Andersons pediatric cardiology 1267
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FIG.47.18 Echocardiographicimagesshowingaleftaorticarch(LAA)
withanaberrantrightsubclavianartery(RSA).(A)Inthedownward
transverseviewanLAAisdisplayedwiththetracheatotheright.(B)The
upwardsweepofthetransducerrevealsthatthefirstbrancharisingfrom
anLAAdoesnotbifurcatebutinsteadcontinuesforward,upward,and
rightward,thisbeingcharacteristicfortherightcommoncarotidartery
(RCCA).(C)InferiorangulationofthetransducerrevealstheaberrantRSA
arisingmoredistallyfromthedescendingaortaontheleftsideofthe
midline.SCV,Superiorcavalvein.
Althoughcatheterizationwithangiographywasoncethegoldstandardforthe
diagnosis,thishasalmostbeencompletelyreplacedbycomputedtomography
andmagneticresonanceimaging.Bothcomputedtomographyandmagnetic
resonanceimagingprovideaclearroadmapallowingtheconstructionofa
precisepreoperativestrategy.6,62,63
Computedtomographyisperfectlysuitedforthesimultaneousevaluationof
theanatomyofthevascularstructuresandtheairways.62–65Recentintroduction
anddevelopmentofthemultidetectortechnologyincomputedtomographyhas
allowedhigh-resolutionacquisitionofdatafromthewholechestwithinafew
seconds.Thereforesedationorgeneralanesthesiaisrarelyrequired,evenin
uncooperativechildren.Althoughcomputedtomographyusesalargeamountof
radiation,thedosecanbesignificantlyreducedbycarefullyadjustingthe
imagingparameters,scandirection,andthevolumeofcoverage.66Becausethe
vesselsinquestionareratherlargestructures,artifactsassociatedwithusinga
lowkilovoltageandlowmilliamperetechniquedonotsignificantlyreducethe
diagnosticaccuracy.Thevolumeoftissuecoveredbycomputedtomographycan
beminimizedbyreferringtothealreadyavailableinformation.Everyeffort
shouldbemadetoreducethedoseofradiationwhencomputedtomographyis
performed.Inperformingadiagnosticprocedureusingradiation,taking
“beautiful”picturesshouldnotberegardedasavirtue.Therealvirtueistotake
imagesofdiagnosticquality,usingthelowestpossibledoseofradiation.The
axialimagesarereviewedbyscrollingupanddownintheworkstation.Threedimensionalreconstructioninvariousplanesismandatory.Three-dimensional
reconstructionisuseful,notonlyfordemonstrationoftheanatomybutalsofor
moreaccuratediagnosis.Bothmaximumintensityprojectionandvolume
renderingalgorithmsareusefulfortheassessmentofthevascularstructures.
Minimumintensityprojectionwithvolumerenderingalgorithmisusedforthreedimensionalreconstructionoftheairway.Thevolume-renderedimagesofthe
vascularstructuresandairwayscanbemergedtoshowspatialrelationships.
Endoluminalvolumerenderingalsoallowsvirtualtracheobronchoscopic
demonstrationoftheairway.67Theseverityofthenarrowingseenintheairways
atroutinecomputedtomographydoesnotalwayscorrelatewithsymptomsand
signs.Inaddition,asignificantdiscrepancyinseverityisoftenfoundbetween
bronchoscopicandcomputedtomographicfindings.Thisisbecauseroutine
computedtomographyhaslimitationsindetectingdynamicairwaynarrowing.
Dynamicnarrowingcanbeassessedbyscanningtheairwayinbothinspiratory
andexpiratoryphaseswhenthepatientcanfollowtheimaginginstructions.68,69
Ininfantsanduncooperativepatients,thesuspectedpathologicregioncanbe
repeatedlyscannedthroughouttherespiratorycycletoassessthedynamicnature
oftheobstruction(Fig.47.19).70However,itdoesrequiresignificantadditional
radiation.
FIG.47.19 Dynamiccomputedtomographicaxialimagesobtainedin
inspirationandexpirationphasesshowingthatthetracheaiscollapsed
duringexpiration.Asshownatright,thepatienthasanaberrantright
subclavianartery(RSA).
Magneticresonanceimagingisalsoanexcellenttoolfortheassessmentofthe
vascularanatomy.62,63,71,72Contrast-enhancedmagneticresonanceangiography
hasbeenusedfortheassessmentofthevascularstructures.Recently,threedimensionalvolumedataacquisitionofthecardiovascularanatomycanbe
acquiredwithoutinjectionofcontrastmedium,byusingan
electrocardiographicallygatedbalancedsteady-statefreeprecessionsequence
andrespiratorynavigation.73Double-inversionrecoverysequenceisatechnique
thatcanbeusedfortheassessmentoftheairway.Real-timecinemagnetic
resonanceimagingisafuturedirectionforadynamicairwayassessment.74
Magneticresonanceimagingisthepreferredtechniqueincooperativechildren
becauseitdoesnotuseradiation.
Apreoperativeorintraoperativebronchoscopyisstillperformedinallpatients
withvascularringsinsomeinstitutions.6,8Bronchoscopyallowsproper
endotrachealtubepositionanddiagnosisofunrecognizedtracheomalaciaor
bronchomalacia.Itshouldbenotedthatnoneofthecurrentlyavailableimaging
modalitiesisabletovisualizeanatreticsegmentofavascularstructure,suchas
anarterialligamentoranatreticsegmentoftheaorticarch.Thepresenceofsuch
fibrousstrandscanbesuspectedonlywhenanarterialbranchshowsan
otherwiseunexplainablekinkedcourseoradiverticularoutpouching.15The
presenceofadiverticulumofKommerellindicatesthataligamentousarterial
ductextendsfromtheapexofthediverticulumtoeitherthepulmonaryarteryor
anatreticarchonthesameside.
