Meningioma, the term coined by Harvey Cushing, refers to a set of tumors that arise contiguously to the meninges (see the image below).
See Brain Lesions: 9 Cases to Test Your Management Skills, a Critical Images slideshow, to review cases including meningiomas, glioblastomas and craniopharyngiomas, and to determine the best treatment options based on the case history and the associated images.
Meningiomas may occur intracranially or within the spinal canal. They are thought to arise from arachnoidal cap cells, which reside in the arachnoid layer covering the surface of the brain. See the images below.
Meningiomas commonly are found at the surface of the brain, either over the convexity or at the skull base. In rare cases, meningiomas occur in an intraventricular or intraosseous location. The problem of classifying meningioma is that arachnoidal cells may express both mesenchymal and epithelial characteristics. Other mesodermal structures also may give rise to similar tumors (eg, hemangiopericytomas or sarcomas). The classification of all of these tumors together is controversial. The current trend is to separate unequivocal meningiomas from other less well-defined neoplasms. Undoubtedly, advances in molecular biology will allow scientists to determine the exact genomic aberration responsible for each specific neoplasm.
The annual incidence of symptomatic meningiomas is approximately 2 cases per 100,000 individuals. Meningiomas account for approximately 20% of all primary intracranial neoplasms. However, the true prevalence is likely higher than this because autopsy studies reveal that 2.3% of individuals have undiagnosed asymptomatic meningiomas. Meningiomas are multiple in 5-40% of cases, particularly when they associated with neurofibromatosis type 2 (NF2). Familial meningiomas are rare unless associated with NF2. 
The frequency of meningiomas in Africa is nearly 30% of all primary intracranial tumors. 
Mortality and morbidity rates for meningiomas are difficult to assess. Some meningiomas are discovered fortuitously when CT or MRI is done to assess for unrelated diseases or conditions. Therefore, some patients die with meningioma and not from it. Estimates of the 5-year survival usually range from 73-94%.
A systematic review of the literature regarding the clinical behavior of small, untreated meningiomas suggests that most meningiomas 2.5 cm or less in diameter do not proceed to cause symptoms in the 5 years following their discovery. Patients with tumors 2.5-3 cm in initial size went on to develop new or worsened symptoms 17% of the time. Those that do cause symptoms can usually be predicted with close radiographic follow-up. 
Meningiomas usually grow slowly, and they may produce severe morbidity before causing death.
Factors that may be predictive of a high postoperative morbidity rate include patient-related factors (eg, advanced age, comorbid states such as diabetes or coronary artery disease, preoperative neurological status), tumor factors (eg, location, size, consistency, vascularity, vascular or neural involvement), previous surgery, or previous radiation therapy.
Meningiomas are more prevalent in Africa than in North America or Europe. In Los Angeles County, meningioma is reported more commonly in African Americans than in others.
Meningiomas afflict women more often than men. The male-to-female ratio ranges from 1:1.4 to 1:2.8.
The female preponderance may be less pronounced in the black population than in other groups.
Meningiomas are equally distributed between boys and girls.
The incidence increases with age. Ages and corresponding incidence rates reported from 2002 are as follows:
Age 0-19 years - 0.12
Age 20-34 years - 0.74
Age 35-44 years - 2.62
Age 45-54 years - 4.89
Age 55-64 years - 7.89
Age 65-74 years - 12.79
Age 75-84 years - 17.04
Age 85 years and older - 18.86
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