The Application Of Intraoperative Nerve Monitoring In Assessing The Function Of The Recurrent Laryngeal Nerve Before And After Central Lymph Node Dissection

Objective:To assess the risk of recurrent laryngeal nerve(RLN)injury and its mechanism of injury in central neck dissection(CND),and to explore the application value of IONM(intraoperative neural monitoring,IONM)in CND.Method:A total of 1,119 patients who underwent thyroid cancer surgery were prospectively studied.The study involved RLN 1,273 roots.Intraoperative application of IONM assisted visual identification of descending thyroid single / double lobectomy + CND.Operate in strict accordance with the IONM standardization procedure during surgery to obtain initial vagus nerve(VN)and RLN signals(R1,V1),VN and RLN signals(V2.0 and R2.0)after thyroidectomy,CNN after VN And RLN signals(V2.1 and R2.1).Routine laryngoscopy was performed before and on the first postoperative day to observe vocal cord movement.Combined with intraoperative electromypgram(EMG)and postoperative laryngoscopy to determine RLN function and possible injury mechanisms.Results:1.The CLN clearance status was 154 cases(13.8%)for bilateral CND and 965 cases(86.2%)for unilateral CND.A total of 6,636 lymph nodes were cleaned out,and the average number of patients cleared was 5.9.2.CLN pathological features: The overall rate of CLN metastasis was 41.9%,the false positive rate of CLN lymph node diagnosis was 6.0%,and the false-negative rate was 28.9%.There was a negative correlation between the number of CLNs and T1a(r=-0.228,P<0.01)and a positive correlation with T1 b,T2,T3 b,and T4a(r1=0.103,P<0.05;r2=0.095,P<0.01;r3= 0.113,P<0.01;r4= 0.192,P<0.01);positive correlation with p N1 b risk(r=0.518,P<0.01).3.CND EMG data: The amplitude of RLN after lobectomy was 1466±721 ?V.After CND,it was 1250±879?V,with significant difference before and after(P<0.0001).4.RLN injury mechanisms and types: postoperative laryngoscopy confirmed vocal cord(VC)dyskinesia 3.8%(49/1273),thyroidectomy 51%(25/49),CND accounting for 16.3%(8 /49).In the CND,25% were traction injuries,12.5% were thermal injuries,25% were crush injuries,and 12.5% were ligatures.5.RLN latent injury factors: The number of CLN dissections was negatively correlated with the amplitude of RLN(r=-0.066,P <0.05),and positively correlated with the latency of RLN(r=0.058,P<0.05).Conclusion:The metastatic rate of CLN in thyroid cancer patients is high,and the sensitivity of CLN to metastasis is low.The metastasis rate in this group is 41.9%.Therefore,the risk of conventional CND cervical lymph node metastasis is to guide the intraoperative treatment strategies and postoperative treatment options.The relationship between tumor size and the risk of CLN metastasis is not a simple linear relationship.It is not advisable for all T1 and T2 patients to recommend conventional CND(2015 version of the ATA guidelines).The RLN injury mechanism in the CND process is mostly caused by poor operation,such as traction,compression,and thermal injury.Intraoperative application of IONM helps to play a pre-emptive role in the CND,prompting potential hazards of nerve injury in real time and reducing the risk of RLN injury.