Andersons pediatric cardiology 1321
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SystemicArteriovenousMalformations
andArteriovenousFistulas
Vascularmalformationsrepresentcongenitalabnormalitiesofvascular
developmentandarethereforenottumors;hencetheyneitherhave
disproportionategrowthpotentialnordotheyinvoluteovertime,butrathertend
togrowcommensuratewiththepatient'sgrowth.7Vascularmalformations
includecapillary,venous,lymphatic,arteriovenous,andmixedtypes.9Ofthese,
theonlylesionsthatposesignificantcardiovascularramificationsareAVMsand
arteriovenousfistulas(AVFs),duetotheirhigh-flowstate.Thesefast-flow
vascularmalformationsarecharacterizedbyrapidflowfromafeedingarteryto
adrainingveinwithoutaninterveningcapillarybed.Animportant
distinguishingfeatureisthatAVMscontainaninterveningnidusofdysmorphic
vessels,whereasAVFsconsistofafeedingarterydrainingdirectlyintoan
arterializeddrainingvein.17ExamplesofcongenitalAVFsincludeveinofGalen
malformationandarterioportalfistula(APF).9AVMsandAVFscanbesporadic
orexistaspartofanAVMsyndrome,suchashereditaryhemorrhagic
telangiectasia(HHT).ImagingmodalitiesincludeDopplerultrasoundandMRI;
inaddition,computerizedtomography(CT)angiographymaybeusefultodefine
thefeedingarteriesanddrainingveins.17,18Thesefast-flowlesionsaretheonly
vascularanomaliesthatrequireconventionalarterialangiographyforoptimal
definition.18
HepaticArteriovenousMalformations
HepaticAVMsaremuchrarerthanhepatichemangiomasandhavenopotential
forspontaneousregression.CongenitalhepaticAVMsaretypicallylocalizedina
singlelobeoftheliverandpresentinneonateswithhepatomegaly,anemia,CHF,
orportalhypertension.7HepaticAVMsaredifferentiatedfromhepatic
hemangiomasbytheusualpresenceofmultipleskinhemangiomasinthelatter.
InhepaticAVMsthepresenceofpulsatilevenoustracingonDopplerultrasound
istypical.18,19MortalityfromuntreatedhepaticAVMsisapproximately50%.19
PharmacologicmanagementofhepaticAVMsislimitedtotherapiesaimedat
supportingadequatecardiacoutputandanticongestivetherapyusingdiuretics.
PercutaneousembolizationofcongenitalhepaticAVMshasbecomethe
mainstayoftherapy.EmbolicagentssuchasalcoholandN-butylcyanoacrylate
shouldbeaimedatthecentralnidustomaximizeeffectiveness;coilsand
vascularplugscannotreachthenidusandthusoccludeonlythefeedingarteries,
whichpredisposestorerecruitmentandrecurrenceoftheAVM.20
HepaticAVMsassociatedwithapredisposingsyndromesuchasHHT(also
knownasOsler-Weber-Rendusyndrome)areusuallyasymptomaticinchildren
butbecomemorecommonlysymptomaticinadulthood.21HHTwillbe
discussedfurtherinthesectiononpulmonaryAVMs.
ArterioportalFistula
APFrepresentsanabnormalcommunicationbetweenasystemicarteryanda
splanchnicvein.APFwasfirstreportedbyGoodhartin188922andSachsin
1892.23AcquiredAPFaremostcommon;theycanoccurduetotumorinvasion
orcirrhosisorasaresultofpenetratinglivertraumaandcanalsobeiatrogenic
followingliverbiopsiesandpercutaneoustranshepaticvascularaccess.24Most
acquiredAPFshavebeenreportedinadults,andtreatmentbytranscatheter
arterialembolizationisperformedtoreverseportalhypertension,ascites,and
varicealbleeding.
GermanetothistextbookaretherarercongenitalAPFs.Thesemaypresent
withsequelaeofportalhypertensionand/orCHFandoccasionallywithcyanosis.
SomeAPFsmayhaveanunderlyingcongenitalcauseandyetnotbepresentat
birth;theseincludesyndromesthatpredisposetoarterialaneurysms(e.g.,
Ehlers-Danlossyndrome)withsubsequentaneurysmalruptureintoanadjacent
portalveinorsyndromesassociatedwiththedevelopmentofliverAVFs(OslerWeber-Rendusyndrome,alsoknownasHHT).24Thesecases,despitea
congenitalpredisposition,arebetterclassifiedasacquiredAPFs.Truly
congenital(i.e.,presentatbirth)APFsareveryrareandcanbeclassified
accordingtotheirlocation:intrahepaticorextrahepatic.Congenitalintrahepatic
APFmayexistinasinglelobeoftheliverorinbothlobesandmayreceive
exclusivehepaticarterialsupplyoradditionalarterialsupplyfromother
arteries.25Inaddition,avenousvarixmayexistatthesiteofthedrainingportal
veinorumbilicalvein.26IthasbeensuggestedthattheoccurrenceofCHFin
congenitalAPFislinkedtothepresenceofapatentductusvenosus:itis
presumedthattheductusvenosusprovidesalow-resistancepathforbloodflow
intotherightheart,whereasintheabsenceofaductusvenosusflowthroughthe
APFmustnecessarilyflowsubsequentlythroughthehepaticparenchymawhich
mayservetolimitshuntingbyposinganadditionalresistancetoflow.25In
neonatesandinfantpresentingwithsevereheartfailure,thepresenceofanatrial
communicationorarterialductmayallowright-to-leftshuntingresultingin
cyanosis.CongenitalAPFspresentinginadulthoodwithsymptomsrelatedto
portalhypertensionhavealsobeenreported.27
TCEhasbeenadvocatedasthetreatmentofchoice27–29giventhatselective
surgicalligationofthefeederarterymaybedifficult,especiallyindeep
intraparenchymallesions.However,reportsofsuccessfultreatmentofcongenital
APFarerare.
ArteriovenousFistulaInvolvingtheUmbilical
VeinorDuctusVenosus
Hartungetal.29reportedontwocasesofAVFspresentinginuterowithfetal
hydrops,oneconsistingofatortuousarteryarisingfromtheaortaandtheother
consistedofabranchofthehepaticartery,bothenteringtheumbilicalvein
directly.Bothcaseshadtrisomy21,andbothsufferedinuterodemise.Postnatal
descriptionsofsimilarfistulasarerarebutillustratetheabilitytosuccessful
ligatethesevesselstocontroltheshunt.28Rarerstillaredirectcommunications
betweenandumbilicalarteryandtheumbilicalvein.Suchacasewasdescribed
byBerginafetuswithtrisomy18andtetralogyofFallot,andtheAVFwas
associatedwiththedevelopmentofacalcifiedaneurysmoftheumbilicalvein.30
ArarecaseofumbilicalAVFdetectedinaninfantwassuccessfullyligatedwith
goodlong-termoutcome.31
VeinofGalenAneurysmalMalformations
VeinofGalenaneurysmalmalformations(VGAMs)arerareandfascinating
lesionsthathavelongpiquedtheinterestofpediatricneurosurgeons,
neurologists,radiologists,andcardiologists.Intheseverestformorifleft
untreated,VGAMscanprovetobefatal.Thetypesofmalformationsthatare
mostcommonlyreferredtoasVGAMsare,infact,amisnomer:Inthese
malformationsthearteriovenousconnectionsactuallydrainintotheprecursorof
theveinofGalen,knownasthemedianprosencephalicveinofMarkowski,and
