Meningiomas are tumors of the meninges, the membrane that covers the brain and spinal cord. Most commonly, these are benign meningiomas, or grade I meningiomas, which remain small and do not grow indefinitely like cancerous tumors. An atypical meningioma, also called a grade II meningioma, is a meningeal tumor that may be malignant and may grow back after treatment or removal. A grade III meningioma grows aggressively, threatening to compress neighboring brain tissue and invade bone. Even a benign meningioma can be dangerous because of its close proximity to the brain.
One of the most common forms of brain tumors, meningiomas account for approximately 30 percent of all these cancers. The diagnosis of meningiomas is most often made by magnetic resonance imaging (MRI). Patients who have symptoms will first undergo a neurological exam and then brain imaging to determine if they have a brain tumor. In asymptomatic patients, the diagnosis sometimes occurs during brain imaging that was ordered for another medical complaint.
Symptomatic patients often have atypical or malignant varieties. They report neurological symptoms such as headaches, seizures, loss of sensation, nausea, blurred vision, and sensitivity to light. They can develop almost anywhere in the nervous system, but most meningiomas occur in the head, often near the brainstem, skull base, sinus venosus, or optic nerve sheath.
An atypical meningioma is more common in women who are middle-aged or older and is rare in children; Spinal meningiomas are rarely found in men. They have a faster growth rate than grade I tumors, but grow less quickly than clearly malignant tumors. Grade II meningiomas comprise less than 10 percent of the total incidence. Grade II malignant cases are about 2 percent.
Scientists have linked the appearance of maningiomas to a mutation in a gene that encodes a tumor suppressor protein. Severe congenital mutations of this gene cause a syndrome in which patients develop multiple benign tumors. Other mutations lead to an increased risk of benign or atypical meningioma. A small percentage of cases have been linked to an inherited form of the disease; Most children who develop grade II meningiomas fall into this category. Grade II and grade III meningiomas in children are often quite severe and progress rapidly.
An atypical meningioma may require treatment to prevent further growth. Any tumor that causes symptoms in the patient is usually treated as malignant. Treatment involves surgical removal and follow-up radiation therapy to kill any remaining tumor cells.
The decision to treat the tumor is weighed against its growth, present and future risks to brain tissue, the patient's age and health, and possible consequences of surgery, such as infection or brain swelling. Sometimes the shock from radiation and surgery can be bigger problems than the risk posed by a slow-growing tumor. For example, in elderly patients who do not have fast-growing tumors, regular observation is often preferred as treatment, because surgery can present more life-threatening complications than the tumors themselves. A grade I tumor rarely comes back if it was surgically removed, but an atypical meningioma has a higher risk of recurrence.