Andersons pediatric cardiology 769
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isderivedfromtheprimaryatrialseptum.Ifdevelopmentproceedsnormally,the
floorofthefossaisusuallyofsufficientdimensiontooverlaptheinfolded
superiorrim,oftendescribedastheseptumsecundum.Thefloorandrim,
however,donotalwaysfusewithoneanother,andfailureofsuchfusion
producestheprobe-patentovalforamen(Fig.29.5).
FIG.29.5 Normalheartsectionedalongitsshortaxis.Theflapvalveof
theovalfossa,derivedfromtheprimaryatrialseptum,hasfailedtofuse
withthesuperiorrim,eventhoughitisofsufficientdimensionstoclosethe
septaldeficiency.Thisconstitutespersistentpatencyoftheovalfossa.
Eveniftheflapvalvefailstofusewiththesuperiorinteratrialfold,therewill
benointeratrialshuntingaslongastheleftatrialpressureishigherthanright,
whichisthenormalpostnatalsituation.Nonetheless,probepatencyisknownto
beresponsibleforparadoxicembolismandcanbeanimportantfindinginthose
undertakingdeepseadiving.Thesuggestedassociationwithmigraine,2
however,hasstilltobeproven.Thesimplesttruedefectwithintheovalfossais
foundwhentheflapvalveisminimallydeficient,sothatitfailstoentirely
overlaptheleftatrialmarginoftherimofthefossa.Withincreasingdeficiency
oftheflapvalveorinpresenceofaperforatedvalve,thedefectbecomeslarger
(Fig.29.6,left).Inextremecasestheremaybenofloortothefossa(seeFig.
29.6,right).
FIG.29.6 Examplesofthelesionsthatcanbefoundwithintheconfinesof
theovalfossa.Left,Showninaflapvalvethatisnotonlyofinsufficientsize
tooverlapthemarginsofthefossabutisalsoperforateposteroinferiorly
andanteroinferiorly.Right,Exampleinwhichtheflapvalveisdeficientover
thefullextentofthefossaincombinationwithaperimembranousinlet
ventricularseptaldefect(VSD).Notethatthedefectextendstothemouth
oftheinferiorcavalvein.
Whenthedeficiencyismarked,theholecanextendtowardthemouthofthe
inferiorcavalvein,whichmaystraddlethepersistingrimtoopeninparttothe
leftatrium(seeFig.29.6,right).Althoughthesedefectsmayexistinisolation
anddonotdisturbthelocationoftheconductiontissues,theyoftenoccurin
combinationwithmanyothercongenitalcardiacmalformations,asshownat
rightinFig.29.6.
VestibularDefect
TheheartshowninFig.29.7,inadditiontothemultipleperforationsinthefloor
oftheovalfossa,hasanadditionaldefectintheanteroinferiorbuttress.This
lesionisthesecondtypeoftrueatrialseptaldefect.7
FIG.29.7 Therightatriumhasbeenopenedtoshowtheperforatedfloor
oftheovalfossa.Inaddition,thereisarelativelylargedefectwithinthe
anteroinferiorbuttressofthefossa.Thisisavestibulardefect.
SinusVenosusDefects
Theessenceofthesinusvenosusdefectsisthattheyexistoutsidetheconfinesof
theovalfossa.8Foundmostfrequentlyinthemouthofthesuperiorcavalvein,
theycanalsobefoundattheorificeoftheinferiorcavalvein9ordrainingtothe
midpointofthesystemicvenoussinus.Inthecaseofthesuperiorsinusvenosus
defect,theorificeofthesuperiorcavalveintypicallyoverridesadefect,which
hasthesuperiorrimofthefossaasitsfloor(Fig.29.8,left).
