Andersons pediatric cardiology 206
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FIG.7.14 Congenitalpulmonarylymphangiectasiasecondaryto
hypoplasticleftheartsyndromewithrestrictiveatrialseptum.TheT2weightedfastspinechoimagingofthelungparenchymashowshighsignal
linearstructuresinthelunginterstitiumcorrespondingtodilatedlymphatics
inthesettingofpulmonaryvenousobstruction.
Newbornswithtranspositionofthegreatarteriesarepronetopulmonary
hypertension.Oneautopsyseriesfromthe1990srevealedahighincidenceof
severepulmonaryvascularobstructivedisease,indicatingthatthisremainsan
importantassociationwithanincreasedriskofmorbidityandmortalityinthe
modernmanagementoftransposition.44Interestingly,historicalautopsyand
morerecentpostoperativeangiographicseriesrevealahighprevalenceof
enlargedbronchialarteriesininfantswithtransposition.45Theseaortopulmonary
collateralshavebeenobservedonfetalechocardiography,andabnormalfetal
hemodynamicshavebeenimplicatedintheseverepulmonaryvasculardisease
associatedwithasmallproportionofpatientswithtransposition.46
Echocardiographicserieshavelinkedthepresenceofpersistentpulmonary
hypertensionofthenewbornwithrestrictionofflowattheductusarteriosusand
foramenovale,whichalsohavebeenassociatedwiththeneedforurgentballoon
atrialseptostomyforneonatalcyanosis.47Inasmallseriesoffetuseswith
transposition,wedemonstratedreducedforamenovaleandductusarteriosus
flowandincreasedsystemictopulmonarycollateralflowcomparedwithnormal
controls.48Followingasuccessfularterialswitchoperationintheneonatal
period,thesubjectwiththemostsignificantreductioninforamenovaleflowin
uterosubsequentlydevelopedseverepulmonaryvasculardiseaseandwaslisted
forlungtransplant.Wehavehypothesizedthatthepulmonarycirculationmight
beexposedtoacombinationofseverehypoxemiaandhighbloodpressurein
fetuseswithtranspositionwithsignificantrestrictionattheforamenovaleand
ductusarteriosus.ThishypotheticalmodelisillustratedinFig.7.15.However,
wehaveyettoobservereducedoxygensaturationsinthepulmonaryarteriesin
thefetuseswithtranspositionwehavestudiedwithMRoximetry.
FIG.7.15 Hypotheticalmechanismforthedevelopmentofpulmonary
vasculardiseaseintranspositionofthegreatarteries.Initially,fetal
streamingresultsinwell-oxygenatedbloodpassingintothelungs(left).
Thisleadstopulmonaryvasodilationandreducedflowacrosstheductus
arteriosusandforamenovale.Thepulmonarycirculationandleftheart
becomeisolatedfromtherestofthecirculationandthushypoxemic
(center).Thisdrivesthedevelopmentofaortopulmonarycollateralvessels,
withthelungsthereforeexposedtohighpressureandhypoxemia:a
potentialcauseofpulmonaryvasculardisease.AAo,Ascendingaorta;DA,
ductusarteriosus;FO,foramenovale;IVC,inferiorvenacava;LA,left
atrium;LV,leftventricle;MPA,mainpulmonaryartery;PBF,pulmonary
bloodflow;RA,rightatrium;RV,rightventricle;UV,umbilicalvein.
Conclusion
AlthoughcardiovascularMRIhasyettocontributesignificantlytopatientcare
infetuseswithCHD,ithasbeenusedtoconfirmfetalhemodynamiceffects
resultingfromtheobstructionstoflowandabnormalconnectionsthat
characterizeCHD.Wehavelearnedhowthedisruptionofthenormalfetal
circulationmayaccountforthedelayedbraingrowthandabnormalitiesofthe
pulmonarycirculationthathavebeendescribedinnewbornswithCHD.
TechnicalchallengestoMRimagequalityarebeingovercomewithmotion
correctionandacceleratedacquisitiontechniques,suchasradialk-space
trajectoriesandundersamplingwithcompressedsensingreconstruction
methods.49Anexampleofthequalityoftheanatomicimagingthatcanbe
achievedinalate-gestationfetuswithtranspositionusingthisapproachisshown
insupplementalfile2.Theanatomicdetailprovidedbythisapproachmay
surpassfetalechocardiographyinlategestation,whenpooracousticwindows
mayhamperultrasound.IfcardiacanatomicimagingwithMRIinthissetting
becomesmorewidelyadopted,itispossiblethattheclinicalsignificanceofthe
additionalhemodynamicdataprovidedbyMRIbecomesmoreapparent.Thus
MRImaycontributetomodifiedmanagementapproachestofetalCHDmade
possiblebynewtechnologysuchastheexuterophysiologicsupportofthefetus
recentlyreportedinfetalsheep.50
