Preliminary Exploration Of Feasibility And Clinical Application Of Preoperative Ultrasonographic Examination Of Carotid Sheath In VNS

Background:Vagus nerve stimulation(VNS)proves an effective and safe method to deal with medically refractory epilepsy.The key procedures in VNS are exposure of the carotid sheath,dissection of the common carotid artery(CCA)and internal jugular vein(IJV)and identification of the vagus nerve.Variation of relative positions of the above significant structures is not uncommon.Therefore,preoperative localization of these structures can facilitate surgeries to expose and dissect them,to.save operation time,and to decrease the incidence of operative complications.Exist evidence demonstrates that ultrasonography,which is a non-invasive,economical and easily available technique,is able to show vagus nerve,CCA,IJV and their localizations in cervical area.However,presently no report has been published related to the practice of preoperative ultrasonographic localization of these structures aiming to assist VNS.Objectives:to explore the feasibility and value of preoperative ultrasonographic examination of vagus nerve,CCA and IJV in VNS,and to study their relative positions in normal population.Methods:45 randomly chosen healthy volunteers were included in this study.They were placed supine without pillows underneath,and their heads were rotated to the right to fully expose the left cervical regions.This position is similar to the operative posture in VNS.Sectional imaging of the left vagus nerve,CCA and IJV was performed at the anterior border of sternocleidomastoid and approximately 2cm above the clavicle with the probe perpendicular to the skin surface.Then the images are analyzed as follows:(1)drawing a line through the assumed centers of CCA and IJV.The angle between this line and the skin surface is named a.The relative position of IJV to CCA can be described by the angle ?.(2)drawing two lines vertical to the above line and through the assumed centers of CCA and IJV,respectively.These lines thus divide the carotid sheath into six regions,which are named anterior(A),anteromedial(AM),anterolateral(AL),posterior(P),posteromedial(PM)and posterolateral(PL).If the nerves mainly locate in between the CCA and IJV,they are assigned to intermediate(I)region.(3)The relative position of vagus nerve to CCA is described by the angle y.Results:Vagus nerves,CCA and IJV can be clearly depicted by ultrasonography in all of the 45 volunteers.The sectional imaging of vagus nerve shows honeycomb appearance with several hypoechoic rounded fascicles surrounded by a hyperechoic epineurium.Nerves can be easily distinguished from connective tissues,lymph nodes and small vessels with Color Doppler technique.The average transverse diameter is(1.13±0.28)mm,while longitudinal diameter(1.01±0.27)mm and mean diameter(1.07±0.24)mm.Results show a(54.18±30.04)°,1p(35.82±30.04)° and y(32.81 ±50.52)°.IJV is anterolateral,anterior,lateral and anteromedial to CCA in 27,15,1 and 2 cases,respectively.As for vagus nerve,7 nerves fall in A region,18 in 1 region and 20 in P region.There is significant difference in the location of IJV relative to CCA between two genders(P=0.043).IJV is more likely to be anterolateral to CCA in men.There is no significant difference in the location of IJV relative to CCA between to two age groups.Considering the fact that IJV is most likely to be anterolateral and anterior to CCA(27/45 and 15/45,respectively),a comparison of the positions of vagus nerves between the two groups show significant difference.The nerve is more likely to be in P region when IJV is anterolateral to CCA while it is more likely in I region when IJV is anterior to CCA.Conclusions:(1)Ultraosonographic examination of vagus nerve,CCA and IJV can show their relative positions clearly and accurately.Therefore,it can be considered as a suitable technique for preoperative localization in VNS.(2)With volunteers in a position similar to the operative posture in VNS,the left vagus nerve and IJV are anterolateral to CCA(approximately at its one o'clock).Generally,vagus nerves can be found posterior to CCA and IJV or between them,but in a small fraction of cases the nerves are anterior to the major vessels.(3)Variation of positions of vagus nerve,CCA and IJV are noted in this study.In view that procedure-related complications have been reported in several studies,it can be inferred that preoperative localization of these important structures can facilitate surgeries to operate,to save operation time,and to decrease the incidence of operative complications.