UltrasoundObstetGynecol:133 - PDF document

UltrasoundObstetGynecol:133–138PublishedonlineinWileyInterScience(www.interscience.wiley.com).Fromnuchaltranslucencytointracranialtranslucency:towardstheearlydetectionofspinabiÞdaR.CHAOUI†*andK.H.NICOLAIDES‡PrenatalDiagnosisandHumanGenetics,Berlin,GermanyandHarrisBirthrightResearchCentreforFetalMedicine,King’sCollegeHospitalandDepartmentofFetalMedicine,UniversityCollege,London,UK Itisnowclearthatthevastmajorityofmajorfetalabnormalitiescanbediagnosedprenatallybyultrasound,thatmostoftheseabnormalitiescanbedetectedinthersttrimesterofpregnancyandthatwomenwantrst-trimesterratherthanlaterdiagnosis.Itisalsoclearthateffectivediagnosisoffetalabnormal-itiesoftennecessitatestheidenticationofeasilyrecogniz-ablemarkerswhichdirecttheattentionofthesonographertothespecicabnormality.Goodexamplesofsuchmark-ersarethescallopingofthefrontalbones(the‘lemon’sign) thoughttobetheconsequenceofleakageofcerebrospinaluidintotheamnioticcavityandhypotensioninthesubarachnoidspacesleadingtocaudaldisplacementofthebrainandobstructivehydrocephalus.InthesecondtrimesterofpregnancythemanifestationsofArnold–Chiarimalformationarethelemonandbananasignsandinthersttrimestercaudaldisplacementofthebrainresultsincompressionofthefourthventricleand ChaouiandNicolaides NBThalamusMBBSCMIT Figure1Exactmid-sagittalplaneofthefetalfaceat13weeks(crown–rumplength,69mm)showingthenasalbone(NB),nuchaltranslucency(NT),thalamus,midbrain(MB),brainstem(BS),cisternamagna(CM)andfourthventricle.Thefourthventricleappearsasanintracranialtranslucent(IT)areabetweentwoechogenicborders,theposteriorborderofthebrainstemanteriorlyandthechoroidplexusofthefourthventricleposteriorly.MeasurementoftheITisachievedbyplacingthecalipersontheanteriorandposteriorechogenicbordersofthefourthventricle.diameterandplacingthecalipersontheanteriorandposteriorechogenicborders.Exactmid-sagittalandparasagittalplanesTheexactmid-sagittalplaneisidealformeasuringITasitisformeasuringNTandassessingthenasalbone.InthisplanewecanidentifytheuidwithinthethirdventriclebetweentherightandleftthalamiandtheaqueductofSylviusbetweenthecerebralpeduncles,althoughthethalamiandpedunclesthemselvesarenotvisible.Theintracranialstructures,includingthethalamus,midbrain,brainstem,fourthventricleandcisternamagna,canbeidentiedeasilyinaslightlydeviatedparasagittalplane.Indeed,asshownintransverseviewinFigure2,thefourthventricleremainswideoneithersideofthemidline,thereforetheeffectofmeasuringtheITinplanesthatareslightlydeviatedfromtheexactmid-sagittaloneshouldbeminimal.GestationalageforassessmentofITTheoptimalgestationalageformeasurementoffetalNTis110to136weeks.Thereasonsforselecting11weeksastheearliestgestationare:rstly,screeningnecessitatestheavailabilityofadiagnostictestandchori-onicvillussamplingbeforethisgestationisassociatedwithtransverselimbreductiondefectsandsecondly,manymajorfetalabnormalitiescanbediagnosedattheNTscan,providedtheminimumgestationis11weeks.Thereasonsforselecting13weeksand6daysastheupperlimitare:rstly,toprovidewomenwithaffectedfetuses NTCPIT Figure2(a)Parasagittalplaneofthefetalfaceat13weeks,withvisiblechoroidplexus(CP).(b)Thetransverseviewoftheheadatthelevelofthefourthventricleobtainedtransvaginallydemonstratesthatmilddeviationsininsonationfromthemidline(solidline)haveminimaleffectonthemeasurementofintracranialtranslucency(IT).NT,nuchaltranslucency.2010ISUOG.PublishedbyJohnWiley&Sons,Ltd.UltrasoundObstetGynecol:133–138. Editorial Figure3Intracranialtranslucency(calipers)infourfetusesscannedtransabdominallyat11–13weeks.Thefetalcrown–rumplengthwas48mminthefetusin(a),63mmin(b),75mmin(c)and81mmin(d).theoptionofrst-ratherthansecond-trimestertermina-tion,secondly,theincidenceofabnormalaccumulationofnuchaluidinchromosomallyabnormalfetusesdecreasesafter13weeksandthirdly,thesuccessratefortakingameasurementdecreasesafter13weeksbecausethefetusbecomesvertical,makingitmoredifculttoobtaintheappropriateimage.At11–13weeksitispossibletodiagnoseseverebrainabnormalities,includingholoprosencephaly,ven-triculomegaly,acrania-exencephalyandencephalocele.Withinthegestationalagerangeof11–13weekstheanteroposteriordiameteroftheITincreaseswithfetalcrown–rumplength(CRL)fromamedianof1.5mmataCRLof45mmto2.5mmataCRLof85mm(Figure3)Extensivesonographicstudiesofthedevelopinghumanbrainhavereportedthatthefourthventricleiseasilyidentiedfrom8weeksasahypoechoicstructureTheextenttowhichtheITinfetuseswithspinabidaisalteredbefore11weeksremainstobedetermined.Thefourthventriclecanalsobeidentiedeasilyafter13weeksandthediameterincreaseswithgestational.However,fromthe14weekonwardsopenspinabidacanbeunmaskedeasilybythelemonandbananasignsanditisthereforeunlikelythatmeasurementofITwillbeusedforthispurposeinthesecondtrimesterofFetalpositionforassessmentofITAt11–13weeksthefetalnasalboneisconsideredtobeabsentinabout60%offetuseswithtrisomy21comparedwith1–3%ofeuploidfetusesandthereforeassessment2010ISUOG.PublishedbyJohnWiley&Sons,Ltd.UltrasoundObstetGynecol:133–138. ChaouiandNicolaides ITIT1 Figure4Visualizationoftheintracranialtranslucency(IT)inthreefetusesinapronepositionat12weeks’gestation(crown–rumplengths,62–64mm).Thereisshadowingofthebrainbytheoccipitalbone.Images(a)and(b)wereobtainedbytransabdominalsonographyandimage(c)wasobtainedtransvaginally. Figure5Transvaginalsonography(mid-sagittalplane)intwofetusesat12weeks.Althoughinbothcasestheresolutionwashigh,in(a)thefourthventricleandotherstructuresofthebrainarenotvisualizedclearlyand,althoughin(b)theintracranialtranslucency(IT)isclearlyvisible,thecontrastdiscriminationispoorerthanthatofmid-sagittalplanesofthefaceobtainedtransabdominally(cf.Figures1–3).ofthenasalboneimprovestheperformanceofrst-trimesterscreeningforaneuploidies.Althoughthenasalbonecanbeexaminedwhenthefetusisinthepronepositiontheassessmentiseasierwhenthefetusisfacingthetransducer.Asforthenasalbone,assessmentofITispreferablewhenthefetusisfacingthetransducer.Althoughthefourthventriclemaybevisiblewhenthefetusisintheproneposition,adequateexaminationofthefetalbrainisoftenhamperedbyshadowingfromthefetaloccipitalbone(Figure4).Transabdominalvs.transvaginalassessmentofITTheexactmid-sagittalplaneofthefetalfacenecessaryformeasurementoffetalNTandassessmentofthenasalboneisobtainedmoreeasilybytransabdominalthantransvaginalsonography,becausethelatterallows2010ISUOG.PublishedbyJohnWiley&Sons,Ltd.UltrasoundObstetGynecol:133–138. Editorial IT Figure6Three-dimensionalvolumeofthefetalheadat12weeksacquiredtransvaginallyanddisplayedintheorthogonalmodecombinedwithstaticvolumecontrastimaging.Thereferencedotisplacedinthecenterofthefourthventricle(a)andtheimageisthenadjustedtoobtainareconstructedmid-sagittalplaneofthebrain(b)formeasurementoftheintracranialtranslucency(IT).lesstransducermanipulation.However,theobjectiveofthe11–13-weekscanisnotrestrictedtoscreeningforfetalaneuploidiesbutincludestheearlydiagnosisofallmajordefectsthroughasystematicexaminationofthewholefetalanatomy.Sincetheresolutionoftransvaginalsonographyintheassessmentofmostfetalorgansissuperiortothatofthetransabdominalroute,fetalmedicineexpertsoftenusebothapproachesfordetailedearlyfetalexamination.Thefourthcerebralventriclecanbevisualizedbothtransabdominallyandtransvaginally.However,asinthecaseoffetalNTandnasalbone,assessmentandmeasurementofITisbestcarriedoutinthemid-sagittalplaneofthefetalface,whichiseasiertoobtaintransabdominally.Additionally,withtransvaginalsonographyeveninthemid-sagittalplaneofthefetalfacethedifferenceincontrastbetweentheITandsurroundingbrainisoftenpoor(Figure5).Ifthetransvaginalrouteischosenforassessmentofthefourthventricleitispreferablethatthetransducerisdirectedtowardstheposteriorfossa(Figure4c)ratherthantheface(Figure5a).Three-dimensionalultrasoundforassessmentofITThree-dimensionalultrasoundisusefulinassessingITparticularlywhenitisdifculttoobtainthemid-sagittalplanedirectlybytwo-dimensionalultrasound.Insuchcasesatransverseviewofthefetalheadatthelevelofthefourthventricleisobtained.Thisisbestachievedbytranvaginalsonographybecausetheresolutionishigher.Athree-dimensionalvolumeisthenacquiredanddisplayedintheorthogonalmode.Thereferencedotisplacedinthecenterofthefourthventricleandtheimageisthenrotatedtoalignthemidlineandobtainamid-sagittalplaneofthebrainforITmeasurement(Figure6).Thisissimilartotheapproachusedinthesecond-trimesterscanfordemonstrationofotherfetalintracerebralstructures,suchasthecorpuscallosumandvermis.Toenhanceimagequality,athinthree-dimensionalslice(volumecontrast)insteadofasimpleplanecanbeused,forexamplebyapplyingastaticvolumecontrastimagingtool.Closingtheloopinthe11Ð13-weekscanInthe1980s,themainmethodofscreeningforopenspinabidawasbymaternalserum-fetoproteinataround16weeksandthemethodofdiagnosiswasamniocente-sisandmeasurementofamnioticuid-fetoproteinandacetylcholinesterase.Althoughitwaspossibletodiag-nosetheconditionbyultrasonographicexaminationofthespine,thesensitivityofthistestwaslow.How-ever,theobservationthatopenspinabidawasassociatedwiththelemonandbananasignshasledtothereplace-mentofbiochemicalassessmentwithsecond-trimesterultrasonography,bothforscreeningandfordiagnosisofthisabnormalityInthe1970s,themainmethodofscreeningfortri-somy21wasbymaternalageandinthe1980sitwasbymaternalserumbiochemistryanddetailedultrasono-graphicexaminationinthesecondtrimester.Inthe1990stheemphasisshiftedtothersttrimesterwhenitwasrealizedthatthegreatmajorityoftrisomicfetuseshaveincreasedNTthatcanbedetectedeasilyinamid-sagittalplaneofthefetalfaceat11–13weeks.Improvedperfor-manceofscreeningwasachievedsubsequentlywiththeobservationthatinthesamemid-sagittalplaneasformeasurementofNTitwaspossibletoexaminethenasalbone,whichisoftenabsentintrisomicfetuses.Itisnowclearthatinthissamemid-sagittalplanethefourthcerebralventricleiseasilyvisibleasanITandthatatleastinsomecasesofopenspinabida,caudaldis-placementofthebrainisevidentfromthersttrimester,2010ISUOG.PublishedbyJohnWiley&Sons,Ltd.UltrasoundObstetGynecol:133–138. ChaouiandNicolaidesresultinginlossofthenormalIT.Itiscertainthatsonogra-phersinvolvedinrst-trimesterscreeningforaneuploidieswillendeavourtoobtaintheexactmid-sagittalplaneofthefetalfaceandastheireyesmovefromtheNTtothenasalboneitisinevitablethattheywillalsoglanceattheIT.Ifthisisnotvisiblethesonographerswillbealertedtothepossibilityofanunderlyingopenspinabidaandwillundertakedetailedexaminationofthefetalspine.ProspectivelargestudieswilldeterminetheproportionofaffectedfetusespresentingwithabsentITandtheextenttowhichthe11–13-weekscancanprovideaneffectivemethodforearlydiagnosisofopenspinabida.1.ChaouiR,BenoitB,Mitkowska-WozniakH,HelingKS,Nico-laidesKH.Assessmentofintracranialtranslucency(IT)inthedetectionofspinabidaatthe11–13-weekscan.ObstetGynecol:249–252.2.NicolaidesKH,CampbellS,GabbeSG,GuidettiR.Ultrasoundscreeningforspinabida:cranialandcerebellarsigns.:72–74.3.VandenHofMC,NicolaidesKH,CampbellJ,CampbellS.Evaluationofthelemonandbananasignsinonehundredandthirtyfetuseswithopenspinabida.AmJObstetGynecol:322–327.4.GhiT,PiluG,FalcoP,SegataM,CarlettiA,CocchiG,SaniniD,BonasoniP,TaniG,RizzoN.Prenataldiagnosisofopenandclosedspinabida.UltrasoundObstetGynecol:899–903.5.PiluG,GhiT,CarlettiA,SegataM,PeroloA,RizzoN.Three-dimensionalultrasoundexaminationofthefetalcentralnervousUltrasoundObstetGynecol:233–245.6.BlaasHG,Eik-NesSH,KiserudT,HellevikLR.Earlydevelop-mentofthehindbrain:alongitudinalultrasoundstudyfrom7to12weeksofgestation.UltrasoundObstetGynecol151–160.7.Timor-TritschIE,MonteagudoA,SantosR.Three-dimensionalinversionrenderingintherst-andearlysecond-trimesterfetalbrain:itsuseinholoprosencephaly.UltrasoundObstetGynecol:744–745.8.KimMS,JeantyP,TurnerC,BenoitB.Three-dimensionalsonographicevaluationsofembryonicbraindevelopment.UltrasoundMed:119–124.9.BlaasHG,Eik-NesSH.Sonoembryologyandearlyprenataldiagnosisofneuralanomalies.PrenatDiagn312–325.10.GoldsteinI,MakhoulR,TamirA,RajamimBS,NismanD.Ultrasonographicnomogramsofthefetalfourthventricle:additionaltoolfordetectingabnormalitiesoftheposteriorJUltrasoundMed:849–856.11.PiluG,GhiT,CarlettiA,SegataM,PeroloA,RizzoN.Three-dimensionalultrasoundexaminationofthefetalcentralnervousUltrasoundObstetGynecol:233–245.12.CampbellS,Pryse-DaviesJ,ColtartTM,SellerMJ,SingerJD.Ultrasoundinthediagnosisofspinabida.1065–1068.13.RobertsCJ,EvansKT,HibbardBM,LaurenceKM,RobertsEE,RobertsonIB.Diagnosticeffectivenessofultrasoundindetectionofneuraltubedefect:theSouthWalesexperienceof2509scans(1977–1982)inhigh-riskmothers.1068–1069.2010ISUOG.PublishedbyJohnWiley&Sons,Ltd.UltrasoundObstetGynecol:133–138.