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| Dr. Peter M. Black examines images. |
A meningioma is a tumor that develops from the tissue covering the brain and spinal cord. This tissue is called the meninges and is comprised of three membrane layers: the outer layer is the dura mater, the middle is the arachnoid, and the inner layer is the pia mater. Meningiomas arise from the arachnoid layer and can appear in different areas of both the brain and spinal cord.
Approximately 96% of meningiomas occur within the skull, with the remaining 4% involving the spinal column. Meningiomas are the most common type of primary brain tumor, accounting for 33.8% of all such tumors. A primary brain tumor originates from the brain, spinal cord or associated tissues (called the central nervous system or CNS), while a secondary brain tumor arises from cancerous cells that have spread (metastasized) to the CNS from elsewhere in the body.
Most meningiomas (90%) are categorized as benign tumors, approximately 7-8% as atypical, and 2-3% as malignant. (See the Types of Meningiomas section for a fuller discussion of these grades of meningioma.) In general, most meningiomas do not actually invade brain tissue, although those that are malignant are likely to do so. Meningiomas affect the CNS by compressing brain tissue, nerves, or associated structures; causing reactive swelling in brain tissue; blocking flow of the fluid (cerebrospinal fluid) in the CNS; and/or blocking blood flow in CNS blood vessels. Each of these effects may result in various disabilities or even be life-threatening. Clearly, the term "benign" can be quite misleading in that such meningiomas may cause significant harm. However, benign meningiomas, as compared to those that are atypical and malignant, are more likely to exhibit slower growth, are less likely to reoccur, and rarely invade brain tissue.
Because most meningiomas often grow slowly, depending upon their location, a meningioma may reach a relatively large size before it causes symptoms. There is no way to know for certain how long a specific tumor was growing before diagnosis. Most people with a meningioma will have a tumor at only one site, but it is also possible to have several tumors growing simultaneously in different parts of the brain and spinal cord.
Meningiomas vary in their symptoms and appropriate treatment options depending on their location. (See related sections Symptoms and Diagnosis and Treatments) The tumors location is most often included in its description. Below is a listing of locations where meningiomas are found.
- Falx and
parasagittal The falx is a groove that runs between the two sides (hemispheres) of the brain (front to back). Running along the top of this groove is a large blood vessel, known as the superior sagittal sinus. Falx tumors arise from the meninges folded down in the groove, whereas parasagittal tumors arise from the meninges that are near or close to the superior sagittal sinus at the top of the groove. - Convex
ity These tumors grow on the surface of the brain not involving the falx or parasagittal region. - Sphenoid wing (also called sphenoid ridge) Sphenoid wing meningiomas lie behind the eyes.
- Olfactory groove Olfactory groove meningiomas grow along the nerves that run between the brain and the nose.
- Suprasellar These meningiomas grow above a bony depression that houses the pituitary gland and are very close to where the optic nerve from each eye intersects with the other.
- Posterior fossa Posterior fossa tumors lie on the underside of the brain.
- Intraventricular Intraventricular meningiomas are associated with the connected chambers of fluid that circulate throughout the central nervous system. This fluid is known as cerebrospinal fluid (CSF).
- Intraorbital Intraorbital meningiomas grow around the eye sockets of your skull.
- Spinal Spinal meningiomas occur within the spinal cord predominantly in the region of the spine between the neck and abdomen (thoracic area).
As previously mentioned, 96% of meningiomas occur within the skull and the incidence at each location is given below:
| Falx or parasagittal | 25% |
| Convexity | 20% |
| Sphenoid wing | 20% |
| Olfactory groove | 10% |
| Supresellar | 10% |
| Posterior fossa | 10% |
| Intraventricular | 2% |
| Miscellaneous (e.g., optic nerve, which is involved in vision) | 3% |
