The delicate tissues of the brain and spinal cord are protected by a layer of bone and an inner covering called the meninges. The meninges are composed of three layers:
- dura mater
- pia mater
The tough, thick dura mater forms the outer layer of the meninges and is attached to the bone of the skull and spinal cord. The arachnoid and pia mater layers are thinner and more delicate than the dura mater. The innermost pia mater layer is attached directly to the brain and spinal cord. Meningiomas arise from the middle arachnoid layer, and most remain attached to the dura mater by a dural tail.
Types of meningiomas
Meningiomas account for 15-20% of all brain tumors, and 25% of all spinal cord tumors. The World Health Organization (WHO) classifies meningiomas into 11 different categories according to their cell type. However, because there are so many different cell types and so much overlap between types, meningiomas are most often placed into three general categories, including benign, atypical, and malignant.
Benign meningiomas are by far the most common, accounting for more than 90% of all meningiomas. These tumors grow slowly and produce symptoms only if they become large enough to compress nearby brain tissue. In some patients, meningiomas can grow very large with almost no symptoms. This happens because the tumor has grown very slowly and has gradually compressed the brain over time. Meningiomas can also cause fluid to build up in the brain, and can sometimes block veins. They may also grow into nearby bone, causing the bone to become thicker.
Up to 7% of meningiomas are classified as atypical. These tumors grow more quickly than benign meningiomas and are more likely to be symptomatic. Malignant meningiomas are fast-growing aggressive tumors and are the most rare, accounting for only about 2% of all meningiomas. It is extremely unusual for meningiomas to metastasize to other organs. When they do, the lungs are the most common site.
Only about one tenth of meningiomas are found in the spine. These slow-growing tumors cause symptoms when they begin to compress the spinal cord. Spinal meningiomas usually grow in the spinal canal between the neck and the abdomen, and are almost always benign.
Only one person in every 50, 000 is diagnosed with a symptomatic meningioma annually. Most of these patients are women. Women develop brain meningiomas almost twice as often as men and spinal meningiomas four to five times more often than men. The disease usually strikes middle-aged and elderly patients. Men are most affected between the ages of 50 and 60 years, while women are most affected between the ages of 60 and 70 years. Atypical and malignant meningiomas are more common in men. Meningiomas do not occur very often in children.
Causes and symptoms
Although no single factor has been found that causes meningiomas, several risk factors are known. Some patients have developed a meningioma after being exposed to radiation. These patients tend to be younger than typical meningioma patients, and their tumors often grow more quickly.
There is also a genetic component to meningioma. Patients who suffer from neurofibromatosis, a rare genetic disease, often develop multiple meningiomas.
Since meningioma cells recognize the female sex hormone progesterone, some researchers believe that female sex hormones may play a role in the development of meningiomas. This possible link is still being investigated.
Up to 75% of meningiomas produce no symptoms because they grow slowly and remain small. Often, tumors are discovered only when patients are being investigated for an unrelated illness. When symptoms do appear, it results that the tumor has grown large enough to compress part of the brain or spinal cord.
Patients experience different symptoms depending on the location of the tumor. Most brain meningiomas are located either just below the top of the skull, or between the two hemispheres of the brain. If the tumor is located in these areas, symptoms include:
- problems with memory
- behavior changes
More rarely, tumors are near sensory areas of the brain such as the optic nerve or close to the ears. Patients with these tumors experience vision or hearing losses.
Spinal meningiomas are usually found in the spinal column between the neck and the abdomen. The most common symptoms are:
- weakness and stiffness of the arms and legs
- episodes of partial paralysis
Meningiomas are diagnosed using a painless, non-invasive technique called magnetic resonance imaging (MRI). MRI works by exposing the patient to harmless radio waves and a magnetic field, which produce clear images of the brain and the spine that show the size and location of tumors. No special preparation is required for the test.
Diagnosis can also be made by computed tomography (CT) scan. The CT scan uses low-dose x rays to generate a picture of the inside of the body. Sometimes a dye is injected into the patient's vein to improve the visibility of tissues. If the meningioma has grown into nearby bone, a CT scan will show the extent of bone invasion better than MRI. Women who are pregnant, or who think they might be pregnant, should tell their doctor before having a CT scan.
The treatment team for a patient with a symptomatic meningioma may include a radiologist, a neurologist (specialist of the nervous system), and a neurosurgeon.
If surgery is necessary, a neurosurgeon will perform the procedure with the help of a surgical team. The team includes two or three nurses, and an anesthesiologist.
A small number of patients receive radiotherapy for their meningioma either because the tumor is too difficult to remove surgically, or because the surgeon had to leave some tumor behind. These patients will be referred to a radiation oncologist (specialist in giving radiation to cancer patients).
Clinical staging, treatments, and prognosis
Meningiomas are classified into three different grades depending upon the likelihood of recurrence and aggressive growth:
- Grade I: Low risk of recurrence and slow growth
- Grade II: Greater likelihood of recurrence and/or aggressive growth
- Grade III: High recurrence rates and aggressive growth.
The vast majority of meningiomas are grade I. Atypical tumors are grade II, and malignant tumors are grade III.
Medical treatment for meningiomas is necessary when tumors cause symptoms. Fortunately, only about a quarter of meningiomas become symptomatic. Most patients are cured by surgery.
The objective of surgery is to remove not only the entire meningioma, but also the tail that attaches the tumor to the meninges. If the tumor has grown into bone, the bone is removed, too. If the tumor is in a difficult location in the brain, the surgeon may leave some tumor behind in order to preserve brain tissue.
The prognosis following brain meningioma treatment is very good. For the few patients who are not cured, prognosis depends on how completely the tumor is removed. If some tumor is left behind, recurrence is more likely, particularly for patients with grade II or grade III meningiomas. Ten years after surgery, 7-20% of patients with benign grade I tumors have a recurrence. For patients with malignant grade III tumors, up to 78% have a recurrence. A second surgery is sometimes necessary for patients with recurrent tumors.
Spinal meningioma is the most successfully treated meningioma, and the most successfully treated of all spinal tumors. Most of these tumors are removed completely, and they rarely recur. Even patients with quite severe symptoms fully recover after surgery.
For the few patients who are inoperable (usually because of tumor location), radiation therapy can stop the growth of tumors. Recently, stereotactic radiosurgery has been successfully used. This procedure uses images of the patient's skull to construct a frame that allows precise aiming of radiation, thus minimizing harm to nearby healthy tissue.
Not every patient with a meningioma receives surgery or radiation. Asymptomatic patients with small or slow-growing tumors can receive periodic MRI tests to check tumor growth. Treatment may also not be necessary for patients with mild or minimal symptoms.
Alternative and complementary therapies
Unlike many other cancers, conventional medical treatment of meningioma has very high success rates. As a result, alternative therapies are not commonly used for these tumors.
Coping with cancer treatment
When first diagnosed with a meningioma, many patients experience anxiety, resulting in nervousness, sleepless nights, and even nausea. However, patients can often relieve many of their fears by learning more about the disease and its course of treatment.
The majority of meningioma patients are treated with surgery alone. Surgery will involve a hospital stay of at least a week. Before going home, patients are usually given medications to help prevent pain and swelling. Once home, patients can expect to feel some headache pain, and will become tired easily. If headaches and weakness become worse, a doctor should be contacted. Patients should make sure they get plenty of rest and eat a balanced, nutritious diet. Most patients can begin to resume their normal activities in about six to eight weeks.
Chemotherapy is seldom given to meningioma patients because surgery (and/or radiotherapy) is usually successful. For patients with tumors that do not respond to these treatments, however, chemotherapy is available within a clinical trial.
Clinical trials have investigated several drugs to treat patients whose meningioma recurs following failure of both surgery and radiotherapy. Hydroxyurea , a drug used to treat some other cancers, has been shown to slow the growth of meningioma cells. Studies of hydroxyurea continue. Some trials have explored the link between meningioma and female sex hormones. Tamoxifen , an anti-estrogen drug used to fight breast cancer , has produced disappointing results. Trials using RU-486, an anti-progesterone agent, are underway. Information on these and other open clinical trials is available on the Internet from the National Cancer Institute at <http://www.nci.nih.gov>.
The most avoidable risk factor for the development of meningioma is exposure to radiation. Children exposed to small amounts of radiation in the 1950s to treat tinea captis, a fungal infection of the scalp, developed meningiomas at an unusually high rate. There is also a clear relationship between radiation dose and meningioma: the higher the radiation dose, the greater the probability of developing a meningioma.
The very elderly
In very elderly people, the symptoms of a meningioma can be very similar to normal aging. These patients typically experience difficulty with learning and remembering things as a result of the tumor. Headaches, a classic symptom of a meningioma, are not usually reported. Treatment of very elderly patients may be difficult if the patient is too frail for surgery.
On the rare occasions that meningiomas are diagnosed in children, they tend to be large, fast growing, and located in unusual positions. Treatment for children is the same as for adults: complete tumor removal with surgery and/or radiotherapy.
Neurofibromatosis (NF) is actually two different genetic diseases: NF Type 1 and NF Type 2. NF Type 2 is the more rare of the two diseases, affecting only one in 40, 000 individuals. These patients often develop multiple brain meningiomas. Although there is no cure for NF, meningioma tumors can be removed with surgery.
Al-Mefty, Ossama, ed. Meningiomas. New York: Raven Press, 1991.
Kleihues, Paul, and Webster K. Cavenee, ed. World Health Organization Classification of Tumours: Tumours of the Nervous System. Lyon: IARC Press, 2000.
DeAngelis, Lisa M. "Brain Tumors." New England Journal of Medicine 344 (2) (11 January 2001): 114-23.
Yamasaki, Fumiyuki, et al. "Recurrence of Meningiomas." Cancer 89 (5) (1 September 2000): 1102-10.
The Brain Tumor Society. 124 Watertown Street, Suite 3-H, Watertown, MA 02472. (800) 770-8287. <http://www.tbts.org>.
Alison McTavish, M.Sc.
QUESTIONS TO ASK THE DOCTOR
- Will I need to have surgery?
- Can I expect a full recovery after surgery?
- Will I need radiotherapy?
- How often will I need to return for an MRI or CT scan?
- How soon can I return to work after surgery?
—A growth that is non-cancerous.
Computed tomography (CT) scan
—A method of imaging the inside of the body using x rays.
Magnetic resonance imaging (MRI)
—A method of imaging the inside of the body using radio waves and a magnetic field.
—Membranes that cover and protect both the brain and spinal cord.
—A rare, genetic disease that causes tumors to grow in the nervous system.
—The use of radiation to treat a medical condition.