Meningioma: A relatively common neoplasm of the CENTRAL NERVOUS SYSTEM that arises from arachnoidal cells. The majority are well differentiated vascular tumors which grow slowly and have a low potential to be invasive, although malignant subtypes occur. Meningiomas have a predilection to arise from the parasagittal region, cerebral convexity, sphenoidal ridge, olfactory groove, and SPINAL CANAL. (From DeVita et al., Cancer: Principles and Practice of Oncology, 5th ed, pp2056-7)Meningeal Neoplasms: Benign and malignant neoplastic processes that arise from or secondarily involve the meningeal coverings of the brain and spinal cord.Arachnoid: A delicate membrane enveloping the brain and spinal cord. It lies between the PIA MATER and the DURA MATER. It is separated from the pia mater by the subarachnoid cavity which is filled with CEREBROSPINAL FLUID.Skull Neoplasms: Neoplasms of the bony part of the skull.Hyperostosis: Increase in the mass of bone per unit volume.Skull Base Neoplasms: Neoplasms of the base of the skull specifically, differentiated from neoplasms of unspecified sites or bones of the skull (SKULL NEOPLASMS).Cerebellopontine Angle: Junction between the cerebellum and the pons.Brain Neoplasms: Neoplasms of the intracranial components of the central nervous system, including the cerebral hemispheres, basal ganglia, hypothalamus, thalamus, brain stem, and cerebellum. Brain neoplasms are subdivided into primary (originating from brain tissue) and secondary (i.e., metastatic) forms. Primary neoplasms are subdivided into benign and malignant forms. In general, brain tumors may also be classified by age of onset, histologic type, or presenting location in the brain.Dura Mater: The outermost of the three MENINGES, a fibrous membrane of connective tissue that covers the brain and the spinal cord.Genes, Neurofibromatosis 2: Tumor suppressor genes located on the long arm of human chromosome 22. Mutation or loss of these genes causes NEUROFIBROMATOSIS 2.Magnetic Resonance Imaging: Non-invasive method of demonstrating internal anatomy based on the principle that atomic nuclei in a strong magnetic field absorb pulses of radiofrequency energy and emit them as radiowaves which can be reconstructed into computerized images. The concept includes proton spin tomographic techniques.Neuroma, Acoustic: A benign SCHWANNOMA of the eighth cranial nerve (VESTIBULOCOCHLEAR NERVE), mostly arising from the vestibular branch (VESTIBULAR NERVE) during the fifth or sixth decade of life. Clinical manifestations include HEARING LOSS; HEADACHE; VERTIGO; TINNITUS; and FACIAL PAIN. Bilateral acoustic neuromas are associated with NEUROFIBROMATOSIS 2. (From Adams et al., Principles of Neurology, 6th ed, p673)Optic Nerve Neoplasms: Benign and malignant neoplasms that arise from the optic nerve or its sheath. OPTIC NERVE GLIOMA is the most common histologic type. Optic nerve neoplasms tend to cause unilateral visual loss and an afferent pupillary defect and may spread via neural pathways to the brain.Hemangiopericytoma: A tumor composed of spindle cells with a rich vascular network, which apparently arises from pericytes, cells of smooth muscle origin that lie around small vessels. Benign and malignant hemangiopericytomas exist, and the rarity of these lesions has led to considerable confusion in distinguishing between benign and malignant variants. (From Dorland, 27th ed; DeVita Jr et al., Cancer: Principles & Practice of Oncology, 3d ed, p1364)Neurosurgical Procedures: Surgery performed on the nervous system or its parts.Ear Neoplasms: Tumors or cancer of any part of the hearing and equilibrium system of the body (the EXTERNAL EAR, the MIDDLE EAR, and the INNER EAR).Neurofibromatosis 2: An autosomal dominant disorder characterized by a high incidence of bilateral acoustic neuromas as well as schwannomas (NEURILEMMOMA) of other cranial and peripheral nerves, and other benign intracranial tumors including meningiomas, ependymomas, spinal neurofibromas, and gliomas. The disease has been linked to mutations of the NF2 gene (GENES, NEUROFIBROMATOSIS 2) on chromosome 22 (22q12) and usually presents clinically in the first or second decade of life.Craniotomy: Any operation on the cranium or incision into the cranium. (Dorland, 28th ed)Cerebral Ventricle Neoplasms: Neoplasms located in the brain ventricles, including the two lateral, the third, and the fourth ventricle. Ventricular tumors may be primary (e.g., CHOROID PLEXUS NEOPLASMS and GLIOMA, SUBEPENDYMAL), metastasize from distant organs, or occur as extensions of locally invasive tumors from adjacent brain structures.Neurilemmoma: A neoplasm that arises from SCHWANN CELLS of the cranial, peripheral, and autonomic nerves. Clinically, these tumors may present as a cranial neuropathy, abdominal or soft tissue mass, intracranial lesion, or with spinal cord compression. Histologically, these tumors are encapsulated, highly vascular, and composed of a homogenous pattern of biphasic fusiform-shaped cells that may have a palisaded appearance. (From DeVita Jr et al., Cancer: Principles and Practice of Oncology, 5th ed, pp964-5)Tomography, X-Ray Computed: Tomography using x-ray transmission and a computer algorithm to reconstruct the image.Meninges: The three membranes that cover the BRAIN and the SPINAL CORD. They are the dura mater, the arachnoid, and the pia mater.Foramen Magnum: The large hole at the base of the skull through which the SPINAL CORD passes.Chromosomes, Human, Pair 22: A specific pair of GROUP G CHROMOSOMES of the human chromosome classification.Neurofibromin 2: A membrane protein homologous to the ERM (Ezrin-Radixin-Moesin) family of cytoskeleton-associated proteins which regulate physical properties of membranes. Alterations in neurofibromin 2 are the cause of NEUROFIBROMATOSIS 2.