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

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Box2.5
Thedominantcerebralhemisphereisdefinedasthehemispherethatcontrolslanguage.In right-handedpeople,thisisinvariablythelefthemisphere.Inleft-handedpeople,it’sabout 80/20,rightversusleft-dominant.
Aphasiaisanacquireddisorderoflanguagecomprehensionand/orproduction.Don’tgetthisconfused withdysarthria,whichisamotordeficitcharacterizedbytheimpairedabilitytocontrolthemusclesused forspeech,resultinginuncleararticulationofspeech(oftendescribedas“slurred”)thatisotherwise normal.Therearetwomainlanguagecentersinthebrainthatcausetwodistinctlanguagedeficitswhen damaged:
1. Broca’s are aislocatedintheinferiorfrontalgyrusofthefrontallobeandisresponsibleforlanguageproduction.Brocaaphasia(also known as expressive, or nonfluent, aphasia) is characterized by halting and effortful speech, often with long pauses and difficulty naming objects. The abilityto repeat words spoken to themis also lostbutcomprehension remains intact. Damage to the cortex surroundingBroca’sareaproducesasimilarexpressiveaphasiabutwithpreservedrepetition(calledtrans corticalmotoraphasia).
2.  Wernicke’s area is located in the superior temporal gyrus of the temporal lobe and is responsible for language comprehension. PatientswithWernickeaphasia(alsoknownasreceptive,orfluent,aphasia)demonstratefluentspeechwithintactsyntaxandprosody butdevoidofcontent ormeaning.ListeningtoapatientwithWernickeaphasiaspeakislikelisteningtosomeonespeakinginaforeign languagethatyoudon’tunderstand;itcanbeprettybutitismeaningless.Patientsareunabletofollowspokencommandsand,likethose withBrocaaphasia,losetheabilitytorepeat. DamagetothecortexsurroundingWernicke’sareaproducesasimilarreceptiveaphasia butwithpreservedrepetition(calledtrans corticalsensoryaphasia).
FewpatientsactuallypresentwithapureBrocaorWernickeaphasia.Mostaphasiasaremixed, althoughtheytendtofavoroneortheother,meaningtheypresentwitheitherpredominantlyexpressiveor receptivedeficits.
ThearcuatefasciculusisthebundleofnervesthatconnectsBrocaandWernicke’sareasandis responsibleforrepetition;thus,damagehereresultsintheinabilitytorepeat,withpreservedfluencyand comprehension.
Globalaphasiaismostoftenseeninthesettingofbigleft-sidedMCAinfarcts(somewherebetween 70%and95%ofthepopulationisright-handed),whichknockoutcomponentsofthearcuatefasciculus, Wernicke’sareaandBroca’sarea,resultinginimpairedabilitytorepeat,understandandproduce language.
https://t.me/med1917
Majordomainsofthebrain,illustratingtheregionsthat,whendamaged,produceBrocaandWernicke aphasia.
TypeofAphasia LocationoftheLesion Presentation
Brocaaphasia Inferiorfrontalgyrus Expressive(nonfluent)aphasia,withretainedcomprehension Transcorticalmotoraphasia CortexsurroundingBroca’sarea Asabove,withpreservedrepetition Wernickeaphasia Superiortemporalgyrus Receptive(fluent)aphasia,withretainedfluency Transcorticalsensoryaphasia CortexsurroundingWernicke’sarea Asabove,withpreservedrepetition Conductionaphasia Arcuatefasciculus Isolatedinabilitytorepeat Globalaphasia Somecomponentofalloftheabove Inabilitytospeakfluently,comprehend,orrepeat
Neglect. Neglect is the second classic sign of a cortical stroke. It usually localizes to the nondominantparietalcortexbutcanoccurwithdominantaswellasnondominantcortical lesions.
Neglectcanbedramatic,suchaswhenpatientsfailtorecognizetheirownarmoronlyappropriately dresshalfoftheirbody,or—amuchmoresubtlefindingonexamination—whenpatients(likeLaura, whomwemetatthebeginningofthischapter)extinguishtodoublesimultaneousstimuli(seepage31 forareviewonneglectandextinction).
https://t.me/med1917
Adrawingofaclockbyapatientwithneglectduetoastrokeinthenondominantparietalcortex.
Visualfieldcuts.Visualfieldcutsinwhichtheentirecontralateralvisualfieldislost(homonymous hemianopia), or in which the upper or lower quadrant of the contralateral visual field is lost (homonymousquadrantanopia)areduetolesionsthatinvolvethevisualcortexintheoccipitallobe orlesionsimpactingtheopticradiations,whicharealsobyandlargecorticalpathways.
https://t.me/med1917
Parisasseenthroughtheeyesofapatientwitharighthomonymoushemianopia.
Gazepreference.Gazepreference(seepage32)ismostoftenduetoinvolvementofthefrontaleye fields,whichare tractslocatedinthefrontal cortex.Forinstance,when stimulated(asinseizure), theleftfrontaleyefieldpushestheeyestotheright,andviceversa.Whenknockedout(asinstroke), theleftfrontaleyefieldlosesitsinfluenceandtherightfrontaleyefield“wins,”pushingtheeyesto the left. Theresultis that patientswho are seizing“lookawayfromthe lesion,”and patients with stroke“looktowardthelesion.”
https://t.me/med1917
Thefrontaleyefields.(A)Whentheleftfrontaleyefieldisstimulated,therightsixthnervenucleusand(via themediallongitudinalfasciculus[MLF];seepage232)theleftthirdnervenucleusarestimulated, resultinginrightgaze.(B)Whentheleftfrontaleyefieldisknockedout,therightfrontaleyefieldtakes over,andtheeyesdeviatetotheleft.
Again(becausethisisimportant!):aphasia,neglect,visualfieldcuts,andgazepreferencearethe fourmajorcorticalsignsyouneedtoknow.Thereareothercorticalsignstobeawareofthatarenot
partoftheofficialNIHstrokescale(NIHSS)usedtoassessstrokeseverity(seethenextpage)butwhich canbeequallyashelpful.Listedbelow,thesetendtolocalizetotheparietallobe.
Apraxia—the inability to execute a previouslyknownmotor task,not explainedbyother deficits (suchasweaknessorblindness).Totestforvariousapraxias,youcanaskyourpatientstoshowyou howtheybrushtheirteeth,combtheirhair,orbuttontheirshirt. Astereognosis—theinability torecognizeobjects through touch alone. Askyour patientstoclose theireyesandthenplaceanobject—apennyorapaperclip—intheirhand.Iftheycannotfigureout whattheobjectis,theyhaveastereognosia. Agraphesthesia—theinabilitytorecognizewritingontheskin.Askyourpatientstoclosetheireyes, butthistimedrawaletterornumberonthepalmofthehand.Iftheycannotfigureoutwhatyou’ve written,theyhaveagraphesthesia. Anosognosia—aconditioninwhichpatientsdonotrecognize—orhavesignificantlyreducedinsight into—theirowndeficit.
Box2.6TheNIHSS
TheNIHSSbecamethegold-standardscaleforratingstrokeseverityfollowingthe publicationoftheNationalInstituteofNeurologicalDisordersandStroke(NINDS)trialin
1995.aItrangesfrom0(nodeficits)to42.Itcanbeusefulinanacutesettingtogetaquick senseofjusthowbadapatient’ssymptomsarebutshouldnotbesubstitutedforareal neurologicexamination.Itsignificantlyunderrepresentsbothright-sidedandposterior circulationsymptoms,and—althoughhighscoresaremeanttoconveymoresevere symptoms—lowscorescanhidedevastatingdeficits:pureaphasia,forinstance,mayresult inonlya1,2,or3onthisscale.
1a.LevelofConsciousness 0-Alert
https://t.me/med1917
1b.Whatismonth/age 0-Answersbothcorrectly 1c.Open/closeeyesandhand 0-Performsbothcorrectly
2.Bestgaze 0-Normal
3.Visualfields 0-Novisualloss
4.Facialpalsy 1-Minor 5a.Motor—leftarm 0-Nodrift 5b.Motor—rightarm 0-Nodrift 6a.Motor—leftleg 0-Nodrift 6b.Motor—rightleg 0-Nodrift
7.Limbataxia 0-Absent
8.Sensory 1-Mildtomoderateloss
9.Bestlanguage 0-Noaphasia
10.Dysarthria 0-Normal
11.Extinction/inattention 1-Extinctiontoonemodality
OurpatientLaura’sNIHSSresult.Althoughyoupickeduponsubtleleftupperextremityweaknessonyourexamination,Lauraisableto holdherleftarmupagainstgravityforafull10secondswithoutanydownwarddrift;thus,shescores0forleftarmweakness.Asisoften thecase,theNIHSSdoesnotcapturethefullextentofherdeficits.
a
seeNationalInstituteofNeurologicalDisordersandStrokert-PAStrokeStudyGroup.TPAforacuteischemicstroke.NEnglJ
Med.1995;333(24):1581-1587.
ACA,MCA,andPCAStrokes.MCAstrokesarebyfarthemostcommon,butACAandPCAstrokesare notrare.Thetablebelowisfarfromcomprehensivebutgivesagoodoverviewofthemostimportantand mostfrequentsignsandsymptomstorecognize.You’llnotethatallofthesesyndromesincludethe corticalsignswejustdiscussedabove.
Symptom Localization
MCA Contralateralhemiparesis(face/arm>leg) Motorcortex
Contralateralhemisensoryloss(face/arm>leg) Sensorycortex Contralateralhomonymoushemianopia Opticradiations Aphasia(dominantMCA) BrocaorWernicke’sareas Neglect(eitherdominantornondominantMCA) Parietalcortex
ACA Contralateralhemiparesis(leg>face/arm) Motorcortex
Contralateralhemisensoryloss(leg>face/arm) Sensorycortex Abulia—i.e.,apathy(inabilitytoactwillfully),oftenassociatedwithdecreasedspontaneous speechandmovement
Uncertain;thoughttoinvolvethe
cingulategyrus Aphasia(dominantACA) Transcorticalmotorarea Gaitapraxia—i.e.,difficultyinitiatinggait Frontalcortex
PCA Contralateralhomonymoushemianopia Visualcortex
Contralateralhemisensoryloss Thalamus Memoryimpairment(dominantorbilateralPCA) Hippocampus Alexiawithoutagraphia(dominantPCA)—i.e.,theinabilitytoreadwiththeretainedabilityto write
Temporal/Occipitalcortex
Prosopagnosia(nondominantPCA)—i.e.,theinabilitytorecognizefaces Fusiformgyrus
https://t.me/med1917
https://t.me/med1917
(A)Areminderoftheanteriorcerebralartery(ACA),middlecerebralartery(MCA),andposteriorcerebral artery(PCA)territories.(B)Thehomunculus(i.e.,“smallhuman”)isatopographicrepresentationofthe corticalmotorareasdedicatedtodifferentpartsofthebody(asimilarversionexistsforthecortical sensoryareas).Asyoucansee,ACAstrokeswillpredominantlyaffectthelowerextremities,whereas MCAstrokeswillaffecttheupperextremitiesandface.
https://t.me/med1917
Box2.7AFewStrokeSyndromestoKnow
Gerstmannsyndromeischaracterizedbytheclinicaltetradofleft/rightconfusion,finger agnosia(theimpairedabilitytodiscriminateamongone’sownfingers),acalculia(theinability toperformmathematicalcalculations),andagraphia(theinabilitytowrite).Itiscausedby lesionsinthedominantparietalcortex,typicallyMCA(butoccasionallyPCA)territory.
Balintsyndromeiscausedbylesionsinthebilateralparieto-occipitalcortex,corresponding totheMCA/PCAborderzone.Itpresentswithoculomotorapraxia(theabsenceof controlled,purposefuleyemovements,oftencausingsignificanttroublewithreading),optic ataxia(poorvisual-motorcoordination),andsimultagnosia(theinabilitytoperceivemorethan oneobjectatatime).
AntonSyndromeisaformofcorticalblindnessassociatedwithanosognosia,inwhichthe patientisunawarethatheorsheisblind.Patientswillcontinuetoinsist—oftenquite adamantly,andinthefaceofclearevidencetothecontrary—thattheycansee,andwill oftenconfabulate(meaningtheywillfabricateimaginaryinformation)whenaskedabout objectsorimagesplacedinfrontofthem.Thisiscausedbybilateraldamagetotheoccipital cortex,aresultofbilateralPCAortop-of-the-basilararteryocclusion.
BasilarArteryStroke.Basilararteryocclusionscanbedevastatingduetothalamic,brainstem,and cerebellarinvolvement.UnlikeACA,MCA,andPCAstrokes,theycanbedifficulttorecognizegiven theirhighlyvariableandoftenstutteringpresentation.Symptomsrangefromisolatedoculomotorpalsies tolocked-insyndromeorcoma.Importantly,unlikemostACA,MCAandPCAstrokes,basilarocclusions canpresentwithadecreasedlevelofconsciousness,aresultofinvolvementofthereticularactivating system(RAS).
The“topofthebasilar”syndromeisastrokecausedbyaclotlodgedattheverytopofthebasilar artery,justbeforeitsplitsintothetwoPCAs.Thepontineperforatorsarespared,butbothPCAterritories areatrisk,resultinginischemiaofthebilateralthalami,midbrain,posteriortemporalandoccipitallobes. Classicsymptomsincludeadecreasedlevelofconsciousness,verticalgazepalsy,corticalblindnessand —ifthesuperiorcerebellararteriesareinvolved—vertigo,nausea,vomiting,andataxia.
Locked-insyndromeisacatastrophicconditioncausedbybilateralpontineischemiaduetobasilar arteryembolismorthrombosis(pontinehemorrhage,usuallyrelatedtohypertension,isanothercause).It ischaracterizedbyquadriplegiaandtheinabilitytospeakorswallow,butconsciousness,cognitive functionandverticaleyemovementsarespared.Patientsareeffectively“lockedin”—wideawakebut onlyabletocommunicatebyblinking.
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Anteroposterior(AP)angiographicviewshowingatopofthebasilarocclusionpre-(A)andpost-(B) thrombectomy.InfigureA,bloodflowisblockedandyoucan’tseetheposteriorcerebralarteries(PCAs); butinfigureB,followingthrombectomy,thePCAsfillwithbloodandcannowbeclearlyvisualized. (ReprintedfromBarkovichAJ,RaybaudC.PediatricNeuroimaging.6thed.WoltersKluwer;2018.)
BrainstemStrokeSyndromes.Thebrainstemstructures—themidbrain,pons,andmedulla—aresmall butimportant:theycontainthemajorityofthecranialnervenucleiaswellasthesensoryandmotortracts thatruntoandfromthecortexandthespinalcord.Theresultisthataverysmallbrainstemstrokecan haveverybigconsequences.Therearedozensofspecificbrainstemstrokesyndromes,butifyoukeepthe followingprinciplesinmindyouwon’tneedtomemorizemuchatall.
Crossed symptoms, a term referring to ipsilateral cranial nerve deficits (affecting the face) and contralateralsensorimotor deficits (affectingthebody), are a classic feature ofbrainstem strokes. Remember,thecranialnerves(CNs)donotdecussate(withtheexceptionofCN4andthebranchof CN3that innervates the contralateral superior rectus; don’t worry aboutthis!), but the motor and sensorypathwaysdo(i.e.,thecorticospinaltractsanddorsalcolumnmediallemniscaltractsinthe medullaandthespinothalamictractsinthecord;seepages18and23). Themajormotorpathway(thecorticospinaltract)runsmediallyinthebrainstem. Thepain/temperaturepathway(thespinothalamictract)runslaterallyinthebrainstem,oftenside-by­sidewiththesympathetictract. Cranialnerves3through12exitfromthebrainstem(CN3and4exitfromthemidbrain;5,6,7,and8 exitfromthepons;and9,10,11,and12exitfromthemedulla;seethepicturebelow).Thus,among other symptoms,midbrainstrokesoften presentwith CN3and4 involvement,pontinestrokeswith somecombinationofCN5,6,7,and8involvement,andmedullarystrokeswithCN9,10,11,and12 involvement.Keepinmindthatthetrigeminalnerve(CN5)nucleusisthelargestofthecranialnerve nucleiandactuallyextends from the midbrainthrough the ponsandmedulla into the highcervical spinalcord.Ipsilateralfacialnumbnessisthereforenotaparticularlyhelpfullocalizer,asitcanbe seeninstrokesaffectinganyoftheabovementionedstructures.
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