Atypical meningioma refers to a more aggressive form of meningioma and denotes a WHO grade II tumor (along with two histological variants, clear cell ...×ArticlesLogInCasesSignUpCoursesQuizBlogDonateAbout×MenuSearchADVERTISEMENT:Radiopaediaisfreethankstooursupportersandadvertisers.BecomeaGoldSupporterandseenoads.ArticlesCasesCoursesLogInLoginSignup{"url":"/signup-modal-props.json?lang=us\u0026email="}ArticlesCasesCoursesQuizAboutBlogGoad-freeSearchAtypicalmeningiomaDrMostafaEl-Feky◉andAssocProfFrankGaillard◉◈etal.AtypicalmeningiomareferstoamoreaggressiveformofmeningiomaanddenotesaWHOgradeIItumor(alongwithtwohistologicalvariants, clearcellmeningioma andchordoidmeningioma).Atypicalmeningiomasaccountfor20-30%ofallmeningiomas1,3. Itshouldbenotedthatepidemiology,clinicalpresentation,andradiographicfeaturesdonotreliablydistinguishgradeI(benign) fromgradeII(atypical)meningiomas,andthustheyarenotunnecessarilyrepeatedhere.Generally,thesetumorsgrowfaster,havemoreheterogeneous/aggressiveimagingappearances,andhaveatendencytorecurearly. Onthispage:Article:TerminologyPathologyRadiographicfeaturesTreatmentandprognosisRelatedarticlesReferencesImages:CasesandfiguresTerminologyTheuseoftheword"atypical" todenoteahighergrade,referstothehistologicalappearances(seebelow).However,itisperhapsunfavorableasitcausesconfusionformanyotherclinicianswhoareusedtoreferringtosomethingbeing'atypical'toindicatethatitdoesn'tlooklikethe'usual'garden-varietytumor/condition.Oneshouldthereforenotconfuse"atypicalmeningioma"withhistologicalvariants,manyofwhichhaveunusualimagingandhistologicalfeaturesbutarenonethelessWHOgradeItumors(seemeningiomaarticleforfurtherdiscussionofhistologicalvariants). PathologyAtypical(WHOgradeII)meningiomasarecharacterizedhistologicallyby1: 4to19mitosespertenhigh-powerfields3ormoreofthefollowing5histologicfeatures:necrosissheet-likegrowthsmallcellchangeincreasedcellularityprominentnucleolidirectinvasionofbrainparenchymaItisimportanttonotewhenreadingolderliterature,thatitisonlysin