MORPHOLOGYLesionsofteninvolvedeepgraystructures,aswellasthewhitematterandthecortex.Periventricularspreadiscommon.Thetumorsarerelativelywelldefinedascomparedwithglialneoplasms,buttheyarenotasdiscreteasmetastases.EBV-associatedtumorsoftenshowextensiveareasofnecrosis.ThetumorsarenearlyalwaysaggressivelargeB-celllymphomas,althoughotherhistologictypesmaybeencountered.Microscopically,malignantlymphoidcellsaccumulatearoundbloodvesselsandinfiltratethesurroundingbrainparenchyma.ThediagnosisisconfirmedbyimmunohistochemistryforBcellmarkerssuchasCD20,whichalsoisatargetoftherapeuticantibodies.
Primary brain germ cell tumors occur along the midline, most commonly in the pineal and the suprasellar regions. They account for 0.2% to 1% of brain tumors in individuals of European descent but in as many as 10% of brain tumors in individuals of Japanese ethnicity. They are a tumor of the young, with 90% occurring during the first 2 decades of life. Germ cell tumors in the pineal region show a strong male predominance. The most common primary CNS germ cell tumor is germinoma, a tumor that closely resembles testicular seminoma (Chapter 18). Secondary CNS involvement by metastatic gonadal germ cell tumors also occurs.
Meningiomas are predominantly benign tumors that arise from arachnoid meningothelial cells. They usually occur in adults and are often attached to the dura. Meningiomas may be found along any of the external surfaces of the brain as well as within the ventricular system, where they arise from the stromal arachnoid cells of the choroid plexus. They often come to attention because of vague nonlocalizing symptoms, or with focal findings referable to compression of adjacent brain. Most meningiomas are easily separable from underlying brain, but some tumors are infiltrative, a feature associated with an increased risk for recurrence. The overall prognosis is determined by the lesion size and location, surgical accessibility, and histologic grade.
When an individual has multiple meningiomas, especially in association with eighth-nerve schwannomas or glial tumors, the diagnosis of neurofibromatosis type 2 (NF2) should be considered (Chapter 22). About half of meningiomas not associated with NF2 have somatic loss-of-function mutations in the NF2 tumor suppressor gene on the long arm of chromosome 22 (22q). These mutations are found in all grades of meningioma, suggesting that they are involved in tumor initiation. Among sporadic tumors that lack mutations in NF2, several other driver mutations have been identified including in genes that regulate the Hedgehog pathway as well as in various signaling molecules and transcription factors.
Fig.23.33A ).Extensionintotheoverlyingbonemaybepresent.Thevariedhistologicpatternsinclude:meningothelial, namedforwhorled,tightclustersofcellswithoutvisiblecellmembranes;fibroblastic, withelongatedcellsandabundantcollagendeposition;transitional, withfeaturesofthemeningothelialandfibroblastictypes;psammomatous, withnumerouspsammomabodies(see
Fig.23.33B );andsecretory, withglandlikespacescontainingPAS-positiveeosinophilicmaterial.