Definition (What is it?) – Meningiomas are predominantly benign tumors, arising from the covering (“meninges”) of the brain (90%) and spine (10%). These tumors arise from the arachnoid “cap cells” which are the cells forming the outer lining of the arachnoid layer (the middle of the three meningeal layers). Strictly speaking, these are not “brain tumors” per se as they do not take their origin from the brain tissue proper.
Epidemiology (How common is it?) – The incidence of symptomatic meningiomas (“how common?”) is approximately 2/100,000 population per year while the incidence of asymptomatic (tumors causing no symptoms) meningiomas is 5.7/100,000 population per year. Therefore, the overall combined incidence of all meningiomas (both symptomatic and asymptomatic) is nearly 8/100,000 population/year. This roughly translates into the yearly incidence of roughly 800 new meningioma patients in a geographic area the size of Los Angeles County which has a total population of 10 million. Symptomatic meningiomas account for about 15-20% of all primary brain tumors, second most common after glioblastoma multiforme (GBM). When incidental (i.e. asymptomatic) tumors are included, however, meningiomas account for nearly 60% of all primary brain tumors. In reality, meningiomas are the most common primary “brain tumors”.
The average age at diagnosis for those requiring surgery, based on the review of my personal operative series of 1200 cases, is 54 years. For some unknown reason, meningiomas are more common in women by a ratio of 2-2.5:1.
Meningioma (JH Lee, ed.), Springer-Verlag, London, 2008