Atypical meningiomas (WHOgradeII)arerecognizedbythepresenceofeitheranincreasedmitoticrate,orprominentnucleoli,increasedcellularity,patternlessgrowth,highnucleus-tocytoplasmratio,ornecrosis.Thesetumorsdemonstratemoreaggressivelocalgrowthandahigherrateofrecurrenceandmayrequiretherapyinadditiontosurgery.Somehistologicpatterns—clearcellandchordoid—alsocorrelatewithmoreaggressivebehavior,asdoesthepresenceofbraininvasion.
Anaplastic (malignant) meningiomas (WHOgradeIII)arehighlyaggressivetumorsthatmayresembleahigh-gradesarcomaorcarcinomamorphologically.Mitoticratesaretypicallymuchhigherthaninatypicalmeningiomas.
Metastatic lesions, mostly carcinomas, account for approximately one-fourth to one-half of intracranial tumors. The most common primary sites are lung, breast, skin (melanoma), kidney, and gastrointestinal tract, which together account for about 80% of cases. Metastases form sharply demarcated masses, often at the grey-white matter junction, and elicit local edema (
Fig. 23.34 ). The boundary between tumor and brain parenchyma is sharp at the microscopic level as well, with surrounding reactive gliosis.
In addition to the direct and localized effects produced by metastases, paraneoplastic syndromes may involve the peripheral and central nervous systems, sometimes even preceding the clinical recognition of the malignant neoplasm. Many patients with paraneoplastic syndromes have antibodies against tumor antigens. Some of the more common patterns include the following: • Subacute cerebellar degeneration resulting in ataxia, with destruction of Purkinje cells, gliosis, and a mild inflammatory infiltrate http://ebooksmedicine.net
Fig. 23.33 Meningioma.(A)Parasagittalmultilobularmeningiomaattachedtothedurawithcompressionofunderlyingbrain.(B)Meningiomawithawhorled patternofcellgrowthandpsammomabodies.
Limbic encephalitis causing a subacute dementia, with perivascular inflammatory cells, microglial nodules, neuronal loss, and gliosis, all centered in the medial temporal lobe
Subacute sensory neuropathy leading to altered pain sensation, with loss of sensory neurons from dorsal root ganglia, in association with inflammation
Syndrome of rapid-onset psychosis, catatonia, epilepsy, and coma associated with ovarian teratoma and antibodies against the N-methyl-D-aspartate (NMDA) receptor.
Several inherited syndromes caused by mutations in various tumor suppressor genes are associated with an increased risk for particular types of cancers. Those with particular involvement of the CNS are discussed here; familial syndromes associated with tumors of the peripheral nervous system are covered in Chapter 22.
Fig.23.34 Metastaticmelanoma.Metastaticlesionsaredistinguishedgrosslyfrommostprimarycentralnervoussystemtumorsbytheirmulticentricityandwell-demarcatedmargins.Thedarkcolorofthetumornodulesinthisspecimenisduetothepresenceofmelanin.