Definition:

Meningiomas are the second-most common central nervous system tumor in adults. These tumors arise from arachnoid cells of the meninges, the covering layer of the brain. The majority of meningiomas tend to be benign, localized, and non-invasive. However, some meningiomas tend to be more aggressive with tendencies toward invasion of the surrounding brain, high propensity for recurrence, and in rare cases extracranial metastasis. Hereditary factors and ionizing radiation play an important role in the initiation of at least some meningiomas. Inactivation of the NF2 tumor suppressor gene is likely responsible for the initiation of more than half of all meningiomas and may cause a mesenchymal-like cytomorphology. Recently, novel mutations have been discovered in non-NF2 meningiomas. The recent identification of somatic mutations in components of the SHH-GLI1 and AKT1-MTOR signaling pathways indicates the potential for cross talk of these pathways in the development of meningiomas.