[Application value of intraoperative neuromonitoring plus "classification of EBSLN" to protect the external branch of the superior laryngeal nerve].

Objective: To investigate the application efficacy of the classification of external branch of superior laryngeal nerve (EBSLN) combined with intraoperative neuromonitoring (IONM) in the dissection of for protecting the nerve from injuery, compared with ligation of branches of the superior thyroid vessels without attempts to visually identify the nerve. Methods: A prospective randomized controled study was performed in our center. Patients subjected to thyroidectomy from January 2017 to June 2019 were randomly divided into 2 groups, patients in experimental group underwent thyroidectomy and classification of EBSLN with IONM to dissect EBSLN, and patients in control group received synchronous surgery without attempts to visually identify the nerve. The anatomical subtypes of in experimental group were recorded. The voice handicap index 10 (VHI-10) score was evaluated and the movement of bilateral vocal cords was examined by laryngoscope before surgery, 1 month, 3 months, and 6 months after surgery, respectively. SPSS 26.0 statistical software was used for statistical analysis. Results: Among the 1 377 from 827 patients (317 males and 510 females, aged 24-58 years old), 691 EBSLNs in experimental group and 686 EBSLNs in control group. Totally 98.3% of EBSLNs in experimental group were identified by IONM including 16.4% (113/691) for type Ⅰ, 21.3% (147/691) for type Ⅱa, 31.4% (217/691) for type Ⅱb, 10.4% (72/691) for type Ⅲa, 3.9% (27/691) for type Ⅲb, 16.6% (115/691) for type Ⅲc. There was no statistical significance difference in baseline data between 2 groups (all P>0.05). All patients were followed up for more than 6 months. The postoperative nerve injury rate of experimental group was significantly lower than that of control group (1.2% vs. 7.5%, χ²=12.659, P<0.001), and the VHI-10 scores and laryngoscope results of experimental group were better than those of control group in three follow-up visits (P<0.001). With postoperative laryngoscope examination, 3 patients in the experimental group and 23 patients in the control group showed vocal cord relaxation, bilateral oblique asymmetry and other phenomena, which were considered as the results of permanent injury. Other patients with symptoms were relieved to varying degrees during the follow-up, and their symptoms were considered as the results of temporary injury. Conclusion: IONM combined with classification of EBSLN can reduce significantly the risk of injury in thyroidectomy, which is better than direct ligation of branches without attempts to visually identify the nerve.