Fig.23.29A ).Infiltrationbeyondthegrosslyevidentmarginsisalwayspresent.Thecutsurfaceofthetumoriseitherfirmorsoftandgelatinous;cysticdegenerationmaybeseen.Inglioblastoma,variationinthegrossappearanceofthetumorfromregiontoregionischaracteristic(see
Fig.
23.29B ).Someareasarefirmandwhite,othersaresoftandyellow(theresultoftissuenecrosis),andstillothersshowregionsofcysticdegenerationandhemorrhage.
Microscopically,low-grade(WHOgradeII)astrocytomasarecharacterizedbyamildtomoderateincreaseinthenumberofglialcellnuclei,somewhatvariablenuclearpleomorphism,andaninterveningfeltworkoffine,glialfibrillaryacidicprotein(GFAP)-positiveastrocyticcellprocessesthatgivethebackgroundafibrillaryappearance.Thetransitionbetweenneoplasticandnormaltissueisindistinct,andtumorcellscanbeseeninfiltratingnormaltissuemanycentimetersfromthemainlesion.Anaplasticastrocytomasshowregionsthataremoredenselycellularandhavegreaternuclearpleomorphism;mitoticfiguresarepresent.Glioblastomahasahistologicappearancesimilartothatofanaplasticastrocytoma,aswellaseithernecrosis(commonlypresentasserpiginousbandsofnecrosiswithpalisadedtumorcellsalongtheborder)ormicrovascularproliferation(see
Fig.23.29C
Oligodendrogliomas account for 5% to 15% of gliomas and most commonly are detected in the fourth and fifth decades of life. Patients may have had several years of antecedent neurologic complaints, often including seizures. The lesions are found mostly in the cerebral hemispheres, mainly in the frontal or temporal lobes. The combination of surgery, chemotherapy, and radiotherapy yields an average survival of 10 to 20 years for well-differentiated (WHO grade II) oligodendrogliomas or 5 to 10 years for anaplastic (WHO grade III) oligodendrogliomas.
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Fig. 23.29 Diffuseastrocytomas.(A)GradeIIastrocytomaisseenasexpandedwhitematteroftheleftcerebralhemisphereandthickenedcorpuscallosumandfornices.(B)Glioblastomaappearingasanecrotic,hemorrhagic,infiltratingmass.(C)Glioblastomaisadenselycellulartumorwithnecrosisandpseudo-palisadingoftumorcellnucleialongtheedgeofthenecroticzone.
MORPHOLOGYWell-differentiatedoligodendrogliomas(WHOgradeII)areinfiltrativetumorsthatformgelatinous,graymassesandmayshowcysts,focalhemorrhage,andcalcification.Onmicroscopicexamination,thetumoriscomposedofsheetsofregularcellswithsphericalnucleicontainingfinelygranularchromatin(similartothatinnormaloligodendrocytes)surroundedbyaclearhaloofcytoplasm(
Fig.23.30 ).Thetumortypicallycontainsadelicatenetworkofanastomosingcapillaries.Calcification,presentinasmanyas90%ofthesetumors,rangesinextentfrommicroscopicfocitomassivedepositions.Mitoticactivityusuallyislow.Ana-plasticoligodendroglioma(WHOgradeIII)isamoreaggressivesubtypewithhighercelldensity,nuclearanaplasia,increasedmitoticactivity,andoftenmicrovascularproliferation.
Several classes of tumor-causing genetic alterations have been described in gliomas.