Andersons pediatric cardiology 1346
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leafletofthemitralvalve.
Theproximalpartsoftheoutflowtractsareboundedbythesemilunarleaflets
ofthearterialvalves.Theoutflowtractoftherightventricleisexclusively
muscular.Onlytwosinusesoftheaorticroot,incontrast,havemyocardial
supportwithintheleftventricle.Thesesinusesgiverisetothecoronaryarteries.
Theyarealsosinusesthatareadjacenttothepulmonarytrunk(seeFig.51.1C
andD).Onrareoccasion,thenonadjacentsinusoftheaorticrootcangiveriseto
oneorotherofthecoronaryarteries.Thatiswhyweprefertodescribeitasthe
nonadjacentratherthanthenoncoronarysinus.Fig.51.1Bshowshow
extracavitaryfibroadiposetissueinterposesbetweentherightventricular
infundibulumandtheaorticroot.Forquitesometime,thisareawasdescribedas
beingan“outlet”or“conal”septum.Thisisclearlynotthecasebecausethe
subpulmonaryinfundibulumisafreestandingmyocardialsleeve.Thearterial
rootsthemselvesaremadeupofthesemilunarvalvarleafletssupportedbythe
sinusesofValsalva.Themyocardiumoftheproximalpartoftheoutflowtractsis
foundsupportingthebasesofallthepulmonaryvalvarsinuses.Myocardiumis
alsofoundsupportingthebasesofthetwoaorticsinusesgivingrisetothe
coronaryarteries.Thepresenceofthemyocardiumwithinthesinusalbases
reflectsthefactthatthesemilunarhingesofthearterialvalvarleafletscrossthe
anatomicventriculoarterialjunction.AsdescribedinChapter2,thesemilunar
hingesoftheleaflets,whenreconstructedinthreedimensions,haveacrownlike
configuration.Thisiswhyitisbestnottodescribethehingesintermsofan
“annulus.”Inaddition,echocardiographersdescribethevirtualringmadeby
joiningtogetherthebasalattachmentsoftheleafletsasthe“annulus.”The
structureofthehingesoftheleafletsandthenatureoftheirsupportarekeyto
understandingthemorphologyandetiologyofbothaortoventriculartunnelsand
aneurysmsofthesinusesofValsalva.Wealsoprefertoavoidusingtheword
“cusp”whendescribingthecomponentsofthearterialroots.Thiswordis
frequentlyusedinterchangeablytodescribeboththevalvarsinusesandthe
valvarleaflets.Aswewillshow,toappreciatethemorphologyofthe
malformationsdiscussedinthischapter,itisimportanttodistinguishbetween
theleafletsandtheirsupportingsinuses.Thethird,anddistal,partsofthe
outflowtractsareoccupiedbytheintrapericardialarterialtrunks.Eachofthe
trunksalsohasitsowndiscretewalls,sothatthereisnoseptalstructure
interposingbetweenthem(seeFig.51.1B).Thepericardialreflectionsdividethe
ascendingaortaintointrapericardialandextrapericardialcomponents.In
contrast,therightandleftPAsbranchfromthepulmonarytrunkatthemargins
ofthepericardialcavity.Thereforetheoriginofthearterialductis
extrapericardial.
NormalDevelopmentoftheOutflow
Tracts
WhenfirstformedduringCarnegiestages12through14inhumansandduring
embryonicdays9.5and10.5inthemouse,theoutflowtract,derivedby
additionalmigrationofcellsintothehearttubefromthesecondheartfield,isa
tubewithexclusivelymyocardialwallsthatextendsfromtheoutletofthe
developingrightventricletothemarginsofthepericardialcavity.Ithasan
obviousdoglegbendinitsmiddlepart(seeFig.51.2A).
FIG.51.2 Imagestakenfromepiscopicdatasetspreparedfrom
developingmicesacrificedatembryonicday10.5.(A)Frontalviewofthe
heart.(B)Obliquesectiontakenacrosstheoutflowtract.Ascanbeseenin
A,theoutflowtracthasadoglegconfiguration.(B)Cardiacjellythatlines
thelumen.Thewallsofthetubeareinitiallyexclusivelymyocardialallthe
waytothemarginsofthepericardialcavity(arrows).Thedistalmarginsare
beginningtoachieveanonmyocardialphenotypeduetoingrowthofnew
tissuesfromthesecondheartfield.
Whenfirstformed,thelumenoftheoutflowtractislinedincircumferential
fashionthroughoutitslengthbyalayerofcardiacjelly.Theinitialstagesofits
conversionintoseparateoutflowtracts,whicheventuallyhavepredominantly
nonmyocardialwalls,involvetheadditionoffurthermaterialtothetubefrom
