Tải bản đầy đủ (.pdf) (3 trang)

Andersons pediatric cardiology 1308

Bạn đang xem bản rút gọn của tài liệu. Xem và tải ngay bản đầy đủ của tài liệu tại đây (58.66 KB, 3 trang )

questionableifangiographyisnowrequiredfordiagnosis.Interpretationofthe
images,considereddifficultinthepast,shouldnowbeverymucheasier.Evenin
potentiallysuitablecases,survivorsofattemptedseparationhavethusfarbeen
rare.Aswithexteriorizationoftheheart,thesituationmustbeanticipated
rapidlytoimprove,dependingofcourseonthedegreeoffusionofthecardiac
structures,andtheseverityoftheintracardiaclesionsineachtwin.


AbnormalPositioningoftheHeart
Theheartisnormallylocatedinthemediastinum,withone-thirdofitsbulkto
theright,andtwo-thirdstotheleftofthemidline.Withthisarrangement,the
apexusuallypointsinferiorlyandtotheleft.Thiscombinedpatternis
traditionallydescribedas“levocardia.”Theheartcanbedeviatedfromthis
position,oritsapexbepointedinanunexpecteddirection,forvariousreasons,
andnotalwaysbecauseofacongenitalcardiacmalformation.Forexample,the
heartcanbepushedtotherightbyaspace-occupyinglesionintheleftlungor
leftpleuralcavity,suchashyperinflationoftheleftlung,orpleuraleffusionand
pneumothoraxinvolvingtheleftpleuralcavity.Theheartcanalsobepulledto
therightwhentherightlungisunderdevelopedorcollapsed.Anabnormal
rightwardpositionoftheheartisalsotypicallyseeninassociationwithright
pulmonaryhypoplasiainscimitarsyndrome,ligamentousorductaloriginof
rightpulmonaryartery,oratresiaofstenosisoftherightpulmonaryvein.
Nonetheless,theabnormalpositioninitselfdoesnotnecessarilyimplyan
abnormalityoftheheart.Normalindividualswithmirror-imagedarrangementof
theorgansusuallyhavearight-sidedheart.Thereforewhenassessingthe
significanceofaright-sidedheartoraheartwithitsapexpointingtotheright,it
isnecessarytotakeaccountofallthesevariousfeatures.Severalquestions
shouldbeasked.Whatistheoverallarrangementoftheorgans?Istherean
abnormalityofthelungsorthethoraciccontents?Ifpresent,isitofcongenitalor
acquiredetiology?Istheheartitselfabnormallystructured,orareitschambers
grotesquelyenlarged?Onlywhenthesequestionshavebeenposed,and


answered,canthesignificanceofanabnormallypositionedheartbefully
appreciated.Attemptstocompressallthisinformationintoshortphrasesor
singlewordshaveledtocomplexandconfusingterms,suchasdextrocardia,
levocardia,dextroversion,levoversion,anddextroposition.21Ourpreferenceis
toavoidusingthesecrypticconventions.
Amuchsimplerapproachwhenconsideringtheabnormallypositionedheart,
isfirsttoaccountforitsoveralllocation.Thiscanbeleft-sided,central,orrightsided.Itisnecessarytoaccountfortheorientationofitsapex,whichcan
similarlybeleft-sided,central,orright-sided.Alllocationscanbecategorized
solelyintermsofthepositionoftheheart,andtheorientationofitsapex.This
information,ofcourse,mustbeplacedinthecontextoftheoverallarrangement
ofthethoracicandabdominalorgans,andthepresenceofacquiredorcongenital


diseaseofeithertheheartorthelungs.Thereforeabnormalpositioningofthe
heartshouldnolongerberegardedasadiagnosisinitsownright.Findinga
right-sidedheart,forexample,givesnoclueastowhatishappeninginsidethe
organ.Theheartitselfmaybeentirelynormal.Thedescriptionofanabnormal
locationisbutonepartoffullsequentialsegmentalanalysis(seeChapter1).
Nonethelesscertainwell-recognizedlesions,orcombinationsoflesions,are
associatedwithright-sidedhearts,orleft-sidedheartsinthosewithmirror
imagery.Asalreadyemphasized,theheartistypicallyright-sidedinassociation
withhypoplasiaoftherightlunginthescimitarsyndromeanditsvariants,which
isalsoknownasthebronchopulmonaryforegutmalformation.22Rightward
displacementoftheheartisalsoseeninassociationwithligamentalductalorigin
oftherightpulmonaryartery,withunilateralabsenceoftherightpulmonary
artery,andwithunilateralatresiaorstenosisoftherightpulmonaryveins.The
heartisalsoright-sidedinwelloverathirdofindividualswhohaveanisomeric
arrangementoftheirorgans(seeChapter22).Thesinglelesionmostassociated
witharight-sidedheart,orleft-sidedheartwithmirror-imagedarrangement,is
congenitallycorrectedtransposition(seeChapter38).Atbest,thesearecluesto

thefinaldiagnosis.Thevarietyoflesionsthatcanexistwhentheheartis
abnormallypositionedisprotean.



×