Background: Avoiding injury of the external branch of the superior laryngeal nerve(EBSLN) is one of the major challenges during thyroid surgery, especially in transoral endoscopic thyroidectomy vestibular approach (TOETVA). This study aimed to investigate the protective strategies of the EBSLN during TOETVA.
Methods: In order to protect the EBSLN during TOETVA, we adopted the method of identification the nerve by anatomy and localization. The method of anatomy involves the dissection of EBSLN by complete transection of the sternothyroid muscle in the attachment of the thyroid cartilage. The method of localization involves nerve stimulation localization, which produces cricothyroid contractile activity through intraoperative nerve monitoring stimulation (IONM). Concurrently, patients were evaluated preoperatively and at 1 and 3 weeks postoperatively in an individual prospective cohort study using a stroboscopic laryngoscope and the voice handicap index-10 (VHI-10). The VHI-10 score was used to evaluate voice changes.
Results: We retrospectively analyzed patients with papillary thyroid cancer (PTC) who underwent TOETVA in the thyroid center of the Beijing Tongren hospital between February 2018 and June 2020. Patients with recurrent laryngeal nerve(RLN)damage were excluded. Sixty patients were enrolled in this study, of which four underwent total thyroidectomy. Intraoperatively, 56 EBSLNs were located (56/64, 87.50%). Among these, the left EBSLN was identified in 20/25(80.00%) and the right EBSLN was identified in 36/39 (92.31%) cases. One week postoperatively, a blinded stroboscopic laryngoscope examination showed that no patient had paresis of the EBSLN. However, the VHI-10 score was significantly higher than the preoperative value (10.58 ± 4.54 vs. 3.00 ± 1.54, p<0.01). At three weeks postoperatively, the overall score was still different from that preoperatively (4.83 ± 3.34 vs. 3.00 ± 1.54, p<0.01); however, the vast majority of patients returned to their preoperative status.
Conclusion: In TOETVA, the EBSLN can be well exposed by transection of the sternothyroid muscle, and combined with IONM, the protection of the function of the EBSLN can be guaranteed. Simultaneously, we observed that TOETVA could cause a short-term voice handicap in patients, with such changes generally returning to normal within three weeks.