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Ростовский Государственный Медицинский Университет

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Книга_186_библиотеки_им_акад_М_И_Перельмана

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massivemiddlecerebralartery(MCA)stroke—shouldbemanagedwithaguidingsetofprinciplesand treatmentstrategiesknownas“ICPprecautions”thatattempttopreventfurtherelevationinpressureand mitigateitsdownstreameffects.Theseprecautionsincludemaintainingnormotension,normothermia,and euglycemiaandkeepingtheheadofthebedelevated30°.

ManagementofacutelyelevatedICPinvolvesseveralsteps:

Hemodynamicstabilization(rememberyourABCs:airway,bloodpressure,andcirculation).This preventstheevolutionofvalueslyingoutsidethecerebralautoregulationwindowandensuresstable cerebralbloodflow. Sedationdecreasescerebral metabolic activity,whichinturn reducescerebralbloodvolumeand ICP. Hyperventilationcausescerebralvasoconstriction,againreducingcerebralbloodvolumeandICP (ingeneral,thisisatemporizingmeasureandshouldnotbeperformedformorethan15minutesor so, as prolonged vasoconstrictioncanincrease the riskof strokeandresultin a rebound spikein ICP). Hypertonicosmoticagentssuchasmannitolandhypertonicsalinecanbegiventodrawfluidoutof braintissueandintothebloodvessels,temporarilydecreasingbothvasogenicandcytotoxicedema. Thekeywordhereistemporarily:theseagentsbuyyoutimebutwillnotfixtheunderlyingproblem. Surgicaldecompressionis anotheroption, oftenperformed viahemicraniectomy, whereby a large pieceoftheskullisremovedtoallowfortheexpansionofswollenbraintissueandareductionof ICP.Theoptimaltimingofsurgery,aswellaswhoaretheoptimalsurgicalcandidates,arestillup fordebate.Ingeneral,hemicraniectomyhasbeenproventobealife-savingprocedure,butitisnot always a quality-of-life-saving procedure, as surgery can leave patients extremely disabled. Wheneverpossible,itisimportanttodiscusstherisksandbenefitsofsurgeryinpatients atriskof ICPcrisesearlyon,todetermineifsurgicalmanagement,shoulditbecomeaconsideration,iswithin theirgoalsofcare.

Box14.2DecerebrateandDecorticatePosturing

Thetermposturingreferstoabnormalflexionorextensionoftheextremitiesthatoccurs eitherspontaneouslyorinresponsetoanexternalstimulussuchaspain,andcanindicate severebraininjury.

Decorticateposturingischaracterizedbyarmflexionintothechestandlegextensionwith feetinternallyrotated.Decorticateposturingisindicativeofdamagetothecerebral hemispheresabovetheleveloftherednucleus,astructurelocatedinthemidbrainthatis involvedinmotorcoordination.

Decerebrateposturingcanbeclinicallydifferentiatedfromdecorticateposturingbythe presenceofbothupperandlowerextremityextension.Itiscausedbybrainstemdamage belowtheleveloftherednucleus.Progressionfromdecorticatetodecerebrateposturing canbeindicativeofuncalortonsillarherniation(seepages365–366).

Inreality,theclinicaldistinctionbetweendecorticateanddecerebrateposturingisoftenof littlelocalizingvalue.Thetakeawayhereinsteadisthatabnormalposturingofanysortisan ominoussignandmostoftenindicativeofdangerousunderlyingpathologyandapoor

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prognosis.

Hereisahelpfulsortofmnemonic:deCORticateposturing(A)presentswitharmsflexedinto theCOREofthebody,whereasdecErebrateposturing(B)presentswiththearmsExtended away.

Box14.3ICPMonitoring

InvasiveICPmonitoringcanbeusedinneurologicalorneurosurgicalICUsinpatientswho areathighriskofdevelopingelevatedICPandforwhommonitoringhasthepotentialto significantlyguidemanagementandhopefullyimproveclinicaloutcome.Intraventricular monitoring,withacathetersurgicallyplacedintotheventricularsystem,allowsforthemost precisemonitoringand,ifindicated,canalsotreatelevatedICPviaCSFdrainage. Intraparenchymaldevicesarealsosometimesused.

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AnormalICPwaveformasmeasuredbyanICPmonitor.P1correlateswiththearterial pulse,P2withcerebralcompliance,andP3withclosureoftheaorticvalve.NormalICPis5 to15mmHginasupineadult.

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ACTscanseveraldaysafterdecompressivehemicraniectomy,withherniationofedematousbraintissue throughthehemicraniectomyskulldefect.Thehemicraniectomyenablesincreasedskullcomplianceand expansionofintracranialvolumebyreplacingthehardboneoftheskullwithmoreelasticskin.(Reprinted fromLouisED,MayerSA,RowlandLP.Merritt’sNeurology,13thed.WoltersKluwer;2013.)

HerniationSyndromes

Forbetterorworse,therearemultiplewaysinwhichbraintissuecanbeforcedintoplacesitshouldn’t be.Itisimportanttobeabletorecognizethesedifferentsyndromes—bothclinicallyandradiographically —sothatyoucanquicklyjumpintoaction.

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Herniationhereisdefinedasthedisplacementofbraintissuefromitsnormalpositioninsidetheskull. Beforewegetintothedetails,itisimportanttounderstandwhythiscanbesodevastating.Displacement canresultincompressionofcriticalarteriesandveins(causingischemiaorhemorrhage)aswellascrush injuryofbraintissueitself.Becausetheskullisreallyjustahardspherewithasingle,approximately3cm-diameterholeatthebottom(theforamenmagnum),theonlyrealwayoutisdown.Consequently,the finalcommonpathwayoftheherniationpatternslistedbelowisbrainstemcompression,resultingin damagetopathwayscontrollingrespiratoryandcardiacfunctionand,eventually,death.

WhenICPrises,wherecanbraintissuego?Thereareseveralpossibilities:

Fromonesideofthecraniumtotheother(subfalcineherniation) Fromthetopofthecraniumtothebottom(centralherniation) Fromthesideofthecraniumtothebottom(uncalherniation) Fromthebottomofthecraniumtooutsideofthecranium(tonsillarherniation) Fromtheinsidetotheoutsideofthecranium,throughafractureorsurgicalsiteopeningintheskull (transcalvarialherniation)

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Thevariousherniationpatterns.

Subfalcineherniationisthemostcommonherniationpattern.Itoccurswhentheinnermostpartofthe frontallobeisforcedunderneaththefalxcerebri(theduralsheetthatdividestherightandleftcerebral hemispheres).Subfalcineherniationisoftenaprecursortoothermoredangeroustypesofherniation.The presentationisoftennonspecific:headacheandincreasingsomnolencearethemostcommon manifestations.Lowerextremityweaknesscanoccurowingtocompressionoftheanteriorcerebralartery. Thebrainstemisgenerallyspared.

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Subfalcineherniationduetoanexpandingright-sidedbleed.(ModifiedfromDaffnerRH,HartmanM. ClinicalRadiology.4thed.WoltersKluwer;2013.)

Uncalherniationischaracterizedbythedisplacementofthemedialtemporallobe(i.e.,the“uncus”) beneaththetentoriumcerebelli(theduralsheetthatoverliesthecerebellum)andintothesuprasellar cistern(locatedabovethesellaturcicaandbelowthehypothalamus).IpsilateralCN3palsy,aresultof nervecompression,andcontralateralhemiparesis,aresultofcompressionofthecorticospinaltract runningwithinthecerebralpeduncleofthemidbrain,aresignstowatchoutfor.

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Uncalherniation,characterizedbydisplacementoftheuncusresultingincompressionofthemidbrain. (ModifiedfromStrayerDS,SaffitzJE,RubinE.Rubin’sPathology.8thed.WoltersKluwer;2019.)

Box14.4TheKernohanPhenomenon

Ipsilateralhemiparesis,aso-calledfalselocalizingsign,canoccurwhenthebrainis compressedagainsttheoppositeedgeofthetentorium.ThisiscalledtheKernohan phenomenon.Aright-sidedsubduralhematoma,forinstance,cancauseleftward displacementofthebrain,resultingincompressionofthedescendingmotorfiberslocatedin theleftanteriormidbrainagainstthelefttentoriumcerebelli(atKernohannotch,hencethe name).Theresultisright-sidedweaknesscausedbyaright-sidedsubduralbleed.

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Centraltentorialherniationoccurswhenthecerebralhemispheresareforceddownwardthroughthe tentorium.Thiscancausecompressionofthebilateralthirdcranialnerves(causingbilateralblown pupilsand“downandout”eyedeviation),aswellascompressionoftheposteriorcerebralandbasilar arteries(resultinginposteriorcirculationischemia).

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Centraltentorialherniation(thearrowspointtoareasofinfarctioncausedbydownwarddisplacementof thecerebralhemispheres).(ReprintedfromShrierDA,ShibataDK,WangHZ,NumaguchiY,PowersJM. Centralbrainherniationsecondarytojuvenilediabeticketoacidosis.AmJNeuroradiol.1999;20(10):1885-

1888.)

Tonsillarherniationischaracterizedbythedownwarddisplacementofthecerebellartonsilsthrough theforamenmagnum,resultinginbrainstemandupperspinalcordcompression.Theearlystagesof

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