What is a meningioma?
A meningioma is a type of tumor that develops from the meninges, the membrane that surrounds the brain and spinal cord. There are three layers of meninges, called the dura mater, arachnoid and pia mater. Most meningiomas (90%) are categorized as benign tumors, with the remaining 10% being atypical or malignant. However, the word "benign" can be misleading in this case, as when benign tumors grow and constrict and affect the brain, they can cause disability and even be life threatening.
In many cases, benign meningiomas grow slowly. This means that depending upon where it is located, a meningioma may reach a relatively large size before it causes symptoms. Other meningiomas grow more rapidly, or have sudden growth spurts. There is no way to predict the rate of growth for a meningioma, or to know for certain how long a specific tumor was growing before diagnosis.
Most people with a meningioma will only 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. When multiple meningiomas occur, more than one type of treatment may have to be used.
Meningiomas vary in their symptoms and appropriate treatment options depending on where they are located.
A primary brain tumor originates in the central nervous system, while metastatic brain tumors spread to the brain from other parts of the body. Meningiomas account for about 27% of primary brain tumors, making them the most common of that type.
Who is at risk?
Meningiomas are most common in people between the ages of 40 and 70. They are more common in women than in men. Among middle-aged patients, there is a marked female bias, with a female: male ratio of almost 3:1 in the brain and up to 6:1 in the spinal cord. Meningiomas are very rare in children, with pediatric cases accounting for only 1.5% of the total.
How is the diagnosis made?
Meningiomas may cause seizures, headaches, and focal neurological defects, such as arm or leg weakness, or vision loss. Patients often have subtle symptoms for a long period before the meningioma is diagnosed. Sometimes memory loss, carelessness, and unsteadiness are the only symptoms.
Diagnosis is made by a contrast enhanced CT and/or MRI (magnetic resonance imaging) scan. While MRIs are in some ways superior, the CT can be helpful in determining if the tumor invades the bone, or if itís becoming hard like bone.
How are meningiomas classified?
Meningiomas were originally classified into 9 major subtypes based on their structure and form. However, more recently itís become more common to group them into three major classes, or not to distinguish subtypes at all. Multiple classifications exist today, but the most commonly used is the World Health Organizationís (WHO) "Classification of Tumours of the Nervous System," most recently updated in 2000. The WHO 2000 Classification of Meningiomas is located below
What difference does the location of the tumor make?
These grow on the surface of the brain, often toward the front. They may not produce symptoms until they reach a large size. Symptoms of a convexity meningioma are seizures, focal neurological deficits, or headaches.
Falx and Parasagittal meningiomas
The falx is a groove that runs between the two sides of the brain (front to back), and contains a large blood vessel (sagittal sinus). Parasagittal tumors lie near or close to the falx. Because of the danger of puncturing the blood vessels, removing a tumor in the falx or parasagittal region can be difficult. Large parasagittal meningiomas may result in bilateral leg weakness.
Olfactory groove meningiomas
Olfactory groove meningiomas grow along the nerves that run between the brain and the nose. These nerves allow you to smell, and so often tumors growing here cause loss of smell. If they grow large enough, olfactory groove meningiomas can also compress the nerves to the eyes, causing visual symptoms. Similarly, meningiomas growing on the optic nerve can cause visual problems, including loss of patches within your field of vision, or even blindness. They can grow to a large size prior to being diagnosed due to changes in the sense of smell and mental status changes being difficult to catch.
Sphenoid meningiomas lie behind the eyes. These tumors can cause visual problems, loss of sensation in the face, or facial numbness. Tumors in this location can sometimes involve the blood sources of the brain (e.g. cavernous sinus, or carotid arteries), making them difficult or impossible to completely remove.
Posterior fossa meningiomas
Posterior fossa tumors lie on the underside of the brain. These tumors can compress the cranial nerves causing facial symptoms or loss of hearing. Petroclival tumors can compress the trigeminal nerve, resulting in sharp pain in the face (trigeminal neuralgia) or spasms of the facial muscles. Tentorial meningiomas or those near the area where your spinal cord connects to your brain (foramen magnum) can cause headaches, or other signs of brain stem compression like trouble walking.
Intraventricular meningiomas are associated with the connected chambers of fluid that circulate throughout the central nervous system. They can block the flow of this fluid causing pressure to build up, which can produce headaches and dizziness.
Intraorbital meningiomas grow around the eye sockets of your skull and can cause pressure in the eyes to build up, giving a bulging appearance. They can also cause an increasing loss of vision.
Spinal meningiomas account for less than 10% of meningiomas. They tend to occur in women (with a female/ male ratio of 5:1), usually between the ages of 40 and 70. They are intradural (within or enclosed within the dura mater), extramedullary (outside or unrelated to any medulla) tumors occurring predominantly in the thoracic spine. They can cause back pain, or pain in the limbs from compression of the nerves where they run into the spinal cord.
How common is each location?
Falx or parasagittal 25%
What factors predispose people to meningiomas?
The only known predisposing factors associated with meningiomas are exposure to radiation, and certain genetic disorders (e.g. neurofibromatosis). Some have reported an association between meningiomas and the site of a previous injury (e.g. head trauma). However, the relationship with previous head injury isnít well understood. Some have suggested that viruses may play some role as well, but this is unsubstantiated at this point.
Meningiomas are also more common in women than in men, and have shown increased growth during pregnancy. They have hormone receptors and progesterone and estrogen may play a role in their development, but that role is still unclear.
Meningiomas have been found at the site of previous trauma (such as near a previous skull fracture, scarred dura, or around foreign bodies), but the relationship isnít fully understood.
Exposure to radiation has been found to be associated with a higher incidence of meningiomas. For example, survivors of Hiroshima have an increased incidence of these tumors. The more recently developed methods of delivering radiation therapy that use focused beams help to limit unnecessary exposure to areas outside the target, and so are expected to be safer. Patients who have undergone broad radiation treatments in the past should take care to watch for symptoms and monitor themselves for meningiomas. Meningiomas caused by radiation exposure are generally more aggressive.
People with a genetic disorder known as neurofibromatosis type 2 (Nf2) are more likely to develop meningiomas. Of people with malignant meningiomas, a higher percent have mutations in NF2.
There are some genes that may act as tumor suppressors, and the lack or deletion of these genes may make people more susceptible to tumors. For example, patients with Nf2 are, unfortunately, more likely to develop meningiomas because they have inherited a gene which has the potential to cause normal cells to become cancerous.
There is a possibility that viruses may be related to meningioma formation, but the relationship is not defined.
What are the indicators of a good or less good outcome?
The age of the patient at the time the tumor is removed influences outcome. Younger patients tend to do better after surgery than older patients do do. However, older patients in otherwise good health should not assume that their chances of a good outcome are diminished.
Tumor location and accessibility
People with tumors that invade the brain tend to do more poorly than patients with tumors that do not invade. Similarly, people with tumors on the outer surface of the brain (convexity) tend to better than those with tumors that are difficult to access, like those on the undersurface of the brain, in regions adjacent to important structures like those needed for breathing or movement, or near large blood vessels. Incomplete removal of the tumor, which is usually due to limitations caused by the location of the tumor, is associated with a higher chance of tumor recurrence. Residual tumor cells are a potential source of new tumor growth.
Extent of removal
The major clinical factor in recurrence is the extent of resection/ removal. How completely the surgeon is able to remove the tumor is highly effected by the location of the tumor, whether it is adjacent or attached to anything else, and the age of the patient.
Survival estimates show a marked difference when grouped by type. Atypical meningiomas have the highest survival rate, followed by benign and then malignant.
Age at the time of diagnosis is also indicates an increased chance of survival. The younger patients have better survival rates.
Brain invasion indicates an increased chance of recurrence. Brain-invasive benign meningiomas act like atypical meningiomas overall.
Classification of Meningiomas:
WHO Grade 1
WHO Grade 2
WHO Grade 3
Of these subtypes, meningiothelial, fibrous and transitional are the most common. Most of these subtypes behave similarly, however anaplastics are the most aggressive.