简介：Nonalcoholicfattyliverdisease(NAFLD),definedasabnormalaccumulation(>5%)ofhepatictriglyceridewithoutexcessalcoholintake,isthemostcommonformofchronicliverdiseaseinadultsandchildrenintheUnitedStates.NAFLDencompassesaspectrumofhistologicfindingsincludinguncomplicatedsteatosis,steatosiswithinflammationandsteatohepatitis[nonalcoholicsteatohepatitis(NASH)];thelattercanadvancetocirrhosisandhepatocellularcarcinoma.NASHiscurrentlyacceptedasthehepaticmanifestationofthesetofcardiovascularriskfactorscollectivelyknownasmetabolicsyndrome.In1999asystemforhistologicgradingandstagingforNASHwasproposed;thiswasrevisedbytheNASHClinicalResearchNetworkin2005fortheentirespectrumoflesionsinNAFLD,includingthelesionsandpatternsofpediatricNAFLD,andforapplicationinclinicalresearchtrials.Diagnosisremainsdistinctfromgradeandstage.ArecentEuropeanproposalseparatessteatosisfromactivitytoderiveanumericdiagnosisofNASH.Eventhoughtherehavebeenpromisingadvancementsinnon-invasivetesting,thesetestsarenotyetdetailedenoughtoreplacethefullrangeoffindingsprovidedbyliverbiopsyevaluation.Limitationsofbiopsyareacknowledged,butliverbiopsyremainsthe'goldstandard'fordiagnosisanddeterminationofamountsofnecroinflammatoryactivity,andlocationoffibrosis,aswellasremodelingoftheparenchymainNASH.ThisreviewfocusesonthespecifichistologiclesionsofNAFLDandNASH,gradingandstaging,differentialdiagnosestobeconsidered,andthecontinuingroleoftheliverbiopsyinthisimportantliverdisease.