIM 3.0 system (Medtronic) at Hanoi Medical University Hospital from September 2021 to September 2024. EBSLNs were identified using a standardized intermittent stimulation protocol (1?mA) during superior pole dissection and classified according to the Cernea system. Voice outcomes were assessed using the Voice Handicap Index-10 (VHI-10) and laryngoscopy preoperatively and at 3 months post-surgery. A total of 31 EBSLNs were assessed (1 total thyroidectomy). IONM facilitated a 100% identification rate. The anatomical distribution according to Cernea classification was: Type 1: 11/31 (35.5%, 95% CI: 19.2–54.6%), Type 2a: 18/31 (58.1%, 95% CI: 39.1–75.5%), and Type 2b (high-risk variant): 2/31 (6.5%, 95% CI: 0.8–21.4%). No loss of EBSLN signal was recorded before the end of surgery. Mean VHI-10 scores showed no clinically significant change from baseline (2.1?±?1.5) to 3 months postoperatively (3.4?±?2.2; mean difference 1.3, 95% CI: ?0.2 to 2.8, p =?0.08). Only 3/30 patients (10%) had VHI-10 increase >5 points (minimal clinically important difference). Transient recurrent laryngeal nerve palsy occurred in 1/30 (3.3%) and fully recovered within one month. No permanent nerve injuries were recorded. IONM-assisted EBSLN mapping during TOETVA is technically feasible and allows consistent intraoperative identification. In this preliminary series, no clinically apparent deterioration in voice function was observed. However, given the descriptive design and limited functional assessment tools, comparative studies incorporating objective acoustic measures are required to determine the incremental benefit of routine IONM use for EBSLN preservation.

Introduction:
In thyroid surgery, while the recurrent laryngeal nerve (RLN) has long been the primary focus of intraoperative preservation, the external branch of the superior laryngeal nerve (EBSLN) remains frequently overlooked—earning it the designation of the “neglected nerve” ( 1 ). This small nerve (0.2–0.8?mm in diameter) innervates the cricothyroid muscle, which is responsible for tensing and lengthening the vocal cords during phonation. Injury to the EBSLN does not cause overt hoarseness but results in subtle yet…

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