Andersons pediatric cardiology 72
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FIG.2.10 Multidetector-rowcomputedtomographicdatasetreconstructed
andsegmentedtoshowthelocationoftheinferiorpyramidalspace.The
fibro-adiposetissuesoftheatrioventriculargroovesarereconstructedin
yellow,showinghowtheyinterposebetweentheseptalvestibuleofthe
rightatriumandthecrestofthemuscularventricularseptum.The
atrioventricularcomponentofthemembranousseptumformstheapexof
thetriangleofKoch.
TheatrialwallofthesandwichformsthefloorofthetriangleofKochandis
confluentwiththeso-calledsinusseptum,whichseparatestheorificesofthe
coronarysinusandtheinferiorcavalvein(seeFig.2.8).Thesinusseptum,
however,isnomorethantheadjacentwallsofthetwovenousstructures.
MorphologicallyLeftAtrium
Theleftatrium,likeitsright-sidedcounterpart,possessesavenouscomponent,
anappendage,andavestibule(Fig.2.11).
FIG.2.11 Morphologicallyleftatriumwindowedtoshowitsconstituent
partsandisphotographedfromtheleftside.
Thebody,whichistheremnantoftheatrialcomponentofthedeveloping
hearttube,islargelyincorporatedintothemorphologicallyleftatrium.Itiswell
seeninthesettingoftotallyanomalouspulmonaryvenousconnection.Even
whenthepulmonaryvenouscomponentislacking,thesmooth-walledbody
formsthesiteofunionfortheappendage,vestibule,andseptum.Theappendage
isagainthemostcharacteristicandconstantcomponent.Itisatubularstructure,
usuallywithseveralconstrictionsalongitslength.Itsopeningwiththevenous
componentisrestricted,butitsmostcharacteristicfeatureisthatitspectinate
musclesarecontainedwithintheappendage,orelsespillonlymarginallyinto
thesmooth-walledcomponent.Thevestibule,whichsurroundstheposteriorpart
oftheleftatrioventriculargroove,ispartofthissmooth-walledcomponent.The
coronarysinusislocatedwithintheatrioventriculargroove,andhenceisan
integralcomponentofthemorphologicallyleftatrioventricularjunction,even
thoughitopensintothecavityofthemorphologicallyrightatrium(Fig.2.12).
FIG.2.12 Multidetector-rowcomputedtomographicdatasetreconstructed
toshowthelocationofthecoronarysinus.Althoughitopenstotheright
atrium,itoccupiesthemorphologicallyleftatrioventriculargroove.Notethe
locationofthecoronaryvenoustributaries.
Thewallsofthecoronarysinusareseparatefromthoseoftheleftatrium
itself.7Thepulmonaryveinsopenintothecornersoftheroofoftheextensive
smooth-walledvenouscomponent.Theseptalsurfaceisformedbytheflapvalve
oftheovalfossa,whichisderiveddevelopmentallyfromtheprimaryatrial
septum.Itoverlapstheinfoldedsuperiorrim(Fig.2.13)withtwohornswhich
anchoritontheleftatrialside.
