Download Microvascular Decompression for Trigeminal Neuralgia

TheNeurosurgicalAtlas byAaronCohen-Gadol,M.D.
MicrovascularDecompressionfor
TrigeminalNeuralgia
Trigeminalneuralgiaisconsideredoneoftheworstpainsthatcan
affectahumanbeing.Theseverityofthisdisablingpainanditsrelief
throughsuccessfuloperativeinterventionhavecausedmicrovascular
decompression(MVD)surgerytoberecognizedasoneofthemost
satisfyingoperationsinneurosurgery.
Thetypicalpainoftrigeminalneuralgiaisrelativelyeasytodiagnose.
Thecharacterofthepainistypicallyunilateral,episodic,severe,
stabbing,shock-like,orlancinating,andexacerbatedbycutaneous
stimulisuchastactilepressure,chewing,brushing,abreezeofair,or
shaving.Atfirst,itisoftenmistakenasatoothproblembecauseofits
presentationinthetwolowerbranchesofthetrigeminalnerve.
Patientsmayundergounnecessary,andsometimesirreversible,
dentaltreatmentbeforethecorrectdiagnosisismade.
Acrudeannualincidenceoftrigeminalneuralgiaisapproximately5.7
per100000womenand2.5per100000men.Peakincidenceliesin
peoplebetweenages50and60years,withprevalenceincreasing
withage.Initially,asmalldoseofanantiepileptic/antineuralgicdrug
(suchascarbamazepine),ratherthanananalgesicdrug,canprovide
excellentpainrelief.However,upto10%ofpatientswillnotrespond
tothesedrugsandwillstillqualifyascandidatesforMVDsurgeryif
nootherunderlyingetiologyisfound.
History
In1773,JohnFothergillwasthefirsttofullydescribetrigeminal
neuralgiainanarticlepresentedtotheMedicalSocietyofLondon
titledOnaPainfulAfflictionoftheFace.In1829,CharlesBell
distinguishedthespecificfunctionsofthetrigeminalandfacialnerves
andintroducedtheideathattheparoxysmalpainintrigeminal
neuralgiaisdirectlyrelatedtonervedysfunction.
In1934,WalterDandy,whoroutinelyusedalateralsuboccipital
craniectomy(or“cerebellarapproach”)toperformretrogasserian
trigeminalneurotomiesfortreatmentoftrigeminalneuralgia,made
theseminalobservationthatinmanypatientswhosufferfromthis
pain,thenerveiscompressedbyanoverlyingbloodvessel.Later,in
1967,PeterJanettapopularizedtheMVDprocedurefortrigeminal
neuralgia.
Figure1:OneofthefirstpatientsofHarveyCushingsuffering
fromanattackoftrigeminalneuralgia.Thisimageismostlikely
oneoftheearliestphotographsofapatientwiththisdisease
(topimage).Cushing’soriginalsketchesdemonstratehis
techniqueofsubtemporalsensorynerveavulsion(middleand
bottomimages)(CourtesyofCushingCenteratYaleUniversity).
Pathogenesis
Thepathogenesisofcranialnervehyperactivitysyndromes,suchas
trigeminalneuralgia,hemifacialspasm,geniculateneuralgia,
paroxysmalpositionalvertigo,andglossopharyngealneuralgia,has
remainedelusive.Vascularcompressionoftherespectivenervesat
thebrainstem(neurovascularconflict-peripheralhypothesis)has
beenproposedastheprincipalfactorinvolvedinthegenesisof
cranialnervehyperactivitythroughdemyelinationoftherootentry/exit
zoneofthenerve(ephaptictransmission).
However,insomepatients,nocompressivearterycanbefound
duringdetailedexploratoryposteriorfossasurgery.Inaddition,
cadavericstudieshaverevealedanintimaterelationshipbetweenthe
cranialnervesintheposteriorfossaandtheneighboringvessels,but
thesecadavershadnohistoryofcranialhyperactivitysyndrome
beforetheirdeath.Recently,investigatorshaveimplicatedother
factors(centralhypothesis:hyperactivityofthetrigeminalandfacial
nuclei),inadditiontoperipheralvascularconflict,ascausesforthe
disorder.
Theoffendingvesselismostoftenthesuperiorcerebellarartery
(75%)ortheanteriorinferiorcerebellarartery(10%).Inaddition,a
veinmaycontributetothecompression(68%),andsometimesitis
theonlycompressingvessel(12%).Becauseofthelamination
patternoffiberswithinthenerveroot,medialcompressiontendsto
causeV2(themaxillarydivision)symptoms.Lateralorcaudal
compressionmaycauseV3(mandibulardivision)symptoms,and
rarely,cranialcompressioncausesV1(ophthalmicdivision)
symptoms.
Regardlessoftheresponsibleetiologyinthepathogenesisofthis
pain,MVDsurgery,throughmobilizingtheoffendingvesselor
performingarhizotomy,providesaneffectiveanddurablepalliative
optionforsymptomaticrelief.Althoughpercutaneousprocedures
offeralessinvasiveroutetotheGasserianganglionforrhizotomy,
posteriorfossaexplorationofferstheonlyopportunitytoidentifyan
offendingvesselthroughanondestructiveprocedurewithamore
lastingresult.
Thepatient’sageandmedicalcomorbiditiesareimportantfactors
thatcanlimittheapplicationofanMVDoperation.IofferMVD
surgerytomypatientswhoareyoungerthan70yearsandwhohave
noprohibitivemedicalcomorbidities,iftheirpainisconsistentwith
trigeminalneuralgia.
Inthischapter,Idescribethedetailsandkeystepsinmaximizing
safetyandefficiencywhileminimizingcomplicationsduringMVD
operationsfortrigeminalneuralgia.Mytechniquehasevolvedfroma
combinationofpearlsfrommultipleschoolsofneurosurgical
teaching.
DiagnosisandEvaluation
Thediagnosisoftrigeminalneuralgiaisbasednearlyentirelyonthe
patient’shistory.Asmentionedabove,thecharacterofthepainin
trigeminalneuralgiaistypicallyunilateral,episodic,severe,stabbing,
shock-likeorlancinating,andexacerbatedbycutaneousstimulisuch
astactilepressure,chewing,brushing,abreezeofair,orshaving.
Thischaracterisconsideredneuralgicincontrasttoneuropathic
pain:Aburningpainassociatedwithnumbness.
Periodsofremissiontendtogetshorterovertimeandattacksofpain
oftengetlonger.Patientsmayhaveasfewasthreetofouroras
manyas70attacksperday.Thereisoftenarefractoryperiodwhen
thepaincannotbetriggered.Painoccursatnightinathirdof
patients.Itisunusualtohaveneuralgiaonlyinthefirstophthalmic
divisionofthetrigeminalnerve.
Apositiveresponsetoneuropathicpainmedications,suchas
carbamazepineorgabapentin,oftensupportsthediagnosisoftypical
trigeminalneuralgiaandpotentiallypredictsagoodoutcomeforMVD
surgery.Thecharacterofthepainmaychangewiththeuseof
neuropathicpainmedicationsorpreviouspercutaneousprocedures,
andthepainmaybecomemoreconstant.Therefore,theclinician
shouldinquireaboutthecharacterofthepainatitsinceptionbefore
anytreatmentwasrendered.
Patientswithburningpain,facialnumbness,or(only)constantpain
withouttriggeringstimuliaresufferingfromatypicalorneuropathic
pain,notneuralgicfacialpain.Theyarenotidealcandidatesfora
posteriorfossaexploratoryoperation.Itisimportanttocarefully
examinethefaceandoralcavityalongwiththecranialnerves.A
detailedneurologicexaminationofthesepatientsisusually
unremarkable;minorsensorychangesinthecorresponding
distributionofthetrigeminalnervearenotuncommonandnota
contraindicationforconsideringMVDsurgery.
AllpatientswhoareplanningtoundergoanMVDoperationshould
havebrainmagneticresonanceimaging(MRI)oracomputed
tomography(CT)scantoexcludestructuralpathologiessuchasa
meningioma,acousticneuroma,andepidermoidtumors.OnhighresolutionT2Wimaging,avascularloopisoftenevident
compressingthetrigeminalnerve.
Evenifahigh-resolutionMRIdoesnotidentifyanoffendingvascular
loop,theconsiderationforaposteriorfossaexplorationisappropriate
ifthepatient’spainisconsistentwithtypicaltrigeminalneuralgia.I
haveroutinelyofferedMVDtopatientswhodonotharboran“MRI
evident”vascularloop,andIhaveoftenfoundcompressivearterial
loopsduringtheirsurgerywithdesirableoperativeresults.
Figure2:AnaxialT2WMRIdemonstratesavascularloop(red
arrow)causingcompressionoftherighttrigeminalnerveatits
cisternalsegment.
Figure3:Asmallrighttentorialmeningioma(leftimage)andCP
angleepidermoid(rightimage-diffusion)causingTN.Both
patientsunderwentresection.
DifferentialDiagnosis
Thereisanextensivedifferentialdiagnosisforfacialpain,and
severalelementsfromthepatient’shistoryandexaminationare
criticaltoconfirmingthediagnosisoftrigeminalneuralgia.
Dentalpathologies,temporomandibularjointpain,eyepain
(includingglaucoma,orbitalcellulitis,andtrauma),facialtraumaand
bonyfractures,tumorofthefacialbonesorthetrigeminalnerve,giant
cellarteritis,Tolosa-Huntsyndrome(idiopathicinflammationinor
aroundthecavernoussinus),trigeminalautonomiccephalgias(such
asclusterheadacheandparoxysmalhemicrania)andotherprimary
headachesyndromes(includingmigraineandtension-type
headache)cancausefacialpainandarenotamenabletoMVD.
Othercranialnervehyperactivitydisorderssuchasglossopharyngeal
neuralgiaandnervusintermediusneuralgiararelyco-existwith
trigeminalneuralgia.
Structuralpathologiessuchastumorsorcystsofthe
cerebellopontineangle,anddemyelinationorischemiclesionsofthe
brainstemshouldalsobeconsideredinthedifferentialdiagnosis.
Secondarycausesoftrigeminalneuralgiashouldbesoughtifanyof
thefollowingredflagsarepresent:significantsensorychanges,
deafnessorotherearproblems,difficultyachievingpaincontrol,poor
responsetocarbamazepinetherapy,historyofskinlesionsororal
lesionsthatcouldleadtoperineuralspread,isolatedophthalmic
trigeminalneuralgia,orbilateraltrigeminalneuralgia.These
manifestationsaresuggestiveofbenignandmalignantlesionsor
multiplesclerosis.
Importantly,Iquestionthediagnosisoftypicaltrigeminalneuralgiain
patientsyoungerthan<40years.Thesepatientsshouldundergoa
carefulinvestigationtoexcludeoverunderlyingcausesfortheirpain
includingmultiplesclerosis.Furthermore,bilateraltrigeminal
neuralgiaandahistoryofsinustraumaorsurgeryshouldalarmthe
surgeonregardingthesuitabilityofofferingMVDtothepatient.
MedicalTherapy
Thepreferreddrugformedicaltreatmentoftrigeminalneuralgiais
carbamazepine,ananticonvulsantmedication.Itinitiallyprovides
100%painrelieffor70%ofpatients.However,manypatientshave
sideeffectstothisdrug,mainlyaffectingthecentralnervoussystem
—suchasfatigueandpoorconcentration—andthereisahighriskof
druginteractions.
Theseconddrugofchoiceisoxcarbazepine,aketoderivativeof
carbamazepinethathasshownsimilarefficacyascarbamazepine,
butbettertolerabilityandfewerdruginteractions.Ifapatientdevelops
anallergytothesedrugs,internationalrecommendationssuggestthe
useofbaclofenandlamotrigine.
IndicationsforSurgery
Despitetheuseofneuropathicpainmedications,somepatients’pain
becomesrefractoryandtheyseekmoredurablesurgicaltreatment.
AcutefacialpainisnotamenabletoMVD,and,inmyopinion,the
patient’ssymptomsshouldatleastlast1yearwithaggressive
medicalinterventionbeforesurgeryisconsidered.Thisphilosophyis
justifiedsincethepainmaybeshort-livedinsomepatients.
Indicationsforsurgeryinclude,butarenotlimitedto,failureofor
adversesideeffectsfrommedicaltreatment.
Patientsolderthan70yearsorwithassociatedprohibitivemedical
morbidityshouldseeklessinvasivepercutaneousproceduressuch
asGasserianganglionballooncompression,radiofrequency,or
glycerolrhizotomy.Radiosurgeryisalsoanoptionbutthechanceof
painfreedomwithoutmedicationsisless.Youngerpatients(<40
years)shouldbecarefullyevaluatedbeforeinterventionbecause
disappointingrecurrenceofpaininthisgroupafteranyprocedureis
common.
Atypicalpainassociatedwithburningneuropathic,ratherthan
neuralgicpain,isnotamenabletoMVDsurgery,andmayactually
worsenaftersurgery.Occasionallypatientssufferfromboth
trigeminalneuralgiaandhemifacialspam,knownasticconvulsif.
SurgicalOptions
Surgicaloptionsfortrigeminalneuralgiafallintotwocategories:
1. Palliativedestructiveprocedures(oneofthreepercutaneous
proceduresorradiosurgery),and
2. PhysiologicnondestructiveMVD
Palliativedestructiveproceduresinvolvecontrolleddamagetothe
trigeminalnerverootwiththeaimofpainrelief.Theseprocedures
includeradiofrequencylesioning,glycerolrhizolysis,gasserian
ganglionballooncompressionrhizotomy,andstereotactic
radiosurgeryrhizotomy.Thesepalliativedestructiveprocedureshave
arecurrencerateofabout50%after3to5years.Incontrast,MVD
surgeryisassociatedwithanapproximately80%chanceofpain
freedomamongcarefullyselectedpatients.Thiseffectlastsformore
than10-20yearswitharecurrencerateof10%.
ForpatientswhocannotundergoanMVDoperation,Igenerally
preferballooncompressionrhizotomybecauseitiseasytoperform
andimmediatelyeffective.Ifthepatientharborscomorbiditiesthat
precludetheuseofgeneralanesthesiaandimmediatepainreliefis
notaconcern,Iofferradiosurgeryasareasonableoption.
Radiosurgeryoftendoesnotofferanimmediatepainreliefandmany
patientscontinuetorequireneuralgicmedicationsfortheirpain
control.
Iusethefollowingalgorithmicapproachforselectionofoperative
intervention.
PreoperativeConsiderations
Neuralgicpainmedicationsshouldbecontinuedintheperioperative
periodandtaperedoffifthepatientremainspainfreefor1weekafter
surgery.Idonotroutinelymonitorbrainstemauditoryevoked
responsesduringMVDoperationsaimedattrigeminalneuralgia,but
anovicesurgeonmayusethismodeofmonitoringduringhisorher
earlylearningcurve.Somepatientsmaysufferfromsevereacute
exacerbationoftheirtrigeminalneuralgia(statustrigeminus)andmay
requireurgentsurgeryduetoaninabilitytoeatordrink.
OperativeAnatomy
Thefollowingimagesdemonstratetherelevantoperativeanatomy.
Figure4:Exposureofcerebrovascularstructureswithintheleft
cerebellopontineanglethroughtheretromastoidapproach.
PleasenotethatCNVisdeeperwithintheoperativefieldand
furtherawayfromthesurgeon,whereastheCNVII/VIIIcomplex
ismoresuperficialandfollowsanobliqueinferiortoasuperior
trajectory.Thisanatomicalinformationshouldreadilyallow
identificationofthesenerves(ImagesCourtesyofALRhoton,
Jr).
Figure5:Relationshipbetweenthetrigeminalnerveandthe
superiorcerebellarartery(S.C.A.).Theposteriorrootentersthe
midponsbelowtheS.C.A.(A).TheS.C.A.loopsdownwardand
contactstheposteriortrigeminalrootatthepontinejunction(B).
Therostraltrunkloopsdownwardafterearlybifurcationand
indentstheuppersurfaceofthetrigeminalnerve(C).TheS.C.A.
bifurcatesaboveandawayfromthetrigeminalnerve(D)(Images
CourtesyofALRhoton,Jr).
MVDforTRIGEMINALNEURALGIA
TheoperativeanatomyexposedduringMVDsurgeryispristineand
pleasingtothesurgeon.Neurovascularstructuresaremicrosurgically
handledandpreservedinabloodlessdissectionfield,andthis
surgeryshouldbeassociatedwithminimalsideeffects.Iroutinely
employthesupralateralcerebellarapproachforMVDaimedat
trigeminalneuralgia.
Pleaserefertothechapteronextendedretromastoidcraniotomyfora
detaileddescriptionoftheapproachtotherootentryzoneofCNV.
Figure6:Theoperativecorridorsandtrajectoriesforaccessing
thecerebellopontineangle:Thesurgicalcorridorsfor
microvasculardecompressionfortrigeminalneuralgia
(supralateralcerebellarapproach-bluearrow)andhemifacial
spasm,andglossopharyngealneuralgia(infralateralcerebellar
orinfrafloccularapproach-greenarrow)areillustrated.
Mobilizationofthecerebelluminapurelymedialdirectionmust
beavoidedsincethisvectorofretractionwillbeparalleltothe
sensitiveCNVIII,increasingtheriskofhearingloss.
INTRADURALPROCEDURE
Theintraduralmicrosurgeryshouldbeexecutedinabloodless
manner.
Figure7:Inframedialcerebellarmobilizationjustbelowthe
petrous-tentorialjunction
Apieceofglove(cutslightlylargerthanthecottonoid)actsasa
rubberdamandprotectsthecerebellarhemispherefrompotential
injurycausedbyfrictionfromthecottonoid’ssurface.Iadvancethe
cottonoidparallelandjustinferiortothejunction(groove)ofthe
tentoriumandpetrousapex,towardthepetrousside.Identificationof
theselandmarksprevents1)theunintentionalexposure(and
resultanttear)ofthesupracerebellarbridgingveinssuperiorly,and2)
placementofretractiondirectlyagainsttheCNVII/VIIIcomplex
inferiorly.
Gentleinferomedialretractionofthecerebellarhemisphereexposes
thesuperiorpetrosalvein.Thearachnoidmembranesjustinferiorto
theveinaresharplyopenedandadditionalcerebrospinalfluid(CSF)
isreleased.However,thearachnoidmembraneoverthepetrosal
veinandCNVII/VIIIareleftintacttoprotectthesestructures.
Gentledynamicretraction,usingsuctionapparatus,isexertedover
thelateralcerebellumjustinferiortothesuperiorpetrosalvein,
placingthisveinunderslighttension.Oftenthismaneuverprovides
alltheworkingspaceneededcaudaltothevein.Iexceedinglyrarely
needtosacrificethesuperiorpetrosalvein.Strategicplacementof
thesuctionapparatuswillfacilitateselectiveexposureofthe
necessaryoperativeviewandworkinganglesatthelevelofCNV’s
rootentryzone,obviatinganeedforfixedrigidretractorsandthe
sacrificeofthesuperiorpetrosalvein.
IfIencounterbleedingfromthesuperiorpetrosalvein,Icoagulatethe
veinasfarawayfromtheduraandtentoriumaspossibleandas
closeaspossibletothecerebellarsurface.Thismaneuveravoids
retractionandavulsionoftheveinfromitspedicleattheduradueto
itsshrinkagebycoagulation.Ifexcessivevenousbleedingoccurs,
thepatient’sheadshouldbegentlyelevated;asuddencessationof
bleedingcouldbeasignofvenousairembolism.ApieceofGelfoam
coveredbyapieceofcottonoidsupplementedwithgentlepressure
willcontrolbleedingfromanavulsedendofthesuperiorpetrosal
sinusatthelevelofthetentorial-petrousjunction.
Figure8:CarefularachnoiddissectionandcorrectCN
identificationareparamount.Caremustbetakentopreserveall
ofthevesselsaroundthebrainstem.Deeperarachnoid
membranesshouldbecutwithcautionandfirstdissectedfree
oftheirentangledvesselswithafineball-tipprobe(topimage).
Thetrigeminalnerveislocateddeeperandmoremedialthanthe
CNVII/VIIIcomplex.CNVII/VIIIcomplexhasamoresuperficial
obliqueinferiororsuperiortrajectoryandshouldnotbe
mistakenforCNV(bottomimage).
Figure9:Carefulsharparachnoiddissectionexposesthe
trigeminalnerverootentryzone.
Themostcommonpatternofvascularcompressionbythesuperior
cerebellararteryisalongthesuperiorshoulderoftherootentryzone.
Thepatternsofneurovascularconflictintheorderoftheirincidence
areillustratedinthefollowingsketches:
Figure10:Variationsofneurovascularconflictleadingto
trigeminalneuralgia:Thenerveiscompressedbythemaintrunk
oftheSCA(A)anditsbranches(BandC)(leftupper);combined
compressionbytheSCAandAICA(rightupper).Thenerveis
sandwichedbetweenthetrigeminal(A)andpetrosal(B)veins
(leftlower).Thenerveiscompressedbythesuperiorpetrosal
vein(rightlower).SCA:superiorcerebellarartery,AICA:anterior
inferiorcerebellarartery.
Thearachnoidmembranescoveringtheregionofneurovascular
conflictareoftenthickened.Alackofadequatevisualizationand
inspectionaroundthesemembranesmayleadtoinadequate
decompression.Therefore,widecarefulopeningofthese
membranesisparamounttoallowcircumferentialvisualizationofany
neurovascularconflictalongtheCNVentryzone.
Thesmallworkingspacealongtheshoulderofthenervecoveredby
themotorrootsofCNVcanpreventsufficientdissectionand
exposure,leadingtoanincompletedecompression.Gentle
mobilizationofthenervewillallowathoroughcircumferential
inspectionalongthemedialandanterioraspectsoftherootentry
zone.
Itiscriticaltoemphasizethatmanypatientshavemultipleoffending
vessels,andidentificationofoneoffendingvesseldoesnotpreclude
thesearchforanotherone.Therootentryzonemustbethoroughly
andcircumferentiallyinspectedbeforeplacementoftheimplant.
Figure11:ImplantingpiecesofshreddedTeflonbetweenthe
nerveandtheoffendingvessel:Thearteryisgenerously
mobilizedandaseriesofsmallpiecesofshreddedTeflonare
placedalongtherootentryzoneandpushedaheadparallelto
thenerve(inset)topreventanyvascularconflictalongtheroot
entryzoneandentirecisternalsegmentofthenerve.
PiecesofshreddedTeflonimplantareusedtopreventcontact
betweenthenerveandsurroundingvessels.Theuseofunshredded
Teflonshouldbeavoidedbecauseoftheriskofimplantdisplacement
later.PiecesofTeflonareinsertedandpushedahead,alongthe
nerve.Thismaneuverallowsthesmallpiecesofimplanttoconform
totheshapeoftheartery,minimizingtheriskoftheirdelayed
displacement.
Figure12:IspecificallyinsertapieceofshreddedTeflonalong
theshoulderandmedialaxillaofthenervetopreventany
contactbetweenthevesselandtherootentryzoneor
brainstem.
Figure13:Thefinalconstructmobilizesthearteryalongits
entirelength.Thevesselismobilizedandgenerouslypadded
awayfromthenervetopreventanycontactwithneuraltissue.
Fibringluemaybeusedtoreinforcethisconstruct.Iavoid
excessiveTeflonimplantationtopreventTeflongranuloma
formation,whichmayplayaroleinpainrecurrence.
Centralmyelinmayextendfardistallyalongthetrigeminalnerve—as
farastheMeckel’scave—andthereforedecompressionshouldbe
completedalongtheentirelengthofthenerve.Anybony
protuberancealongthepetrousbonethatobstructsthesurgeon’s
viewshouldbedrilledawaytoallowinspectionoftheentirelengthof
thenerve.Allvesselsshouldbemobilizedalongthenerve:arteries
andlargeveinsshouldbemobilizedandpaddedandsmallerveins
coagulatedandcut.
Figure14:Classicneurovascularconflictthroughaleft
retromastoidcraniotomy:Thebluearrowhighlightsthesiteof
impressiononthenerve(N)(topimage).Theartery(A)andthe
potentialoffendingvein(V)weremobilizedusingpiecesof
Teflon(T)implant(bottomimage).
Figure15:Duralclosure
Closure
Iattemptawatertightduralclosureandmayuseapieceofmuscleto
plugsmalldefectsnotrepairablethroughprimaryclosure.ForMVD
operations,Idonotpersistonperformingawatertightduralclosure
becausetheseoperationsareassociatedwithaverylowrateofCSF
leakthroughtheincisionorthenose.Unliketumoroperations,the
MVDproceduresarepristineandassociatedwithasmallriskof
increasedCSFpressurespostoperatively.
Themastoidaircellsarerewaxedthoroughly.Icovertheepidural
spacewithapieceofGelfoam.Theboneflapisreplacedoramethyl
methacrylatecranioplastyisperformed.Andfinally,themuscleand
scalpareclosedinanatomicallayers.
NeurovascularConflict:Variations
Figure16:IntraoperativeimagesoffindingsduringMVD
procedures:Commonly,therearemultiplearterial(A)and
venous(V)offendingvessels,andoneoffendingartery(A)is
hiddenbehindthemotorroot(MR)ofthetrigeminalnerve(V)
(upperleftandrightimages).TheuseofshreddedTeflon(T)can
thoroughlymobilizethecompressivearterialandvenousloops
(middleleftimage).Hypertrophiedpetrousbone(HB)mayhidea
vascularloop(middlerightimage).Followingdrillingofthe
hypertrophiedpetrousbone,apreviouslyhiddenvascularloop
isvisible(lowerleftimage).Avenousloopcanbethesole
sourceofvascularconflict(lowerrightimage).
NegativeExploratorySurgery
Ifcarefulcircumferentialinspectionofthenervedoesnotdisclosean
offendingvessel,Iusefineforcepsandgentlypinchthetrigeminal
nerve.Thismaneuverleadstoarhizotomyandisofteneffectivefor
providingpaincontrol.Iperformthissamemaneuverinsomeofmy
MVDoperationswhenonlyavenousoffendingvesselispresent.
Ihavenotyetbeenconvincedthatvenouscompressioncanbethe
solepaingeneratorinTNandmoreoftenperformarhizotomyafter
thoroughinspectionandimplantationoftheTeflonaroundthevein.I
donotperformpartialnervetransectionbecauseofthepotentialrisk
ofdisablinganesthesiadolorosa.
PostoperativeConsiderations
Aftersurgery,patientsareusuallyadmittedtotheneurointensive
careunitovernightforobservationandthentransferredtotheregular
wardforacoupleofdaysbeforetheycanbedischargedhome.
Specialattentionshouldbepaidtohemodynamicparameters,
neurologicexamination,andwoundcare.
Steroidsareadministeredprophylacticallytopreventaseptic
meningitisandminimizepostoperativenauseaandheadaches.Ido
notroutinelyperformaheadCTpostoperatively.Preoperative
neuralgicpainmedicationsareweanedoffstarting1weekafter
surgeryifthepatientremainspainfree.Occasionally,thebenefitsof
surgerymaybedelayed,andpatientsshouldbeinformedofthis
possibledelayedeffecttoavoidearlydisappointment.
ManagementofPostoperativeComplications
Sensorineuralhearinglossisanexceedinglyrarecomplicationfrom
MVDsurgeryfortrigeminalneuralgia.Thishearinglossshouldbe
distinguishedfrommiddleeareffusion,whichisidentifiedasasense
offullnessintheearcausedbyfluidaccumulationinthemiddleear
fromopeningthemastoidaircellsduringcraniotomy.Thisfeelingof
earfullnessistemporary.
IfthepatientsuffersfromCSFrhinorrhea,wereturnhimorhertothe
operatingroomimmediatelyforrepackingofthemastoidaircellsand
inspectionoftheduralclosure.IfCSFleaksfromthewound,we
“oversew”theincisionandmayusealumbardrainfor72hoursifthe
initialincisionreinforcementisinadequate.Ifdrainagecontinues
whenthelumbardrainisdiscontinued,wereturnthepatienttothe
operatingroomforawatertightduralclosureandwoundrevision.
RepeatMVD
IconsiderrepeatMVDsurgeryanoptionforhealthypatientswho
harboredaconvincinglyoffensivearterialloopduringtheirinitial
surgery.Thesepatientsshouldhaveexperiencedarelativelylasting
periodofpainfreedomaftertheirinitialMVDoperation.IfIdidnotfind
aconvincingoffendingvascularloopduringthefirstsurgery,Ioffer
thepatientapercutaneousprocedurefortheirpainrecurrence.
Teflongranulomaisarelativelyunder-recognizedoccurrenceand
maybecausal,soexcessiveTeflonimplantationshouldbeavoided.
FinalThoughts
Percutaneousrhizotomyproceduresarereservedforolderpatients
withassociatedprohibitivemedicalcomorbidities.Intraneuralvessels
transectingthenervecancausetrigeminalneuralgia.Aggressive
manipulationsofthenervetodecompressintraneuralvesselsshould
beavoided.Suchaggressivemanipulationsmayleadtounpleasant
postoperativenumbnessandneuropathicpain.
Anoffendingneurovascularrelationshipmaychangeduringsurgery
withthepatient’sposition.IntraoperativeretractionandCSFdrainage
mayfurtheraltertheserelationships.Therefore,theoffendingvessel
mayactuallybefound1-2mmawayfromthetrueareaof
neurovascularconflict.
Thesurgeonshouldtakeadvantageofmicrosurgicaltechniques
whenperformingthisoperation.Inthepresenceofalternative
methodsoftherapy,includingpercutaneousproceduresthatcarry
relativelyminimalrisk,MVDoperationsshouldbeperformedwith
verylowrisktothepatient.
Andfinally,thereisalearningcurveinvolvedwiththisoperation,and
thesurgeonshouldremainalwayscriticalofhis/herperformanceand
aspireforaperfectresult.Thepatientswhohaveundergonethis
operationareamongthemostthankfulpatientsinmypracticeand
havemadethepracticeofneurosurgeryaprivilegeforme.
PearlsandPitfalls
Trigeminalneuralgiaischaracterizedbyparoxysmalattacksof
unilateral,sharp,stabbingfacialpain,withinoneormore
divisionsofthetrigeminalnerve,lasting<1secondto2
minutes,andprecipitatedbystimulationofcertaintriggerzones.
Differentialdiagnosisoftrigeminalneuralgiaincludesdisorders
ofdentition,temporomandibularjoint,andcertainheadache
syndromes.Theseconditionsshouldberuledoutwithan
extensivepatienthistoryanddetailedneurologicexamination.
Patientswithburningpain,facialnumbness,or(only)constant
painwithouttriggeringstimulimaybesufferingfromatypicalor
neuropathicpain,andnotneuralgicfacialpain.Theymaynot
becandidatesforaposteriorfossaexploratoryoperation;
judiciouspatientselectionforoperativeinterventionisadvised.
Manypatientshavemultipleoffendingvessels,and
identificationofoneoffendingvesseldoesnotprecludethe
searchforanotherone.Therootentryzonemustbe
circumferentiallyinspectedbeforeplacementoftheimplant.
Contributor:AqueelPabaney
DOI:https://doi.org/10.18791/nsatlas.v6.ch01.1
References
AmadorN,PollockBE.Repeatposteriorfossaexplorationfor
patientswithpersistentorrecurrentidiopathictrigeminal
neuralgia.JNeurosurg.2008;108:916-920
BarkerFG2nd,JannettaPJ,BissonetteDJ,LarkinsMV,JhoHD.The
long-termoutcomeofmicrovasculardecompressionfor
trigeminalneuralgia.NEnglJMed.1996;334:1077-1083.
Cohen-GadolAA.Microvasculardecompressionsurgeryfor
trigeminalneuralgiaandhemifacialspasm;nuancesofthe
techniquebasedonexperienceswith100patientsandreview
oftheliterature.ClinNeurolNeurosurg.2011;113:844-853.
GranitR,LeksellL,SkoglundCR.Fibreinteractionininjuredor
compressedregionofnerve.Brain.1944;67:125-140
HitotsumatsuT,MatsushimaT,InoueT.Microvascular
decompressionfortreatmentoftrigeminalneuralgia,hemifacial
spasm,andglossopharyngealneuralgia:threesurgical
approachvariations:technicalnote.Neurosurgery.
2003;53(6):1436-1441
HoweJF,CalvinWH,LoeserJD.Impulsesreflectedfromdorsalroot
ganglia.BrainRes.1976;116:139-144
JannettaPJ.Hemifacialspasm,in:SamiiM,JannettaPJ(eds):The
CranialNerves:Anatomy,Pathology,Pathophysiology,
Diagnosis,Treatment.Berlin:Sprinter-Verlag;1981.
MatsushimaT,InoueT,FukuiM.Arteriesincontactwiththecisternal
portionofthefacialnerveinautopsycases:Microsurgical
anatomyforneurovasculardecompressionsurgeryof
hemifacialspasm.SurgNeurol.1990;34:87-93.
MillerJP,AcarF,BurchielKJ.Classificationoftrigeminalneuralgia:
clinical,therapeutic,andprognosticimplicationsinaseriesof
144patientsundergoingmicrovasculardecompression.J
Neurosurg.2009;111:1231-1234.
MøllerAR.VascularcompressionofcranialnervesII:
Pathophysiology.NeurolRes.1999;21:439-443.
PrasadS,GalettaS.Trigeminalneuralgia:historicalnotesand
currentconcepts.Neurologist.2009;15(2):87-94
RhotonA.Thecerebellopontineangleandposteriorfossacranial
nervesbytheretrosigmoidapproach.Neurosurgery.
47(3):S93-129,2000
ZakrzewskaJM,LinskeyME.Trigeminalneuralgia.BrMedJ.2014
17;348:g474
RelatedVideos
ClassicVascularCompressionforTrigeminalNeuralgia
ClassicVascularCompression:TrigeminalNeuralgia
ShortcomingsoftheLinearIncisionforRetromastoidCraniotomy
PatientPositioningandIncisionforRetromastoidCraniotomy
RetromastoidBonyopening
RetromastoidCraniotomy
DuralOpening:RetromastoidCraniotomy
OpeningtheArachnoidMembranesduringRetromastoidCraniotomy
DuralClosure:RetromastoidCraniotomy
VariationofVascularCompressioninTrigeminalNeuralgia
VascularLoopattheAxillaoftheNerveinTrigeminalNeuralgia
DifficultMVDwithChallengingAnatomy
DolichoectaticBasilararteryandTrigeminalNeuralgia
MultipleOffendingVesselsinMVDforTrigeminalNeuralgia
MultipleOffendingVessels:TrigeminalNeuralgia
MicrosurgicalForcepsRhizotomyforQuestionableVenousornoVascular
Compression
VenousDecompression-TrigeminalNeuralgia
IntraneuralVeinsinMVD
IntraneuralVeinduringMVD:ManagementStrategies
PetrousHyperostosisduringMVD
RedoMVD:NuancesofTechnique
RepeatMVDforTrigeminalNeuralgia
TeflonGranulomaandMVD
BleedingfromBridgingVeinsandSuperiorPetrosalSinus
MVDforTrigeminalNeuralgia:UneditedSurgicalVideo
RetromastoidIncision:Details
VenousCompression:LargeBrainstemVein
VenousCompressioninTN:Strategies
MVDforTN-UnremarkableFindings
TrigeminalNeuralgia:PatientInterview
GrandRoundswithDr.Jannetta:MVDforTrigeminalNeuralgia
GrandRounds:RetromastoidCraniotomyandExpandingtheOperative
Corridor
GrandRounds:MVDforTrigeminalNeuralgiaandHemifacialSpasm:Pearls
andPitfalls
RhotonCollection:CerebellopontineAngleandFourthventricle
MVDforTrigeminalNeuralgia:FacingCerebellarSwelling
MVDforTrigeminalNeuralgia:TortuousArtery
MVDforTrigeminalNeuralgia:ChallengingArterialLoops
RelatedMaterials
OtherAtlases
MeyerAtlas:PercutaneousProceduresforTrigeminalNeuralgia
AvailableThroughtheAtlas
Thelong-termoutcomeofmicrovasculardecompressionfortrigemin...
Microvasculardecompressionofcranialnerves:Lessonslearnedaf...
PracticeParameter:Thediagnosticevaluationandtreatmentoftr...
A10-yearexperienceinthetreatmentoftrigeminalneuralgia.Co...
Mechanismoftrigeminalneuralgia:Anultrastructuralanalysisof...
AAN-EFNSguidelinesontrigeminalneuralgiamanagement
Evaluationofmicrovasculardecompressionandpartialsensoryrhi...
Microvasculardecompressionfortrigeminalneuralgia:Commentson...
Microvasculardecompressionfortrigeminalneuralgiacausedbyve...
Microvasculardecompressionforprimarytrigeminalneuralgia:Lon...
Demonstrationofneurovascularcompressionintrigeminalneuralgi...
Fullyendoscopicmicrovasculardecompressionfortrigeminalneura...
Atentorialslinginmicrovasculardecompressionfortrigeminaln...
Techniqueofmicrovasculardecompression:Technicalnote
Predictorsofoutcomeinsurgicallymanagedpatientswithtypical...
Bilateraltrigeminalneuralgia:A14-yearexperiencewithmicrova...
Successofmicrovasculardecompressionwithandwithoutpriorsur...
Neurovascularcompressionintrigeminalneuralgia:Aclinicaland...
Predictorsoflong-termsuccessaftermicrovasculardecompression...
Repeatposteriorfossaexplorationforpatientswithpersistento...
UnavailableThroughtheAtlas
MicrovasculardecompressionsurgeryintheUnitedStates,1996to...
Istherootentry/exitzoneimportantinmicrovascularcompressio...
Microvasculardecompressionfortrigeminalneuralgia.Afive-year...
Microvasculardecompressionfortrigeminalneuralgiaintheelder...
Repeatoperationsinfailedmicrovasculardecompressionfortrige...
Long-termresultsofmicrovasculardecompressionfortrigeminaln...
Acomparisonofpercutaneousradiofrequencytrigeminalneurolysis...
Findingsandlong-termresultsofsubsequentoperationsafterfai...
Operativefindingsandoutcomesofmicrovasculardecompressionfo...
Seriouscomplicationsofmicrovasculardecompressionoperationsf...
Patient'sassessmentofoutcomeafterthreesurgicalproceduresf...
Trigeminalneuralgiacausedbyvenouscompression
Adjunctiveuseofendoscopyduringposteriorfossasurgerytotre...
Microvasculardecompressionfortrigeminalneuralgia:Theimporta...
OtherMaterials
MVDfortrigeminalNeualgiaandHemifacialSpasm-PDF
GrandRoundsSlides