Andersons pediatric cardiology 1324
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PulmonaryArteriovenousMalformations
Background
Pulmonaryarteriovenousmalformations(PAVMs)arestructurallyabnormal
vesselsthatbypassthepulmonarycapillarybedthroughdirectcommunication
betweenthepulmonaryarteryandpulmonaryveinandthuscreateananatomic
right-to-leftshunt.Thesemalformationsresultinalow-resistance,high-flow
statecausingimpairmentingasexchangeandimpairedfiltrationofthesystemic
venousblood(Fig.50.6).46,47Thedegreeofright-to-leftshuntingcausesvarying
degreesofhypoxemia,fromasymptomatictoprofoundlysymptomatic.PAVMs
predisposetocomplicationssuchasparadoxicalsystemicembolization,stroke,
andcerebralabscess.TreatmentofasymptomaticPAVMsisrecommendedto
preventlong-termcomplications,TCEiscurrentlytheacceptedstandardof
care,46,47andthiscanbeachievedusinglowdosesofx-rayradiation.47–50
PAVMswerehistoricallyconsideredtoberarebasedonearlyautopsystudies,51
butmodernsophisticateddiagnostictoolshavesuggestedaprevalenceof2to3
per100,000,52,53withamaletofemaleratiorangingfrom1:1.5to1.8.54A
population-basedcancerscreeningprogramsuggeststheincidencetobe1in
2630ofPAVMsthataresufficientlylargetobedetectedbyCT.55PAVMsmay
besingleormultiple,simpleorcomplex,ordiffuse,whicharemostlyconfined
tothelowerlobes.56–58ThesimplePAVMsreceivebloodfromasingleartery
involvingasinglesac(Figs.50.7and50.8),whereascomplexPAVMscan
involvetwoorthreearteriescreatingaplexiformmassofdilatedvascular
channelsortortuouscommunicationsbetweenarteryandvein(seeFig.50.7).59
AsmallsubsetofpatientshaveamorediffuseandseveretypeofPAVMs
involvingsingleorseveralsegmentalpulmonaryarteries.ThediffusePAVMs
aremorecommoninbothlungs(72%).
FIG.50.6 Primaryfunctionsofthepulmonarycapillaryvascularbedsthat
arebypassedinpatientswithpulmonaryarteriovenousmalformations.
(ModifiedfromSholvinCL,ChamaliB,SanthirapalaV,etal.Ischaemic
strokesinpatientswithpulmonaryarteriovenousmalformationsand
hereditaryhemorrhagictelangiectasia:associationswithirondeficiency
andplatelets.PLoSOne.2014;9[2]:e88812.)
FIG.50.7 Illustrationdemonstratingnormalpulmonarycapillarybed(A)
andtypesofpulmonaryarteriovenousmalformation(PAVM):SimplePAVM
(B)andcomplexPAVM(C).(ModifiedfromTrerotolaSO,PyeritzRE.PAVM
embolization:anupdate.AJRAmJRoentgenol.2010;19[4]:837–845.)
FIG.50.8 Thoracicchestcomputedtomography(A)andangiogram(B)
demonstratingsolitarypulmonaryarteriovenousmalformation(PAVM)with
afferent(blackarrow)andefferentlimbs(whitearrow).Embolizationatthe
neckoftheaneurysm(C)usinganAmplatzervascularplug.
MostPAVMsarehereditary,occurringin90%ofpatientswithHHT,andthe
remainingaresporadicoridiopathic.46,60–62HHTisthemostcommoncauseof
PAVMs.Itisageneticdisorderwithanautosomaldominanttrait,affecting1in
50,000to80,000people.63,64Itischaracterizedbydermal,mucosal,andvisceral
telangiectasiasandvisceralAVMs(pulmonary,hepatic,gastrointestinal,and
cerebrovascular).GenecodingmutationsareresponsibleforHHT,and85%of
thecasesarecausedbyoneofthreegenemutations:ENGcodingforendoglin
(HHT1)onchromosome9,ACVLR1/ALK1(HHT2)(ActivinAReceptor,Type
II-LikeKinase1)mutationonchromosome12,orSMAD4(HTJP)genecoding
onchromosome18thatisassociatedwithjuvenilepolyposis.46,60–62,65,66There
arecurrentlytwofurtherunidentifiedgenescausingHHT,mappedto
chromosome5q(HHT3)andchromosome7p(HHT4).61Theprevalenceof
PAVMsisrelatedtothegenotypeofHHT.Inonelargestudy,PAVMwas
commonlyassociatedwithENGmutationin58%comparedwithonly18%with
ACVL1/ALK1.67TherecognitionofPAVMshasincreasedduetoawarenessof
HHT,suchthat59%ofpatientswithPAVMswhowerepreviouslyunawarewere
diagnosedwithHHT.68TheHHTFoundationinternationalguidelinesworking
groupestablishedtheCuracaocriteriaasthebasisofdiagnosisandanindication
forsubsequentgenetictestingtoconfirmthediagnosis.Thediagnosisofdefinite
HHTisacceptedifatleastthreeofthefollowingcharacteristicsofthedisease
aremet:(1)spontaneousandrecurrentepistaxis,(2)familyhistoryofafirst-
