医学影像学诊断

1、浅谈医学影像学诊断,1）特点,有两层构成,在颅盖部与颅骨疏松结合,在颅底部与颅骨紧密结合,硬脑膜：,脑膜中动脉,翼点,由硬脑膜形成的结构,大脑镰,小脑幕,大脑镰,小脑幕,小脑镰,鞍隔,幕切迹,3）由硬脑膜形成的静脉窦：内外两层分开形成。,上矢状窦,下矢状窦,直窦,窦汇,横窦,乙状窦,海绵窦,岩上窦,岩下窦,颈内静脉,2.蛛网膜：,蛛网膜下隙、蛛网膜下池、蛛网膜颗粒：渗入脑脊液。,3.软脑膜：,硬脑膜,蛛网膜,蛛网膜下隙,蛛网膜颗粒,软脑膜,大脑镰,上矢状窦,脉络丛，可以产生脑脊液。,CerebrospinalFluid,正常脑室,3DCT脑室造影,脑室包括侧脑室、第三脑室和第四脑室。脑室内充满

2、脑脊液。各脑室内都有可以产生脑脊液的脉络丛。1侧脑室侧脑室左、右各一,分别位于左、右大脑半球内。2第三脑室第三脑室是两侧间脑之间的矢状裂隙，前上方经室间孔与侧脑室相通，向下经中脑水管与第四脑室向通。3第四脑室第四脑室位于脑桥、延髓与小脑之间。第四脑室向下通脊髓中央管,向背侧和两侧分别借第四脑室正中孔和第四脑室外侧孔通蛛网膜下腔。,脑脊液循环,侧脑室,室间孔,脉络丛产生,第三脑室,脉络丛产生,中脑水管,第四脑室,脉络丛产生,正中孔、外侧孔,蛛网膜下隙,蛛网膜颗粒,上失状窦,CerebralFeatures:,SulciSmallgroovesdividingthegyri,CentralSulc

3、usDividestheFrontalLobefromtheParietalLobe,FissuresDeepgrooves,generallydividinglargeregions/lobesofthebrain,LongitudinalFissureDividesthetwoCerebralHemispheres,TransverseFissureSeparatestheCerebrumfromtheCerebellum,Sylvian/LateralFissureDividestheTemporalLobefromtheFrontalandParietalLobes,GyriEleva

4、tedridges“winding”aroundthebrain.,颈总动脉,64排螺旋CT血管造影,NECKANGIO,BRAINANGIO,Anteriorcerebralartery(ACAinred)TheACAsuppliesthemedialpartofthefrontalandtheparietallobeandtheanteriorportionofthecorpuscallosum,basalgangliaandinternalcapsule.Middlecerebralartery(MCAinyellow)ThecorticalbranchesoftheMCAsupplyt

5、helateralsurfaceofthehemisphere,exceptforthemedialpartofthefrontalandtheparietallobe(anteriorcerebralartery),andtheinferiorpartofthetemporallobe(posteriorcerebralartery).ThedeeppenetratingLSA-branchesarediscussedabove.Posteriorcerebralartery(PCAingreen)P1extendsfromoriginofthePCAtotheposteriorcommun

6、icatingartery,contributingtothecircleofWillis.PosteriorthalamoperforatingarteriesbranchofftheP1segmentandsupplybloodtothemidbrainandthalamus.CorticalbranchesofthePCAsupplytheinferomedialpartofthetemporallobe,occipitalpole,visualcortex,andspleniumofthecorpuscallosum.,PosteriorInferiorCerebellarArtery

7、(PICAinblue)ThePICAterritoryisontheinferioroccipitalsurfaceofthecerebellumandisinequilibriumwiththeterritoryoftheAICAinpurple,whichisonthelateralsideThelargerthePICAterritory,thesmallertheAICAandviceversa.SuperiorCerebellarArtery(SCAingrey)TheSCAterritoryisinthesuperiorandtentorialsurfaceofthecerebe

8、llum.BranchesfromvertebralandbasilararteryThesebranchessupplythemedullaoblongata(inblue)andthepons(ingreen).AnteriorChoroidealartery(AchAinblue)TheterritoryoftheAChAispartofthehippocampus,theposteriorlimboftheinternalcapsuleandextendsupwardstoanarealateraltotheposteriorpartofthecellamedia.Lenticulo-

9、striatearteriesThelateralLSAs(inorange)aredeeppenetratingarteriesofthemiddlecerebralartery(MCA).Theirterritoryincludesmostofthebasalganglia.ThemedialLSAs(indicatedindarkred)arisefromtheanteriorcerebralartery(usuallytheA1-segment).Heubnersarteryisthelargestofthemediallenticulostriatearteriesandsuppli

10、estheanteromedialpartoftheheadofthecaudateandanteroinferiorinternalcapsule.,CerebrovascularAccidentAnatomyofCerebralCirculation,BloodSupplyAnterior:CarotidArteriesmiddlepartofthediencephalon(thalamusmetabolismstopsin2minutes;braincelldeath5mins.,CBFtheRosenthalvein(basalvein)anditstributaries;andthe

11、medullaryandsubependymalveins,whichdrainthehemisphericwhitematter.Thedeepsystemdrainstheinferiorfrontallobe;mostofthedeepwhitematterofthefrontal,temporal,andparietallobes;thecorpuscallosum;theupperbrainstem;thebasalganglia;andthethalamus.Theparenchymalalterationsthatoccurwithdeepvenousocclusiontypic

12、allyinvolvethethalami,probablybecausetheprimaryvenouspathwaysthatdrainthethalamiextenddirectlyintotheinternalcerebralveins.Thebasalduralsinusesarecomplexandareinterconnectedwiththecavernoussinuscomplex.Multipleemissarychannelsintheskullbaseconnectwiththesigmoidsinusandjugularbulb.Thesestructuresarem

13、uchmorecommonlyseenatcontrastenhancedMRvenographythanattime-of-flight(TOF)MRvenography.,MIPimagefromcontrast-enhancedMRvenography,withacoloroverlay,demonstratesthesuperiorduralsinuses.Theyincludethesuperiorsagittalsinus(green),inferiorsagittalsinus(lightblue),straightsinus(darkpurple),confluenceofth

14、esinuses(orange),transversesinuses(darkblue),andsigmoidsinuses(yellow).Theinternaljugularveinsandbulbs(lightpurple)alsoaredepicted.,LateralMIPimagefromcontrast-enhancedMRvenography,witheditingofthedeepveinstoimprovethevisibilityoftheascendingveinsthatdrainintothesuperiorsagittalsinusfromthelateralhe

15、misphericcortex(thefrontopolar1,anteriorfrontal2,andposteriorfrontal3veins;Trolardveinsuperioranastomoticvein4;andanteriorparietalveins5)andthelargernamedveinsonthelateralsurfaceofthecerebrum(thesuperficialsylvianveinsuperficialmiddlecerebralvein6,whichtypicallydrainsintothesphenoparietalsinusorthec

16、avernoussinus,andtheLabbevein7,whichdrainsintothetransversesinus).TherelativeluminaldiametersoftheTrolardvein,Labbevein,andsuperficialsylvianveinsarereciprocal.,原始数据(RawData)是CT扫描后由探测器接收到的信号，经模数转换后传送给计算机，其间已转换成数字信号经预处理后，尚未重建成横断面图像的这部分数据被称为原始数据。重建(Reconstruction)原始扫描数据经计算机采用特定的算法处理，最后得到能用于诊断的一幅横断面图像，

17、该处理方法或过程被称为重建或图像的重建。重组(Reformation)是不涉及原始数据处理的一种图像处理方法。如多平面图像重组、三维图像处理等。实际上，目前CT的三维图像处理基本都是在横断面图像的基础上，重新组合或构筑形成了三维影像。,ComputedTomography,CT值=密度值,CT值=(欲求组织的衰减系数水的衰减系数)水的衰减系数1000。骨的衰减系数=1.992。空气的衰减系数=0.00130。水的衰减系数=1。密度值=数字化的密度=CT值。骨的CT值=1000HU；空气的CT值=1000HU；水CT值=0HU。高密度，CT值大，低密度，CT值小。CT胶片画面：高密度：白色。等密

18、度：灰色。低密度：黑色。脑白质CT值：24，脑灰质CT值：36，脂肪CT值：100，凝血CT值：40，钙质CT值：60。,ComputedTomography,ACTimageisapixel-by-pixelmapofX-raybeamattenuation(essentiallydensity)inHounsfieldUnits(HU),HUwater=0,Bright=“hyper-attenuating”or“hyper-dense”,像素和矩阵（pixelandmatrix）：图像的每一个小单元称为像素。某一矩形面积内每一行和每一列的像素数目称为矩阵。像素大小=视野/矩阵。视野：FO

19、V（fieldofview）。视野(FOV)：重建影像的最大直径，通常在12-50cm的范围内。小的FOV可增加影像的空间分辨率.,像素(pixel),ComputedTomography,灰阶（greyscale）CT图像是将重建矩阵中的每一个象素经D/A转换成相应的亮、暗信号在显示器上显示，这些亮暗信号的等级差别称为灰阶，一般将灰阶分为16阶，每阶又有4级连续变化的灰度，共有64个连续的过度等级，因CT值在-1000+1000范围内，所以每级分别代表约31个连续的CT值。,ComputedTomography,TypicalHUValues:,Air1000Fat100to40Water0

20、Otherfluids(e.g.CSF)020Whitematter2035Graymatter3040Bloodclot5575Calcification150Bone1000Metallicforeignbody1000,Brain,ComputedTomography,“SoftTissueWindow”“BoneWindow”,窗口技术（windowstechnology）人眼不能分辨微小的灰度差异，为了提高组织结构的细微显示效果，分辨相邻组织的差别，突出显示诊断需要的图像信息（感兴趣区），通常通过调节图像的对比度和亮度来完成，这种技术称为窗口技术，窗口技术分为窗宽和窗位。,Windo

21、wlevel/widthTechnologywindowlevelwidth/2,例如头颅软组织窗脑组织灰质CT值为40HU窗宽100窗宽上下限=40100/2上限为：90HU高于90HU为白色下限是：10HU低于10HU是黑色,窗宽(windowwidth)指CRT图像上所包括16个灰阶的CT值范围。,窗位(windowlevel)以某组织CT值为中心观察其细节结构。,窗技术=窗位窗宽/2,双窗技术（doublewindowtechnique）双窗技术主要用于CT扫描图像中密度相差太大组织的观察，既要看见低密度组织，又要看见高密度组织，如胸部的肺窗和纵隔窗、骨髂肌肉系统的骨窗和软组织窗等。,

22、窗宽、窗位调节,肺窗,纵隔窗,resolutionratioofDigitizationPixel=FOV（fieldofview）matrixSpatialresolution,contrastofDigitizationCT(value)=(xw)w1000Densityresolution,BrainCirculation,-Totalcessationofbloodflowtothebraincausesunconsciousnesswithin5to10seconds.CBF(adult)Normal50-65ml/100g/minuteIschemia(reversible)8-2

23、3ml/100g/minuteInfarction(irreversible)8ml/100g/minute,CerebrovascularAccidentPathophysiology,Atherosclerosis:majorcauseofCVAThrombusformation由于并发脑水肿呈占位表现可轻度压迫脑室;基底节丘脑区的小梗死称为腔隙性梗死灶;大片脑梗死局部脑组织坏死、软化形成边缘清楚的囊腔,周围脑萎缩,使邻近脑室扩大;中线结构可向病侧移位;出血性脑梗死即在梗死灶中有小的出血,呈低密度影中有高密度出血区。;小脑梗死较少见,见于小脑半球低密度灶。,出血性脑梗死-CT表现脑梗死低密

24、度区内出现出血斑点或团块;密度值7080HU;周围仍见脑水肿带于梗死灶周围;出血灶吸收较快最后仍成低密度区;与高血压脑出血比较,此种出血量较少,影像密度稍低。,Corticalcontusion1cmindiameterThisisascanofapatientwhohassustainedasevereheadinjury.Thereisextensivebruisingoftherightsideofthebrain,showingupasalarge,diffusegreyarea.Youcanalsoseethattherearepatchesofwhitewithinthegreya

25、rea.Thisrepresentsbleeding.Thegreyarearepresentsswelling(oedema).Theareaofthecorticalcontusionisoutlinedinpurple.YouwillnormallyfindacentimetrescaleattherighthandsideofaCTscan.ThisscanwouldbeclassifiedontheEarlyOutcomeFormasCorticalcontusion-greaterthan1cmindiameter.,Oneormorepetechialhaemorrhageswi

26、thinthebrainThepresenceofpetechialhaemorrhagesisusuallyanindicationofaverysevereprimarybraininjury.Petechialhaemorrhagestendtooccurattheinterfaceofgreyandwhitematter.Itcanalsooccurinthedorsolateralquadrantofthemidbrainatthemiddleorangearrow,aswellaselsewherewithinthebrainsubstance.Noteonthisscan,tha

27、tthelateralventriclesandthethirdventriclearevisibleandthereisnomidlineshift.Itisoftenacharacteristicofdiffuseaxonalinjury,inwhichtherearenumerouspetechialhaemorrhagesthatthereisnoevidenceofbrainswelling,ormidlineshift.Thisscanwouldbeclassifiedasshowingone,ormore,petechialhaemorrhageswithinthebrain.,

28、脑挫裂伤(comtusionandlacerationofbrain)是指颅脑外伤所致的脑组织器质性损伤。脑挫伤(contusionofbrain)是外伤引起的皮质和深层的散发小血肿、脑水肿和脑肿胀；脑裂伤(lacerationofbrain)则是脑与软脑膜血管的断裂。两者多同时发生，故称脑挫裂伤。,脑皮质挫伤在脑外伤中多见，外伤机理同前脑皮质表浅部针尖大，线状出血。部位：脑回硬膜嵴，骨嵴处多见颞极，脑下表面，侧颞皮质额极，脑回顶叶凸面。,脑干挫伤剪切伤脑干背外处撞击小脑幕切迹,弥漫性脑损伤(diffuseinjuryofbrain)包括弥漫性脑水肿、弥漫性脑肿胀和弥漫性脑白质损伤。弥漫性脑白

29、质损伤是因旋转力作用导致脑白质、脑灰白质交界处和中线结构等部位的撕裂。病理表现为上述部位神经轴突弥漫性断裂，即所谓轴突剪切伤，部分病例可见小灶出血。,女，20岁车祸伤后意识模糊10h,SWI,弥漫性轴突损伤（diffuseaxonalinjury）,同一病人,SWI,SWI,颅脑损伤后引起颅内继发性出血，血液积聚在颅腔内达到一定体积（通常幕上出血20ml，幕下出血10ml），形成局限性占位性病变，产生脑受压和颅内压增高症状，称为颅内血肿(intracranialhematoma)。颅内出血积聚于颅骨与硬膜之间，称为硬膜外血肿(epiduralhematoma)，约占颅脑损伤的2%3%。硬膜外血

30、肿多发生于头颅直接损伤部位，损伤局部多有骨折。因硬膜与颅骨粘连紧密，故血肿范围局限，形成双凸透镜形。颅内出血积聚于硬脑膜与蛛网膜之间称为硬膜下血肿(subduralhematoma)。为急性、亚急性和慢性硬膜下血肿三类。其血源多为脑对冲伤处的静脉、小动脉或由大脑血上矢状窦汇入的桥静脉撕裂出血。硬膜下血肿常与脑挫裂伤同时存在，可视为脑挫裂伤的一种并发症。,AcuteHemorrhage,IntraparenchymalSubarachnoidSubduralEpidural,ParenchymalHemorrhage,Findings:Largeintraaxialhighattenuation

31、abnormalityintherightparietallobe.Thereismasseffectwitheffacementoftherightlateralventricleandofthesulciintherightcerebralhemisphere.Theleftlateralventricleisdilated.Thereismidlineshifttotheleft.Themostcommoncauseofnontraumaticintracranialhemorrhageishypertension.Thepenetratingbranchesofthemiddleand

32、thebasilararteriesarecommonlyaffected.Therefore,hemorrhageintheexternalcapsule,putamen,thalamusandponsisseen.TeachingPoint:TheleftlateralventricleisdilatedsecondarytoocclusionoftheforamenofMonro.,脑出血,SubarachnoidHemorrhageRuptureofanintracranialaneurysmisthemostcommoncauseofnon-traumaticsubarachnoid

33、hemorrhage.90-95%ofallintracranialaneurysmsarelocatedinthecarotidsystem.Theanteriorcommunicatingarteryisthemostcommonsite(30%),followedbytheposteriorcommunicatingartery(25%)andthemiddlecerebralartery(20%).,Thebromocriptinehadnoeffect,andthepatientwenttoaneurosurgeonforasurgicalopinion.Theneurosurgeo

34、norderedthisMRI.ThelesionpartlyintherightcavernoussinusandpartlyinthesellaturcicaispredominantlyblackonthisT1-weightedimage.IngeneraltherearethreethingsthatareblackonMRI:air,boneandrapidbloodflow.Inthiscaseitisblackduetorapidbloodflowinacarotidaneurysm.,Thisisthecorrespondingangiogram.Obviously,this

35、isnotalesiontobeoperatedontranssphenoidally!,AneurysmvsMeningiomaOneofthemostdifficultdifferentialdiagnosesonCTisaneurysmversusmeningioma.Inthispatientthereisalargemassontherighthandside,possiblyoriginatingfromthemeningesorcavernoussinus.OnCTitisimpossibletotellwhetherthismassisananeurysmorameningio

36、ma.,ThisisanMRIofthesamepatient.Themassispredominantlyblackandthereisalargeflowartefactrunninginthephase-encodingdirection.Thesefindingscorrespondtorapidbloodflow,andthemassmustthereforebeananeurysm.,Angiogramofthesamepatient.Itdemonstratesthattheflowintheaneurysmisnotlaminar,butthatitswirls,gradual

37、lyfillingthelumenwithcontrast.,Intracranialhaematoma-non-evacuatedThisscandemonstratesaleftsidedacutesubduralhaematoma.Thescanistakenthroughaslightlyhigherpartofthebrainandshowsthebodiesofthelateralventricles.Theleftlateralventriclehasbeencompressedandthemidlineisdeviatingtotheright.Therightlateralv

38、entricleisactuallyslightlylargerthannormalandthisisbecausetheincreasedpressureispreventingescapeofthecerebrospinalfluidfromthatventricle.Dilatationofthecontralateralventriclelikethisindicatesthatthereisverysignificantpressureonthebrain.ThisscanwouldbeclassifiedasIntracranialhaematoma-nonevacuatedont

39、heEarlyOutcomeForm.,颅内出血(intracranio-hemorrhage)硬膜外血肿是指外伤后聚集于硬膜外腔的血肿多伴有骨折和硬膜A撕裂病理：头颅直接损伤，骨折，脑膜血管破裂，血液流至颅骨内板与硬膜之间，7080%颞骨、颅骨骨折脑膜中A破裂，由于硬膜与颅骨粘连紧密，出血局限，呈梭形,Tumor,大脑的髓质,（1）联络纤维：联系同侧半球内各部皮质的纤维。上纵束：连接额、顶、枕、颞叶下纵束：连接枕、颞叶钩束：连接额、颞叶扣带：连接边缘叶各部弓状纤维：短纤维,上纵束,钩束,扣带,下纵束,弓状纤维,MENINGIOMA,Meningiomasaccountfor15%ofalli

40、ntracranialtumorsandarethemostcommonextra-axialtumor.Theyoriginatefromtheduraorarachnoidandoccurinmiddle-agedadults.Womenareaffectedtwiceasoftenasmen.Meningiomasarewell-differentiated,benign,andencapsulatedlesionsthatindentthebrainastheyenlarge.Theygrowslowlyandmaybepresentformanyyearsbeforeproducin

41、gsymptoms.Thehistologicpictureshowscellsofuniformsizethattendtoformwhorlsorpsammomabodies.Theparasagittalregionisthemostfrequentsiteformeningiomas,followedbythesphenoidwings,parasellarregion,olfactorygroove,cerebello-pontineangle,andrarelytheintraventricularregion.Meningiomasofteninduceanosteoblasti

42、creactionintheadjacentbone,resultinginacharacteristicfocalhyperostosis.Theyarealsohypervascular,receivingtheirbloodsupplypredominantlyfromduralvessels.,MENINGIOMA,MostmeningiomasareisointensewithcortexonT1-andT2-weightedimages.Aheterogeneousinternaltextureisfoundinallbutthesmallestmeningiomas.Themot

43、tledpatternislikelyduetoacombinationofflowvoidfromvascularity,focalcalcification,smallcysticfoci,andentrappedCSFspaces.Hemorrhageisnotacommonfeature.Aninterfacebetweenthebrainandlesionisoftenpresent,representingaCSFcleft,avascularrim,oraduralmargin.MRhasspecialadvantagesoverCTinassessingvenoussinusi

44、nvolvementandarterialencasement.Occasionally,adenselycalcifiedmeningiomaisencounteredthatisdistinctlyhypointenseonallpulsesequences.Meningiomasshowintenseenhancementwithgadoliniumandaresharplycircumscribed.Theyhaveacharacteristicbroadbaseofattachmentagainstaduralsurface.Associatedhyperostosismayresu

45、ltinthickeningoflowsignalboneaswellasdiminishedsignalfromthediploicspaces.Althoughmeningiomasarenotinvasive,vasogenicedemaispresentintheadjacentbrainin30%ofcases.Contrastscansareespeciallyhelpfulforimagingtheenplaquemeningiomasthatoccurattheskullbase.,脑膜瘤,鞍区脑膜瘤,PituitaryMacroadenomaBydefinition,pitu

46、itarymacroadenomasareadenomasover10mminsize.Theytendtobesoft,solidlesions,oftenwithareasofnecrosisorhemorrhageastheygetbigger.Astheygrow,theyfirstexpandthesellaturcicaandthengrowupwards.Inthisexampleofapituitarymacroadenomathereissuprasellarextensionwithelevationandcompressionoftheopticchiasm.,Becau

47、setheyaresofttumors,theyusuallyindentatthediaphragmasellae,givingthemasnowmanconfiguration.Thisisonefeaturethatcanhelpdistinguishbetweenapituitarymacroadenomaandameningioma.Anotherfeaturewhichcanhelpdifferentiatethemisenlargementofthesellaturcica-thisgenerallyonlyoccurswithpituitarymacroadenomasthat

48、originateinthesella,听神经瘤,T1WIC-,T2WI,T1WIC+,FLAIR,DWI,ADC,扣带回,放射冠,上纵束,脑膜瘤,CEREBRALGLIOMAS,Gliomasaremalignanttumorsoftheglialcellsofthebrainandaccountfor30-40%ofallprimaryintracranialtumors.Theyoccurpredominantlyinthecerebralhemispheres,butthebrainstemandcerebellumarefrequentlocationsinchildren,andt

49、heyarealsofoundinthespinalcord.Thepeakincidenceisduringmiddleadultlife,whenpatientspresentwithseizuresorsymptomsrelatedtothelocationofthegliomasandthebrainstructuresinvolved.Astrocytomasaregradedaccordingtotheirhistologicappearance.Grade1astrocytomashavewell-differentiatedastrocytesandwell-definedma

50、rgins.Theclinicalcourseoftenproceedsovermanyyearsandcompletecuresarepossible.Thepilocyticvariantisalow-gradetumorwithadistinctcapsulethatiscommonlyfoundinchildren.Thegiantcellastrocytomaisaspecializedtumorthatdevelopsfrompre-existinghamartomasinpatientswithtuberoussclerosis.,Grade2astrocytomasarewel

51、l-differentiatedbutdiffuselyinfiltratingtumors.Thefibrillarytypeismostcommon,andalthoughinitiallybenign,theymayevolveintoahighergradetumorovertime.Thischangingcharacterofgliomasmakeshistologicalclassificationdifficultfromsamplebiopsies,becausedifferentpartsofthetumoroftenexhibitvaryingdegreesofmalig

52、nancy.Thehighergradeastrocytomasareverycellularandpleomorphic.Anaplasticastrocytomas(Grade3)areveryaggressivetumors,readilyinfiltrateadjacentbrainstructures,andhaveauniformlypoorprognosis.Glioblastomamulti-forme(Grade4)hastheaddedhistologicfeaturesofendothelialproliferationandnecrosis.Multicentricfo

53、cioftumormaybeseenin4to6%ofglioblastomas.Gliomatosiscerebriisanunusualconditionwithdiffusecontiguousinvolvementofmultiplelobesofthebrain.Oligodendrogliomasarethemostbenignofthegliomas.Calcificationiscommon,andtheyoccurpredominantlyinthefrontallobes.Themixedneuronalandglialtumorsarefoundmostlyinchild

54、renandyoungadults.Theyareslow-growingandarefoundpredominantlyinthetemporallobesandaroundthethirdventricle.Intratumoralcystsandcalcificationarecommon.,CEREBRALGLIOMAS,Thecommonsignalcharacteristicsofintra-axialtumorsincludehighsignalintensityonT2-weightedimagesandlowsignalonT1-weightedimages,unlessfa

55、torhemorrhageispresent.Fatandsubacutehemorrhage(methemoglobin)exhibithighsignalonT1-weightedimages,andacutehemorrhage(deoxyhemoglobin)andchronichemorrhage(hemosiderin/ferritin)showlowsignalintensityonT2-weightedscans.GliomashavepoorlydefinedmarginsonplainMR.Theyinfiltratealongwhitematterfibertracts,

56、andthedeeperlesionshaveapropensitytoextendacrossthecorpuscallosumintotheoppositehemisphere.Theyareoftenquitelargebythetimeofclinicalpresentation.Thehighergradegliomas,particularlyglioblastomas,appearheterogeneousduetocentralnecrosiswithcellulardebris,fluid,andhemorrhage.Peritumoraledemaandmasseffect

57、arecommonfeatures.,CEREBRALGLIOMAS,Followinginjectionofgadolinium,T1-weightedimagesshowirregularringenhancement,withnodularityandnonenhancingnecroticfoci.Asmentionedabove,gliomasareinfiltrativelesions,andmicroscopicfingersoftumorusuallyextendbeyondthemarginofenhancement.Enhancedscansareparticularlyh

58、elpfultooutlinesubependymalspreadoftumoralongaventricularsurface,aswellasleptomeningealinvolvement.Althoughhighlymalignant,anaplasticastrocytomasmayormaynotexhibitbreakdownoftheblood-brainbarrier.Ingeneral,thepresenceorlackofenhancementaloneisnothelpfulingradingastrocytomas.Thelowergradeastrocytomas

59、tendtobemorehomogeneouswithoutcentralnecrosis.Largecysticcomponentsmaybepresent.Thecystshavesmoothwalls,andthefluidisofuniformsignal,todistinguishthemfromnecrosis.Enhancementisvariable,dependingontheintegrityoftheblood-brainbarrier.,CEREBRALGLIOMAS,III级星形细胞瘤低等密度,长T1长T2信号，边缘清或不清.钙化1520%，囊变、坏死及出血少见.90%瘤周无水肿，少数轻度水肿.占位效应：无或轻中度.+C:无强化，或少许轻度强化.血管包埋：脑干.,低度恶性星形细胞瘤,毛细胞型星形细胞瘤,I级，好发于儿童及青少年.小脑（80%）、鞍区、视觉通路、脑干.多为囊性或囊实性，实体及附壁结节强化，囊壁强化.预后较好.,毛细胞型星形细胞瘤,pilocyticastrocytoma,pilocyticastrocytoma,juvenilepilocyticastrocytoma,astrocytomagr