Anterior Choroidal Artery Aneurysm...Anterior Choroidal Artery Aneurysm Aneurysms of the posterior...
Transcript of Anterior Choroidal Artery Aneurysm...Anterior Choroidal Artery Aneurysm Aneurysms of the posterior...
AnteriorChoroidalArteryAneurysm
Aneurysmsoftheposteriorwalloftheinternalcarotidartery(ICA,)namelytheanteriorchoroidalartery(AChA)andposteriorcommunicatingartery(PCoA)aneurysms,representthemostcommonsiteforintracranialaneurysms(upto35%oftotalaneurysms.)
TheAChAarisesafewmillimetersdistalandslightlylateraltotheoriginofthePCoAfromthesupraclinoidICA.Ithasaslightlysmallercaliber,canimmediatelybranchafteritsorigin,andsuppliesveryimportantterritories,suchastheposteriorlimboftheinternalcapsule,basalganglia,opticapparatus,cerebralpeduncle,lateralgeniculatebody,andlimbicsystem.
Thereisminimalcollateralsupportforthisvessel,anditspreservationisofparamountimportanceduringclipligationofposteriorcarotidwallaneurysms.Thedistalendsofthebladesshouldnotcompromisetheintegrityofthisvessel,whichisoftenserpentineandhidden,drapingovertheAChAaneurysmdome.
MostAChAaneurysmspresentwithsuprasellarandambiencisternsubarachnoidhemorrhage(SAH.)Theyrarelypresentwithintracerebral/intaventricularhemorrhageoroculomotornervedysfunction.
Inthischapter,IwilldescribetheoperativetechniquesforclipligationofAChAaneurysms.Thesimilarprocedureforposteriorcommunicatingarteryaneurysmsisdescribedinitsowndedicatedchapter.Ihaveabbreviatedtherelevantcontenthereandencourage
TheNeurosurgicalAtlas byAaronCohen-Gadol,M.D.
youtorefertothechapteronPCoAaneurysmsbeforeproceedingwiththefollowingdiscussion.
IndicationsforSurgery
ModerntreatmentoptionsforAChAaneurysmsincludeobservation,endovasculartreatment,ormicrosurgicalclipligation.Observationisareasonableoptionforsmallunrupturedaneurysmsorlargeronesinolderpatients(>75yearsold.)Patientswithunderlyingmedicalproblemsthataffecttheirsurvivalmayalsobetreatedconservatively.
AswithPCoAaneurysms,patientswithsignificantlifeexpectancyshouldbeconsideredformoreaggressiveinterventionthanthosewithothersmallanteriorcirculationaneurysms.Aneurysmschosenforobservationshouldbereconsideredforinterventioniftheyincreaseinsizeorcauseanoculomotornervepalsy.
TheAChAfrequentlyemergesfromtheneckoftheaneurysm.Thisneckconfigurationcomplicatesendovasculartherapyandplacesthesmall-caliberAChAatriskduringcoildeployment.Thus,microsurgicalclippingcontinuestoplayanimportantroleinthemanagementofAChAaneurysmsthatrequirerelativelyminimalmicrodissectionorbrainretraction.
Calcifiedaneurysms,identifiedonCTA,arebestmanagedviaendovascularmethodsbecauseclipligationhasareasonablelikelihoodofcompromisingtheoriginsoftheAChAandtheICAbythethickcollapsedwallsoftheparentvesselsafterclipdeployment.
PreoperativeConsiderations
InitialradiologicevaluationoftheseaneurysmsgenerallyincludeseitheraconventionalcatheterarteriographyorCT/MRangiography.CTangiography(CTA)hasbecomethemainstreaminitialstudyforevaluationbecauseofthefinevasculardetailitprovides.Moreover,it
showsthesurroundingskullbaseanatomy,includingthelocationoftheanteriorandposteriorclinoidprocesses,withrespecttotheaneurysmneck.
BonewindowingofaCTscancanrevealthepresenceofamiddleclinoidprocess,whichisrelevantwhenthesurgeonispreparingforproximalcontrol.Araresubsetoftheseaneurysmsprojectlaterallyintothetemporallobe.Thisanatomicvariationwarnstheoperatoragainstearlytemporalloberetractioninthesettingofarupturedaneurysmuntilproximalcontrolisreliablyestablished.
Figure1:AtypicalAChAaneurysmisshownoriginatingfromthejunctionoftheICAandAChA(leftimage).Theaneurysmarisingfromtheposteriorcarotidwall,justdistaltothePCoAoriginisconsideredanAChAaneurysmandistypicallymorelaterallyprojectingthanPCoAaneurysms.ClipligationiseffectiveforcompleteexclusionoftheaneurysmwhilemaintainingthepatencyoftheAChA(rightimage).
Intraoperativeneurophysiologicmonitoring,includingsomatosensoryandmotorevokedpotentials,canmonitorthepatient’stolerancetotemporaryocclusionandwarnthesurgeonaboutpotentiallyinvisiblecompromiseoftheperforatingvesselsafterclipligation.ThismonitoringstrategyisespeciallybeneficialfortheAChAarteryand
itsassociatedperforatingvesselsthatsupplythemotorsystem.
OperativeAnatomy
TheAChAarisesslightlymorelaterallythanthePCoAfromtheposteriorwallofthesupraclinoidICA.Identificationofbothvesselsattheposteriorcarotidwallisimportantbeforeoperativemanipulationbegins.
TheAChAmayconsistofuptothreebranches.Itcoursesthroughthecruralcisternenroutetoitsentrypointintothetemporalhornofthelateralventricle,providingseveralcriticalperforatorsalongitsway.Therefore,theAChAisdividedintocisternalandplexalsegments.
TheAChAclassicallyarisesjustdistaltothePCoA,butitcanoccasionallyarisemoredistally,eitherfromtheICAbifurcationortheM1segment.ItcanevenemergefromthePCoAitself.BoththePCoAandAChAprojectposteriorlyandmediallyfromthedorsalaspectoftheICA.Theanterior-to-posteriorsurgicalviewofthepterionalapproachplacesthesevesselscoursingawayfromthesurgeon’slineofsight.AllthesurgeonseesisaknuckleoftheveryproximalarteryatitsoriginbeforeitbecomeshiddenbehindtheICA.
Figure2:AlateralnonoperativeviewacrosstheposteriorICAdemonstratestheanatomicrelationshipsbetweenthePCoA(mobilizedwiththerightdissector,)itsperforatingvessels,andtheAChA(inbrightred.)Theoculomotornerveisvisible(imagecourtesyofALRhoton,Jr.)
Figure3:AviewoftheAChA(brightred)throughtherighttransventriculartranschoroidalapproachisshown.Notetheedgeofthetentoriumandtheoculomotornerveforanatomicorientation(imagecourtesyofALRhoton,Jr.)
ThereareinconsistentanastomosesbetweenthePCoAandAChAalongthelateralgeniculatebody.ThisfindingexplainsthevariabilityinthesizeoftheischemicterritoriescausedbyAChAocclusion.
MICROSURGICALCLIPLIGATIONOFANTERIORCHOROIDALARTERYANEURYSMS
PleaserefertotheCranialApproachesvolumefordescriptionoftheextendedpterionalcraniotomythatissuitableforalmostallAChAaneurysms.Aposterolateralorbitotomymaybeaddedforlarge
aneurysms.Inthissection,Ielaborateonthespecificsofthepterionalapproachasitpertainstotheexposureofthisaneurysm.
Themainobjectivesofpatientpositioningaretopreventthetemporallobefromobstructingyourdissectionoftheaneurysmwhileexploitinggravitytomovethefrontallobeawayfromtheanteriorcranialfossa.Thesemaneuversexpandtheposteromedialsubfrontaloperativecorridorandareaccomplishedbyextendingthepatient’sheadandlimitingitsrotationto20degrees.
Thesphenoidwingmustbeaggressivelydrilleduntilthesuperiororbitalfissureisreached.Themostmedialextentofthewingisthemostimportantbecauseitcoversthecarotidcistern.Ifthislastobstructionisnotremoved,substantiallymorefrontallobeelevationisneededtoexposethecistern.Theroofoftheorbitisalsodrilledsothataflatoperativetrajectoryovertheorbitisavailable.
Figure4:Schematicrepresentationoftheposteriorsubfrontaloperativepathway(greenarrow)towardtheAChAaneurysm.ThispathwayispossibleviaaproximalSylvianfissuresplit,leadingdirectlytotheanteriorandlateralaspectsofthesupraclinoidICA.EarlyexposureoftheproximalICAwithouttemporalloberetractionisnecessarytoavoidprematuresacrupture.
INTRADURALPROCEDURE
InitialExposure
Therearethreemaingoalsthatmustbeaccomplishedbeforetheaneurysmcanbedirectlyhandled.
ThefirstgoalisaproximalSylvianfissuresplit.
Thesecondgoalismobilizationofthefrontallobeanddissectionofitsarachnoidbandsoverthechiasmandfloorofthefrontalfossa.
ThethirdgoalisestablishingproximalcontroloverthesupraclinoidICA.Theaneurysmmustbeexposedsolelyviafrontalloberetraction.Thecruxoftheinitialexposureisfreeinguptheposteriorsubfrontallobesothatitcanbesafelyandgentlymobilizedwithoutanytransmissionofforcetotheaneurysmdome.
Figure5:Theinitialintraduralexposureisillustrated.Adequatesphenoidwingremovalisevidentwhentheduracanbemobilizedflatovertheorbitalroofandalongtheanterioredgeofthecraniotomy.
Theinitialstepsoftheintraduralprocedure,includingtheexposureoftheposteriorcarotidwall,arediscussedinthePosteriorCommunicatingArteryAneurysmchapter.ThefollowingparagraphsspecificallyrefertoAChAaneurysms.
Figure6:Theposterolateralwalloftheleftcarotidarteryisexposed.TheoriginofthePCoAisapparentonlyasasmallknuckleafewmillimetersinferiortotheaneurysmsac.TemporaryclippingoftheICAisoftennecessary,especiallyforrupturedaneurysms,duringthenextstepsofneckdissection.
Withthebrainrelaxed,thefrontallobecompletelyreleased,andproximalcontrolsecured,thefocusofdissectioncannowshifttowardthecircumdissectionoftheneck,themostcriticalpartoftheoperation.Applicationoftheclipisarelativelystraightforwardaffair.Thecreationofspacefortheclipbladesisthechallenge,andpreclippingdissectionrequiressurgicalintellectandappreciationofthree-dimensional(3D)anatomybasedonadetailedstudyofpreoperativeimages.
AneurysmDissection
TheaneurysmsacandAChAtravelawayfromtheoperator.Asaresult,onlyasmallknuckle,representingtheoriginoftheAChA,isvisible.IprefertousebriefperiodsoftemporaryproximalICAocclusion;IdonotbelieveetomidateburstsuppressionisnecessaryduringtemporaryproximalICAocclusionifcollateralsupportisrobustviaafunctionalcircleofWillis.Thelossofturgorintheaneurysmremarkablyfacilitatesitsneckdissectionduringhigh-riskmaneuvers.
TheneckdissectionproceedsbetweenthisknuckleandtheproximalneckoftheaneurysmandproceedsdistallyalongthelateralaspectoftheICA.Althoughthismaneuvercanbetedious,sharpdissectionunderhighmagnificationwillalmostalwaysfindaplanebetweentheAChAandtheaneurysmneck.
Onlyafewmillimetersoftheaneurysmneckisisolated,justenoughtoplaceaclipblade.Thereisnoneedtodissectmoreofthearteryordissectoutontotheaneurysmdome.IftheAChAcannotbereadilyidentified,theICAcanbegentlyretractedmediallytoallowthesurgeontoexploretheoriginofthearterymoredistallyalongtheneck.
Figure7:ThedistalneckisthespacebetweentheICAandtheaneurysm;similarmicrosurgicalprinciplesmentionedaboveapplytothisspaceaswell.TheAChAissometimesadherenttothemidbodyorfundusoftheaneurysm.TemporaryproximalICAclippingisespeciallybeneficialtosoftentheaneurysm,allowingdissectionoftheAChAawayfromtheneckwithout
placingtheAChAatrisk.OncetheproximalanddistalneckshavebeendissectedandthecoursesofthePCoAandAChAidentified,definitiveclippingoftheaneurysmcancommence.
WithtemporaryICAocclusioninplace,Imobilizetheproximalanddistalneckanddissecttheportionoftheneckthatisturningawayfrommylineofsight,ensuringthatIcanseewheretheneckisturningaroundtoformitsmedialborderwithrespecttowalloftheICA.Thismaneuverisimperativebecausealackofunderstandingofthe3DneckanatomywillleadtheoperatortoapplytheclipatawrongangleawayfromtheICAaxis,partiallyclippingtheneckandprecipitatinganintraoperativerupture.
Completingdissectionblindlyusingtheclipbladesand“guessingatthedeeperaneurysmneckborders”arerecipesfordisaster.Thesenovicemaneuversarearesultofanervoussurgeonwhoisallowinghisorheremotionstocontrolmicrosurgery.
Inrupturedaneurysmcases,thesubarachnoidclotaroundthedomeisleftundisturbeduntiltheaneurysmissecured.ThedissectionshouldbelimitedalongtheposterolateralwallofthesupraclinoidICAandtheneck;theoperatorshouldnotwanderandunintentionallypunctureoruncovertheaneurysmdome.Thesequenceofdissectionshouldproceedmethodicallyfromproximaltodistal,revealingtheknuckleofthePCoAorigin,theproximalneckandAChAorigin,thesacitself,thedistalneckandthenthedistalsectionoftheAChAawayfromthepathwayoftheclipblades.Next,theclipisdeployed.
ClipApplication
MostAChAaneurysmsaresmallandhaverelativelynarrownecks.Iligatetheseaneurysmswithabayonetedsimplestraightclip,angledperpendiculartotheICAaxiswiththetipspointinglaterally.AlthoughanaccordioneffectcanpotentiallycausestenosisoftheICAlumen,
thisislessofaconcerniftheaneurysmhasanarrowneck.
Figure8:TheaneurysmcanbebestmanipulatedanddissectedunderbriefperiodsoftemporaryICAocclusion.Clipapplicationfollows;theoriginoftheAChAshouldnotbecompromised.Invariably,asmallneckremnantisnecessarytopreservetheAChA’sorigin.BayonetedclipsareidealforallowingmetovisualizetheoriginoftheAChAaroundthebulkoftheclipappliers.ThelowerphotodemonstratesoneoftheperforatingbranchesoftheAChA(arrow)justdistaltotheblades.
Figure9:TheclipwasdeployedandtheAChA(redarrows)atthetipofthebladeswasinspectedforitspatencyviaintraoperativefluorescenceangiogram.
Astheclipbladesaregraduallyclosed,attentionisfocusedonthetipsofthebladestoensurethattheyarefreeoftheAChAasitturnsaroundthedome.
Figure10:Oncetheclipisplaced,IgentlyrotatethebladestoensurethatthebladesarenotcompromisinganysegmentoftheAChA.Thisinspectioniscrucialforavoidingcomplications;cliprepositioningmaybenecessary.ThearrowontheupperphotopointsattheoriginoftheAChAbeforeclipdeployment,whilethearrowinthelowerintraoperativephotopointsatthemoredistalrouteofthevesselaroundtheaneurysm.
FluorescencevideoangiogramhassomelimitationsforevaluationofAChAaneurysmsaftertheirligation.Mostoften,becauseofthedeepoperativecorridorandthehiddenaneurysm,enoughexcitationlightcannotreachthefluorescentagentwithinthesacforadequateemissionsignals.Thisphenomenonleadstofalsenegativeresults.Therefore,punctureofthedomeorintraoperativecatheterangiogramisnecessaryforconfirmationofaneurysmexclusion.
AdditionalConsiderationsandAneurysmVariations
Iprefertouseasimplebayonettedstraightclip.Ifthisisnotanatomicallyfeasible,asinthecaseofaposteriorly-projectingAChAaneurysms,Iuseanangledfenestratedclip,encasingtheICA.Thisconstructavoids“dogears”andismosteffectiveforcollapsingthe
neck.Furthermore,delayedclipdisplacementisunlikely.
Figure11:Iclipposteriorly-projectingAChAaneurysmsusinganangledfenestratedclip.ThefenestrationencirclestheICA.TheAChAisseenjustdistaltotheheeloftheclip,proximaltotheICAbifurcation.ThisconstructdoesnotroutinelyrequireisolationoftheAChAincaseofitsattachmenttothedome.
Figure12:Theupperintraoperativephotosdemonstratetheconfigurationofaright-sidedposteriorlyprojectingAChAaneurysm.Thetipoftheball-tippeddissectorpointsattheoriginoftheAChA(upperimage).TheangledfenestratedclipwaseffectivewhileobviatingtheneedforsignificantmanipulationoftheAChA(middleimage).IntraoperativefluorescenceangiographydemonstratedpatencyoftheAChA(arrow)andexclusionoftheaneurysm.
Figure13:AnoperativeviewofafusiformAChAaneurysmwithoutadefinableneckisdemonstrated.Thisaneurysmisnotamenabletoclipligation.Wrappingtheaneurysmwithmuslinisthemostreasonablestrategyinthiscase.TheAChAshouldnotbesacrificed.
PostoperativeConsiderations
InadvertentsacrificeoftheAChAleadstoananteriorchoroidalsyndromethatconsistsofcontralateralhemiplegia,hemianesthesia,andhemianopsia.ThissyndromeisverydisablingandnearlyalwaystheresultoftrappingtheAChAorperforatorsarisingfromthePCoAandAChA.Everyeffortshouldbemadetoavoidthisunfortunateoutcome.
Standardpostoperativecareisused.Anticonvulsantsarerecommendedandtaperedoffaboutoneweekaftersurgery.
PearlsandPitfalls
ThetakeoffoftheAChAcanbemistakenfortheproximalneckoftheaneurysm.ThisanatomymustbecarefullydissectedtoavoidocclusionoftheAChAduringaneurysmclipping.
TheproximalsegmentoftheAChAtypicallydrapesovertheaneurysmsac.CarefulmicrodissectionisnecessarytosavetheAChAduringclipdeployment.
DOI:http://dx.doi.org/10.18791/nsatlas.v3.ch01.11
References
LawtonM.SevenAneurysms:TenetsandTechniquesforClipping.NewYork:ThiemeMedicalPublishers,2011
SamsonD,BatjerHH.Aneurysmsoftheposteriorinternalcarotidwall,in:IntracranialAneurysmSurgery:Techniques.MountKisco,NY:FuturaPublishingCompany,1990.
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