Temporal/SubtemporalCraniotomyLastUpdated:March11,2018

GeneralConsiderations

Temporalcraniotomyisasimpleapproachthathasvastapplicabilitytointra-axialandextra-axialpathologies.Thesubtemporalapproachprovidesawideoperativecorridortothefloorofthemiddlefossaandupperpetroclivalterritoriesandtheirassociatedcisterns.Morespecifically,thiscorridorreachestheanteriorupperbrainstemthroughtheanteriorpetrosectomy.

Thelateralneocorticaltemporallobeandmorespecificallythedominantsuperiorandposteriorpartsofthemiddletemporalgyriaffectimportantfunctionssuchaslanguage.Theexactfunctionoftheanteriormiddletemporalgyrusisunknown,butitmaybeinvolvedinprocessessuchascontemplatingdistance,recognitionofknownfaces,andaccessingwordmeaningwhilereading(seeWikipedia).

Theinferiortemporalgyrusisinvolvedwithvisualprocessing,associatedwiththerepresentationofcomplexobjectfeatures,suchasglobalshape.Itmayalsoprocessfaceperceptionandtherecognitionofnumbers(seeWikipedia).

IndicationsfortheProcedure

Temporalcraniotomyisbeneficialforresectionofmidtoposteriorintraparenchymalandconvexitytemporallobetumors.Thisroutealsoaffordsaccesstomidhippocampallesionsthroughthetranssulcalapproachandreacheslateralthalamictumorsandbasalcisternsthroughthetranscorticaltransventriculartranschoroidal

TheNeurosurgicalAtlas byAaronCohen-Gadol,M.D.

pathway.TheexposureoftheSylvianfissureislimited.

Asubtemporalcraniotomyismoreversatileandexposesvariousneoplasticandtumorousintraduralandextraduralpathologiesofthemiddlefossafloor,anteriorbasalcisterns,andupperclivus.Middlefossameningiomas,smallacoustictumorsandtrigeminalschwannomas,low-lyingbasilarcaput/upperbasilararteryaneurysms,andupperpetroclivalmeningiomas(throughtheanteriorpetrosalapproach)aresomeexamplesoflesionsreadilyreachedviathisroute.

Inaddition,thisapproachallowsrepairofthesuperiorsemicircularcanaldehiscence.Thesubtemporalapproachcanbeusedincombinationwiththeextendedpterionalrouteforaccesstocomplexvascularabnormalitiesoftheinterpeduncularcisternsandfibrousmulticompartmentmenigniomasfillingthemedialincisuralandparachiasmaticspace.

PreoperativeConsiderations

ThelocationoftheveinofLabbeanditsdrainagesiteintothetransversesinusshouldbeestimatedpreoperativelybasedonmagneticresonance(MR)venogramforcasesthatrequireposteriorsubtemporalexposure.Thisdrainagesiteisabout1cmsuperiortoalineparalleltothesuperiorborderofthezygomaticarchand2to5cm(mean2.9cm)posteriortotheopeningoftheexternalauditorymeatus.

Thedisplacementofotherarterialandvenousstructuresalongthemedialtentoriumshouldbedefined.Thepotentialneedforacombinedapproachtotumorswithbothsupratentorialandinfratentorialextensionsshouldbeplannedpreoperatively.

Mannitol(1g/Kg)shouldbeadministeredduringskinincisionifa

“tight”brainisexpected.Ifcorticalstimulationforfunctionalmappingiscontemplated,coldlactatedRinger’ssolutionshouldbeavailable.Inexpectationofasubtemporalapproach,Igenerallyplacealumbardrainformostpatients,regardlessoftheirtumorsize,inordertominimizetheriskoftemporalloberetractioninjuryduringintraduralorextraduralelevationofthelobe.Sincethebasalcisternsarenotreacheduntilafterelevationofthelobe,alternativeroutesforearlycerebrospinalfluid(CSF)drainageisbeneficial.

Thesurgeonispositionedattheheadoftheoperatingroomtablewiththesurgicaltechnicianateithertherightorleft,dependingonthehandednessofthesurgeon.Theanesthesiologistmaybesituatedatthefootofthetable,allowingmoreworkingroomfortheassistantandmicroscopeifnecessary.

OperativeAnatomy

Dependingontheskinincision,thesuperficialtemporalarterymayormaynotbeinvolvedinexecutionoftheapproach.Thearterytypicallyrunsonefinger-breadthanteriortothetragusandbifurcatesintoitsfrontalandparietalbranchesapproximately5cmsuperiortothezygoma.Thetemporalbranchofthefacialnerveislocatedmoreanteriorlyoverthezygomaandsuperficialtothetwolayersoftheanteriorsuperficialtemporalfascia.

Therootofthezygomaisanessentiallandmarktodefinethelevelofthemiddlefossafloor.Thislandmarkshouldbeusedforplanningtheinitialburrholeandsubsequentcraniotomy.PreservationoftheveinofLabbeisessential.Itsanatomicrelationshipsareillustratedinthefollowingimages.

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Figure1:RelationshipofthecranialsuturestothetemporallobeandSylvianfissure(Topimage).NotethesquamosalsutureoverlyingtheSylvianfissure,inadditiontodelineatingthesuperiorlimitofthetemporallobe.Also,theimportanceofperformingthecraniectomytothelevelofthezygomaticarchisillustratedinthisdissection.Corticaltopographyofthetemporallobeisillustratedintheotherimages(ImagescourtesyofALRhoton,Jr).

Figure2:VenousanatomyofSylvianandposteriortemporalregions.TheveinofLabberunsavariablecoursetowardthetransversesinus,butmustalwaysbepreserved,especiallyduringcombinedapproachestotheposteriortemporalregion.Locatingthisvesseliscriticalforpreventingitsinjuryandtemporallobevenousinfarction.MiddletemporalveinshouldnotbeconfusedwiththeveinofLabbe(ImagecourtesyofALRhoton,Jr).

TEMPORAL/SUBTEMPORALCRANIOTOMY

Appropriateheadpositionisparamountforsurgeryondeepskullbaselesions.Thepatient’sheadpositionshoulddirectthesurgeontotheregionofinterestthroughapaththatallowsadequateexposureofthelesion,minimizesbrainretraction,andaffordsflexibleworkingangles.Furthermore,thepatient’sheadpositionshouldenableacomfortableergonomicbodypostureforthesurgeonduringtheoperation.

Figure3:Thepatientisfrequentlyplacedinthesupineposition(ifthepatient’sneckissupple)orrarelyinthelateralposition,iftheneckisrelativelyrigid.Thepatient’sneckshouldberotatedasmuchaspossiblewhileutilizingalargeshoulderrollunderneaththeipsilateralshouldertominimizenecktorsion.Nonphysiologicneckrotationleadstocompromisedjugularvenousreturnandpostoperativeneckpain.

Olderandheavy-setpatientsshouldbeplacedinalateralposition.Ifthepatienthasahistoryofsignificantcervical

spondylosis,thisdictatestheneedforalateralposition.Theheadisthentilted~20degreestowardthefloorforgravityretractiontomobilizethetemporallobeawayfromthemiddlefossa.

Theexactlocationandsizeofthelesionwilldeterminethecorrespondingskinincision.Ingeneral,smallerlesionsthatarewithinthesuperiorormiddletemporalgyriareamenabletolinearincisions,whereaslargesubtemporallesionsbenefitfromahorseshoe-shapedincision.Forlesionsthatrequireaccesstotheanteriortemporalpole,asmallreversequestionmarkincisionwouldbeappropriate.

Figure4:Alternativeincisionstylesandpinplacementfortemporalandsubtemporalcraniotomies.Anincisionthatextendstothelevelofthezygomashouldsparethemaintrunkofthesuperficialtemporalartery.Manualpalpationofthearteryguidesplanningofthescalpflap.Ipreferalinearincisionwhenpossiblesincethistypeofincisionhealsmorereadily.Horizontaldisconnectionofthetemporalismuscleattachmentsfromthesuperiortemporallinethroughthelinearincisionoftenmaximizesretractionofthescalpflapsandprovidesadequate

bonyexposure.

Afterplacingageneroussingleburrholejustaboveherootofthezygoma,Iusea#3Penfielddissectortomobilizetheduraawayfromtheinnertableofthecalvariuminpreparationforthecraniotomy.Ifanextraduralapproachtothemiddlefossaisplanned,itisessentialtoavoidearlyinjurytothedurainordertoprotectthelobeduringextraduralsubtemporaldissectionandpetrosectomy.

Iftheduraisadherenttotheinnerskullbone,Iplacenumerousburrholes.Thelumbardrainisusedtoremove~30to40ccofCSFgradually(in10–20ccaliquots)torelaxthebrain.Thisdrainagefacilitatesdissectionofthedurafromthecalvariumandreducestheriskofaduraltear.Acraniotomeisthenusedtocompletethecraniotomy.

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Figure5:Notethelocationoftheinitialburrholenearthesigmoidsinusforlinear(top)andhorseshoe(bottom)incisions.Inthecaseofasubtemporaloperativecorridor,thecraniotomyshouldbecreatedasclosetothemiddlefossaflooraspossible.Thistaskmaybeaccomplishedbyidentifyingoneimportantlandmark:theupperedgeoftherootofzygomamarksthelevelofthemiddlefossafloor.Itisalsoimportanttorememberthatthefloorofthemiddlefossaisobliqueandslopesslightlysuperiorlyfromtheanteriortoposteriordirection.Therefore,theinferioredgeofthecraniotomyshouldbeonlyslightlyabovethelevelofthezygoma.

Figure6:Thecraniotomyinrelationtotherootofzygoma(*)isevident(top).Mostoften,theinferioredgeofthecraniotomyleavesastripofoverhangingbone,obscuringaclearoperativepathtowardthemiddlefossafloor.Subsequently,aLeksellrongeurmaybeusedtoremovethisoverhangingboneuntiltheedgeofthecraniotomyisatthelevelofthefloor(bottom).A

handhelddrillfurtherassistswiththistask.

Figure7:Removaloftheoverhangingboneovertheinferiorcraniotomywillallowanunobstructedviewofthemiddlefossafloor,minimizingtheneedfortemporalloberetraction.Thelocationoftherootzygoma(*)ismarked.ThetemporalboneandmastoidaircellsarethoroughlywaxedtopreventdevelopmentofapostoperativeCSFfistula(arrows).DuralTackupsuturesareplaced.

Figure8:Theduramaynowbeincised,asillustrated,forresectionofintraparenchymallesions.

Alternatively,anextraduraldissectionalongthemiddlefossamayberesumedforskullbaselesions.Importantly,thelocationoftheveinofLabbeshouldbeestimatedpreoperatively.Theduralopeningandextraduraltemporallobeelevationshouldbeadjustedforprotectionofthisvitalvenousstructure.AdditionalCSFmaybereleasedthroughthelumbardraintofurtherrelaxthelobe.

PleaserefertotheAnteriorPterosectomychapterforfurthersteps

regardingextraduralmiddlefossadissectionandpetrosalosteotomy.

Closure

Inthepresenceofaircells,Ipreferawatertightduralclosureprimarilyorsecondarilyusingapieceofduralallograft.AdiposetissuewithitsglobulartextureisoneofthebestbarriersagainstCSFleakage.Inthecaseofsubtemporalskullbaseexposuresthatrequireremovalofthetumor-infiltratedduraandbone,stripsofadiposetissueareplacedacrosstheduralopeningtosealtheduraldefect.Beforeplacementoftheadiposegrafts,allaircellsmustbemeticulouslywaxed.

Alternatively,avascularizedmuscleflappreparedfromtheposterioraspectofthetemporalismusclemayberotatedtofillthedefectwithintheboneordura.Thislattermethodisusedduringrepeatoperationsforpatientswhohavepreviouslyundergoneradiationtreatment.

Anyadditionalmastoidandtemporalaircellarerewaxed.Finally,theboneflapisreplacedandthescalpisclosedinanatomiclayers.

PostoperativeConsiderations

Postoperatively,thepatientisadmittedtotheICUforneurologicandbloodpressuremonitoringandpaincontrol.Frequentandcarefulneurologicexamsareparamountbecausetemporallobehematomascanoccurduetolobarretractioninjuryorvenousdrainagecompromise,leadingtorapidbrainstemcompression.

Thepatientisusuallytransferredtotheregularwardonthefirstorsecondpostoperativeday.LumbardrainagemaybecontinuedifthereisahighsuspicionofCSFleakage.Duetomanipulationofthetemporallobe,theuseofprophylacticantiepilepticmedicationsforatleastoneweekaftersurgeryishighlyrecommended.

PearlsandPitfalls

Duringpositioning,tiltingthepatient’sheadtowardthefloorisakeymaneuvertomaximizetheuseofgravityretractionandobtainappropriatesubtemporalexposure.Theupperedgeofthezygomaisagoodlandmarkforlocatingthelevelofthemiddlefossafloor.Removaloftheoverhanginginferioredgeofthecraniotomyisimportantforpreparinganobstructedoperativetrajectorytowardthemiddlefossafloor.ThelocationoftheveinofLabbeshouldbeestimatedpreoperatively.Duralopeningandextraduraltemporallobeelevationshouldbeadjustedforprotectionofthisvitalvenousstructure.

DOI:https://doi.org/10.18791/nsatlas.v2.ch05

References

Apuzzo.M,BrainSurgery:ComplicationAvoidanceandManagement,Volume1.ChurchillLivingstone,1983.

CamperoA,TróccoliG,MartinsC,Fernandez-MirandaJC,YasudaA,RhotonALJr.Microsurgicalapproachestothemedialtemporalregion:Ananatomicalstudy.Neurosurgery.2006;59(Suppl2)S279-308.

RhotonALJr.Thecerebralveins.Neurosurgery.2002;51(Suppl4)S159-205.

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