Precision and Future Medicine 2020;4(2):75-80 CASE https://doi.org/10.23838/pfm.2020.00086 REPORT pISSN: 2508-7940 · eISSN: 2508-7959 Three-dimensional reconstruction of the facial nerve course in parotid gland tumor using double echo steady state with water-excitation magnetic resonance images 1 2 2 1 Yong Gi Jung , Yi-Kyung Kim , Hyung-Jin Kim , Han-Sin Jeong 1 DepartmentofOtorhinolaryngologyHeadandNeckSurgery,SamsungMedicalCenter,SungkyunkwanUniversitySchoolof Medicine,Seoul,Korea 2 DepartmentofRadiology,SamsungMedicalCenter,SungkyunkwanUniversitySchoolofMedicine,Seoul,Korea Received: May 7, 2020 Revised: May 28, 2020 Accepted: May 29, 2020 ABSTRACT Functionalpreservationofthefacialnerve(FN)isessentialinparotidtumorsurgery. Corresponding author: Han-Sin Jeong Recently,directvisualizationoftheFNintheparotidgland(double-echosteady-state Department of sequencewithwaterexcitationmagneticresonanceimaging[DESS-WE-MRI])hasbeen Otorhinolaryngology Head attemptedwithpromisingdiagnosticaccuracy.Inthisreport,wepresentthree-dimen- and Neck Surgery, Samsung sional(3D)reconstructionoftheFNcourseintwoparotidglandtumorcasesusing Medical Center, Sungkyunkwan DESS-WE-MRIimagesforthefirsttime.Onepatienthadarecurrentbenignparotid University School of Medicine, glandtumor,whiletheotherpatienthadamalignantparotidglandtumor.Re- 81 Irwon-ro, Gangnam-gu, gions-of-interestincludingtheFNandthetumorsweremanuallyselectedineachsec- Seoul 06351, Korea tionoftheDESS-WE-MRIimages.The3DrenderingswerethencreatedwithanIn-Vesal- Tel: +82-2-3410-3579 iussoftware.TheFNswerewell-demarcatedtothetemporofacialandcervicofacial E-mail: [email protected] branches.ThisvirtualreconstructionoftheFNnervecoursecanprovidecomprehen- siveandimmediateunderstandingoftheanatomicalrelationshipbetweentumorand theFN,evenforsurgeonsunaccustomedwithDESS-WE-MRIimages. Keywords: Facialnerve;Magneticresonanceimaging;Neoplasms;Parotidgland;Surgery INTRODUCTION Tumors(benignormalignant)arisingfromtheparotidglandarenotcommon,withaninci- denceoffivetosixper100,000inthepopulation[1].Primarytreatmentforparotidglandtu- morsiscompletesurgicalremovalforseveralreasonsincludingcontinuousgrowthofthetu- This is an Open Access article mor,lackofeffectivemedicaltreatment,difficultyindifferentiatingbetweenbenignandmalig- distributed under the terms of the nanttumors,andthepotentialformalignanttransformationinasubsetofbenigntumors[2]. Creative Commons Attribution Thesurgicalgoalofparotidglandtumorsiscompleteremovalofthetumorswithoutcomplica- Non-Commercial License (https:// creativecommons.org/licenses/ tions[2].Amongthepotentialcomplicationsassociatedwithparotidglandsurgery,facialnerve by-nc/4.0/). weaknessisthemostdisturbing,resultinginaseverelyloweredpatientqualityoflife[2,3]. Copyright © 2020 Sungkyunkwan University School of Medicine 75 3Dimagingofthefacialnerve Evenwithvarioustechniques(describedbelow),14%to mor,whounderwentparotidectomy.Bothpatientsexhibited 64%ofparotidectomycasessufferfacialnerveweakness nofacialweaknessatpresentation.Thestudyprotocolwas postoperatively[4-6].Forsmallandsuperficialtumorsinthe previouslyapproved(IRBfileno.2017-07-084-003,Clinical- parotidgland,theriskoffacialnerveweaknessisnothigh Trials.govIDNCT03822728),andallpatientssubmittedwrit- (lessthan5%withanexperiencedsurgeon)[3].However,its teninformedconsent. incidencehasincreaseddramatically(upto30%)inlargetu- Thefirstpatientwasa50-year-oldmanwitharecurred mors,deepseatedtumors,revisionsurgery,andmalignant massinhisrightparotidgland.Twentyyearsprior,hehad tumors(requiringmoreextensivesurgicaldissectionofthe undergonesurgeryforabenigntumorinhisrightparotid parotidgland)[7]. gland.CTscansrevealeda3-cm-sizedbenignlookingtumor. Duringparotidectomy,severalmeasureshavebeencom- Aspirationcytologysuggestedapleomorphicadenoma.An monlyusedtopreventorminimizefacialnerveinjury[8,9]. MRIexaminationincludingtheDESS-WEsequencewasper- Surgicallandmarks(tympanomastoidsutureline,tragal formed,andthepatientunderwentsuperficialparotidecto- pointandtheposteriorbellyofthedigastricmuscles)consis- mywithpreservationofallfacialnervebranches.Thefinal tentlyindicatethefacialnervetrunk,whichisthestarting pathologyrevealeda3.3-cm-sizedtumorthatprovedtobea pointofantegradefacialnervedissection[8,9].Mostsur- pleomorphicadenomawithclearresectionmargins. geonsusesurgicalmagnificationinparotidglandsurgery Thesecondpatientwasa30-year-oldmanwithatumorin (surgicalloupesormicroscopes).Inaddition,intraoperative hisleftparotidgland.Thetumorwassuspectedtobeamalig- monitoringofthefacialnervegreatlyhelpssurgeonsidentify nanttumorfrompreoperativecytologyandCTimages.Based thefacialnerve[4,5]. onthefindingsoftheinitialwork-ups,positronemissionto- Withtheadvancementofimagingtools,preoperativecom- mographywithCTandDESS-WE-MRIscanswereperformed, putedtomography(CT)ormagneticresonanceimaging andnometastasiswasfound.Thepatientunderwentcom- (MRI)imagescandelineateandlocatetumorsintheparotid pleteparotidectomywithpreservationofthefacialnerveand gland,andestimatetheanatomicalrelationshipbetween prophylacticneckdissection.Thefinalpathologyrevealeda thetumorandthefacialnerve[10-12].Typically,therelative 4.0-cm-sizedmucoepidermoidcarcinomawithextraparen- locationofthetumortothefacialnerveplane(superficialor chymalextensionandnolymphnodemetastasis(pT3N0). deepseatedtumor)canbepredictedpreoperativelybyindi- Thetwopatientsweredischargedhomeuneventfullyat rectmethodsusingafacialnervelineorretro-mandibular postoperativeday7.Nofacialweaknesswasobservedpost- veinline[11].Recently,directvisualizationoftheperipheral operatively. nerveandfacialnervehasbeenattemptedwithimproved accuracyoflocalizationusingparticularsequencesofMRIsto MRI images and interpretation enhancevisualizationoftheperipheralnerve[13,14].Among AllMRIexaminationswereperformedwithaSiemensSkyra themethods,double-echosteady-statesequencewithwater 3-Tscannerusinga20-channelheadandneckcoil.Afterob- excitationMRI(DESS-WE-MRI)isonepromisingtoolthatcan tainingconventionalspin-echoT1-weightedimagesand directlyvisualizetheperipheralnervesinvariousregions fat-suppressedT2-weightedimages,the3D-DESS-WEse- [13,14].Ourdata(unpublished)andthoseofotherstudies quenceswereobtained(repetitiontime/echotime/number showthatDESS-WE-MRIoftheparotidglandcanvisualize ofexcitation,13.62ms/5ms/1;flipangle,30°;field-of-view, thefacialnervearoundparotidglandtumorsaccurately[15]. 200×200mm;matrix,384×230;effectivesectionthick- Inthisreport,wepresenttwocasesofvirtualreconstruc- ness,0.5mm;slabthickness,10.4cm;acquisitiontime,4 tionofthethree-dimensional(3D)anatomyofthefacial minutes35seconds).Finally,contrast-enhancedaxialand nervecoursearoundparotidglandtumorsusingDESS-WE- coronalspin-echoT1-weightedimageswithfatsuppression MRIimages,forthefirsttime.Itcanprovideopportunitiesto wereobtainedafterintravenousinjectionof0.1mmol/kgof thesurgeonforbettersurgicalplanningandbetterpreserva- gadolinium-basedcontrastmaterial. tionofthefacialnerveduringparotidectomy. TheMRIimageswereevaluatedbytwoneuro-radiologists (YKK,HJK)withmorethan5yearsofheadandneckMRIin- CASE REPORT terpretationexperience.OnaxialDESS-WE-MRIimages,we evaluatedthevisibilityofthemaintrunk,temporofacialdivi- Inthisreport,wepresenttwopatientswithparotidglandtu- sion,andcervicofacialdivisionoftheintraparotidfacial 76 http://pfmjournal.org YongGiJung,etal. nerveontheaffectedside.MRIinterpretationwasperformed Zbrush2020(Pixologic,LosAngelesCA,USA)wasusedto independentlyandanyambiguitywassolvedbyajointcon- smoothlytrimthesurface.Finally,3D-Coat(www.3dcpat. sensus.Toavoidanypotentialmisinterpretationoftheduc- com)wasusedtotexturethefacialnerveandtumor.Mandi- tal/vascularstructuresforneuralstructures,wefocusedon bleandlateralskullbasewerealsoreconstructedand3Dvi- thecontinuityofthefacialnerveandfolloweditscourse sualizedfromtheinformationofMRIimagesforanatomic alongtheintra-temporalandextra-mastoidsegments.Once orientationofthefacialnerveandparotidtumors(Fig.1). thenervepenetratedtheposteriorcapsuleoftheparotid gland,itwastracedanteriorly.Inaddition,thetumorloca- Surgical findings and 3D reconstructed images tioninrelationtotheentirerangeofthevisiblefacialnerve Inthefirstcase,thetumorwaslocatedinthesuperficiallobe fromthemaintrunktoitsdivisionalbrancheswasdeter- oftheparotidglandatthelevelofthefacialnervetrunk.The minedonthereformatted3mmthickaxial,sagittal,andcor- facialnervebranchedoffjustbeforethetumor,andthetem- onalDESS-WEimages. porofacialandcervicofacialbranchesransuperiorlyandinferi- orlyoverthesurfaceofthetumor.Thetumorwaswell-demar- 3D visualization of the parotid tumor and facial nerve: catedfromtheparotidgland.However,antegradedissection technical notes ofthefacialnervetrunkfromthetumorwasnoteasybecause DigitalImagingandCommunicationsinMedicine(DICOM) offibrosisfromaprevioussurgery.Thetwomainbranches formatdataoftheaxialimageswereextractedfromtheMRI werefurtherdividedintofiveperipheralbranches,deeptothe scansofthetwopatients.The3Dmodel,includingthetumor tumor,attheanteriorboundaryofthetumor.Thetumorwas andthefacialnerve,wasfabricatedusingInVesalius3.3.1 resectedsafelywithsomesurroundingparotidglandtissues (CTI,SaoPaulo,Brazil)software,andthemodelwasexport- andallthebrancheswerepreservedduringsurgery.DESS-WE- edintheStandardTriangleLanguage(STL)format.The MRIand3Dreconstructedmodelsclearlyvisualizedthemas- Meshmixer3.5program(Autodesk,SanRafael,CA,USA)was toidportionofthefacialnerve,thefacialnervetrunk(ex- usedtoremoveunnecessarypartsofthe3Dmodel,and tra-mastoidportion),andthetwomainbranches(Fig.2A). Parotidtumor DESSWEMRI Imageprocess 3DRendering CT&Cytology(orneedlebiopsy)