Andersons pediatric cardiology 1173
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anomalousattachmentofthetensionapparatusoftheleftatrioventricularvalve
(Fig.44.8).
FIG.44.8 Lesionproducingobstructionofthemorphologicallyleft
ventricularoutflowtract.Theyproduceaorticobstructionwhenthe
ventriculoarterialconnectionsareconcordantbutsubpulmonaryobstruction
inthesettingofdiscordantventriculoarterialconnections.
Thelasttwolesionsarealsomorelikelytobefoundwhenthereisa
ventricularseptaldefectorinthesettingofcommonatrioventricularjunction
anddeficientatrioventricularseptation.Whentheventricularseptumisintact,
themostsignificantlesionisthesubvalvarfibrousridge,ordiaphragm(Fig.
44.9).
FIG.44.9 (A)Anautopsiedheartinwhichtheaorticoutflowtracthas
beenopenedtorevealafibroussubaorticdiaphragm.Notethattheshelflikelesionisalsoattachedtheaorticleafletofthemitralvalve(arrow).The
aorticvalveinthisinstanceisnormal.(B)Shelf,asremovedatsurgery.
Thislesionhasbeendescribedinmanyways.Althoughoftentermed
“membranous,”almostalwaysthelesionisafirmfibrousshelfthatencirclesthe
outflowtract,oftenextendingtobeattachedalsototheaorticvalvarleaflets.
Theseptalcomponentoftheobstructivelesionoverliestheleftbundlebranchas
itcrossestheventricularseptum.Adiscreteplanofcleavagealmostalways
existsbetweentheshelfandthemusculature.Becauseofthis,itcanreadilybe
strippedawaybysurgery(seeFig.44.9B).
Becausethelesionisacquired,thereisalwaysthelikelihoodofrecurrence.
Thepositioncanvarywithregardtoitsproximitytothevalvarleaflets.If
extensive,itcanproducetunnelstenosis.Infloridcases,thereisamarked
abnormalityinthealignmentbetweentheplaneoftheaorticrootandthe
ventricularseptum.Thishasbeenpromotedasapotentialcauseofthe
malformation.13
SupravalvarAorticStenosis
Supravalvarstenosisaccountsforonly1%to2%ofcasesofaorticstenosisseen
inchildhood.Theconditionmaybefamilialormaybeassociatedwithdisorders
ofcalciummetabolism.14Theoriginaldescriptionincludedfailuretothrive,
gastrointestinalupset,andmentalretardation.15Thestenosistypicallyliesabove
theaorticsinusesandthecoronaryorificesbutincorporatesthesinutubular
junction(Fig.44.10).
FIG.44.10 Typicalhourglassvariantofsupravalvaraorticstenosis.The
stenosisisatthelevelofthesinutubularjunction(double-headedarrow)
andinvolvestheperipheralattachmentsofthezonesofapposition
betweenthevalvarleaflets.Notethedisproportionatelengthofthefree
edgeoftheleafletsrelativetotheirsupportingsinuses.
Theaorticsinusesthemselvesareenlargedandbulgelaterally,whereasthe
aorticleafletsareoftenslightlythickenedandaredisproportionatelylongin
relationtotheportionofsinutubularjunctiontowhichtheyarerelated.The
coronaryarteries,whichtakeoriginbelowtheobstruction,aretypicallydilated,
thickwalled,andectatic.Thenatureofthenarrowingisvariable.16Themost
commonformisthe“hourglass”varietywithdilationofthedistalaorta(seeFig.
44.10).Therearealsodiffuseortubularvarietiesand,veryrarely,a
diaphragmaticorlocalizedform.Irrespectiveofthetype,theascendingaortais
usuallygrosslyabnormal,withathickenedwallanddisorganizationofthe
media.Thenarrowingandscarringarenotexclusivetotheaortaandmaybe
