Andersons pediatric cardiology 56
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showsuchlateralization.Instead,thereisisomerismoftheatrialappendages.In
thesepatterns,thetwoappendagesaremirrorimagesofeachother,with
morphologiccharacteristicsattheirjunctionswiththerestoftheatriumsonboth
sidesofeitherrighttypeorlefttype.
RecognitionofAtrialArrangement
Thearrangementoftheappendages,ideally,isrecognizedbydirectexamination
oftheextentofthepectinatemusclesroundthevestibules(seeFig.1.2).Ithas
beenquestionedforsometimeastowhetherthesefeaturescanbedistinguished
intheclinicalsetting.Withmodern-dayequipment,itisourbeliefthatthe
arrangementsshouldnowberecognizableusingcross-sectional
echocardiography,particularlyfromthetransesophagealwindow.Theextentof
thepectinatemusclescanbedemonstratedbyusingcomputedtomography.
However,inmostclinicalsituations,itisrarelynecessarytorelyonlyondirect
identification.Thisisbecausethemorphologyoftheappendagesisalmost
alwaysinharmonywiththearrangementsofthethoracicandabdominalorgans.
Inpatientswithlateralizedarrangements,thatis,theusualandmirror-imaged
patterns,itisexceedinglyrarefortheretobedisharmonybetweenthelocationof
theorgans(Fig.1.9).
FIG.1.9 Usualandmirror-imagedarrangementsoftheorgans,whichare
lateralized.Almostalwaysthereisharmonybetweenthearrangementof
therightandleftatrialappendagesandtheremainingthoracoabdominal
organs.Thenumbersshowthethreelobesofthemorphologicallyrightand
thetwolobesofthemorphologicallyleftlungs.LAA,Leftatrialappendage;
RAA,rightatrialappendage.
Whentheappendagesareisomeric,incontrast,usuallytheabdominalorgans
aretypicallyjumbledup,althoughthelungsandbronchusesaretypically
isomeric(Fig.1.10).
FIG.1.10 Typicalfeaturesofthethoracoabdominalorgansinso-called
visceralheterotaxy.Theabdominalorgansarejumbledup,butthelungs
andatrialappendagesareusuallyisomeric,havingthesamemorphologic
featuresontherightandleftsides.Itisusualforrightisomerismtobe
associatedwithabsenceofthespleenandleftisomerismwithmultiple
spleens,buttheseassociationsarefarfromconstant.Thusdifferent
picturesemergewhenso-calledheterotaxyissubdividedonthebasisof
isomerismasopposedtosplenicmorphology.However,cardiac
assessmentshouldstartwithanalysisofatrialmorphologybasedonthe
structureoftheatrialappendages.
Evenwhenthereisabdominalheterotaxy,thelungsandbronchialtreeare
almostalwayssymmetric.Itisrareforthebronchialarrangementtoshow
disharmonywiththemorphologyoftheappendages.Thepresenceofisomerism
thereforecanalmostalwaysbeinferredfromthebronchialanatomy.The
morphologicallyleftbronchusislong.Itbranchesonlyafterithasbeencrossed
byitsaccompanyingpulmonaryartery,makingthebronchushyparterial.In
contrast,themorphologicallyrightbronchusisshortandiscrossedbyits
pulmonaryarteryafterithasbranched,givinganeparterialpatternofbranching.
Thefourpatternsofbronchialbranchingarealmostalwaysinharmonywiththe
arrangementoftheatrialappendages.Similarinferencestothoseprovidedfrom
bronchialarrangementcanalsousuallybeobtainednoninvasivelybyusing
cross-sectionalultrasonographytoimagetheabdominalgreatvessels.These
vesselsbearadistinctrelationtoeachother,andtothespine,whichgenerally
reflectsbodilyarrangement,althoughnotasaccuratelyasdoesbronchial
anatomy.Thevesselscanbedistinguishedultrasonicallyaccordingtotheir
patternofpulsation.Whentheatriumsarelateralized,almostwithoutexception
theinferiorcavalveinandaortalietooppositesidesofthespine,withthecaval
veinonthesideofthemorphologicallyrightappendage.Whenthereis
