Andersons pediatric cardiology 1111

InfundibularStenosis
Purenarrowingofthemuscularsubpulmonaryinfundibulumisrareinthesetting
ofanintactventricularseptum.Probablymanyofthecasesdescribedashaving
isolatedinfundibularstenosisalsohadaventricularseptaldefect,whichthen
closedspontaneously.

CombinedValvarandInfundibularStenosis
Hypertrophyofthesubpulmonaryinfundibulumoccursalongwithhypertrophy
oftherestoftherightventricleinresponsetovalvarstenosis.Thisreducesthe
infundibulardiameter.Endocardialfibroelastosismayalsobeseenalongwith
thehypertrophy.Suchreactivestenosisisanimportantcomponenttobenoted
whentheresultsofballoonvalvoplastyarejudged,sincetimeisneededforits
regression.

OtherTypesofStenosisOccurringWithinthe
RightVentricle
Othertypesofstenosiswithintherightventriclearerarewhentheventricular
septumisintact.Hypertrophyofthebodyoftheseptomarginaltrabeculation,
whichinitsseverestformproducesthetypicaltwo-chamberedrightventricle,is
usuallyfoundwithaventricularseptaldefect.7Itcanoccurwithanintact
septum.Inotherpatientsthevalvesoftheembryonicvenoussinuscanpersist
andbecomesoexpandedandaneurysmalthattheypassthroughthetricuspid
valveandobstructthepulmonaryoutflowtract.Thisiscalledspinnaker
syndrome.8Aneurysmaldilationofthemembranousseptumcanalsoproduce
subpulmonarystenosis,9ascancardiactumors10oraneurysmoftheright
coronarysinusoftheaorta.11Hypertrophiccardiomyopathycanalsoafflictthe
rightventricle,particularlyinthesettingoflentiginosis,althoughleftventricular
obstructionusuallydominates.

PulmonaryArterialStenoses
Stenosesofthepulmonaryarterialtreearefrequentinassociationwithcomplex

malformationssuchastetralogyofFallotortransposition.Theycanalso
complicatemoresimplelesions,suchaspulmonaryvalvarstenosisorventricular


septaldefect.Stenosesinthepulmonaryarteriescanalsooccurinisolationand
canbefoundinvariouspartsofthepulmonaryarterialtree.12Thusthestenosis
maybelocalizedandcentralwithinthepulmonarytrunk,involvethe
intrapericardialpartoftherightandleftpulmonaryarteries,orbelocalizedand
peripheralatthesitesofbranchingofmajorintrapulmonaryarteries.Itcanalso
bemoreextensive,producinghypoplasticarterialsegmentscommencingeither
attheendoftherightorleftpulmonaryarteryoratamajorintrapulmonary
branchpoint.Whenfound,thechangesareoftennotlimitedtothepulmonary
arteriesbutalsoinvolvethesystemicvessels.13

DevelopmentalConsiderations
AsdescribedinChapter3,theheartdevelopsasatubularstructure,initiallywith
asolitarylumen.Remodelingofthelumenoftheoutflowtracttoproducethe
aorticandpulmonarychannels,eachwithitsownarterialvalve,involvestissues
derivedfromseveralsources.Thewallsoftheoutflowtractarederivedfromthe
secondheartfield,withthewallsinitiallybeingmyocardialtothemarginsofthe
pericardialcavity.Additionalcontributionsfromthesecondheartfieldthen
producethenonmyocardialwallsoftheintrapericardialarterialtrunksandthe
arterialvalvarsinuses.14Septationtheninvolvescomponentsdevelopedwithin
theoutflowtractitselfbutalsoanextrapericardialcomponentgrowingfromthe
dorsalwalloftheaorticsac.Bothsourcescontaintissuesinitiallyderivedby
migrationfromtheneuralcrest.15Theprotrusiongrowingfromthedorsalwall
oftheaorticsacdividesthedistalpartoftheoutflowtractintothe
intrapericardialcomponentsofthearterialtrunks.Thecushionsdeveloping
throughouttheoutflowtract,incontrast,separatethecomponentsofthe
developingarterialrootsand,similarly,separatetheventricularoutflowtracts.

Thesecushions,packedwithcellsderivedfromtheneuralcrest,fusewitheach
otherinadistal-to-proximaldirection.However,onlythecentralpartsofthe
distalcushionsfusetogether.Theperipheralparts,whichoccupythe
intermediatepartoftheoveralllengthoftheoutflowtract,remainunfused.
Togetherwiththeintercalatedcushions,whicharealsodevelopedinthe
intermediatepartoftheoutflowtract,theyproducetheprimordiaofthe
developingaorticandpulmonaryvalves.Atthebeginningofthesechanges,
whichwilleventuallyleadtoformationofthearterialroots,thecushions
themselvesremainencasedinaturretofmyocardium.Already,however,the
mostdistalpartoftheoutflowtracthasseparatedintotheintrapericardial


componentsoftheaortaandthepulmonarytrunk,witheachtrunkdevelopingits
owndiscretewalls(Fig.42.10).Thedistalendsoftheoutflowcushions
themselvesthenexcavatetoproducethevalvarleafletsandtheirsemilunar
hinges(Fig.42.11).16

FIG.42.10 Imagestakenfromanepiscopicdatasetpreparedfroma
developingmousesacrificedatembryonicday12.5.Theseshowhowthe
primordiaofthedevelopingarterialrootsarederivedfromthedistalendsof
theoutflowcushions,whichareseparatingtheintermediatepartofthe
outflowtract.(A)Acutreplicatingtheobliquesubcostalechocardiographic
plane.(B)Acrosssectionacrosstheventricularmassasviewedfromthe
aspectoftheventricularapex.