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Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_186_библиотеки_им_акад_М_И_Перельмана

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https://t.me/med1917
(A)ThecircleofWillis,highlightedinpink,and(B)Acomputerizedtomography(CT)angiogramofthe circleofWillis.
Therearenearlyasmanyanatomicalvariantsinthecerebralcirculationastherearepeople.It’snot uncommon,forinstance,forthePCAstobefedpredominantlyfromtheanteriorcirculationviathe Pcomms,withonlyweakorevenabsentconnectionstothebasilarartery(theseareknownasfetal PCAs).Butforourpurposes,it’senoughtobeawarethatvariationexistsandthatitcanbeimportantin determiningbothstrokeetiologyandmanagement.
IschemicStroke
Etiology
Ischemicstrokeistheresultofcriticallydecreasedbloodflowtoanareaofbraintissue(orspinalcord orretinaltissue).Manythingscancausethis;thecategoriesbelowshouldhelpyoukeepthingssimple. ThisisknownastheTOASTclassification—theacronymdoesnotrefertoburntbreadbutrathertothe TrialofOrg10,172inAcuteStrokeTreatment,whichhelpedsettheframeworkforthiscategorization system.
Cardioembolism. Cardioembolic infarcts are due to thrombi that form within the heart and then embolize into the cerebral circulation. Atrial fibrillation is the most common cardiac source of emboli.Othercardiacsourcesincludeintracardiactumorsorthrombi,infectiveendocarditis(with septic emboli originating from affected valves), a severely reduced ejection fraction, and aortic archatheroma(althoughnottechnicallyofcardiacorigin,theseemboliactthesameasiftheycame fromtheheart).Apatentforamenovale(PFO)isalsoconsideredacardioembolicsource,because itcanallowforthrombithatforminthedeepveinsofthelegstopassthroughtheheartviaright-to­leftshuntingandultimatelylodgeinthecerebralcirculation.
Cardioembolicstrokescanbebig,knockingoutentirevascularterritories,orsotinythattheycause virtuallynoneurologiccompromiseatall.Eitherway,theytendtoinvolvethecerebralcortex.Clinically, theneurologicsymptomstheycauseareoftenmaximalatonsetbutcanalsorapidlyresolve—embolic clotsareunstableandcansometimesdissipatebeforecausinganysignificantdamage.
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Anelectrocardiogram(EKG)showingtheclassicirregularlyirregularrhythmofatrialfibrillation,apotential sourceofcardioembolicstroke.
Largearteryatherosclerosis.Thespecificvesselsthatqualifyas“large”remaindebatable,butfor our purposes we’re talking about the big vessels that bring blood into the brain, including the commonandinternalcarotidarteries,thevertebralandbasilararteries,andtheproximalportionsof theACAs,MCAs,andPCAs.Thesevesselsarepredisposedtoatheroscleroticnarrowingatsitesof bifurcation (e.g., where the common carotid artery splits into the internal and external carotidarteries)andsitesoforigin(e.g.,atthetake-offofthevertebralarteriesfromthesubclavian arteries),butatherosclerosiscan—andoftendoes—occurwhereveritlikes.Therearethreemajor mechanismsbywhichthisprocesscancauseischemicstroke:
1.
Artery-to-arteryembolism. Justas embolicanshootup from theheartinto t hebrain,bits of atheroscleroticp laquecanbreakoff fromthe walls of large vessels,traveltoandultimatelyblockthemoredistalcirculation.
2.
Thromboticocclusion.At somepoint,anatheroscleroticlesioncanbecomesufficientlylargethatitoccludesthelumenofthevessel.Thesest rokestendt o belessseverethanthosecausedbyembolism.Becauseatherosclerot iclesionsdonotdevelopovernight,thebrainhasoftenhadtimetoadjust,formingwell­develop edcollateralvesselsthatsupplyt heat-risktissueandcanhelp maintainperfusioninthesett ingofthromboticocclusion.
3.
Hypoperfusion.Undernormalconditions,alargevesselmustbemorethan99%narrowedinordertocauseischemiafromhypoperfusionalone.However,in thesettingofsepsis,cardiacarrest,orevenseveredehydration—thatis,conditionscausingsignificantlyloweredbloodp ressure—tightvesselscanresultin watershedinfarcts,definedasstrokesthataffectareaslocatedattheborder zonebetweent wovascular territories.Theseareasarethefarthestfromt he vascularsupplyandthusmostvulnerabletoreducedperfusion.
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(A)Classicwatershedareas,(B)Acutewatershedinfarctscorrespondingtothecorticalborderzones (betweenACA/MCAandMCA/PCAterritories;bigarrows)andinternalborderzones(betweentheMCA anditslenticulostriatebranches;smallarrows).(B,reprintedfromPopeTLJr,HarrisJHJr.Harris&Harris’ TheRadiologyofEmergencyMedicine.5thed.WoltersKluwer;2012.)
Smallvesselocclusivedisease.Smallvesseldiseaseisoftencausedbylipohyalinosisofthesmall penetrating arteries, a process characterized by thickening, weakening, and degeneration of the vesselwallwitheventualvesselocclusion,mostoftentheresultoflong-standingpoorlycontrolled cardiovascular risk factors such as hypertension anddiabetes. Smoking is also an important risk factor.Microatheromaisanothercauseofsmallvesseldisease—essentiallythesameatherosclerotic process we talked about with large arteries but affecting the smaller vessels. Infarcts due to microatheroma tend to be a little larger and more ovoid than those due to lipohyalinosis. Hyperlipidemiaisanimportantriskfactor.Ineithercase,thesmallarteriesthatcanbeaffectedare:
TheperforatingarteriesoftheMCA(thelenticulostriates,whichsupplythebasalgangliaandinternalcapsule) TheperforatingarteriesofthePCA(whichpredominantlysupplythethalamus) Theperforatingarteriesofthebasilarartery(thepontineperforators,whichsupplythepons).
Theterritoriesatriskofsmallvesseldiseasearethereforetheinternalcapsule,basalganglia, thalamus,andpons.Small,deepinfarctsintheseareascausedbysmallvesseldiseasearereferredtoas lacunarstrokes.
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Asubacuteleftinternalcapsulelacunarinfarct.(ReprintedfromPopeTLJr,HarrisJHJr.Harris&Harris’ TheRadiologyofEmergencyMedicine.5thed.WoltersKluwer;2012.)
Strokeof other determined etiology.We can divide this category up intothreeless commonbut importantetiologicgroupings:(1)nonatheroscleroticvesseldisease(suchasvasculitis,vasospasm,
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and dissection), (2) hypercoagulability (such as antiphospholipid syndrome), and (3) genetic syndromes that predispose to stroke (such as cerebral autosomal dominant arteriopathy with subcorticalinfarctsandleukoencephalopathy[CADASIL]andmoyamoya;moreontheselater). Strokeofundetermined etiology.Despiteall oftheprecedingcategorizations, nearlyone-thirdof allstrokesareultimatelyclassifiedas“cryptogenic.”
Adiagramsummingupsomeofthepotentialetiologiesofischemicstroke.
Box2.2EmbolicStrokeofUndeterminedSource(ESUS)
ESUSisasubcategoryofcryptogenicstroke.Itisdefinedasanimage-positive(i.e.,itcan bevisualizedonCTorMRI)nonlacunarstrokeforwhichnohigh-riskcardioembolicsource, significantlargearterystenosis,orothernonembolicsource(suchasdissectionorvasculitis) hasbeenidentified.Theselooklikeembolicstrokes,butwithoutaknownembolicsource. Occultparoxysmalatrialfibrillation,atrialcardiopathy,aandnonstenoticplaqueinthecervical andintracranialarteriesarethoughttobethemostlikelyetiologies.ESUSisimportantto recognizebecauseitmayrequiredifferentmanagementthan“non-ESUS”cryptogenic
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strokes;thejury’sstillout,butongoingstudiesareassessingtheefficacyofanticoagulation inthispatientpopulation.Atthetimeofthiswriting,however,thereisnoconcreteevidence supportingtheuseofanticoagulationinthemanagementofpatientswithcryptogenicstroke. Onlyproven(asopposedtosuspected)atrialfibrillation,forinstance,isanofficially approvedindicationforanticoagulation.
a
Atrialcardiopathyisdefinedasastructuralabnormalityoftheleftatriumintheabsenceofatrialfibrillation;itisthoughtto increasetheriskofstrokeeitherasaprecursortoatrialfibrillationorasanindependentriskfactorfortheformationofatrial thrombi.
Box2.3StrokeintheYoung
Thetypicalculpritsthatincreasetheriskofischemicstroke—hypertension,hyperlipidemia, atrialfibrillation,etc.—arefarlesscommoninyoungpatients,whichinthiscontextisanyone lessthan50yearsofage.Whenyoungpatients—likeourpatient,Laura—presentwith stroke,theyoftenrequireabitmorethinkingandamoreextensivework-uptodeterminethe underlyingcause.Inthispopulation,themostcommonetiologiestoconsiderare:
Arterialdissection(seepage84)  Hypercoagulability: Keep in mind that in the setting of stroke we need to consider conditions that predispose to arterial thromboembolism, such as antiphospholipid syndrome,underlying malignancy,and the useof estrogen-containing birth controlpills when combined with cigarette smoking. Conditions that predispose only to venous thromboembolism, suchasprotein Cor Sdeficiency,are relevant to stroke only inthe settingofaPFOorsomeothertypeofatrialseptaldefect.  Cardioembolism: Unlike in older patients, cardioembolism is less often the result of atrialfibrillationandmoreoftentheresultofconditionssuchascongenitalheartdisease, dilatedcardiomyopathies,infectiveendocarditis,intracardiactumors,andaPFO. Vasculitis:Thesecanbeinfectious,autoimmune,anddrugrelated;seepage88.Genetic syndromes: Specific syndromesthat predispose to stroke includesickle cell disease,CADASIL,andmoyamoya,seeBox2.4.  Illicit drug use: Cocaine, methamphetamines, and other stimulants can cause rapid elevationsinbloodpressure,cardiacarrhythmias,anddiffusevasospasm.
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Drugs,suchascocaine,areamongthemorecommonprecipitantsofstrokeinthoseundertheageof
50.
Box2.4GeneticSyndromes
CADASILisasmallvesselarteriopathyassociatedwithmutationsintheNOTCH3geneon chromosome19.Itclassicallypresentsinyoungadultswithsomecombinationofmigraine withaura,cognitivedecline,andstroke(mostoftenlacunarinfarctsinvolvingtheexternal capsuleandanteriortemporallobes).Thereisnospecifictreatment.
Moyamoyaisanothernonatheroscleroticprogressivearteriopathy.Theincidenceishighest intheAsianpopulation.Althoughtheetiologyisunknown,thereappearstobeastrong geneticcomponent.Moyamoyatypicallypresentsinchildrenoryoungadultswithischemicor hemorrhagicstrokes.Angiographyisdiagnostic,demonstratingprogressivevesselnarrowing affectingthearteriesaroundthecircleofWillisassociatedwiththegrowthofprominentbut flimsynewvessels(or“neovascularization”)thatisoftenreferredtoas“hazy”or“smoky”
https://t.me/med1917
(moyamoyaactuallymeans“puffofsmoke”inJapanese).Surgicalrevascularizationwith directexternal-to-internalcarotidarterybypassorindirectbypass(theprocedureiscalled encephaloduroarteriosynangiosis;EDASforshort—you’rewelcome),isoftennecessary.
(A)AnMRangiogram(MRA)fromapatientwithmoyamoya,demonstratingocclusionoftheproximalright middlecerebralartery(MCA,yellowarrow)withsignificantlydilatedlenticulostriatevessels(redarrows) providingcollateralflow.(B)Anangiogramdemonstratingsignificantvesselirregularitiesinvolvingtheright internalcarotidartery(ICA)bifurcationandrightproximalMCA.Again,youcanseeanextensive surroundingnetworkofthinandflimsylenticulostriatecollaterals(arrows)resemblinga“puffofsmoke” (seeimageinsertinupperrightcornerforanactualpuffofsmoke!).(CourtesyofJonathanHoward.)
StrokeSyndromes
Theabilitytorapidlyrecognizevariousstrokesyndromesisessentialbecauseacutestroketreatmentisa highlytime-sensitiveendeavor.Thefasteryouintervene,thebettertheoutcomeforthepatient.
CorticalSigns.Thefirststrokesthatwe’lldiscuss—andthemostimportanttorecognize—arethosethat affectthecerebralcortex.Corticalstrokesaremostoftenduetolargevesselocclusion(LVO),whichin turnismostoftentheresultofeithercardioembolismorartery-to-arteryembolism.Thesebloodclotsare oftenretrievableviaendovascularthrombectomy(i.e.,mechanicalremovaloftheclot,seepage73). UrgentheadCTandCTangiogramarethereforeessential,becauseifanLVOisidentifiedandthepatient iseligible,heorshecanbewhiskedofftotheoperatingroomformechanicalthrombectomy.
Whatmakesyoususpectacorticalstroke?Thereareonlyafewsignsyouneedtoknow.
Aphasia.BothBrocaandWernicke’sareas(seethediscussionthatfollows)arepartofthedominant cerebralcortex.
https://t.me/med1917
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