Application of external branch of superior laryngeal nerve monitoring in thyroid surgery of tumor in upper pole

Abstract

Objective To explore the value of monitoring techniques of the external branch of superior laryngeal nerve (EBSLN) in thyroid surgery and to study its protective effects on vocal function after thyroid surgery. Methods We retrospectively analyzed the clinical data of 139 patients who underwent primary surgery of papillary thyroid cancer with neurological monitoring from Jun. 2017 to Mar. 2018 in the General Surgery Department of PLA General Hospital. The tumors of 31 cases were located in the upper pole of the gland and elsewhere in 108 cases. The patients’ vocal function was assessed at one week and one month after surgery. The rate of EBSLN identified visually and by the intraoperative nerve monitoring (IONM) were counted. EBSLN recognition efficiency and prevalence of EBSLN damage during the operation of tumor in upper pole of thyroid and in other location were compared. Results In the 139 patients, there were 218 upper poles (218 EBSLN) treated intraoperatively, of which 145 were recognized visually (126 (57.8%) confirmed by IONM, and 203 (93.1%) were identified by IONM, OR=8.27 (χ2=59.345, P=0.00) . The percentage of EBLSN located in the upper pole accurately identified by the naked eye was 20/46 (43.5%) while by IONM was 43/46 (93.4%) . The percentage of EBSLN at the other position accurately identified visually was 106/172 (61.6%) , and by IONM was 160/172 (93.0%) . The number of visually identified cases in different locations showed significantly differences according to the chi-square test (χ2=4.901, P=0.027) , and no significant difference by IONM identification according to chi-square test (χ2=0.012, P=0.914) . Five patients had a low voice at one week postoperatively and low voice and vocalization change were not observed after one month. Conclusions IONM can effectively increase the proportion of intraoperative EBSLN identification to ensure the safety of surgery. The difficulty of visual identification of EBSLN during the surgery of tumor in upper pole is greater than that in other locations. IONM can provide more evidences for nerve protection and reduce the risk of injury. Key words: External branch of superior laryngeal nerve (EBSLN); Thyroid gland surgery; Intraoperative neural monitoring (IONM); Thyroid tumor in upper pole