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ParietalCraniotomyLastUpdated:March11,2018
GeneralConsiderationsandOperativeAnatomy
Parietalcraniotomyisdesignedtoprovideanoperativeexposureofthemidtoposteriorhemispherewhilesparingthehighlyfunctionalanteriorlylocatedsensorimotorcorticesandtheposteriorlylocatedvisualcortex.Theapproachcanbedevisedtolateralandmesialparietallobelesionsaswellastointerhemisphericmedianorparamedianlesions.
Thevariationsofthiscorridorallowaccesstolesionsthroughthetranscorticalroute(throughthemorefunctionally“silent”superiorparietallobule)ortheinterhemisphericfissure.Theparasagittalveinsareoftenlessnumerousintheposteriorparietalregion,thereforeprovidinganopportunitytoreachdeeplesionsthroughtheinterhemispherictrajectory.
Therightornondominantparietallobe(seeWikipedia)isimplicatedinspatialawarenessandnavigation.Operativeinterventionsthatplacetheentirerightlobeatriskareassociatedwithhemibodyneglect.Thisneglectdoessignificantlyimproveovertime,butsomeresidualdisabilitypersists.
Theleftordominantparietallobe(seeWikipedia)isinvolvedinsymbolicfunctionsinlanguageandmathematics.Damagetotheleftloberesultsinproblemswithmathematics,longreading,writing,andunderstandingsymbols.Gerstmann'ssyndromeisassociatedwithlesionsinthedominantinferiorparietallobe,whereasBalint'ssyndrome(simultanagnosia,oculomotorapraxia,opticataxia)is
TheNeurosurgicalAtlas byAaronCohen-Gadol,M.D.
associatedwithbilaterallesions.
Theposteriorparietalcortexcanbesubdividedintothesuperiorparietallobule(Brodmannareas5+7)andtheinferiorparietallobule(39+40),separatedbytheintraparietalsulcus.
Figure1:Lateral(A),anterior(B),andposterior(C)viewsofthecerebrum.Notethelocationofthesuperiorandinferiorparietallobulesseparatedbytheintraparietalsulcus(C).Parasagittalbridgingveinsarevariableintheirsizeandlocationandplayan
importantroleindrainingtheparamedianhemispheres.Venouslakesalongthesuperiorsagittalsinuscanbeproblematiciftheduralopeningisextendedclosetothemidline(B)(ImagescourtesyofALRhoton,Jr).
Parietallobeveinsareclassifiedaccordingtosurfaceofdrainage(medialorlateralgroup)andtothedirectionofdrainage(ascendinggroup:draintothesuperiorsagittalsinusordescendinggroup:draintotheinferiorsagittalsinusorthesylvianfissure).Onthelateralsurfaceofthelobe,theascendingveinsarethecentral,postcentral,anteriorandposteriorparietalveins,whileparietosylvianveinsformthedescendinggroup.Onthemedialsurfaceofthelobe,theascendingveinsaretheparacentral,anteromedialandposteriomedialparietalveins.Finally,thedescendinggroupisformedbytheposteriorpericallosalveins.
ThelateralgroupalsoincludestheveinofTrolard,alsoknownassuperioranastomoticvein,whichcrossesthefrontalandparietallobesonitswayfromthesylvianfissuretothesuperiorsagittalsinus.ThemostcommonlocationoftheveinofTrolardisthepostcentralregion,butitcanalsobefoundatthecentralorprecentralregion.Thecorticalveinsdraindirectlytothesuperiorsagittalsinusormayjoinaparasagittalmeningealsinusorlacunaeinthedura,whichisthedrainagechannelofmeningealveinscommonlylocatedattheparietalandposteriorfrontalareas.
Figure2:Superior(upperleft),oblique(upperright)andposteriorviews(lowerrow)ofthecerebrumdemonstratingtheascendinggroupofveinsthatdraintheparietallobe(central,postcentral,anteriorandposteriorparietalveins).Ant.:anterior;Cent.:central;Mid.:middle;Front.:frontal;Par.:parietal;Post.:posterior;Sag.:sagittal;Str.:straight;Sup.:superior;Temp.:temporal;V.:vein.(Modifiedwithpermission,courtesyofALRhoton,Jr.)
IndicationsfortheApproach
Theparietalcraniotomyisusedforbothintra-andextra-axiallesionsoftheregion,includingneoplasmssuchasmetastases,gliomas,andmeningiomas,andvascularlesionssuchasarteriovenous
malformationsandcavernousmalformations.Theparietalinterhemisphericcorridorisusedtoapproachparafalcine,medialparietal,andspleniallesions.
Theparietalcraniotomyismostoftenperformedforconvexity,falcine,andparafalcinemeningiomas.Inthesecases,thepatentsuperiorsagittalsinusandtheassociateddrainingveinsareatriskandshouldbesparedtoavoiddisablingvenousinfarcts.Anydissectionaroundthetumorcapsuleshouldprotectenpassageveinsandarteries.Asdiscussedabove,vascularinjuriesintheparietallobecancausedeficitsinspatialawareness,sensorimotorfunction,andvisualprocessing,andalsoriskinjurytothenearbymotorcortexanddeepwhitemattertracts.
Parietalcraniotomycanalsobeusedtoapproachparamedian(periatrial)lesionsoftheatriumofthelateralventricle.Thetraditionalapproachtotheatriuminvolvesatranscorticalroutethroughthesuperiorparietallobulewithariskofdeficitsinspatialawarenesssuchasastereognosiaandspeechorvisualprocessing.Recentstudieshavesuggestedthat,dependingonthepatient’soccupationandactivities,qualityoflifemayindeedbesignificantlyimpactedbysuchdeficits.
Toavoidtheserisks,lesionsoftheatriumcanbeapproachedthroughaparamedianposteriorparietalcraniotomyandcontralateralinterhemispherictransfalcineapproachthroughtheprecuneus.Thisapproachprovidesalongerandmoretechnicallychallengingpathtotheatrium,butinvolveslesswhitemattertractdisruptionandbrainretraction.
PreoperativeConsiderations
Corticalstimulationmappingunder“awake,”“sleep”conditionsorphasereversalmappingmaybeconsideredforlocalizingthe
sensorimotorcortexforintraparenchymallesionssituatedalongtheanteriorparietalarea.Sinceearlyaccesstothebasalcisternsisnotavailableduringparietalcraniotomies,Ihavealowthresholdforplacingalumbardrain,evenforlargelesionswithsignificantmasseffect.Toavoidtranstentorialherniationinthecaseofmassivelesionswithmidlineshift,Iopenthedraintoremovecerebrospinalfluid(CSF)duringduralopening.ThisCSFdrainagesignificantlyassistswithbrainrelaxationandmanipulationofedematousbrain.
Iftheinterhemisphericcorridorisconsideredandlargeparasagittalveinsaresuspectedonpreoperativecontrast-enhancedmagneticresonance(MR)imaging,anMRorCTvenogramguidesthelocationofcraniotomy.Thevenogramwillalsoconfirmthepatencyofthesuperiorsagittalsinusinthepresenceofaninfiltratingmeningioma.Ifnumerousparasagittalveinsprohibittheipsilateralinterhemisphericcorridor,thecontralateralinterhemispherictransfalcineroutemaybeconsideredforparafalcinelesions.
Ifthetumorpartiallyinfiltratesthelumenofthevenoussinusandtheriskofairembolismissignificant,apreoperativecardiacdiagnosticworkupisnecessarytoexcludetheriskofaparadoxicalairembolism.AtransesophagealechocardiogramandtransthoracicDopplermaybeusedandthereshouldbealowthresholdofsuspicionforairembolismduringtheprocedure.
PARIETALCRANIOTOMY
Figure3:Thepatientispositionedthree-quartersproneontheoperatingroomtable.Thispositionprecludestheneedtoturnthepatient’sheadintoanonphysiologicposture,aswouldbethecaseifthepatientwerepositionedsupine.Moreover,thelateralpositionpromotestheextra-axiallesionstoremainreadilyaccessibleandgravityretractioncanbeexploitedforreachingtheinterhemisphericfissure.Thepatientmustbefirmlysecuredtothetablebecausetiltingthetableduringsurgerycanriskpatientdisplacement.
Thedegreesofthepatient’sheadturnandtiltaredependentontheexactlocationofthelesionwithrespecttothemidline,coronal,andlambdoidsutures.Forparafalcineparietallesions,thesideofthelesioncanbeplacedinthedependentpositiontousegravityretractionwhiletiltingtheheadawayfromthefloortopermitamoreergonomicsittingpositionfortheoperatorduringmicrosurgery.Similarly,whenapproachingtheatriumorperiatrialregionthroughthecontralateraltransfalcineroute,Iprefertoplacethepatientinathree-quarterspronepositionandthenormalhemisphereonthedependentside.
Anaxillaryrollsupportsthecontralateralaxilla.Theipsilateralshoulderisgentlypulledanteriorlyandinferiorlyandsecuredwithtapetokeepitoutoftheoperator’sworkingzone.Forconvexity
lesions,itisadvantageoustotiltthepatient’sheadenoughtoplacethelesionatthehighestpointintheoperativefield.
Figure4:Thepatient’sheadissecuredinaskullclamp.Theapplicationofaskullclampshouldsatisfycertainprinciples.First,alineconnectingthesinglepinwiththemidpointbetweentheoppositetwopins(swivelrockerarm)mustcrosstheequatorofthepatient’sheadtopreventskullclampfixationfailureandheadslippage.Second,thepinsshouldnotbeplacedclosetothevertex.Thispositioningoftheheadwillallowthegravitytoretractthedependenthemisphereandfacilitateamoreexpandedcorridorthroughtheinterhemispherictrajectory.Thisheadpositionisincontrasttothepositioninthenextsketchwhereacorticalorconvexitylesionisexposedandthelesionisplacedclosetothehighestpointoftheoperativefield.
Figure5:Variousincisionstyleshavebeenmarked.Thelinearincision(red)oftenprovidesampleexposure.Thehorseshoeincision(blue)isreservedforlargeconvexitymeningiomas.Theparamediancraniotomyisoutlined(black).IuseneuronavigationorpreoperativeMRvenogram/angiogramstopositionthecraniotomy.Thistoolassistswithlocalizingandavoidingparasagittalbridgingveins,especiallyforproceduresrequiringinterhemisphericdissection.
Figure6:Forlargelateralconvexitymeningiomasandgliomas,atraditionalhorseshoeincisionisreasonable.Theheadisrotateduntilthelesionisplacedatthesummitoftheoperativefield.
Figure7:Forparamedianinterhemisphericlesions,Iplacetwoburrholesoverthesuperiorsagittalsinusasguidedbyneuronavigation.Thesinusistypicallydeviatedtotherightofthesagittalsutureinmostpatients;themaximumdeviationisusuallynomorethan11mm.Earlyidentificationofthesinushelpsmeplanthesizeandlocationoftheboneflap.
APenfield#3dissectorisusedtogenerouslydissectbetweentheinnertableofthecalvariumandthewallofthesuperiorsagittalsinus.Ifthewallofthesinusisadherent,athirdburrholeshouldbeplaced;allburrholesshouldbereadilyincontinuitywithintheepiduralspace.Cerebrospinalfluiddrainagethroughthelumbardrainmobilizesthewallofthevenoussinusandtheduraawayfromthebone,thereforepreventingtheirinjurybythefootplateofthedrill.Thelastbonycutshouldbemadeoverthevenoussinus.Thismaneuver
allowsatimelyelevationoftheboneflapifbleedingisencounteredandaninjurytothesinushasoccured.
Uponelevationoftheboneflap,mildtomoderatebleedingfromthesinuswallmaybecontrolledwiththrombin-soakedgelfoamorSURGICELFibrillar(Somerville,NJ).Thelatterisleftinplaceuntouchedduringclosure.PleaserefertothechapterontheRepairofDuralVenousSinusInjuryinthePrinciplesofCranialSurgeryVolumeforfurtherdetailsregardingmanaginginjuriestothesinus.
Figure8:Forconvexityorintraparenchymallesions,theduraisopenedcircumferentiallyaroundthetumorwitha2-cmmarginawayfromthecontrast-enhancingregionasguidedbyintraoperativenavigation(leftimage).
IfIplantoreachtheinterhemisphericspace(rightimage),Iopenthedurainacurvilinearfashionandcreateaduralflapbasedonthesuperiorsagittalsinus.Careistakentoavoidinjuringthelargedrainingveins.Occasionally,asmalldrainingveinmayneedtobesacrificed.Ifaparasagittalveinisencountereddrainingintothesinus,theduralopeningmustbeadjustedto
protectthevein’sinletintothesinus(leftimage,inset).
Notethatthebridgingveinsmoveintheposterior-to-anteriordirectiontodrainintothesinusandmayhavemultipletributaries.Paramedianextensionsofthesuperiorsagittalsinusorvenouslakesarefrequentlyencounteredinthisregion.Theirpresencemaylimitopeningtheduraclosetothemidlineandrestricttheinterhemisphericexposure.Inthissituation,theduralincisionnearthemidlinemaybeextendedparallelratherthanperpendiculartothevenoussinus.
Becauseofunpredictablelateralreachofthevenouslakes,asmalltearalongthelateralwallofthesinuscanbeencounteredduringtheparamedianduralincision.Thetearshouldbeclosedusingfinesutures.Bipolarcoagulationleadstoshrinkageoftheduraandexpansionofthetear.
Figure9:Toreachtheparafalcinespace,Ireleasetheveinsthroughtheirarachnoidadhesionsanduntethertheminpreparationfortheirmobilization.Thismaneuvermaybetediousbecausethearachnoidmembranescanbethickandhighly
adherent.CSFlumbardrainageaffordsearlymobilizationofthehemisphereawayfromthemidlineandfalx(leftimage).
Iplaceretractionsutureswithinthesuperiorfalxandgentlymobilizeandrotatethesuperiorsagittalsinus,therebyexpandingtheoperativecorridorandworkingangleswithintheinterhemisphericspace(rightimage).
Figure10:Thenextstepsofmicrodissectionwithintheinterhemisphericcorridorcannowbegin.Theparasagittalveinsshouldnotbeplacedundersignificanttension.
Figure11:Toreachthecontralateralperiatrialregion,IcreateaT-shapedincisionwithinthefalx(leftimage).Thefalcineflapsarereflectedandheldinplacewithretractionsutures.Acorticotomythroughthecontralateralprecuneusandobliquewhitematterdissectionwithinthemedialcontralateralhemisphereallowentryintotheatrium(greenarrow,rightimage).Divisionofthefalx,cortex,andwhitematterareperformedusingnavigation.
Closure
Oncethepathologyishandled,hemostasisisachievedandthesurgeon’sattentionturnstoclosure.Iftheventricleisentered,aventriculardrainagecathetermaybeplacedtocleardebriswithintheventriclesduringtheimmediatepostoperativeperiod.
Idonotroutinelyclosethedurainawatertightfashionforsupratentorialcraniotomies.Iavoidallograftduralsubstitutesfortheirriskofasepticinflammationorinfection.Duralclosureshouldnot“kink”orcompromiseflowwithintheparasagittalveins.
PearlsandPitfalls
Thethree-quarterspronepositionisareasonableoptionforparietallesionsasitfacilitatesaccesstotheipsilaterallesion
andallowsgravityretractiontoexpandtheinterhemisphericoperativecorridor.Injurytothesuperiorsagittalsinusduringaparamediancraniotomyshouldbepreventedatallcosts.Keepalowthresholdofsuspicionforairembolism.Parasagittalbridgingveinsoftendonotreceivetherespecttheydeserve.Avenousinfractioninthisregioncanbecatastrophic.
Contributor:MarcusA.Acioly,MD,PhD
DOI:https://doi.org/10.18791/nsatlas.v2.ch03
References
Al-MeftyO.OperativeAtlasofMeningiomas.Philadelphia:Lippincott-Raven,1998.
AlverniaJE,LanzinoG,MelgarM,SindouMP,MertensP.Isexposureofthesuperiorsagittalsinusnecessaryintheinterhemisphericapproach?Neurosurgery.2009;65(5):962-965.
RazaS,Quinones-HinojosaA,OliviA.Convexitymeningiomas,inDeMonteF,McDermottM,Al-MeftyO(eds):Al-Mefty’s
Meningiomas,2nded.NewYork:ThiemeMedicalPublishers,2011.
RhotonALJr:Thecerebrum.Neurosurgery.2002;51(Suppl1):S1-51.
RhotonALJr.Thecerebralveins.Neurosurgery.2002;51(4Suppl):S159-205.
SteinmetM,KrishnaneyA,LeeJ.Surgicalmanagementofconvexity,eningiomasInBadieB.(ed):NeurosurgicalOperativeAtlas:
Neuro-oncology,2nded.RollingMeadows,IL:ThiemeMedicalPublishersandtheAmericanAssociationofNeurologicalSurgeons,2007.
TewJMJr,vanLoverenHR.AtlasofOperativeMicroneurosurgery,Vol1.Philadelphia:Saunders,1994.
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