Failure to Pass Meconium.docx
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Failure to Pass Meconium.docx
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FailuretoPassMeconium
FailuretoPassMeconium:
DiagnosingNeonatalIntestinalObstruction
VERALOENING-BAUCKE,M.D.,and
KENKIMURA,M.D.
UniversityofIowaSchoolofMedicine,IowaCity,Iowa
Timelypassageofthefirststoolisahallmarkofthewell-beingofthenewborninfant.Failureofafull-termnewborntopassmeconiuminthefirst24hoursmaysignalintestinalobstruction.LowerintestinalobstructionmaybeassociatedwithdisorderssuchasHirschsprung'sdisease,anorectalmalformations,meconiumplugsyndrome,smallleftcolonsyndrome,hypoganglionosis,neuronalintestinaldysplasiaandmegacystis-microcolon-intestinalhypoperistalsissyndrome.Radiologicstudiesareusuallyrequiredtomakethediagnosis.Inaddition,specifictestssuchaspelvicmagneticresonanceimaging,anorectalmanometryandrectalbiopsyarehelpfulintheevaluationofnewbornswithfailuretopassmeconium.(AmFamPhysician1999;60:
2043-50.)
Thefirststoolispassedwithin24hoursofbirthin99percentofhealthyfull-terminfantsandwithin48hoursinallhealthyfull-terminfants.1Failureofafull-termnewborntopassmeconiumwithinthefirst24hoursshouldraiseasuspicionofintestinalobstruction.Amongprematureinfants,however,onestudy2revealedthatonly37percentof844preterminfantspassedtheirfirststoolinthefirst24hours;32percenthaddelayedpassageofthefirststoolbeyond48hours.In99percentofthepreterminfants,thefirststoolwaspassedbytheninthdayafterbirth.
ClinicalPresentationofMeconiumRetention
Neonateswhofailtopassmeconiumandhaveprogressiveabdominaldistentionandvomitingmustbeevaluatedforintestinalobstruction.
Failuretopassmeconiumcombinedwithprogressiveabdominaldistention,refusaltofeedandvomitingofbiliousintestinalcontentsaretheclassicclinicalsignsofintestinalobstructioninneonates.Abdominalexaminationoftenrevealsdistendedloopsofbowel,whichmaybevisibleorpalpable.Analinspectionisessentialtoexcludethepresenceofanalatresia,perinealfistulawithanalatresia,themembranousformofanalatresiaandanalstenosis.
Plainradiographsoftheabdomendonotallowdifferentiationofsmallbowelobstructionfromlargebowelobstruction.Thedifferentialdiagnosisforsmallbowelobstructioninneonatesincludesduodenalatresia,malrotationandvolvulus,jejunoilealatresia,meconiumileusandmeconiumperitonitis.Biliousvomiting,withorwithoutabdominaldistention,isusuallythefirstsignofsmallbowelobstruction.ThedifferentialdiagnosisforlargebowelobstructioninneonatesincludesHirschsprung'sdisease,anorectalmalformationsandmeconiumplugsyndrome(Table1).
Incasesofsuspectedneonatalintestinalobstruction,themostdifficultdecisionmaybedecidingbetweenconservativemanagementandemergencysurgery.
Inmanycasesofsuspectedneonatalintestinalobstruction,theclinicalhistoryandphysicalexaminationcombinedwithplainabdominalradiographs,contrastenemaradiographicexamination,anorectalmanometryandrectalbiopsyeventuallyyieldthediagnosis.Themostdifficultmanagementdecisionistodecidebetweenconservativemanagementandemergencysurgery.Ideally,allnewbornssuspectedofhavingbowelobstructionshouldreceivetreatmentatacenterwhereapediatricsurgeonisavailable.
TABLE1
DifferentialDiagnosisofConditionsThatMayBeAssociatedwithFailuretoPassMeconiumintheNewborn
Diagnosis
Frequency
Abnormalfindings
Therapy
Hirschsprung'sdisease
1/4,0003
Tightanus,emptyrectum,transitionzone
Surgery
Meconiumplugsyndrome
1/500to1/1,00010
Meconiumplugs
Rectalstimulation,enema
Meconiumileus
1/2,80012
Abdominaldistentionatbirth,cysticfibrosis
Enemawithintravenousfluids,surgery
Anorectalmalformation
1/4,000to1/8,00014
Absentanus,tightanusorfistula
Dilatation,surgery
Smallleftcolonsyndrome
Rare
Transitionzone*atsplenicflexure
Enema,rarely,colostomy
Hypoganglionosis
Rare
Transitionzone*
Medical,TPN,surgery
NeuronalintestinaldysplasiatypeA
Rare
Transitionzone,*mucosalinflammation
Medical,surgery
NeuronalintestinaldysplasiatypeB
Rare
Megacolon
Medical,rarely,surgery
Megacystis-microcolon-intestinalhypoperistalsissyndrome
Veryrare
Microcolon,megacystis
TPN
TPN=totalparenteralnutrition.
*--Transitionzone(fromsmall-tolarge-diameterbowel)referstoradiographicvisualizationoncontraststudy.
IllustrativeCase
A3,480g(7lb,7oz)maleinfantwasbornafter40weeks'gestation.Therewerenocomplicationsduringthepregnancyanddelivery.Hedidnotpassmeconiumafterbirth,andhehadtheonsetofvomitingonthefirstday.Hisabdomenbecamemildlydistended.Theinfantwasnotabletofeed,andabdominaldistentionincreased.
Rectalexaminationrevealedatightanus.Onthesecondday,flatanduprightabdominalfilmsdemonstratednumerousloopsofdilatedbowel(Figure1a).Bariumenemaradiographicexaminationshowedthatmostofthedilatedbowelwascolon;notransitionzonewasseen(Figure1b).
Thesurgeonperformedananaldilatation,andtheinfantsubsequentlypassedgasandmeconium,whichwasfollowedbyresolutionofallsymptoms.
Afterdischargefromthehospital,theinfant'smothercontinuedperformingperiodicanaldilatationbecausehehaddifficultiesmovinghisbowel.Digitalrectalexaminationbythephysicianwhentheinfantwasfiveweeksofagerevealedatightanusandliquidstoolbutnoimpaction.
Oneweeklater,themothernoticedabloodyringaroundhisbowelmovements.Bariumenemaradiographicexaminationatthistimeshowedatransitionzoneinthedistalportionofthesigmoidcolon,withmarkeddilatationofthedescendingcolonandleftsideofthetransversecolon(Figure1c).Anorectalmanometryshowedanabsentrectosphinctericreflex.Noganglioncellswereseenintherectalbiopsy.ThesefindingswereconsistentwithHirschsprung'sdisease.
FIGURE1A.Plainabdominalradiographdemonstratingnumerousloopsofdilatedbowel.Smallbowelobstructioncannotbedifferentiatedfromlargebowelobstruction.Nogasisvisibleintherectum.
FIGURE1B.Bariumenemaradiographshowinganincompletelyfilled,dilatedcolon.Thisexaminationconfirmsthatmostofthedilatedbowelontheplainfilm(Figure1a)isthecolon.Notransitionzoneisvisible.
FIGURE1C.BariumenemaradiographperformedwhentheinfantinFigures1aand1bwassixweeksofage,revealingatransitionzoneinthedistalportionofthesigmoidcolon,withmarkeddilatationofthedescendingcolonandtheleftsideofthetransversecolon.ThesefindingsareconsistentwithHirschsprung'sdisease.
Hirschsprung'sDisease
Hirschsprung'sdisease,orcongenitalaganglionicmegacolon,hasanoverallincidenceofonein4,000livebirths.3Itaccountsfor20to25percentofthecasesofneonatalbowelobstruction.4Thediseaseaffectsfourtimesasmanyboysasgirls,and8percentofpatientswithHirschsprung'sdiseasealsohaveDownsyndrome.5Theabnormalbowelinnervationaffectstheinternalanalsphincter.Mostoften,therectosigmoidisinvolved,butavariablelengthofgutcanbeinvolved.A30-yearretrospectivestudy6revealedthatthemeanageatdiagnosishasdecreasedto2.6monthsbecauseofvigilanceonthepartofphysicians,theuseofanorectalmanometryforassessmentoftheanalsphincterandearlyrectalbiopsytoconfirmtheclinicaldiagnosis.
AcommonpresentationofHirschsprung'sdiseaseinthenewbornisfailuretopassmeconiumduringthefirstfewdaysoflife,withsubsequentpassageofameconiumplugfollowedbysparsebowelmovements.GastrointestinalbleedinganddiarrheaaredangersignsforHirschsprung'sdiseaseassociatedenterocolitis.Enterocolitiscanbefatalandisthoughttobeduetoproliferationofbacteriaasaresultofstasis.
Physicalexaminationoftenrevealstheanusandrectumtobenarrowandemptyofstool.Plainabdominalradiographsshowgasandstoolinthecolonandoftenthedistentionwithstoolorgasdoesnotreachdistallytothepelvicrim(Figure1a).
Bariumenemaradiographicexamination,performedwiththecolonunprepared,mayrevealatransitionzonethatseparatesthesmall-tonormal-diameteraganglionicbowelfromthedilatedbowelabove(Figure1c).Atransitionzonemaynotberecognizableinupto25percentofneonateswithclassicHirschsprung'sdisease(Figure1b).Similarly,atransitionzonemaynotbediscernibleinpatientswithultrashort-segmentHirschsprung'sdisease,inpatientswithtotalcolonicaganglionosisinwhomthetransitionzoneisabovethecolonandinpatientswhohadanemergencycolostomy.Thepresenceofbariuminthe24-hourdelayedfilmisalsosuggestiveofHirschsprung'sdisease.
FIGURE2A.Anorectalmanometricrecordingofanewbornwithdelayedpassageofstool,showinganormalrectosphinctericreflexasdemonstratedbythedropinanalpressureinresponsetorectaldistention.Thevolumeindicatedisthevolumeusedforrapidrectaldistention.Rectaldistentioninhibitstheinternalanalsphincter,resultinginafallinanalcanalpressure.
FIGURE2B.AnorectalmanometricrecordingofanewbornwithHirschsprung'sdisease.Therectosphinctericreflexisabsent,manifestedbynochangeintheanalcanalpressureinresponsetoballoondilation.
AnorectalManometry
Whenpossible,anorectalmanometryshouldbeperformedinallnewbornswithsymptomsoflowerbowelobstruction.Withanorectalmanometry,changesinanalpressurearerecordedduringandafterrectaldistention.Whenganglioncellsarepresent,rectaldistentionwithaballooninhibitsth
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