A meningioma is a tumor which develops from the protective membranes (the meninges) surrounding the brain and spinal cord. These tumors push away and compress rather than invade the brain. Meningiomas are typically benign and account for 95% of benign brain tumors and approximately 30% of primary brain tumors (those tumors that originate in the brain, as opposed to those tumors that have spread from other parts of the body to the brain.)
Meningioma locations and frequencies
Meningiomas are generally well defined and conform to the space they inhabit, although a tumor—even though benign—may grow to invade surrounding muscle and bone. Most benign tumors do not invade normal surrounding brain tissue, and any abnormal neurological problem is generally the result of increased pressure and compression on the surrounding brain or nerves.
Distributions of meningiomas within the supratentorial space
Meningiomas are rarely cancerous. In fact, only around 10% of meningiomas are cancerous. Atypical or cancerous (malignant) meningiomas possess a higher number of actively dividing cells and grow more rapidly than benign meningiomas. In addition, they are more invasive than their benign counterparts and can project into the normal brain tissue. Malignant meningiomas also have the added potential to spread to other parts of the central nervous system or even the rest of the body, causing additional symptoms and making treatment more difficult.
Cross section of large meningioma along the lateral sphenoid wing
Women are at a higher risk than men, and adults are more prone to developing meningiomas than children. Diagnosis is most common amongst patients between the ages of 40 and 70, with less than 2% of cases reported occur in children.
The symptoms resulting from a meningioma depend on the size, location, and rate of growth of the specific tumor. Small meningiomas are often asymptomatic.
When symptoms do occur, they are usually the result of an overall increase in intracranial pressure (such as headache or seizure) or from the pressure applied by the tumor on the specific nerves or normal brain tissue (such as visual deficits due to pressure on the optic nerves).
Typical symptoms include:
- Progressively worsening headaches
- Problems with memory
- Balance or hearing difficulties
- Problems with eyesight
- Numbness or weakness in an arm or leg
- Personality changes
- Swallowing difficulties
- Hydrocephalus (buildup of brain fluid) due to blockage of brain (cerebrospinal) fluid flow
Since meningiomas are usually very slow-growing tumors, symptoms may be subtle and evolve slowly with time. Thus, patients may go undiagnosed for months or years prior to seeking medical attention.
Your physician has many methods available to aid in the diagnosis of a meningioma. He/she may integrate information from the patient's clinical history, physical examination, and/or radiological evaluations to eliminate other possible explanations and establish the correct diagnosis.
The first step is generally a neurological exam, in which the physician will test the patient’s vision, hearing, coordination, mental abilities, and reflexes. Based on these results, the physician will order one or more of a variety of tests, including:
An MRI (magnetic resonance imaging) scan to exam the brain in detail
This allows the physician to see soft tissues in the head, including the potential tumor. A contrast dye may be used to specifically highlight abnormal structures within and around the brain.
A CT (computerized tomography) scan to image the brain
A CT scan is useful for differentiating structures based on their density, including tumors. Contrast dye may be used to highlight other structures (including the brain’s associated vasculature and abnormal tumors.)
An angiogram to image the vasculature of the brain
An angiogram is often used preoperatively if the surgeon believes major blood vessels are feeding the tumor or contained within the tumor. The angiogram may be used as a chance to "glue" some of the vessels feeding the meningioma. This way, the amount of blood loss during surgery decreases.
If a tumor is found, a biopsy may be performed to collect a small sample of the tumor for testing and identification. Examination of the sample by a pathologist can confirm the diagnosis if necessary, as well as classify the type of meningioma.
Tumor collection for biopsy usually takes place during a surgery to remove the tumor or may be performed in a procedure all on its own.
Like most all other intracranial tumors, treatment varies from person to person and depends on such specifics as the tumor's size, location, and rate of growth, as well as the patient's age and overall health status.
Because of the slow-growing nature of a meningioma, many physicians prefer to leave small asymptomatic tumors untreated. In such cases when no treatment is prescribed, the doctor will order periodic MRIs (usually once every year) to monitor the tumor's growth.
When treatment is necessary, patients may have both surgical and nonsurgical options. These include:
The surgical route is the most common method of treatment and the method of choice for most meningiomas. Because meningiomas originate from the membranes surrounding the brain, and not within the brain itself, they tend to be more clearly defined and easier to remove than infiltrative tumors like gliomas.
The operation involves what is referred to as a craniotomy. The surgeon makes an incision in the scalp and will drill away and remove part of the skull to gain access to the tumor. Surgery specifics vary greatly depending on the tumor's size and location.
Craniotomy for parasagittal meningioma
Surgical removal of convexity meningioma
Meningiomas at the base of skull in close proximity to cranial nerves, or those that are near important blood vessels, are more difficult to remove, have higher complication rates, and may only be amenable to partial resection. In such cases where total tumor removal is not surgically possible, the patient is often observed periodically with MRI scans to carefully monitor the size of the residual tumor. Radiation therapy may be considered following surgery. Surgery along the skull base requires a neurosurgeon with special training in skull base surgery.
Possible risks of surgery include infection, bleeding, and additional neurological damage including weakness and numbness.
Radiation therapy may come in the form of traditional, external-beam radiation or via the more intense, more accurate, stereotactic radiosurgery (e.g., Gamma Knife, Novalis, Cyberknife.)
Traditional external-beam radiation therapy directly delivers a single beam of radiation to the tumor. The procedure is usually performed five times a week, for several weeks. The risk of radiation damaging normal cells in the adjacent neural structures exists, although overall negative effects are rare and variable. Possible side effects include vision loss, memory loss, and stroke.
Stereotactic radiosurgery can deliver higher doses of radiation more accurately by using precise computer imagery and multiple beams to target the tumor. It does not require any incision and is done as a single-session outpatient procedure. Unlike external-beam radiation, surrounding structures are not as prone to damage from the radiation treatment and this method may be better for tumors near important brain structures.
Depending on your tumor size, grade and location, your surgeon or oncologist may recommend radiation therapy even in cases when resection is thought to be nearly complete.
When complete tumor removal is not deemed feasible, your physician may prescribe a variety of medications to control the symptoms. Commonly prescribed medications include:
- Anticonvulsants to help prevent seizures
- Steroid and anti-inflammatory medications to decrease swelling of the brain and/or relieve pressure on the brain (temporary relief and administered prior to surgery)
For patients with increased intracranial pressure due to blockage of CSF flow (a condition known as hydrocephalus), your surgeon may also install a thin tube called a shunt to drain the extra fluid into the abdominal cavity, where it can be reabsorbed.
The prognosis is dependent on many factors, such as tumor grade (aggressiveness), size and location, as well as the patient's age and overall health. In general, the patients with non-aggressive tumors in easily accessible locations are more likely to undergo complete tumor resection and thus have the best outcomes. Younger patients also tend to fair better.
Few meningiomas are malignant, but those which are classified as such generally lead to poorer outcome than those classified as benign. They require radiation treatment after surgery.
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