Incidence

Meningiomas account for 15-20% of all intracranial neoplasms, second only to the incidence of primary gliomas [1,2]. Excluding autopsy data, one study concluded that the most common intracranial tumors are gliomas (43%), meningiomas (21%) and pituitary adenomas (17%) [3]. It should be noted that these incidence data represent only those patients with meningiomas that cause neurological symptoms leading to clinical diagnosis and treatment. With recent advances in neuroimag-ing, many asymptomatic meningiomas are being detected today, raising the true incidence significantly higher than was previously reported. When autopsy data are included, the proportion of meningiomas among common intracranial tumors changes to 40% for meningiomas, 35% for gliomas, and 17% for pituitary adenomas [3]. The incidence of clinically significant meningiomas is approximately 2.3/ 100,000 population, and about 5.5/100,000 population when autopsy data are included [3]. Such discrepancy between these incidence rates underscores the fact that the majority of menin-giomas actually remain asymptomatic and undetected during life. In fact, Nakasu et al. [4] noted that incidental meningiomas are found in as many as 2.3% of autopsy specimens, and that, among people over the age of 60 years undergoing autopsy, 3% are found to have an incidental meningioma.

The male:female ratio ranges from 1:1.4 to 1:2.1 depending on the series, but it is widely accepted to be approximately 1:2. [1,2]. This finding, however, is not necessarily true among blacks, who have been reported to have a fairly even distribution between males and females [5]. The peak age of clinical presentation for all patients with meningiomas is in the sixth decade.

The intracranial distribution of primary meningiomas has been reported by many authors [1,6]. These reports may vary, depending on the type of neuroimaging used and whether autopsy data are included. DeMonte and Al-Mefty [2] summarized the overall intracranial distribution of meningiomas by combining several large reported series, and concluded the following: parasagittal/falcine 25%, convexity 19%, sphenoid ridge 17%, suprasellar (tuberculum) 9%, posterior fossa 8%, olfactory groove 8%, middle fossa/Meckel's cave 4%, tentorial 3%, peri-torcular 3%, lateral ventricle 1-2%, foramen magnum 1-2%, orbit/optic nerve sheath 1-2%.

Meningiomas occur in children, yet they are exceedingly rare, accounting for only 1-4% of all brain tumors in patients less than 18 years old [7]. Furthermore, pediatric meningiomas account for only 1.5-1.8% of all intracranial meningiomas [8]. In children, the male:female ratio is nearly equal or with a slight male predominance [7]. Intraventricular meningiomas are more common in children than in adults, and make up 11% and 3.9% of all meningiomas in these groups, respectively [6]. In addition to this predilection for unusual locations, children are also more likely than adults to harbor

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