Meningiomas are the most common benign intracranial tumors. They originate from cells (arachnoid cap cells) within the arachnoid, a thin, spider web-like membrane that surrounds the brain and spinal cord. There are three layers of meninges; the dura mater, arachnoid and pia mater. Although the majority of meningiomas are benign, undiscovered these tumors can grow slowly until they are very large, and in some locations, can be severely disabling and even life threatening. Most patients develop a single meningioma, however, some patients may develop several tumors growing simultaneously in other parts of the brain or spinal cord.
Meningiomas are found along the dura lining the venous sinuses of the brain and skull base; locations where arachnoid cap cells are most abundant. Therefore, intracranial meningiomas are commonly found at the cerebral convexity, parasagittal/falx, petrous ridge, sphenoid wing, tentorium, foramen magnum, cerebellopontine angle, and cavernous sinus.
In the spine, meningiomas are typically located in the intradural extramedullary space and spread laterally into the subarachnoid space, most frequently in the thoracic region.
Sources: Brain Science Foundation, Central Brain Tumor Registry of the United States.
The World Health Organization (WHO) classification of brain tumors is the most widely utilized. The WHO classification scheme recognizes 15 variations of meningioma according to their cell type, as seen under a microscope. These variations are called meningioma subtypes; the technical term for these cell variations is histological subtypes.
Atypical meningiomas exhibit increased tissue and cell abnormalities. These tumors grow at a faster rate than benign meningiomas and on occasion can invade the brain. Atypical meningiomas have a higher likelihood of recurrence than benign meningiomas.
Malignant meningiomas show increased cellular abnormalities, and grow at a faster rate than either benign or atypical meningiomas. Malignant meningiomas are the most likely to invade the brain and metastasize to other organs in the body, and tend to recur more often than the other two types.
Age: Meningiomas most often occur in people between the ages of 40 and 70.
Gender: Women are more than twice as likely as men to develop meningioma; however, men are three times as likely as women to be diagnosed with malignant meningioma.
Radiation exposure: Exposure to ionizing radiation, especially high doses, has been found to be associated with a higher incidence of intracranial tumors, in particular, meningiomas. There is also evidence indicating an association between meningiomas and lower doses of radiation. The most well-known case involves children in Israel who were given radiation for scale ringworm between 1948 and 1960. These children were observed to have a relative risk for meningioma of almost 10. Within the Unites States, dental x-rays are the most common form of exposure to ionizing radiation. A number of studies have linked the number of full mouth dental radiographs to increased risk of meningioma.
Genetic disorders: The genetic disorder neurofibromatosis type 2 (NF2) is believed to put people at a higher risk of developing meningioma. Patients with NF2 may also be more likely to develop malignant or multiple meningioma.
Hormones: An association between meningiomas and hormones has been suggested by a number of study findings, including: the increased incidence of meningiomas in women; the presence of hormone receptors such as estrogen, progesterone, and androgen on some meningiomas; an association between breast cancer and meningiomas; and indications that meningiomas increase in size during the menstrual cycle and pregnancy. Researchers are just beginning to explore the possible connection between meningioma risk and the use of oral contraceptives and hormone-replacement therapy.
Because meningiomas are commonly very slow-growing tumors, they often do not cause noticeable symptoms until they are quite large. Some meningiomas may remain asymptomatic for a patient’s lifetime or may be detected unexpectedly when a patient has a brain scan for unrelated symptoms. Presenting signs and symptoms depend on the size and location of the tumor. Symptoms of meningiomas may include any of the following:
Symptoms can be related more specifically to the location of the meningioma:
Falx and parasagittal: The falx is a fold of the dura that runs between the brain’s two hemispheres in a front to back direction. So if the tumor is located in the frontal section, it may impair higher levels of brain functioning such as reasoning and memory, whereas if it is located in the middle section, it would more likely cause leg weakness/numbness or seizures.
Convexity: Seizures, headaches and neurological deficits related to the specific location of the tumor on the surface of the brain.
Sphenoid wing (sphenoid ridge): Vision problems, loss of sensation in the face or facial numbness, and seizures.
Olfactory groove: Loss of smell due to compression of the nerves that run between the brain and the nose. If the tumor grows large enough, vision problems may occur due to compression of the optic nerve.
Suprasellar: Vision problems due to compression of the optic nerves/chiasm.
Posterior fossa: Facial symptoms or loss of hearing due to compression of cranial nerves, unsteady gait, and problems with coordination.
Intraventricular: May block the flow of cerebrospinal fluid, causing pressure to build up (obstructive hydrocephalus), potentially leading to headaches, lightheadedness, and changes in mental function.
Intraorbital: Buildup of pressure in the eyes, leading to a bulging appearance and potential loss of vision.
Spinal: Back pain, or pain in the limbs caused by compression of the nerves which run into the spinal cord.
It can be difficult to diagnose meningiomas for several reasons. Because the majority of meningiomas are slow-growing tumors and primarily affect people between the ages of 40 and 70, symptoms may be so subtle that the patient and/or doctor may attribute them to the normal signs of aging. Some of the symptoms associated with meningiomas can also be due to other medical conditions, which may add to the confusion. Misdiagnosis is not uncommon, and in fact, it may take several years to receive a correct diagnosis.
When a patient presents with slowly increasing signs of mental dysfunction, new seizures or persistent headaches, or if there is evidence of pressure inside the skull (e.g., vomiting, swelling of the optic nerve head at the back of the eye), the first step should be a thorough neurological evaluation, followed by radiological studies, if needed.
Sophisticated imaging techniques can help diagnose meningiomas. Diagnostic tools include computed tomography (CT or CAT scan) and magnetic resonance imaging (MRI). Intraoperative MRI is also used during surgery to guide tissue biopsies and tumor removal. Magnetic resonance spectroscopy (MRS) is used to examine the tumor's chemical profile and determine the nature of the lesions seen on the MRI.
Sometimes, the only way to make a definitive diagnosis of the meningioma is through a biopsy. The neurosurgeon performs the biopsy and the pathologist makes the final diagnosis, determining whether the tumor appears benign or malignant, and grading it accordingly.
Meningiomas are primarily benign tumors, frequently with defined borders, often enabling complete surgical resection (removal), which offers the best chance for a cure. The neurosurgeon opens the skull through a craniotomy, to enable full access to the meningioma. The goal of surgery is to remove the meningioma completely, including the fibers that attach it to the coverings of the brain (dura) and bone. However, complete resection can carry potential risks that may be significant, especially when the tumor has invaded brain tissue or surrounding veins.
Although the goal of surgery is to remove the tumor, the first priority is to preserve or improve the patient’s neurological functions. For patients in whom total removal of the tumor carries significant risk of morbidity (any side effect that can cause decreased quality of life), it may be better to leave some of the tumor in place and perform follow-up for future growth with regular imaging studies. In such cases, the patient will be observed over a period of time with regular examinations and MRIs, while for other patients, radiation therapy may be deemed the best approach.
Observation over a period of time may be the appropriate course of action in patients whom meet the following criteria:
Radiation therapy uses high-energy x-rays to kill cancer cells and abnormal brain cells and shrink tumors. Radiation therapy may be an option if the tumor cannot be treated effectively through surgery.
In adults, the patient’s age at the time of diagnosis is one of the most powerful predictors of outcome. In general, the younger the adult, the better his or her prognosis tends to be.
There is generally a better outcome if the entire tumor is surgically removed. However, this is not always possible due to the location of the tumor.
Data from the National Cancer Data Base indicates an overall five-year survival rate for meningioma of 69 percent. Individuals with benign meningiomas had an overall five-year survival rate of 70 percent, while those with malignant meningiomas had an overall five-year survival rate that was lower.