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EDUCATIONEXHIBIT TheThymus:ACom-prehensiveReview LEARNINGOBJECTIVES Afterreadingthisarticleandtakingthetest,thereaderwillbeableto:Describetheem-bryologicandhisto-logicfeaturesoftheListthemedicalconditionsassociatedwiththymicdisease.Discussthespec-trumofthymicdis-easeswithradiologic-pathologiccorrela-MizukiNishino,MDSimonK.Ashiku,MDOlivierN.Kocher,MDRobertL.Thurer,MDPhillipM.Boiselle,MDHirotoHatabu,MD,SinceÞrstbeingdescribedassuchbyGalenofPergamum(130Ð200),thethymushasremainedanÒorganofmysteryÓthroughoutthe2000-yearhistoryofmedicine.Thethymusreachesitsmaximumweightinpubertyandsubsequentlyundergoesinvolution,andthusishardlyaneye-catchingstructureonimagingstudiesperformedinhealthyadults.However,oncetherehasbeeninvolvementofthethy-musbyadiseaseprocess,theglanddemonstratesavarietyofclinicalandradiologicmanifestationsthatrequirecomprehensiveunderstand-ingofeachentity.Furthermore,itisimportantforradiologiststobefamiliarwiththecurrentWorldHealthOrganizationhistologicclassiÞ-cationschemeforthymicepithelialtumorsandtounderstanditsclini-cal-pathologic,radiologic,andprognosticfeatures.RSNA,2006 ßuorodeoxyglucose,H-Ehematoxylin-eosin,SLEsystemiclupuserythematosus,SUVstandardizeduptakevalue,WorldHealthOrganizationRadioGraphics2006;PublishedonlineContentCode: FromtheDepartmentsofRadiology(M.N.,P.M.B.,H.H.),ThoracicSurgery(S.K.A.,R.L.T.),andPathology(O.N.K.),BethIsraelDeaconessMedicalCenter,330BrooklineAve,Boston,MA02215.Presentedasaneducationexhibitatthe2004RSNAAnnualMeeting.ReceivedDecember22,2004;revisionrequestedMay9,2005,andreceivedJune8;acceptedSeptember22.AllauthorshavenoÞnancialrelationshipstodisclose.dresscorrespondencetoM.N.(e-mail:RSNA,2006 RadioGraphics ONLINE-ONLYCME Seewww.rsna See last page TEACHING POINTS acteristicstructuresofthethymusandarefoundexclusivelyinthemedulla(Fig1).Theseentitiesareround,keratinizedformationswithmatureepithelialcellsandundergomarkedcysticchangeintomultilocularthymiccysts(5).Inadditiontoepithelialcellsandlymphocytes,thethymuscon-tainsavarietyofothertypesofcells,includingmacrophagesandmyoidcells.Myoidcellsareofgreatinterestbecauseoftheirpotentialroleinthepathogenesisofmyastheniagravis(discussedlater)(5).Abasicknowledgeofthehistologicfea-turesofthethymusisessentialforunderstandingthevariouspathologicconditionsthataffectthisgland,includingthymicepithelialtumors.Famil-withthecurrentWHOclassiÞcationscheme,whichisbasedonhistologicfeatures,isalsoes-sential(5).FunctionoftheThymusInancienttimes,thethymuswasbelievedtobetheseatofthesoulortheorganofpuriÞcationofthenervoussystem(1Ð4).Later,thethymuswasthoughttobeaprotectivethoraciccushion(10)ortheregulatoroffetalandneonatalpulmonaryfunction(1,11).In1832,SirAstleyCoopersug-gestedthatthisorganmustperformsomeimpor-tantfunction(12);however,theexactnatureofthisÒimportantfunctionÓwasnotyetunder-stood.WhatiscurrentlyknownaboutthymicfunctionisthatthethymusisoneofthecentrallymphoidorgansandplaysanimportantroleincellularimmunitybygeneratingcirculatingTlymphocytes.AlthoughtheneedforthethymustogenerateacontinuoussupplyofTcellsde-creaseswithadvancingage,thethymuscontinuestoserveasthesiteofT-celldifferentiationandmaturationthroughoutlife(5,13).Oneofthema-jorfunctionsofthethymus,thematurationofthymocytes,hasbeenstudiedextensivelywithmolecularandcellularbiology.Itisnowknownthatvariousinductive,hormonal,andprolifera-tivesignalsfromepithelialcellscontributetothematurationofthymocytes(5).Ofnote,T-cellantigenreceptorsofthymocytesinteractwithepi-thelialmajorhistocompatibilitycomplexantigensintheprocessofthymocytematuration(5).DeÞnitionofÒNormalThymusÓinAdultsWhatconstitutesanormalthymusisanotherim-portantissue.Becausethethymusdemonstratesuniquechangesovertime,differentiationofanormalthymusfromathymicdisordercansome-timesbeproblematicforradiologists.Aswasmentionedearlier,GalenwastheÞrsttonotethatthethymusisproportionallylargestduringinfancy(1,4).Thisobservationwasveri-Þedin1777byWilliamHewson,whostudiedtheevolutionofthymicsizeduringfetalandinfantlife(1,11).Afterreachingitsgreatestweightinproportiontobodyweightbeforebirth,thethy-muscontinuestogrow,reachingitsmaximumabsoluteweightatpuberty.Thethymussubse-quentlyundergoesaprocesscalledinvolution,whichisdeÞnedasadecreaseinthesizeandweightoftheglandwithadvancingage.Thispro-cessstartsatpuberty,whenthethymusisatitsmaximumabsoluteweight.Duringinvolution,theepithelialcomponentatrophies,resultinginscatteredsmalllymphocytesinabundantadiposetissue(5).AtCT,thethymusappearsasabilobedtrian-gularstructurelocatedintheanteriormediasti-num,mostcommonlyanteriortotheproximalascendingaorta,thepulmonaryoutßowtract,andthedistalsuperiorvenacavabeforeitenterstherightatrium(Fig2)(14).Differentiationofthethymusfromothermediastinalstructures,suchaslymphnodesorthesuperiorsinusofthepericar-dium,maybedifÞcult.Therefore,itisimportanttobefamiliarwiththelocation,shape,andsizeofthenormalthymus.Thesizeofanormalthymushasbeenexten-sivelystudiedwithCTandMRimaging(14Ð17).Baronetal(14)analyzed154mediastinalCTscansandreportedthatthemeanthicknessofanormalthymusdecreasedwithadvancingagefrom1.1cm(standarddeviation,0.4cm)forthe6Ð19-yearagegroupto0.5cm(standarddevia-tion,0.27cm)forpatientsoverage50years.The Figure2.ContrastmaterialÐenhancedchestCTscanshowsanormalthymus(arrow)asatriangularstructureinthemediastinumanteriortotheascendingaortaandthemainpulmonaryarterialtrunk.Volume26Number2Nishinoetal337 RadioGraphics SeveralproposalstosimplifytheclassiÞcationschemeaccordingtosimilarprognosticappear-ancehavebeenmadetofacilitateclinical-patho-logicunderstandingofthymicepithelialtumors.Riekeretal(53)proposedasimpliÞedclassiÞca-tionschemeconsistingofthreesubtypes:typesA,AB,B1,andB2asonegroup;typeB3;andtypeC.However,thesurvivalratesforpatientswithtypeB2tumorsarelowerthanthoseforpatientswithtypeA,AB,orB1tumors(52,54).Inaddi-tion,alarge-scalereportofthymicepithelialtu-morsstatedthatoverallsurvivalratesforpatientswithtypeA,AB,orB1tumorswerehigherthanthoseforpatientswithtypeB2orB3tumors(54).Jeongetal(30)simpliÞedtheWHOhistologicclassiÞcationschemeintothreesubgroupsÑlow-riskthymomas(typesA,AB,andB1),high-riskthymomas(typesB2andB3),andthymiccarci-nomas(typeC)ÑandcorrelatedCTÞndingsinthethreetumorsubgroupswithprognosis.Insummary,theMasaokaclinical-pathologicstagingsystemisbasedoninvasivenessofthetu-moratsurgery,andthesystemcorrelateswith5-yearsurvivalrates.TheWHOclassiÞcationschemeisrelativelynewandisbasedonhistologicfeatures.Thisschemehasbeenshowntocorre-latewiththeinvasivenessandclinicalbehavioroftumorsandwithprognosis,hasimportantpreop-erativeimplicationsfortreatmentstrategy,andwillbeastandardclassiÞcationschemeforthymicepithelialtumors.ImagingFeaturesofThymicEpithelialTumorsCorrelatedwithHistologicSubtypesComputedTomography.ÑThymicepithelialtumorsmostfrequentlymanifestassoft-tissuemassesintheanteriormediastinum,varyinsize,andcanhavesmoothandlobulatedborders.Be-causeoftheirembryologicbackgroundandana-tomiclocation,theycanoccuradjacenttothejunctionofthegreatvesselsandthepericardium;lesscommonly,inthecardiophrenicanglesoradjacentcardiacborders;and,rarely,intheneckorothermediastinalcompartments(5,18).Con-ventionalradiographymayhelpdetectrelativelylargelesions,especiallyonlateralprojectionsasanopacityintheretrosternalarea;however,thisÞndingisoftenindeterminate,andsmallerlesionsmaygoundetected(18).CT,ofcourse,hasamuchhighersensitivityfordetectingthymicepithelialtumors,andalsoallowsevaluationofinvasionofthesurround-ingmediastinalfat,vascularstructures,andadja-centlung;andthepresenceofpleuralandextrapleuralseeding.OnCTscans,thymicepi-thelialtumorsusuallyappearashomogeneous,oval,roundedorlobulatedsoft-tissuemassesintheanteriormediastinum(Fig5)(18).Incasesof Figure5.WHOtypeB1thymoma(lymphocyterich,predominantlycortical)ina57-year-oldwoman.hancedCTscanshowsawell-circumscribed,ßattenedsoft-tissuelesionintheanteriormediastinum,withamain-tainedfatplanesurroundingthelesion.Photomicrograph(originalmagniÞcation,40;H-Estain)showscellularlobulesconsistingpredominantlyoflymphocytes,alongwithscatteredsmallfociofmedullarydifferentiation.Volume26Number2Nishinoetal341 RadioGraphics invasivethymomaorthymiccarcinoma,invasionofthemediastinalfatoradjacentstructuresaswellaspleuralseedingmaybeseen.WiththeincreasedprevalenceofadvancedCTtechnology,detailedcharacterizationofthymicepithelialtumorsatCThasbecomepossible;therefore,thecorrelationofradiologicÞndingswithWHOclassiÞcations,clinicalbehaviors,andprognosishasalsobeeninvestigated(28Ð30).BecausethecurrentWHOclassiÞcationschemecorrelateswiththeoncologicbehaviorofthymicepithelialtumorsandaffectstreatmentstrategy,familiaritywiththeimagingfeaturesthatsuggestspeciÞchistologicsubtypesisimportantforradi-ologists,allowingthemtocontributetotheclini-caltreatmentofaffectedpatients.Tomiyamaetal(28)assessedtheCTfeaturesofvarioussubtypesofthymicepithelialtumorsin53patientsandreportedthatsmoothcontoursandaroundshapearemostsuggestiveoftypeAtumors,irregularcontoursaremostsuggestiveoftypeCtumors,andcalciÞcationissuggestiveoftypeBtumors.Jeongetal(30)reviewedtheCTÞndingsin91patientswhohadundergoneresec-tionofthymicepithelialtumorsandcorrelatedtheseÞndingswiththeirsimpliÞedclassiÞcationschemeandwithprognosis.Accordingtotheseinvestigators,CTÞndingsthataremorecommoninhigh-riskthymomasandthymiccarcinomasincludelobulatedcontour,mediastinalfatinva-sion,andgreatvesselinvasion(Figs6,7;TableFindingsassociatedwithsigniÞcantlymorefrequentrecurrenceandmetastasisincludelobu-latedorirregularcontour,ovalshape,mediastinalfatinvasionorgreatvesselinvasion,andpleuralseeding(Fig8,Table4).Inthediagnosisofthy-mictumors,radiologistsshouldlookcarefullyattheCTÞndings,whichmayserveaspredictorsoftumorinvasivenessandofpostoperativerecur-renceormetastasis.Table4CTFindingsinThymicEpithelialTumors Findingsmorecommoninhigh-riskthymomasandthymiccarcinomasLobulatedcontourMediastinalfatinvasionGreatvesselinvasionFindingsassociatedwithasigniÞcantlygreaterprevalenceofrecurrenceandmetastasisLobulatedorirregularcontourOvalshapeMediastinalfatinvasionorgreatvesselinvasionPleuralseeding Figure6.WHOtypeB3thymoma(epithelial,well-differentiatedthymiccarcinoma)inan83-year-oldwoman.Contrast-enhancedCTscanshowsalobulatedanteriormediastinalmasswithcalciÞcation,aÞndingthatiscom-monlyseenintypeBtumors.Notethelobulatedcontourofthemassandthelossofthefatplanebetweenthemassandthepleura-pericardium.Photomicrograph(originalmagniÞcation,40;H-Estain)showsapredominanceofpolygonalepithelialcellswithnuclearatypia.342March-April2006Volume26Number2 RadioGraphics TeachingPoint MRImaging.ÑAtMRimaging,thymomahasasignalintensitysimilartothatofmuscleornor-malthymictissueonT1-weightedimagesandappearsheterogeneousonT2-weightedimages(Fig9)(18,29,31).MRimagingmayalsobeuse-fulindifferentiatingbetweenthymomaandthy-miccyststhatdemonstrateincreasedCTattenua-tionduetohemorrhageorhighmucinouscontent(Fig10).T2-weightedandcontrast-enhancedMRimagesalsohelpdetectsolidcomponentsofcysticlesions,aÞndingthatraisesthepossibilityofcysticthymoma(Fig11).FDGPET.ÑFDGPETisanotherpowerfuldiagnostictoolforthediagnosis,staging,andrestagingofneoplasmsingeneral.Inthymicneo-plasms,FDGPETmaybeusefulindifferentiat-ingthymiccarcinomafromotherthymicneo-plasms,thymichyperplasia,andnormalphysi-ologicuptake(27).Sasakietal(32)reportedthatthestandardizeduptakevalue(SUV)forthymiccarcinomawassigniÞcantlygreaterthanthatforinvasiveornoninvasivethymoma.WithanSUVcutoffpointof5.0,thymiccarcinomacanbedifferentiatedfromthymomawithreasonablyhighsensitivity(84.6%),speciÞcity(92.3%),andaccuracy(88.5%).Therewasnostatisticallysig-niÞcantdifferenceinSUVbetweeninvasiveandnoninvasivethymomas.ItisspeculatedthatFDGPETwillprovetobeeffectiveindifferentiatingthymiccarcinomafromotherthymicdiseasesbutfarlesssoindifferentiatingbetweeninvasiveandnoninvasivethymoma(27).UncommonThymicNeoplasmsÑThymolipomaisarare,be-nign,slow-growingtumorthataccountsfor2%Ð9%ofallthymicneoplasms.Itoccursmostfrequentlyinyoungadultsandhasnosexpredi-lection.Thymolipomaisusuallyasymptomaticandmanifestsasalargeanteriormediastinalmass.Athistologicanalysis,itiscomposedofma-turefatandthymictissue(5).Becauseofitssoftandpliablenature,thymolipomatypicallydrapesitselfaroundtheheartandadjacentmediastinalstructures,oftenbecomingquitelargebefore Figure9.WHOtypeABthymomaina68-year-oldwoman.Axialhalf-Fourieracquisitionsingle-shotturbospin-echoMRimageshowsananteriormediastinalmassthatisslightlyhyperintenserelativetoskeletalmuscle.Al-thoughthefatplanebetweenthemassandmediastinalstructuresappearstobemaintained,thepossibilityofmini-malchestwallinvasioncannotbeexcludedwithcertainty.Atsurgery,themassappearedwellcircumscribedandwasexcisedentirely.Noextracapsularinvasionwasnoted.Photomicrograph(originalmagniÞcation,40;H-Estain)demonstratesmixedhistologicfeatures,withfociofmedullaryandspindlecellsadmixedwithlymphocytes.344March-April2006Volume26Number2 RadioGraphics alone(Fig12)(18).Thymiccarcinoidhasapoorprognosisduetoahighprevalenceofrecurrenceandmetastasis.ÑLymphomamayinvolvethethy-musaspartofdisseminateddiseaseorsometimesasanisolatedsite.Hodgkindiseaseaccountsforthemajorityofthymiclymphomas,withnodularsclerosisbeingthemostcommonhistologicÞnd-ingidentiÞedinthethymus(18,24).ThemajorimagingÞndingsincludethymicenlargement,sometimeswithsingleormultiplemasses.Ingen-eral,itisdifÞculttodistinguishlymphomafromotherthymicmasses,especiallythymoma,onthebasisofimagingÞndingsalone.Distinguishingprominentbutnormalthymusinyoungpatientsandthymichyperplasiafromlymphomatousin-volvementofthethymusisalsoproblematic(18,24).UseofchemicalshiftMRimagingandFDGPETinthissettinghavebeendescribedpreviously;however,furtherstudywillbeneededtodeterminetheirutility(26,27).Knowledgeoftheembryologic,histologic,andnormalmorphologicfeaturesofthethymusises-sentialforcomprehensiveunderstandingofthenormalthymusandthymicdiseases.FamiliaritywiththeclassiÞcationschemesforthymicepithe-lialtumors,especiallythecurrentWHOclassiÞ-cationscheme,andawarenessofthecorrelationbetweentheseclassiÞcationschemesandradio-logicÞndingsarenecessaryiftheradiologististocontributetotheclinicaltreatmentofaffectedTheauthorsthankDonnaWolfe,MFA,MichaelLarson,MFA,andRonaldKuklafortheirassistanceinmanuscriptpreparation.1.JacobsMT,FrushDP,DonnellyLF.Therightplaceatthewrongtime:historicalperspectiveoftherelationofthethymusglandandpediatricradi-ology.Radiology1999;210:11Ð16.2.HaubrichWS.Medicalmeanings.Philadelphia,Pa:AmericanCollegeofPhysicians,1997;225.3.SkinnerHA.Originofmedicalterms.2nded.Bal-timore,Md:Williams&Wilkins,1961;404.4.MayMT.Galenontheusefulnessofthepartsofthebody.Ithaca,NY:CornellUniversityPress,1968;30.5.ShimosatoY,MukaiK.Tumorsofthethymusandrelatedlesions.In:ShimosatoY,MukaiK,eds.Atlasoftumorpathology:tumorsofthemedi-astinum,fasc21,ser3.Washington,DC:ArmedForcesInstituteofPathology,1997;158Ð168.6.LeleSM,LeleMS,AndersonVM.Thethymusininfancyandchildhood:embryologic,anatomic,andpathologicconsiderations.ChestSurgClinNAm2001;11:233Ð253.7.SusterS,RosaiJ.Histologyofthenormalthymus.AmJSurgPathol1990;14:284Ð303. Figure12.Thymiccarcinoidina74-year-oldman.Contrast-enhancedCTscandemonstratesalobulated,het-erogeneouslyenhancingmassintheanteriormediastinum.Notethelossofthefatplanebetweenthemassandthepericardium,aÞndingthatsuggestsinvasiveness.Photomicrograph(originalmagniÞcation,40;H-Estain)showstumorcellsinatrabeculargrowthpatternwithoncocyticcytoplasmandovaltoirregularnuclearcontours.346March-April2006Volume26Number2 RadioGraphics 44.RegnardJF,MagdeleinatP,DromerC,etal.Prognosticfactorsandlong-termresultsafterthy-momaresection:aseriesof307patients.JThoracCardiovascSurg1996;112:376Ð384.45.WilkinsKB,SheikhE,GreenR,etal.Clinicalandpathologicpredictorsofsurvivalinpatientswiththymoma.AnnSurg1999;230:562Ð574.46.LardinoisD,RechsteinerR,LangRH,etal.Prog-nosticrelevanceofMasaokaandMuller-Her-melinkclassiÞcationinpatientswiththymictu-mors.AnnThoracSurg2000;69:1550Ð1555.47.RiosA,TorresJ,GalindoPJ,etal.Prognosticfac-torsinthymicepithelialneoplasms.EurJCardio-thoracSurg2002;21:307Ð313.48.MasaokaA,MondenY,NakaharaK,TaniokaT.Follow-upstudyofthymomaswithspecialrefer-encetotheirclinicalstages.Cancer1981;48:49.RosaiJ,SobinLH.Histologicaltypingoftumoursofthethymus.In:Internationalhistologicalclassi-Þcationoftumours.2nded.NewYork,NY:Springer,1999;5Ð14.50.OkumuraM,MiyoshiS,FujiiY,etal.ClinicalandfunctionalsigniÞcanceofWHOclassiÞcationonhumanthymicepithelialneoplasms:astudyof146consecutivetumors.AmJSurgPathol2001;51.ChalabreysseL,RoyP,CordierJF,LoireR,Ga-mondesJP,Thivolet-BejuiF.CorrelationoftheWHOschemafortheclassiÞcationofthymicepi-thelialneoplasmswithprognosis.AmJSurgPathol2002;26:1605Ð1611.52.OkumuraM,OhtaM,TateyamaH,etal.TheWorldHealthOrganizationhistologicclassiÞ-cationsystemreßectstheoncologicbehaviorofthymoma:aclinicalstudyof273patients.Cancer2002;94:624Ð632.53.RiekerRJ,HoegelJ,Morresi-HaufA,etal.Histo-logicclassiÞcationofthymicepithelialtumors:comparisonofestablishedclassiÞcationschemes.IntJCancer2002;98:900Ð906.54.ChenG,MarxA,Wen-HuC,etal.NewWHOhistologicclassiÞcationpredictsprognosisofthy-micepithelialtumors:aclinicopathologicstudyof200thymomacasesfromChina.Cancer2002;95:420Ð429.55.BoisellePM.Mediastinalmasses.In:McLoudTC,ed.Thoracicradiology:therequisites.StLouis,Mo:Mosby,1998;431Ð462.56.Rosado-de-ChristensonML,PugatchRD,MoranCA,GalobardesJ.Thymolipoma:analysisof27cases.Radiology1994;193:121Ð126.57.MatsudairaN,HiranoH,ItouS,MatsuuraK,KanouM,OgawaT.MRimagingofthymoli-poma.MagnResonImaging1994;12:959Ð961.58.BentonC,GerardP.ThymolipomainapatientwithGravesÕdisease:casereportandreviewoftheliterature.JThoracCardiovascSurg1966;51:428Ð433.59.WickMR,ScottRE,LiCY,CarneyJA.Carcinoidtumorofthethymus:aclinicopathologicreportofsevencaseswithareviewoftheliterature.MayoClinProc1980;55:246Ð254.60.EconomopoulosGC,LewisJWJr,LeeMW,Sil-vermanNA.Carcinoidtumorsofthethymus.AnnThoracSurg1990;50:58Ð61.61.LowenthalRM,GumpelJM,KreelL,McLaugh-linJE,SkeggsDB.Carcinoidtumourofthethy-muswithsystemicmanifestations:aradiologicalandpathologicalstudy.Thorax1974;29:553Ð558.62.RosaiJ,HigaE.Mediastinalendocrineneoplasmofprobablethymicoriginrelatedtocarcinoidtu-mor:clinicopathologicstudyof8cases.Cancer348March-April2006Volume26Number2 RadioGraphics This article meets the criteria for 1.0 credit hour in category 1 of the AMA Physicians Recognition Award. To obtain RG Volume 26 • Volume 2 March-April 2006 Nishino et al Teaching Points for The Thym Mizuki Nishino, MD, et al (copy and paste slugline from PDF) Page 336 The thymus arises bilaterally from the third and fourth branchial pouches and contains elements derived from all three germinal layers (5–7). Page 338 A variety of diseases are seen in association with thymoma (Table 1) (5,18,19). Among these diseases, myasthenia gravis is the most common and has the ciation with thymoma. Page 339 The thymus sometimes grows to anrebound hyperplasia (18). Page 340 iveness: Types A and AB are usually clinically benign and encapsulated (stage I), type B has a greater likelihood of invasiveness (especially type B3), and type C is almost always invasive. Page 342 According to these investigators, CT findings that are more common in high-risk thymomas and thymic carcinomas include lobulated contour, mediastinal fat invasion, and great vessel invasion (Figs EDUCATIONEXHIBIT TheThymus:ACom-prehensiveReview LEARNINGOBJECTIVES Afterreadingthisarticleandtakingthetest,thereaderwillbeableto:Describetheem-bryologicandhisto-logicfeaturesoftheListthemedicalconditionsassociatedwiththymicdisease.Discussthespec-trumofthymicdis-easeswithradiologic-pathologiccorrela-MizukiNishino,MDSimonK.Ashiku,MDOlivierN.Kocher,MDRobertL.Thurer,MDPhillipM.Boiselle,MDHirotoHatabu,MD,SinceÞrstbeingdescribedassuchbyGalenofPergamum(130Ð200),thethymushasremainedanÒorganofmysteryÓthroughoutthe2000-yearhistoryofmedicine.Thethymusreachesitsmaximumweightinpubertyandsubsequentlyundergoesinvolution,andthusishardlyaneye-catchingstructureonimagingstudiesperformedinhealthyadults.However,oncetherehasbeeninvolvementofthethy-musbyadiseaseprocess,theglanddemonstratesavarietyofclinicalandradiologicmanifestationsthatrequirecomprehensiveunderstand-ingofeachentity.Furthermore,itisimportantforradiologiststobefamiliarwiththecurrentWorldHealthOrganizationhistologicclassiÞ-cationschemeforthymicepithelialtumorsandtounderstanditsclini-cal-pathologic,radiologic,andprognosticfeatures.RSNA,2006 ßuorodeoxyglucose,H-Ehematoxylin-eosin,SLEsystemiclupuserythematosus,SUVstandardizeduptakevalue,WorldHealthOrganizationFromtheDepartmentsofRadiology(M.N.,P.M.B.,H.H.),ThoracicSurgery(S.K.A.,R.L.T.),andPathology(O.N.K.),BethIsraelDeaconessMedicalCenter,330BrooklineAve,Boston,MA02215.Presentedasaneducationexhibitatthe2004RSNAAnnualMeeting.ReceivedDecember22,2004;revisionrequestedMay9,2005,andreceivedJune8;acceptedSeptember22.AllauthorshavenoÞnancialrelationshipstodisclose.dresscorrespondencetoM.N.(e-mail:RSNA,2006 RadioGraphics ONLINE-ONLYCME Seewww.rsna See last page TEACHING POINTS EDUCATIONEXHIBIT TheThymus:ACom-prehensiveReview LEARNINGOBJECTIVES Afterreadingthisarticleandtakingthetest,thereaderwillbeableto:Describetheem-bryologicandhisto-logicfeaturesoftheListthemedicalconditionsassociatedwiththymicdisease.Discussthespec-trumofthymicdis-easeswithradiologic-pathologiccorrela-MizukiNishino,MDSimonK.Ashiku,MDOlivierN.Kocher,MDRobertL.Thurer,MDPhillipM.Boiselle,MDHirotoHatabu,MD,SinceÞrstbeingdescribedassuchbyGalenofPergamum(130Ð200),thethymushasremainedanÒorganofmysteryÓthroughoutthe2000-yearhistoryofmedicine.Thethymusreachesitsmaximumweightinpubertyandsubsequentlyundergoesinvolution,andthusishardlyaneye-catchingstructureonimagingstudiesperformedinhealthyadults.However,oncetherehasbeeninvolvementofthethy-musbyadiseaseprocess,theglanddemonstratesavarietyofclinicalandradiologicmanifestationsthatrequirecomprehensiveunderstand-ingofeachentity.Furthermore,itisimportantforradiologiststobefamiliarwiththecurrentWorldHealthOrganizationhistologicclassiÞ-cationschemeforthymicepithelialtumorsandtounderstanditsclini-cal-pathologic,radiologic,andprognosticfeatures.RSNA,2006 ßuorodeoxyglucose,H-Ehematoxylin-eosin,SLEsystemiclupuserythematosus,SUVstandardizeduptakevalue,WorldHealthOrganizationFromtheDepartmentsofRadiology(M.N.,P.M.B.,H.H.),ThoracicSurgery(S.K.A.,R.L.T.),andPathology(O.N.K.),BethIsraelDeaconessMedicalCenter,330BrooklineAve,Boston,MA02215.Presentedasaneducationexhibitatthe2004RSNAAnnualMeeting.ReceivedDecember22,2004;revisionrequestedMay9,2005,andreceivedJune8;acceptedSeptember22.AllauthorshavenoÞnancialrelationshipstodisclose.dresscorrespondencetoM.N.(e-mail:RSNA,2006 RadioGraphics ONLINE-ONLYCME Seewww.rsna See last page TEACHING POINTS RadioGraphics2006;PublishedonlineContentCode: EDUCATIONEXHIBIT TheThymus:ACom-prehensiveReview LEARNINGOBJECTIVES Afterreadingthisarticleandtakingthetest,thereaderwillbeableto:Describetheem-bryologicandhisto-logicfeaturesoftheListthemedicalconditionsassociatedwiththymicdisease.Discussthespec-trumofthymicdis-easeswithradiologic-pathologiccorrela-MizukiNishino,MDSimonK.Ashiku,MDOlivierN.Kocher,MDRobertL.Thurer,MDPhillipM.Boiselle,MDHirotoHatabu,MD,SinceÞrstbeingdescribedassuchbyGalenofPergamum(130Ð200),thethymushasremainedanÒorganofmysteryÓthroughoutthe2000-yearhistoryofmedicine.Thethymusreachesitsmaximumweightinpubertyandsubsequentlyundergoesinvolution,andthusishardlyaneye-catchingstructureonimagingstudiesperformedinhealthyadults.However,oncetherehasbeeninvolvementofthethy-musbyadiseaseprocess,theglanddemonstratesavarietyofclinicalandradiologicmanifestationsthatrequirecomprehensiveunderstand-ingofeachentity.Furthermore,itisimportantforradiologiststobefamiliarwiththecurrentWorldHealthOrganizationhistologicclassiÞ-cationschemeforthymicepithelialtumorsandtounderstanditsclini-cal-pathologic,radiologic,andprognosticfeatures.RSNA,2006 ßuorodeoxyglucose,H-Ehematoxylin-eosin,SLEsystemiclupuserythematosus,SUVstandardizeduptakevalue,WorldHealthOrganizationFromtheDepartmentsofRadiology(M.N.,P.M.B.,H.H.),ThoracicSurgery(S.K.A.,R.L.T.),andPathology(O.N.K.),BethIsraelDeaconessMedicalCenter,330BrooklineAve,Boston,MA02215.Presentedasaneducationexhibitatthe2004RSNAAnnualMeeting.ReceivedDecember22,2004;revisionrequestedMay9,2005,andreceivedJune8;acceptedSeptember22.AllauthorshavenoÞnancialrelationshipstodisclose.dresscorrespondencetoM.N.(e-mail:RSNA,2006 RadioGraphics ONLINE-ONLYCME Seewww.rsna See last page TEACHING POINTS RadioGraphics2006;PublishedonlineContentCode: EDUCATIONEXHIBIT TheThymus:ACom-prehensiveReview LEARNINGOBJECTIVES Afterreadingthisarticleandtakingthetest,thereaderwillbeableto:Describetheem-bryologicandhisto-logicfeaturesoftheListthemedicalconditionsassociatedwiththymicdisease.Discussthespec-trumofthymicdis-easeswithradiologic-pathologiccorrela-MizukiNishino,MDSimonK.Ashiku,MDOlivierN.Kocher,MDRobertL.Thurer,MDPhillipM.Boiselle,MDHirotoHatabu,MD,SinceÞrstbeingdescribedassuchbyGalenofPergamum(130Ð200),thethymushasremainedanÒorganofmysteryÓthroughoutthe2000-yearhistoryofmedicine.Thethymusreachesitsmaximumweightinpubertyandsubsequentlyundergoesinvolution,andthusishardlyaneye-catchingstructureonimagingstudiesperformedinhealthyadults.However,oncetherehasbeeninvolvementofthethy-musbyadiseaseprocess,theglanddemonstratesavarietyofclinicalandradiologicmanifestationsthatrequirecomprehensiveunderstand-ingofeachentity.Furthermore,itisimportantforradiologiststobefamiliarwiththecurrentWorldHealthOrganizationhistologicclassiÞ-cationschemeforthymicepithelialtumorsandtounderstanditsclini-cal-pathologic,radiologic,andprognosticfeatures.RSNA,2006 ßuorodeoxyglucose,H-Ehematoxylin-eosin,SLEsystemiclupuserythematosus,SUVstandardizeduptakevalue,WorldHealthOrganizationFromtheDepartmentsofRadiology(M.N.,P.M.B.,H.H.),ThoracicSurgery(S.K.A.,R.L.T.),andPathology(O.N.K.),BethIsraelDeaconessMedicalCenter,330BrooklineAve,Boston,MA02215.Presentedasaneducationexhibitatthe2004RSNAAnnualMeeting.ReceivedDecember22,2004;revisionrequestedMay9,2005,andreceivedJune8;acceptedSeptember22.AllauthorshavenoÞnancialrelationshipstodisclose.dresscorrespondencetoM.N.(e-mail:RSNA,2006 RadioGraphics ONLINE-ONLYCME Seewww.rsna See last page TEACHING POINTS RadioGraphics2006;PublishedonlineContentCode: EDUCATIONEXHIBIT TheThymus:ACom-prehensiveReview LEARNINGOBJECTIVES Afterreadingthisarticleandtakingthetest,thereaderwillbeableto:Describetheem-bryologicandhisto-logicfeaturesoftheListthemedicalconditionsassociatedwiththymicdisease.Discussthespec-trumofthymicdis-easeswithradiologic-pathologiccorrela-MizukiNishino,MDSimonK.Ashiku,MDOlivierN.Kocher,MDRobertL.Thurer,MDPhillipM.Boiselle,MDHirotoHatabu,MD,SinceÞrstbeingdescribedassuchbyGalenofPergamum(130Ð200),thethymushasremainedanÒorganofmysteryÓthroughoutthe2000-yearhistoryofmedicine.Thethymusreachesitsmaximumweightinpubertyandsubsequentlyundergoesinvolution,andthusishardlyaneye-catchingstructureonimagingstudiesperformedinhealthyadults.However,oncetherehasbeeninvolvementofthethy-musbyadiseaseprocess,theglanddemonstratesavarietyofclinicalandradiologicmanifestationsthatrequirecomprehensiveunderstand-ingofeachentity.Furthermore,itisimportantforradiologiststobefamiliarwiththecurrentWorldHealthOrganizationhistologicclassiÞ-cationschemeforthymicepithelialtumorsandtounderstanditsclini-cal-pathologic,radiologic,andprognosticfeatures.RSNA,2006 ßuorodeoxyglucose,H-Ehematoxylin-eosin,SLEsystemiclupuserythematosus,SUVstandardizeduptakevalue,WorldHealthOrganizationFromtheDepartmentsofRadiology(M.N.,P.M.B.,H.H.),ThoracicSurgery(S.K.A.,R.L.T.),andPathology(O.N.K.),BethIsraelDeaconessMedicalCenter,330BrooklineAve,Boston,MA02215.Presentedasaneducationexhibitatthe2004RSNAAnnualMeeting.ReceivedDecember22,2004;revisionrequestedMay9,2005,andreceivedJune8;acceptedSeptember22.AllauthorshavenoÞnancialrelationshipstodisclose.dresscorrespondencetoM.N.(e-mail:RSNA,2006 RadioGraphics ONLINE-ONLYCME Seewww.rsna See last page TEACHING POINTS RadioGraphics2006;PublishedonlineContentCode: RG Volume 26 • Volume 2 March-April 2006 Nishino et al Teaching Points for The Thym Mizuki Nishino, MD, et al Page 336 The thymus arises bilaterally from the third and fourth branchial pouches and contains elements derived from all three germinal layers (5–7). Page 338 A variety of diseases are seen in association with thymoma (Table 1) (5,18,19). Among these diseases, myasthenia gravis is the most common and has the ciation with thymoma. Page 339 The thymus sometimes grows to anrebound hyperplasia (18). Page 340 iveness: Types A and AB are usually clinically benign and encapsulated (stage I), type B has a greater likelihood of invasiveness (especially type B3), and type C is almost always invasive. Page 342 According to these investigators, CT findings that are more common in high-risk thymomas and thymic carcinomas include lobulated contour, mediastinal fat invasion, and great vessel invasion (Figs RG Volume 26 • Volume 2 March-April 2006 Nishino et al Teaching Points for The Thym Mizuki Nishino, MD, et al Page 336 The thymus arises bilaterally from the third and fourth branchial pouches and contains elements derived from all three germinal layers (5–7). Page 338 A variety of diseases are seen in association with thymoma (Table 1) (5,18,19). Among these diseases, myasthenia gravis is the most common and has the ciation with thymoma. Page 339 The thymus sometimes grows to anrebound hyperplasia (18). Page 340 iveness: Types A and AB are usually clinically benign and encapsulated (stage I), type B has a greater likelihood of invasiveness (especially type B3), and type C is almost always invasive. Page 342 According to these investigators, CT findings that are more common in high-risk thymomas and thymic carcinomas include lobulated contour, mediastinal fat invasion, and great vessel invasion (Figs RadioGraphics2006;PublishedonlineContentCode: RG Volume 26 • Volume 2 March-April 2006 Nishino et al Teaching Points for The Thym Mizuki Nishino, MD, et al Page 336 The thymus arises bilaterally from the third and fourth branchial pouches and contains elements derived from all three germinal layers (5–7). Page 338 A variety of diseases are seen in association with thymoma (Table 1) (5,18,19). Among these diseases, myasthenia gravis is the most common and has the ciation with thymoma. Page 339 The thymus sometimes grows to anrebound hyperplasia (18). Page 340 iveness: Types A and AB are usually clinically benign and encapsulated (stage I), type B has a greater likelihood of invasiveness (especially type B3), and type C is almost always invasive. Page 342 According to these investigators, CT findings that are more common in high-risk thymomas and thymic carcinomas include lobulated contour, mediastinal fat invasion, and great vessel invasion (Figs RadioGraphics2006;PublishedonlineContentCode: RG Volume 26 • Volume 2 March-April 2006 Nishino et al Teaching Points for The Thym Mizuki Nishino, MD, et al Page 336 The thymus arises bilaterally from the third and fourth branchial pouches and contains elements derived from all three germinal layers (5–7). Page 338 A variety of diseases are seen in association with thymoma (Table 1) (5,18,19). Among these diseases, myasthenia gravis is the most common and has the ciation with thymoma. Page 339 The thymus sometimes grows to anrebound hyperplasia (18). Page 340 iveness: Types A and AB are usually clinically benign and encapsulated (stage I), type B has a greater likelihood of invasiveness (especially type B3), and type C is almost always invasive. Page 342 According to these investigators, CT findings that are more common in high-risk thymomas and thymic carcinomas include lobulated contour, mediastinal fat invasion, and great vessel invasion (Figs RadioGraphics2006;PublishedonlineContentCode: RG Volume 26 • Volume 2 March-April 2006 Nishino et al Teaching Points for The Thym Mizuki Nishino, MD, et al Page 336 The thymus arises bilaterally from the third and fourth branchial pouches and contains elements derived from all three germinal layers (5–7). Page 338 A variety of diseases are seen in association with thymoma (Table 1) (5,18,19). Among these diseases, myasthenia gravis is the most common and has the ciation with thymoma. Page 339 The thymus sometimes grows to anrebound hyperplasia (18). Page 340 iveness: Types A and AB are usually clinically benign and encapsulated (stage I), type B has a greater likelihood of invasiveness (especially type B3), and type C is almost always invasive. Page 342 According to these investigators, CT findings that are more common in high-risk thymomas and thymic carcinomas include lobulated contour, mediastinal fat invasion, and great vessel invasion (Figs RadioGraphics2006;PublishedonlineContentCode: RG Volume 26 • Volume 2 March-April 2006 Nishino et al Teaching Points for The Thym Mizuki Nishino, MD, et al Page 336 The thymus arises bilaterally from the third and fourth branchial pouches and contains elements derived from all three germinal layers (5–7). Page 338 A variety of diseases are seen in association with thymoma (Table 1) (5,18,19). Among these diseases, myasthenia gravis is the most common and has the ciation with thymoma. Page 339 The thymus sometimes grows to anrebound hyperplasia (18). Page 340 iveness: Types A and AB are usually clinically benign and encapsulated (stage I), type B has a greater likelihood of invasiveness (especially type B3), and type C is almost always invasive. Page 342 According to these investigators, CT findings that are more common in high-risk thymomas and thymic carcinomas include lobulated contour, mediastinal fat invasion, and great vessel invasion (Figs RadioGraphics2006;PublishedonlineContentCode: RG Volume 26 • Volume 2 March-April 2006 Nishino et al Teaching Points for The Thym Mizuki Nishino, MD, et al Page 336 The thymus arises bilaterally from the third and fourth branchial pouches and contains elements derived from all three germinal layers (5–7). Page 338 A variety of diseases are seen in association with thymoma (Table 1) (5,18,19). Among these diseases, myasthenia gravis is the most common and has the ciation with thymoma. Page 339 The thymus sometimes grows to anrebound hyperplasia (18). Page 340 iveness: Types A and AB are usually clinically benign and encapsulated (stage I), type B has a greater likelihood of invasiveness (especially type B3), and type C is almost always invasive. Page 342 According to these investigators, CT findings that are more common in high-risk thymomas and thymic carcinomas include lobulated contour, mediastinal fat invasion, and great vessel invasion (Figs RadioGraphics2006;PublishedonlineContentCode: