of developing meningiomata, with the incidence increasing the closer that they were to the site of the explosion. Dental X-rays are correlated with an increased risk of meningioma, in particular for people who had frequent dental X-rays in the past, when the X-ray dose of a dental X-ray was higher than in the present. Having excess body fat increases the risk. A 2012 review found that mobile telephone use was unrelated to meningioma. People with neurofibromatosis type 2 (NF-2) have a 50% chance of developing one or more meningiomata. Ninety-two percent of meningiomata are benign. Eight percent are either atypical or malignant. Genetics The most frequent genetic mutations (~50%) involved in meningiomata are inactivation mutations in the neurofibromatosis 2 gene (merlin) on chromosome 22q. TRAF7 mutations are present in about one-fourth of meningiomata. Mutations in the TRAF7, KLF4, AKT1, and SMO genes are commonly expressed in benign skull-base meningiomata. Mutations in NF2 are commonly expressed in meningiomata located in the cerebral and cerebellar hemispheres. Pathophysiology Meningiomata arise from arachnoidal cap cells, most of which are near the vicinity of the venous sinuses, and this is the site of greatest prevalence for meningioma formation. Some subtypes may arise from the pial cap cells that migrate during the development together with blood vessels into the brain parenchyma. They most frequently are attached to the dura over the superior parasagittal surface of frontal and parietal lobes, along the sphenoid ridge, in the olfactory grooves, the sylvian region, superior cerebellum along the falx cerebri, cerebellopontine angle, and the spinal cord. The tumor is usually gray, well-circumscribed, and takes on the form of the space it occupies. They usually are dome-shaped, with the base lying on the dura. Locations Parasagittal/falcine (25%) Convexity (surface of the brain) (19%) Sphenoid ridge (17%) Suprasellar (9%) Posterior fossa (8%) Olfactory groove (8%) Middle fossa/Meckel's cave (4%) Tentorial (3%) Peri-torcular (3%) Intraparenchymal (rare) Other uncommon locations are the lateral ventricle, foramen magnum, and the orbit/optic nerve sheath. Meningiomata also may occur as a spinal tumor, more often in women than in men. This occurs more often in Western countries than Asian. Histologically, meningioma cells are relatively uniform, with a tendency to encircle one another, forming whorls and psammoma bodies (laminated calcific concretions). As such, they also have a tendency to calcify and are highly vascularized. Meningiomata often are considered benign tumors that can be removed by surgery, but most recurrent