资源描述:
《胎儿小脑ppt课件》由会员上传分享,免费在线阅读,更多相关内容在行业资料-天天文库。
小脑胚胎发育及MRI表现
1目录(一)小脑大体解剖(二)小脑的内部结构(三)小脑组织胚胎学发育(四)小脑的影像学发育
2(一)小脑大体解剖形态学分叶:以原裂和后外侧裂为分界前叶后叶绒球小结叶小脑扁桃体合称为小脑体(由内向外分为三个纵区)蚓部半球中间部半球外侧部
3后外侧裂:小脑下面绒球和小结后方的深沟
4按结构功能分叶:绒球小结叶(原小脑、前庭小脑):在进化上出现最早(其纤维联系及功能与前庭密切相关,维持身体姿势平衡和协调眼球运动)蚓垂、蚓锥体、前叶—旧小脑(控制运动中的肢体远端肌的肌张力和协调)小脑体外侧部及相关侧齿状核——新小脑(协调肢体的随意运动,使运动更精确)
5(二)小脑的内部结构1.小脑皮质:颗粒层梨状细胞层分子层
6
7
8(四)小脑的影像学发育MRI显示小脑结构的发育晚于组织胚胎学发育体内约晚2周体外约晚6周孕22周前建议不做胎儿小脑MRI
91.小脑沟、裂的发育14~19周:MRI图像上不能观察到小脑的裂。20周:可看到原裂,由原裂分隔的山顶和山坡出现。22周:可见原裂和椎体前裂出现,第四脑室显示清晰。蚓锥体和蚓结节可由椎体前裂区分出;次裂前方的蚓垂也可见。24周:可看到原裂、椎体前裂、次裂和后外侧裂;山顶前方的中央小叶可辩。26周:小脑小叶出现很多,裂隙变得复杂,主要的裂都显示清晰。30周以后:小脑小叶增多,各沟裂也显示清楚,在T2WI图像上可见小脑皮质呈片状排列,沟裂显示清晰。30-31周绒球小结叶在T2上呈低信号。这些分叶在正中矢状面上面积的大小随胎龄增大而变化,随着蚓锥体和蚓结节的形成,原裂下方的部分增长迅速,但其中蚓垂的变化不大,而山坡、蚓结节、蚓锥体增长迅速。
102.小脑白质、核团发育情况14周:灰白质分界不明显,没有核团显示;16周:灰白质信号显示出现差别,隐约可见齿状核;28周:可见小脑蚓与周围白质有清晰界限;30周后:T2WI图像上白质对比灰质呈稍高信号,核团现象清晰,轴位上可见上橄榄核和齿状核;
113.小脑蚓部的发育小脑蚓部是从腹侧到背侧发育过程,下蚓部的VI、VIIa及VIIb叶较晚才显示清楚,且18周前下蚓部沟仍存在。Bromley等发现在孕14、15、16周蚓部开放率分别为56%、23%和13%。下蚓部直到孕17.5周仍然开放,因此蚓部发育不全孕18周前无法获得诊断。
124.小脑体积和形态变化14周:颅后窝内腔隙较大,此后随着小脑体积的增大,颅后窝内腔隙逐渐变小,此时的小脑形态不规则,橫径较大而前后径较小,呈扁圆形;小脑半球较小,而小脑蚓的部分较大。20周左右:小脑前后径和上下径均有所增加,与橫径的差异变小,小脑和颅后窝之间仍有空隙存在。
135.小脑毗邻结构的发育情况第四脑室:小脑参与构成第四脑室的顶;14~17周:第四脑室此阶段是一个开放的空间,矢状面上小脑与脑干之间形成被盖—小脑蚓角(平行于被盖经过薄束核的线与小脑蚓腹侧面的线之间的夹角),14周时此角大约为30°,以后几周角度逐渐减小,至17周左右,小脑腹侧面与脑干基本吻合,此角度消失,第四脑室封闭,此后第四脑室形状趋于平稳。小脑幕:14周:小脑幕在图像上未显示;16周:小脑幕出现,但其下端游离,未完全将大脑和小脑分开;20周:小脑幕的下端有了明确的方位,在下端把端脑和小脑分开;24周:小脑幕起始端清楚显示。脑干—蚓部夹角(约4~17°),若此角大于45°,怀疑Dandy-Walker畸形;脑干—幕夹角(21~44°)
141.被盖-小脑蚓角2.齿状核3.原裂4.第四脑室5.锥体前裂6.次裂7.后外侧裂8.小脑蚓
151.被盖-小脑蚓角2.齿状核3.原裂4.第四脑室5.锥体前裂6.次裂7.后外侧裂8.小脑蚓
1628周胎儿轴位T2图像,小脑半球呈多层样;32+4周(b)及32+5周(c)胎儿轴位及冠状位T2图像,小脑齿状回呈低信号
17
18
19
20(三)小脑的纤维联系和功能
21
22
23
24
25
26
27Thethirdphaseofcerebellardevelopmentbeginsinthe16thGWandinvolvesinwardmigrationofthegranulecells,whichpersiststhroughoutfetallife(NakayamaandYamada1999;tenDonkelaaretal.2003).
28Thelaminadissecansisvisiblebetween20and32GWasatransientzoneofmigratingcells(SidmanandRakic1973;NakayamaandYamada1999).Itseparatestheexternalgranularcelllayerfromthedeepinternalgranularcelllayer(Larroche1981;Abrahametal.2001).Thehighestrateofproliferationoccursinthiszonebetween28and34GW(Abrahametal.2001).ThelaminadissecansdisappearsfromtheflocculusandsubsequentlyfromthehemisphereswhilethePurkinjecelllayerbecomesmoreprominentalongtheoutersurfaceofthelaminadissecansasitdisappears.Postnatally,theexternalgranularlayerdisappearsaround10monthsofage,leavingthreelayersofcerebellarcortex(Larroche1981).
29Thesecondcerebellardevelopmentalphaseiscellproductionintwogerminalmatrixzonesthatdisappearafterbirthwhicharebelievedtobethesourceofcerebellarneurons,theventricularzone,andtherhombiclips(Hynesetal.1986).Thefirstregionistheventricularzoneintheroofofthefourthventricle,fromwhichoriginateinitiallyPurkinjecellsanddeepcerebellarneurons,andsubsequentlybasketcells,stellatecells,andGolgicells(tenDonkelaaretal.2003;Sotelo2004).Cellsmigratefromtheventricularzonetowardthesparselycellularoutermarginallayertoformtheintermediatezoneat5–10GW(Larroche1981).Theinternalgranularlayerdevelopsbymigrationinaradialfashion(Hynesetal.1986).Theexternalgranularlayer,thesecondgerminalzonedevelopsbetweenthe9thand13thGWandoriginatesbymeansoftangentialmigrationfromtherhombiclips(Larroche1981)whicharemoredorsolaterallylocatedinthemetencephalonbetweentheroofplateandthedorsalneuroepitheliumatthecaudalaspectofthefourthventricle(Sotelo2004).Therostralrhombiclipneuroepitheliumgivesrisetomigratingcellswhichbegintomovetothesurfaceat11–13GWinasecondwave,whichbecomesthegranulecelllayerafterbirth(Hynesetal.1986).Pontinenucleiandtheinferiorolivarynucleusarisefromthecaudalportion(NakayamaandYamada1999;Sotelo2004).
30Inthefourthphaseofcerebellardevelopment,thereisfurthercelldifferentiationanddevelopmentofneuronalcircuitsandcerebellarfunction(tenDonkelaaretal.2003).
31Anatomically,thefirstareatoformistheflocculonodularlobe(Adamsbaumetal.2005)andthefirstfissuretoappearistheposterolateralfissureat12–13GW.Theprimaryfissuredevelopsat14–15GW,andisdeepestinthemidline.Prepyramidal,preculminate,andprecentralfissuresareseenat15–16GW.Thehorizontalfissureisvisibleby21GW(Adamsbaumetal.2005).Foliationofthevermisbeginsat14GW.Thedeepgraymatternucleiofthecerebellumoriginatefromtheventricularzone.Thedentatenucleimaybedetectedby11GW(YamaguchiandGoto1997)to16GW(MihajlovicandZecevic1986).Thevermisisformedatthetimeofthefusionofthecerebellarhemispheresattheendofthe8thGW.Thecerebellarhemispheresgrowfasterthanthevermisandattainamaturemorphologyby22GW.