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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 stay small and do not grow indefinitely like cancerous tumors. An atypical meningioma, also called a grade II meningioma, is a meningeal tumor that could be malignant and 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 closeness to the brain.
One of the most common forms of brain tumors, meningiomas account for about 30 percent of all such cancers. Diagnosis of meningiomas is most often made through magnetic resonance imaging (MRI). Patients who have symptoms will have undergone a neurological examination first, and then brain imaging to determine whether they have a brain tumor. In asymptomatic patients, diagnosis sometimes happens during brain imaging that was requested for another medical complaint.
Symptomatic patients often have the 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 brain stem, base of the skull, venous sinus or optic nerve sheath.
An atypical meningioma is more common in women of middle age or above and is rare in children; spinal meningiomas are seldom found in men. They have a faster growth rate than grade I tumors, but they grow less rapid than clearly malignant ones. Grade II meningiomas comprise less than 10 percent of total incidence. Malignant grade II cases are roughly about 2 percent.
Scientists have linked the onset of maningiomas to a mutation in a gene that codes for a tumor-suppressor protein. Severe, congenital mutations of this gene cause a syndrome where patients develop multiple benign tumors. Other mutations lead to a greater risk of benign or atypical meningioma. A small percentage of cases have been linked to a hereditary 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 serious and rapidly progressing.
An atypical meningioma might require treatment to prevent further growth. Any tumor causing symptoms in the patient is usually treated as though it were malignant. Treatment involves surgical removal and follow-up with radiation therapy to kill remaining tumor cells.
The decision to treat the tumor is weighed against its growth, present and future risks to brain tissue, age and health of the patient, and the possible consequences of the surgery such as infection or cerebral edema. Sometimes the shock of radiation and surgery might be greater problems than the risk imposed by a slow-growing tumor. For instance, in elderly patients who don't have fast-growing tumors, regular observation is often preferred as treatment, because surgery might present more life-threatening complications than the tumors themselves. A grade I tumor seldom returns if it has been surgically removed, but an atypical meningioma has a higher risk of recurrence.