The feasibility of laryngeal nerve protection during thyroidectomy using sternocleidomastoid intermuscular approach with intraoperative neuromonitoring: a case series and step-by-step description of surgical procedure

BACKGROUND: Thyroid surgery is increasingly demanding in terms of cosmetic neck outcomes and protection of anterior neck function, so we have adopted an alternative sternocleidomastoid intermuscular approach (SMIA) for open/conventional thyroidectomy. The protection of recurrent laryngeal nerve (RLN) and external branch of superior laryngeal nerve (EBSLN) is the key and difficult point in thyroid surgery. The aim of this study was to testify the feasibility of RLN and EBSLN functional protection during SMIA thyroidectomy with the intraoperative neuromonitoring. METHODS: A total of 39 patients and 39 RLN and EBSLNs who underwent monitored SMIA thyroidectomy were included. Thyroid gland is revealed and excised anterior to the cervical sheath between the sternal and clavicular heads of the sternocleidomastoid muscle. Standardized intraoperative neuromonitoring (IONM) procedures and postoperative laryngeal examination were performed to audit the SMIA. Following the four-step method, V1, R1, R2, and V2 were monitored and the signal values were recorded. Statistical analysis was used to evaluate the change of IONM amplitude of RLN, combined with the results of laryngoscopy before and after operation to determine the status of RLN. EBSLN injuries were identified from changes in cricothyroid muscle (CTM) twitch and EMG. SMIA video vignette is detailed. RESULTS: All RLN and EBSLNs [17 on the left and 22 on the right] were monitored in 39 patients [5 men, 34 women; mean age 34.1±8.7 years; mean body mass index 22.5 (±3.0, 17.0–30.8) kg/m(2)] undergoing SMIA. For RLN of the affected side, we compared the V2 and V1 (1,236±672 vs. 1,240±428, P=0.973), R2 and R1 (1,676±778 vs. 1,656±765, P=0.849) signals separately, and the results were not statistically different (P>0.05). Comparing the V1 (1,240±428 vs. 1,309±395, P=0.601) signals of the bilateral recurrent laryngeal nerve, there was no statistical difference (P>0.05). CTM twitch and EMG were preserved. CONCLUSIONS: The SMIA technique appears feasible. RLN and EBSLN are easier to be exposed during thyroid surgery of SMIA, which is beneficial to the neuroprotection during the operation. At the same time, it can protect the anterior cervical function and improve the cosmetic effect after operation.