| Objective: to study the mechanism of laryngeal nerve(recurrent laryngeal nerve and external branch of superior laryngeal nerve) injury, such as mechanical injury, thermal injury and anatomical variation, and to study the function-diagnosis during thyroid urgery.Methods: the study includes three parts as follows. Firstly, animal study part: swines of study group were divided into two groups, who receiving different degrees of stretch or harmonic scalpel randomly, while the recurrent laryngeal nerves in the control group were exposed only. The parameters of EMG of RLN before and after retracting were recorded. Electron microscope and biochemical studies were performed to assess the changes to cellular organelles, myelin lamellae and axons; Secondly, clinical study of recurrent laryngeal nerve: the standard four steps of intraoperative neuromonitoring method was used to identify and expose the recurrent laryngeal nerve, that is V1( amplitude of vagus nerve before exposion), R1(amplitude of recurrent laryngeal nerve before exposion), V2(amplitude of vagus nerve after exposion) and R2(amplitude of recurrent laryngeal nerve after exposion). All patients received intraoperative neuromonitoring to locate and explore RLN. Laryngoscopy was examined pre and post operation. Meantime, Duplex examination(assessment the origin of the right common carotid artery and to search the brachiocephalic artery) and neuromonitoring was applied to predict and diagnose the non-recurrent laryngeal nerve, which was an unusual anatomical variation causing nerve injury; Lastly, clinical study of external superior laryngeal nerve: the standard three steps of intraoperative neuromonitoring method was used to identify the relationship between EBSLN and the upper pole of the thyroid or the inferior constrictor muscle. The mechanism of nerve injury was analyzed by the anatomical type. At the same time, the nerve injury was diagnosed by the amplitude of the cricothyroid muscle.Results: Firstly, animal study part: significant difference of EMG was proved in 10% group pre and post retraction. Histopathological studies revealed degenerative changes at various stages on the myelinated nerves. Separation of myelin lamellae, swelling and vacuolization were noted. When the activated tip was placed contact with the RLN for ≥2 alarm signal, the EMG signal was lost. Significant EMG changes were observed after the tip was placed 1mm or 2mm from the RLN for 6 alarm signal; Secondly, clinical study of recurrent laryngeal nerve: The following diagnostic accuracy values were calculated for the criterion recommended by INMSG(V2 amplitude ≤100μv): positive predictive value 70%, and negative predictive value 99.75%, sensitivity 87.5%, specificity 99.27%. The ROC curve analysis allowed for calculation of the most optimal criterion(V2 amplitude ≤169μv) in prognostication of postoperative RLN injury,. For this criterion, sensitivity was 99.8%, while specificity was 100%. Overstretching(66.6%), thermal injury of electric scalpel(16.7%) and ligation fault(16.7%) was most important RLN injury mechanism. Preoperative ultrasonography and intraoperative neuromonitoring may correctly predict and identify non-recurrent laryngeal nerve. At last, clinical study of external branch of superior laryngeal nerve: 108 nerves(99.1%) were located successively, 42 of which were visualized(38.9%). 55 nerves(50.9%) crossed the superior thyroid artery more than 1cm, while the other 53 nerves(49.1%) less than 1cm including 24 nerves(more than 0.5cm, less than 1cm) and 29 nerves(less than 0.5cm or below the superior pole of thyroid. The rate of the latter type was significantly elevated in patients with the up and down diameter more than 5cm. There were no significant difference in the ampllitude of external branch of superior laryngeal nerve between pre and post operation(699.02±215.75μvs 686.63±209.35μv, p=0.223). No relationship was found between nerve amplitude and sex, year and nerve lication.Conclusion: IONM was useful to evaluate the function of RLN, to expose the RLN and to identify the RLN injury early, which will contribute to make the next operation strategy. |
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