Meningiomas are predominantly benign tumors that arise from arachnoid meningothelial cells. They usually occur in adults and are often attached to the dura. Meningiomas may be found along any of the external surfaces of the brain as well as within the ventricular system, where they arise from the stromal arachnoid cells of the choroid plexus.They usually come to attention because of vague nonlocalizing symptoms, or with focal findings referable to compression of the adjacent brain. Most meningiomas are easily separable from the underlying brain. Meningiomas (WHO grade I/IV) grow as well-defined dura-based masses that may compress the brain but do notinvade it. Among the varied histologic patterns are syncytial, named for whorled clusters of cells without visible cell membranes that sit in tight groups; fibroblastic, with elongated cells and abundant collagen deposition between them; transitional, which shares features of the syncytial and fibroblastic types; psammomatous, with numerous psammoma bodies ; and secretary, with gland-like PAS-positive eosinophilic secretions known as pseudopsammoma bodies. Atypical meningiomas (WHO grade II/IV) are recognized by the presence of ceain histologic features (prominent nucleoli, increased cellularity, pattern-less growth), and often have a higher mitotic rate. These tumors demonstrate more aggressive local growth and a higher rate of recurrence; they may require therapy in addition to surgery. Anaplastic (malignant) meningiomas (WHO grade III/IV) are highly aggressive tumors that may resemble a high-grade sarcoma or carcinoma, although there usually is some histologic evidence of a meningothelial cell origin.