囊腔型肺癌影像和臨床Cysticprimarylungcancerisoftenmissedormisinterpreted,whichismostlikelyduetotheiruniqueimagingappearance,showingoverlapwithbenignentitiessuchasinfection.Theappearanceisdifferentfromsolidandsubsolidnodules,whicharethemorecommonlyknownCTappearancesoflungcancer.fig.CTimagingmorphologyofpulmonarynodules.fig.Examplesofcysticlungcancerwithanexophytic(leftpanel)andendophytic(rightpanel)solidcomponent.Acysticpulmonarynodulemaybedefinedassolidand/orgroundglassattenuationinrelationtoawell-definedparenchymalairspace.Acysticnodulemaydemonstrate:Exophyticorendophyticsolidcomponentadjacenttothecysticairspace.Irregularpartialorcircumferentialwallthickening.Complexappearancewithsubsolidcomponentsandmultilocularairspaces.Theimagesshowmoreexamplesofcysticlungcancerwithathin(leftpanel)andthick(middlepanel)irregularwallthickening,andamorecomplexappearancewithextensivegroundglassandmultilocularairspaces(rightpanel).Severalclassificationsystemshavebeenproposedbasedonthisimagingmorphology.Clinicalimplicationsofanysubclassificationareyetunknownandthereforetheyareoflimitedvalueforroutineradiologycare.fig.Cysticlungcancerwithincreaseofthesolidcomponentovera2-yearscaninterval.SolidificationSolidificationistheoppositeofcavitation.Solidificationisaprocessthatisoftendemonstratedbycysticlungcancers–wherethesolidtissuecomponentincreasesovertimeandmayeventuallyevenobliteratepreviousgroundglassand/orcysticairspacescompletely,leadingtoasolidmass.fig.Cysticlungcancerdemonstrating‘solidification’Hereanotherexampleofacysticlungcancerdemonstrating‘solidification’fromabaselineprecursorlesionwithsubtleirregularwallthickeningintoasolidmassattimeofdiagnosis.Itisimportanttonotethatcavitation–whichistheprocessofcentrallucencyformationduetoexpulsionofnecrotictumourcontent–canonlybeassessedonserialCT.AlthoughveryoftenencounteredinreportsofsingletimepointCT,thistermshouldbeappliedwithcaution.Itmayinsinuateadifferentialdiagnosisofinfectionorotherdiseasethatsteersawayfromthecorrectdiagnosisofaprimarylungcancerthatismostlikelyanadenocarcinoma.fig.PatientwithaT1cadenocarcinomaintheleftupperlobe(leftpanel).Growingsynchronouscysticlesionintherightlowerlobe(rightpanel)thatrepresentedanunrelatedsecondprimaryadenocarcinomaonhistopathology.DailypracticeTheprevalenceofcysticlungcancerisnotwellestablishedandrangesbetween0.5%and12%,dependingonstudypopulationselection.Presumably,cysticlungcancermorphologyisnotuncommonatall.SeveralrecognizedassociationsareofspecificimportancetoradiologistsduringdailyCTreporting,asincreasedawarenessandactivesearchshouldbedemonstratedinthispopulation.First,ithasbeenrecognizedthatcysticlungcancerregularlyrepresentsasecondaryprimarymalignancy,eithermetachronousorsynchronouswiththefirstlungcancer(figure).Second,ahighpercentageofpatientswithcysticlungcancerare(ex-)smokersandhavepre-existentemphysema,althoughcysticlungcancersundeniablydooccurinotherwisenormallungs.Third,cysticlungcancerstendtooccurintheperipheryofthelung,whichmakesitarelevantentitytoallradiologistswhoimagepartofthelungs,specificallyneuro,abdominalandERradiologists.fig.Cysticsquamouscellcarcinoma.Theseimagesareofapatientwithaleftlowerlobecysticsquamouscellcarcinoma(leftpanel),whodevelopedarightlowerlobecysticlesion(rightpanel)andsubcarinallymphadenopathy3yearsintofollow-up.Althoughinitiallyconsideredcontralateralmetastaticdisease,recommendedtissueanalysisshowedanunrelatedsecondprimarysquamouscellcarcinomaonhistopathology.fig.Check-valvemechanismduetotumorcells(inred)interminalairway.HistopathologyCysticlungcancersarepredominantlyadenocarcinomasinabout80%ofcases,withsquamouscellcarcinomasasthesecondmostcommonsubtype.Ararenumberofothertumourtypeslikeadenosquamous,neuroendocrineandlymphomahavebeenreported.Multipleunderlyinghistopathologicsubstrates(eg.focaltumourproliferation,fibrosis,lepidictumourgrowthalongalveolarwalls,emphysema)relatetotheimagingfeaturesofcysticlungcancerandareresponsibleforeitherthesolidcomponent,septations,groundglass,andcysticairspaces.Themostwidelyquotedmechanismofairspaceformationis“check-valve”ventilation.Theaircanenterininspirationbutcannotreturnduringexpirationduetopartialobstructionoftheterminalairwayproximaltothecysticairspaceduetotumourcellsandfibrosis.Thisleadstodevelopment,persistencyandenlargementofthecysticairspace.Radiologic-histopathologiccorrelationofasquamouscellcarcinoma.Acysticairspacelinedisbytumourcells(asterisk)mostlikelyrepresentsadilateddistalairway.Check-valveventilationduetomoreproximalairwaynarrowingbymalignantcellsand/orfibrosisispresumed.Ajuxtaposedpulmonaryarterywithsurroundingmalignantcellsprojectsintothelumen(arrow).fig.Exampleshowingtransitionfrompuregroundglass(leftpanel)tocysticlungcancermorphology(rightpanel).NaturalhistoryCysticlungcancersareprogressivelesions,inherenttotheirmalignantaetiology.Althoughtheymaybeaggressive,manyareratherslow-growingadenocarcinomas.CTmorphologymayremaincysticovertime,however,whentheindependentcontributionoftheunderlyinghistopathologicsubstrateschanges,lesionmorphologymaychangeovertime.fig.Exampleshowingtransitionfromcystic(leftandmiddlepanel)topart-solidlungcancermorphology(rightpanel).Cysticnoduleswilleithershowincreaseofsolidcomponents,developadditionalgroundglassandcysticcomponentsanddemonstrateincreaseintotallesionsize.Ithasretrospectivelybeenshownthatcysticlungcancerscanbothdevelopfromsmallsubsolidprecursorlesions,aswellaschangefromcysticprecursorlesionsintosolidorsubsolidcancersattimeofdiagnosis.Lungcancermorphologyisthusfluentandcysticcomponentsmaybetemporary.fig.Thisexampleshowstransitionfrompart-solid(leftpanel),totemporarilycystic(middlepanel),tosolidlungcancermorphology(rightpanel).MimickersTherearemultiplebenigndiseasesthatmaylooklikecysticprimarylungcancer,including:Infection(bacterial,granulomatousandfungal)VasculitisRheumatoidarthritisAmyloidMetastases,etc.Previousimaging(includingnon-chestimaging),clinicalinformationandlabvalues,aswellaspastmedicalhistoryareoftenhelpfultodifferentiateasuspectedprimarylungcancerfromotheraetiology.Intheabsenceofanovertunderlyingbenigncause,anynewlungcystorcysticairspacewithassociatedsubsolidcomponentshouldraisethesuspicionforaprimarylungmalignancyandmanagedaccordinglywithCTsurveillanceorbiopsy,ifappropriate.fig.Mimickersofcysticlungcancer:Persistentloculatedairspace-leftpanel,rheumatoidnodule-middlepanelandascar-rightpanel.Theimagesareexamplesofmimickersofcysticlungcancermorphology.Apersistentloculatedairspaceafterspontaneouspneumothoraxandsubsequentwedgeresection(leftpanel)RheumatoidnoduleinapatientwithpulmonaryandpleuralRAinvolvement(middlepanel)Incidentallunglesionthatrepresentedchronicchangesandscarwithoutsignsofactiveinfectionormalignancy(rightpanel)Absolutemalignancyriskofsolitarycysticnodulesiscurrentlyunknown,asthatwouldrequireprospectivesurveillanceofallbenignandmalignantcysticnodulesinagivencohort.fig.Multiloculatedcysticlesion(leftpanel)interpretedas“non-specific”,despitea6-monthfollow-upCT(foranotherreason)showedmildincreaseofgroundglass,cysticairspacesandoveralllesionsize.ThenextCTwasobtainedforchestpain2yearslater,showingalargemassinvadingthechestwall(rightpanel).Patientdiedfrommetastaticlungadenocarcinoma.NodulemanagementThecurrentlyavailablescreening(Lung-RADS)orclinical(BTSandFleischner)nodulemanagementguidelinesdonotincludecysticlungnodules.Althoughnouniformguidanceisprovidedandoptimalsurveillancestrategyisunknown,itiscrucialthattheselesionsarenotlosttofollow-upinordertopreventdiagnosticdelayandassociatedpatientburden.Pendingpotentialincorporationintofutureguidelineversions,thefollowingstrategymightbereasonablewhenasuspiciouscysticnoduleisencountered:Excluderapidgrowthona3-monthfollow-upCTContinuesurveillancewithserialannualchestCTfor5years,similartopart-solidnodulesurveillance.Considerbiannualfollow-upifthereisstabilityandonlyatinyornomeasurablesolidcomponentatall,similartopuregroundglassnodulesurveillance.Theimagesshowasmallcysticprecursorlesion(leftpanel)initiallyinterpretedas“thin-walledcavity,likelyinfection”.ThenextC