Andersons pediatric cardiology 162

producea3Dvolume(Video6.8).Thereareseveraluniquematurationalfeatures
ofthenormalearlyhumanfetalheart.Onexternalexaminationat11weeks’
gestation(Fig.6.6),theatrialappendagesarelargecomparedwiththerelatively
smallatrialchambers,andthecoronaryarteriesareprominent.Internallythe
normaloff-setofthemitralandtricuspidvalvesisinfrequentlyappreciated
before13gestationalweeks,andtheperimembranousregionandmuscularpart
oftheventricularseptumarethickened.Thesemilunarvalvesaregelatinousand
poorlydelaminatedfromthearterialwalls.Thearterialwall-to-lumenratiointhe
firsttrimesterfetusisthreefoldthatofthemid-secondtrimesterspecimens.
Histologicstainingofthe3-µmresolutionslicesisfeasibleandprovidesmore
informationaboutgestationalchangesinthenormalandmalformedheart.A
comparisonoftheinformationavailablefrom4Dhigh-resolutiontransvaginal
sonographyofthefirst-trimesterfetalheartandHREMconfirmstherelatively
poorultrasounddetailavailabletousclinicallyatthisearlygestationalage.47



FIG.6.6 Inthisnormal11-weekheart(modeledwithanisotropic
resolutionof3µm),severalspecificfeaturesofthehumanfetalheartcan
clearlybeobserved,includinglargeatrialappendages,prominentcoronary
arteries,andtherelativelysmallsizeoftheatrialchambers(BandF).
Detailedstructurescanbeseenmoreclearlyinthehigh-resolution
episcopicmicroscopyreconstruction(B)thanintheoriginalphotograph(A).
Volumerendering,whichallowsinternalmorphologyofthehearttobe
examinedathighresolution,showsthickenedgreatarterialwalls(C–E)
anddetailsofvalveandseptalarchitecture(CandD).Multiplanar
reconstructedimagesdemonstratedetailedstructuresoftheinsideof
cardiacchambers(EandF).Ao,Aorta;AV,aorticvalve;EV,eustacian
valve;FF,foramenflap;LA,leftatrium;Lapp,leftatrialappendage;LV,left
ventricle;MV,mitralvalve;PT,pulmonarytrunk;PV,pulmonaryvalve;RA,
rightatrium;Rapp,rightatrialappendage.(FromMatsuiH,MohunT,

GardinerHM.Three-dimensionalreconstructionimagingofthehuman
foetalheartinthefirsttrimester.EurHeartJ.2010;31[4]:415.)

Theseobservationssuggestwecontinuetoexercisecautioninthe
interpretationoffirsttrimesterechocardiographicstudiesas2Dechoandcolor
Dopplerimagingmayerroneouslygivetheimpressionofvalvarstenosisand
narrowedoutflowtracts,orofanatrioventricularseptaldefect.

Micro-ComputedTomography
Micro-CTprovidesnear-histologiclevelsofdetailintheearlygestationhuman
heart.Ithasexposuretimesbetween500and1000msandproducesisotropic
voxelsizesbetween19and31µm,dependingonspecimensize.48Similarto
HREM,postprocessingtechniquesallowthedigitalremovalofsupporting
material,andmultiplanarreconstructions,tocreatevirtualdissectionsofthefetal
heart(Fig.6.7).IthastheadvantageoverHREMofbeingnondestructivesothe
imagescanbereexaminedbyotherspecialiststoprovideadditionaldiagnostic
opinions(whilereducingtheneedfortransportationoftissues),anditcanimage
largersizedspecimensthanHREM.Itmaybesuperiortotraditionalautopsyin
assessmentofthemyocardium,anditsresolutionissuperiorto1.5Tesla
MRI49,50andusesfarshorterimagingtimes,usuallylessthan1hour.Current
challengesincludetheeffectsoftissuecolorationanddistortionsecondaryto
fixationandtheuseofcontrast.Inaddition,thefilesizesareverylarge(10to30
GB),andthismayprovideapracticalbarriertoitsroutineimplementationfor
fetalpostmortem.