Andersons pediatric cardiology 1108

MorphologyandEmbryology
Obstructionatthevalvarlevelisbyfarthemostcommonlesionproducing
stenosiswithinthepulmonaryoutflowtract.Anunderstandingofthe
mechanismsresponsibleforstenosisrequiresaproperappreciationofnormal
valvaranatomy.2Atpresentsuchunderstandingisconstrainedbyvaryinguseof
thetermannulusinaccountingforthestructureofthenormalvalve.
Paradoxically,itisonlywhenthevalveisstenoticthattheattachmentsofthe
leafletsapproximatetoanannulararrangement.Theessenceofnormalvalvar
anatomyisthesuspensionofthevalvarleafletsinsemilunarfashionwithinthe
sinusesofthepulmonarytrunk.Properunderstandingthenrequiresappreciation
thatthehingesoftheleafletscrosstheanatomicventriculoarterialjunction.The
arrangementisbestseenwhenthenormaloutflowtractisspreadopen,having
alreadyremovedthevalvarleaflets(Fig.42.1).


FIG.42.1 Thenormalpulmonaryoutflowtracthasbeenopenedand
spreadtoshowitsfullwidth(leafletsofthepulmonaryvalvehavebeen
removed).Thedissectionshowshoweachleafletisattacheddistallyatthe
sinutubularjunctionbutproximallytothemuscularinfundibulum.The
semilunarlineofattachmentofeachleaflet,markingthehemodynamic
ventriculoarterialjunction,crossestwicetheanatomicjunctionbetweenthe
wallofthepulmonarytrunkandthemuscularinfundibulum,leaving
trianglesoffibrouswall(redstars)aspartoftheventriclebutsequestering
crescentsofmusculature(whitestars)aspartsofthevalvarsinuses.

Inthenormalheart,eachvalvarleafletisattachedbyitstwoextremitiesatthe
sinutubularjunction,withthebasalattachmentsupportedbythemusculatureof
thesubpulmonaryinfundibulum.Trueanatomicringscanthenbeidentifiedat
thelevelofthesinutubularjunctionandalsoattheanatomicventriculoarterial
junction.Thelatterstructureisthelocusoverwhichthefibroelasticwallsofthe
pulmonarytrunkaresupportedbythemuscularsubpulmonaryinfundibulum.A

thirdringcanthenbeconstructedbyjoiningtogetherthebasalattachmentsof
theleaflets.Thisthirdring,however,isageometricconstructionratherthanan
anatomicreality.Thesemilunarlineofattachmentofeachoftheleaflets
markingthehemodynamicventriculoarterialjunctioncrossestwicetheanatomic
ventriculoarterialjunction.Byvirtueofthisgeometry,crescentsofmuscular
infundibulumareincorporatedatthebaseofeachpulmonaryvalvarsinus,while
threetaperingtrianglesoffibrouspulmonarytruncalwallextendbeyondthe
anatomicventriculoarterialjunctionaspartsoftheventricularoutflowtract,
reachingtothelevelofthesinutubularjunction(Fig.42.2).


FIG.42.2 Effectsofthehingelinesofthevalvarleafletsassessedinthree
dimensions.Onehingeline(showninpurple)crossestheanatomic
ventriculoarterialjunction.Trianglesofarterialwallareincorporatedintothe
ventricularoutflowtracttothelevelofthesinutubularjunction,and
crescentsofmuscularinfundibulumaresequesteredatthebaseofeach
valvarsinus.

Inthenormalarrangement,thefreeedgeofeachvalvarleafletisappreciably
longerthanthecordofthesinusthatsupportsit,thuspermittingthethree
leafletstofitsnuglytogetherwhenclosedsoastoproduceacompetentvalvar
orifice.Itisthesemilunarnatureofsuspensionoftheleaflets,therefore,that
permitscompetentclosureandunobstructedopeningofthevalve.Whenseenin
closedposition,thezonesofappositionbetweentheadjacentleafletsextendin
triradiatefashionfromthecentroidofthevalvarorificetotheirperipheral
attachmentsatthesinutubularjunction(Fig.42.3).