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1、305jum_online.qxp:Layout14/21/111:20PMPage591COMMENTARYTheIsolatedMildlyEnlargedCisternaMagnaintheThirdTrimesterMuchAdoAboutNothing?AshaJ.Heard,MDAdamC.Urato,MDTuftsMedicalCenterBoston,MassachusettsUSAase—A30-year-oldwoman,gravida1,presentsat32weeksCforsonographytoassessfetalgrowth.She
2、isotherwisehealthy,andherpregnancyhasbeenuncomplicated.Her18-weekanatomyscanresultswerenormal.Herserumscreenforaneuploidywaslowrisk.Onthissonographicexamination,thefetusisfoundtohavenormalgrowthandfluid.Theanatomicsurveyre-sultsarenormalasidefromacisternamagnathatmeasures11mm.Theremain
3、deroftheintracranialanatomyisnormal.Howdoyoucounselher?Withadvancesinfetalsonography,varia-tionsinfetalanatomyandstructurearebeingidentified.Inparticular,posteriorfossaab-normalitiesposeachallengingdiagnos-ticandmanagementdilemma,astheyInparticular,posteriorfossaareoftendifficulttointe
4、rpret,andabnormalitiesposeachallengingtheneonataloutcomeisdifficulttodiagnosticandmanagementaccuratelypredict.Outcomesforneonateswithposteriorfossaab-dilemma,astheyareoftendiffi-normalitiesdiagnosedantenatallyculttointerpret,andtheneona-canrangefromnormaltoseverede-taloutcomeisdifficul
5、ttovelopmentaldisabilities.accuratelypredict.Thecisternamagnacontainscere-brospinalfluidandislocatedbehindthecerebellumintheposteriorfossaofthebrain.ItcommunicateswiththefourthventricleviatheforaminaofMagendieandLuschka.Measurementoftheanteroposteriordiameterofthecisternamagnacanbeusef
6、ulindiag-nosingposteriorfossaabnormalities.Anenlargedcisternamagnahasbeendefinedasmeasuringgreaterthan10mm.1Theoptimaltimetoassesstheposteriorfossafordiagnosisofabnormalitieshasbeendebatedintheliterature.Embryologically,completeposteriorfossadevelopmentisthoughtAddresscorrespondencetoA
7、shaJ.Heard,MD,tooccurbetween18and22weeks.Therefore,cautioninmakingaTuftsMedicalCenter,800WashingtonSt,Boxdiagnosisofcerebellardysgenesisbefore18weeksiswarranted.2360,Boston,MA02111USA.However,false-positivefindingshavealsobeenreportedatlaterges-E-mail:aheard@tuftsmedicalcenter.orgtat
