Andersons pediatric cardiology 1325
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degreerelativewithHHT,(3)cutaneous-mucoustelangiectasia,and(4)visceral
AVMs.46,65Possiblehypothesesforthepathogenesisofvascularmalformations
includeimpairmentofbloodvesselformationorimbalanceinmultiple
proangiogenicandantiangiogenicfactors,anddelayedvascularremodelingwith
inappropriateproliferativeresponseoftheendothelialcellsduetoendoglin
depletionorabsence.69Thisleadstotheformationofbloodvesselsbetweenan
arteryandaveinwithoutinterveningcapillaries;thesesegmentsarefragilewith
highpropensityforruptureandbleeding.Theseconnectingbloodvesselsare
termedtelangiectasiaforsmall-caliberandAVMsforlarge-calibervessels.54
OutsideofHHT,PAVMscanalsooccurinpatientswithsingleventricle
variantswhoundergosuperiorcavopulmonaryanastomosisintheformofa
“classic”GlennorbidirectionalGlenn.Inaddition,PAVMsareparticularly
commoninpatientswithsingleventriclevariantswithinterruptedinferiorcaval
veinwithazygousorhemiazygouscontinuationtothesuperiorcavalvein
(typicallyinthesettingofleftisomerismoftheatrialappendages)followingthe
Kawashimaprocedure(Fig.50.9).Inthesepatients,PAVMscandevelopdueto
absenceorpaucityofhepaticvenouseffluentintothelungs.70,71Afterinclusion
ofhepaticvenousflowintothepulmonarycirculationtocompletetheFontan
circulation,PAVMsmayregresscompletelyinsomecases,whereasinothersthe
anatomicpathwayandflowdynamicscanleadtostreamingofhepaticvenous
flowprimarilytoasinglelung,predisposingtheoppositelungtoPAVM
formation(seeFig.50.9).72UnilateralPAVMsinpatientswhohavealready
undergoneFontancompletionmaybecorrectablebyreconfigurationofthe
pathwaybetweenthehepaticveinsandthepulmonaryarteries.Various
approacheshavebeendescribed,butthedirecthepaticvein–azygousvein
connectionoff-pumpsurgicallythroughalateralthoracotomyisprobablythe
mostreliablemethodofdistributionofhepaticvenousbloodtobothlungs.72,73
FIG.50.9 Largediffuserightupperlobe(blackarrows)pulmonary
arteriovenousmalformation(PAVM)inapatientwithinterruptedinferior
cavalveinandextracardiacFontan(A).Thehepaticvenouseffluentfrom
theFontanconduitflowspredominantlytotheleftpulmonaryartery(B).
TherightsuperiorcavalveinflowisdirectedacrosstheKawashima
anastomosistotherightpulmonaryarterycausingrelativepaucityof
hepaticvenouseffluenttotherightupperlobe(B,whitearrow)causing
diffusePAVMsinthatlobe(C).Thereissomehepaticbloodstreaming(B,
blackarrow)torightlowerlobewithrelativelyfewerPAVMsnotedinthat
lobe.
PAVMswithdyspneaandhypoxemiaarealsoseeninpatientswith
hepatopulmonarysyndrome(HPS).HPSisacomplicationoflivercirrhosisand
portalhypertensionandisseenrarelyinacuteandchronichepatitis.The
vascularpathologyinvolveslocalizeddilatedpulmonarycapillariesandless
commonlydiscretemacroscopicPAVMs.TheclinicaltriadthatdefinesHPS
comprisesofportalhypertensionwithandwithoutcirrhosis,hypoxemia,and
intrapulmonaryvasculardilations.74ThehypoxemiaisdefinedbymostasPaO2
lessthan70mmHgandanalveolar-arterialoxygengradientgreaterthan20mm
Hgonroomair.TheprecisepathogenesiscausingHPSisunknown,andseveral
vascularmediators,includingnitricoxide,endothelin-1,andtumornecrosis
factor-α,havebeenpostulatedtocauseintrapulmonaryvasculardilations
resultinginright-to-leftshuntingandhypoxemia(Fig.50.10).Thedegreeof
hypoxemiadoesnotcorrelatewiththeseverityofliverdisease.However,
cirrhoticpatientswithHPShavehighermortalitythanpatientswithoutHPS.75
TherearenodefinitivetherapeuticoptionsforHPSexceptforliver
transplantation.75,76OthercausesofPAVMsincludeinfectionsinvolving
schistosomiasis,tuberculosis,actinomycosis,andFanconisyndrome,anditis
veryrarelyacquiredduetotrauma.77–79
TheclinicalfeaturesseeninPAVMvarywidelybasedonthesize,number,
anddegreeofshunting.Asymptomatichypoxemiaduetoright-to-leftshuntingis
themostcharacteristicclinicalfinding.80Onlyafewpatientsdemonstrate
dyspneaordyspneawithexertion.50Commonlyorthodeoxia(worsening
hypoxemiawhenupright)andrarelyplatypnea(dyspnearelievedbylyingdown)
areattributedtoPAVMsbecausetheyarepredominantlyinthelowerlung
fields,80with17%intheupperand83%inthelowerlungzones.81Theclassic
triadofdyspnea,cyanosis,andclubbingisuncommon.82Clinicalexamination
canrevealcyanosis,clubbing,andtelangiectasiainvolvingthenails,skin,and
mucousmembranesofthemouth.Asystolicorcontinuousmurmurmaybe
heardatthesiteofasuperficiallylocatedPAVMorintheanteriororposterior
basilarbilaterallungsegments.
PAVM-associatedneurologiccomplicationsarecommonandaregrossly
underrecognized.Severalserieshavereportedincidenceofcerebralabscessto
rangefrom7.8%to19%,withischemicstrokeratesof9%to18%andprojected
clinicalstrokeinatleast25%ofpatientswithuntreatedPAVMbytheageof65
years;thestrokeriskwasreducedafterembolizationofthePAVMs.65,68,83–85
Interestingly,mostofPAVM-relatedischemicstrokesorcerebralabscess
occurredinpatientswhohadnotreceivedthediagnosisofPAVMs.Themedian
delayfromacerebraleventtoPAVMdiagnosiswas2years.68,86Migraine
headachesarerelativelycommoninpatientswithassociatedPAVMsandcan
improvefollowingtreatment.Theriskofischemicstrokecorrelateddirectlywith
theseverityofPAVMshunting.Paradoxicalemboliceventsweremorecommon
withhigher-gradecontrastechocardiography(CE)shunts(grade3shunts)in
patientswithvisiblePAVMsseenonCT.87,88Thesefeatureswereassociated
witha10.4-foldincreaseinstroke/abscesscomparedwithpatientswithgrade1
shuntswhohadnoenhancedrisk.88Thestrongeststrokeriskfactorsidentified
were:lowserumironduetoinadequateironintakefromhemorrhagiclosses,
lowpulmonaryarterypressurelikelyfacilitatingparadoxicalembolicprocess,
andhighserumfibrinogen,whichpromotesplateletaddition.89Theorganisms
involvedinPAVM-associatedcerebralabscesseswereanaerobicfacultative
organismsofperiodontalorigin.RiskfactorsidentifiedforPAVM-associated
cerebralabscessweremalegender,poordentalhygieneandinterventions,and
lowerSaO2.68ArelativelyrarebutpotentiallyfatalcomplicationisPAVM
hemorrhage,leadingtohemoptysisorhemothoraxduetolackofstructural
integrityinthethin-walledlayerofendotheliumandweakconnectivetissue
support.82ThehighestrisksforhemorrhagewereinthesettingofPAVM
perfusedatsystemicpressuresduetopulmonaryhypertensionorsystemic
