Meningiomas are the most common benign tumors of the brain (95% of benign tumors). However they can also be malignant. They arise from the arachnoial cap cells of the meninges and represent about 15% of all primary brain tumors. They are more common in females than in males (2:1) and have a peak incidence in the sixth and seventh decades. Most cases are sporadic while some are familial. There has been some evidence that persons who have undergone radiation to the scalp are more at risk for developing meningiomas. The most frequent genetic mutations involved in meningiomas are inactivation mutations in the neurofibromatosis 2 gene (merlin) on chromosome 22q.