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beendescribedandcanbetechnicallysimpleandfunctionallyallowforequal
hepaticflowdistribution.Withregardtobiventricularrepairsinthesettingof
isomerism,therearenoparticularspecialconsiderationsthatarenecessarily
present.

ArrangementofThoracoabdominalOrgans
Ajumbled-uparrangementoftheabdominalorganshaslongbeenrecognizedas
thehallmarkofthe“splenicsyndromes.”Eventhoughthethoracicorgansare
isomeric,theabdominalorgansarenot.Thismeansthatisomerismcannot
reliablybediagnosedonthebasisofthedispositionoftheabdominalorgans,in
particularthearrangementofthespleen.Ifsplenictissueisabsent,thisshouldbe
documentedsincethisfeaturecarriesconnotationsfortheimmunestateofthe
patient(seebelow).Thespleen,nonetheless,whileexpectedtobeabsentin
thosewithrightisomerism,canalsobeabsentinthosewithisomericleftatrial
appendages.Thearrangementoftheremainingabdominalorgansisalsoof
significance.Ashortmesenterycanleadtointestinalvolvulusandoccursin
rightorleftisomerism.8Thepancreastendstobeshortorannularonlyinthe
presenceofleftisomerism.
Themorphologyofthethoracicorgans,incontrast,specificallythebronchial
tree,isamuchbetterguidetothepresenceofisomerismoftheatrial
appendages.Bilaterallongandhyparterialbronchiareindicativeofleft
isomerism(Fig.26.18A),whilebilateralshortandeparterialbronchi(seeFig.
26.18B)arefoundinthosewithrightisomerism.Notallpatientswithisomeric
atrialappendages,however,havebronchialisomerism.Thebronchialanglecan
alsobetellinginthosewithisomerismwithatracheobronchialangleoflessthan
135degreesbeingmoreconsistentwithleftisomerismandatracheobronchial
angleofgreaterthan135degreesbeingmoreconsistentwithrightisomerism.
Thus,whileexaminationofthepenetratedchestradiographwasconsidereda
usefulstepintheevaluationoftheinfantorchildsuspectedofhavingisomeric
atrialappendages,itisnowrarelyusedasadiagnostictool.68–70

FIG.26.18 (A)Posteriorviewdemonstratingbilateral,long,hyparterial
mainbronchiinapatientwithisomerismoftheleftatrialappendages.Both
morphologicallyleftbronchiarebelowthepulmonaryarteryextendingto
thelowerlobeofthelung.(B)Posteriorviewdemonstratingbilateral,short,
hyparterialmainbronchiinapatientwithisomerismoftherightatrial
appendages.Thefirstbranchofbothmorphologicallyrightbronchiis
eparterialorabovethepulmonaryarterythatextendstothelowerlobeof
thelung.Notetherightandleftpulmonaryveinsjoininginaconfluenceto
drainviaasinglevein(star)belowthediaphragm.

VisceralSymmetryWithoutIsomericAtrial
Appendages


Althoughthefocusofthischapterisonisomerismoftheatrialappendages,there
isincreasingevidencetosuggestthatvaryingdegreesofthoracicsymmetrymay
occurinthepresenceofusualatrialarrangement.Indeed,asymmetrical
arrangementofthelungs,withajumbled-uparrangementoftheabdominal
organs,appearstooccurwithsignificantlygreaterfrequencythandoes
isomerismoftheatrialappendages.16,23Inageneticanalysisofisomerism,a
healthysiblingofaprobandwithrightisomerismwasnotedtohaveleft
bronchialisomerism.24Abnormallateralization,withatendencytothoracic
symmetry,canthereforebefoundinpatientswithstructurallynormalhearts.
Theseobservationshaveimportantimplicationsforresearchintotheetiologyof
abnormallateralizationandforgeneticcounseling.25Forthepurposesofgenetic
studies,casesshowinganydegreeofabnormallateralizationshouldbe
distinguishedfromthe“normal.”Externalphenotype,andcardiacmorphology,
isaninadequateindicatoroftheoverallarrangementoftheorgans.Thuseach
systemoforgansrequiresindividualandspecificanalysis.Itisbesttoavoid

inferringthemorphologyofonegroupoforgansbasedonobservationsin
another.Atthesametime,forthesepurposesaboveall,itisnecessarytostratify
theso-called“splenicsyndromes,”or“visceralheterotaxy,”intothesubsetsof
rightandleftisomerism.