Andersons pediatric cardiology 1268
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PulmonaryArterialSling
Thisisararecongenitalanomalyinwhichtheleftpulmonaryarterydoesnot
ariseintrapericardiallyfromthepulmonarytrunkbuttakesitsorigin
extrapericardiallyfromtheposterioraspectoftherightpulmonaryarterytothe
rightsideofthetrachea(Fig.47.20AandB).75–78Theleftpulmonaryarterythen
makesahairpinturntotheleftandcoursestowardthehilumoftheleftlung
throughthespacebetweenthelowertracheaandesophagus.Asaconsequence,a
vascularslingisformedaroundtherightsideofthetrachea.Thearterialductor
itsligamentconnectsthepulmonarytrunktothedescendingaortaontheleft
sideofthetrachea.Theslingisalmostalwaysassociatedwithanabnormalityof
theairways.Theanomalouscourseoftheleftpulmonaryarterymaycausedirect
mechanicalcompressionofanotherwisenormaltrachea,resultingin
tracheomalacia.However,anabnormalityoftheairways,occursfarmore
commonlyasanassociatedlesion.Anabnormalbranchingpatternofthe
tracheobronchialtreeisseeninupto80%ofpatientswithapulmonaryarterial
sling.75–77Typicallythetracheabifurcatesintothebronchitotherightandleft
lungsatalowerlevelthannormal,withawideanglebetweentherightandleft
bronchi,producinganinvertedTappearance.Inapproximately30%ofthecases
withalowinvertedTbifurcationoftheairways,therightupperlobarbronchus
arisesfromthetracheaslightlyabovethelevelofnormaltrachealbifurcation.
Theleftpulmonaryarterythenformsaslingontherightsideoftheairway
immediatelyabovethelowerbifurcation.ThelowinvertedTpatternof
bifurcationhaspreviouslybeendescribedasa“bridgingbronchus.”76Inthis
ratherconfusingconcept,ithasbeenconsideredthatthispartoftheairway
betweenthesupposedlynormallevelofbifurcationandthelowerbifurcation
intotherightandleftbronchiiserroneouslyassumedtobetheleftmain
bronchusandthatthebronchustotheentirerightlung,ortotherightmiddleand
lowerlobes,arisesabnormallyfromtheleftmainbronchus.Thereforethis
bronchuswasthoughttocreateabridgebetweentherightandleftlungs.Almost
allcaseswiththelowinvertedTbifurcationoftheairways,withorwithouta
separateoriginoftherightupperlobebronchus,areassociatedwithnarrowing
ofalongsegmentofthelowerairwaysabovethebifurcation.Thenarrowingis
duetocompletecartilaginousrings,withabsenceofthemembranouspartofthe
tracheaposteriorly.Thenarrowingmayalsoextendintothemainbronchi.In
addition,therightand,lessfrequently,theleftbronchusmayshow
bronchomalacia.10One-thirdofpatientswithtrachealstenosisduetocomplete
cartilaginousringshaveanassociatedpulmonaryarterialsling.However,the
presenceofcompleteringsdoesnotnecessarilyimplyimportantstenosis,
althoughthetracheaisnarrowerthannormal.Imperforateanusisseenin16%of
caseswithalowinvertedTbifurcationbutnotincaseswithatracheal
bifurcationatnormallevel.76
FIG.47.20 (A)Volume-renderedcomputedtomographicangiogramsseen
fromthefrontandabove(left)andfrombehindandabove(right)showa
pulmonaryarterialslingwithabnormaltracheobronchialbranchingand
stenosis.Theleftpulmonaryartery(LPA)arisesfromtheproximalright
pulmonaryartery(RPA),makesahairpinturnaroundtheairwayinthe
mediastinumandcoursestothehilumoftheleftlung.Theairwayhastwo
bifurcationsinthemediastinum,withanarrowintermediarysegment,
characteristicofcongenitalstenosisduetocompletecartilaginousrings.
(B)ThisdiagramshowingapulmonaryarterialslingalsoillustratesaleftsidedarterialligamentconnectingthedistalLPAtothedescendingaorta.
(C)Chestradiographsareshowntogetherwithcomputedtomographic
correlationofapulmonaryarterialsling.Thediagnosiscanbeentertained
whencarefulobservationshowstheabnormalityseeninthechest
radiograph.Thearrowsindicatethenarrowedverticalsegmentoftrachea
betweenitsupperandlowerbifurcations.MPA,Mainpulmonaryartery.
Theleftpulmonaryarteryisoftenrelativelyhypoplastic,beingconsiderably
smallerthantherightpulmonaryartery.Stenosisoftherightpulmonaryartery,
withhypoplasiaoftherightlung,hasalsobeenreported.79Rarely,theslingis
associatedwithagenesisoftherightlung.80Alsorarely,thepulmonaryarteryto
theleftupperlobemayariseanomalouslyfromtheproximalrightpulmonary
artery,withnormalpulmonaryarterialsupplytotheleftlowerlobe.Inaddition,
therightupperlobemayhaveanaberrantsupplyfromtheanomalousleft
pulmonaryartery.Theslingisreportedtobeassociatedwithcongenitalcardiac
diseaseinfrom30%to80%ofcases.77,79,81,82Themostcommonreported
defectsareatrialseptaldefect,patencyofthearterialduct,ventricularseptal
defect,tetralogyofFallot,coarctationoftheaorta,andpersistenceoftheleft
superiorcavalvein.Theanomalyhasalsobeenreportedinassociationwith
imperforateanus,congenitalmegacolon,biliaryatresia,andgenitourinary
anomalies.Rarely,anaberrantleftpulmonaryarteryarisingdistallyfromthe
rightpulmonaryarterydoesnotformavascularslingbutisassociatedwith
trachealstenosis.83,84Aslinginvolvingtherightpulmonaryarteryhasbeen
