There is an unwritten rule, or axiom, in medicine that there is no such thing as a benign brain tumor. This is because the brain is contained and protected within a rigid shell, known as the skull. Because the brain cannot expand within the skull, anything that grows within the brain must by necessity displace vital brain tissue. While growths and tumors may arise within the brain and be pathologically benign, they are not benign in a clinical sense because as they grow, they push away normal brain tissue. Take, for example, the most common brain tumor, the meningioma. Meningiomas account for about 36 percent of all brain tumors and are almost always pathologically benign (more than 95 percent are benign). They arise from the meninges, which are the membranes that cover the brain and spinal cord. Because meningiomas start outside of the brain at the meninges and grow into the brain, they are technically not brain tumors as they do not arise from within the brain itself, but they are classified as brain tumors for simplicity’s sake.
Meningiomas are seen in about two percent of the population. They grow very slowly, often taking decades before they reach a size that causes symptoms, if they ever do. They are most commonly discovered by accident, either on a brain scan being done for another reason, or at autopsy. While they rarely cause symptoms, symptoms can develop once a meningioma grows to a critical size. Symptoms may include vision changes such as double or blurred vision, headaches that worsen over time, hearing loss or tinnitus, memory loss, loss of the sense of smell, seizures, and leg and/or arm weakness. Because meningiomas grow slowly, symptoms, if present, appear and worsen very slowly. If any of these symptoms appear suddenly, it is a medical emergency.
The cause(s) of meningiomas are unknown, but there are risk factors. As there is thought to be a genetic component, having a family member with a meningioma is a risk factor. Other risk factors include female sex (they occur more commonly in women), use of female sex hormones like estrogen and progesterone (known as HRT, or hormone replacement therapy, which includes birth control medication), a history of brain irradiation, and a family history of an inherited nervous system disorder such as neurofibromatosis Type 2. Because meningiomas grow so slowly, advanced age is also a risk factor. While studies show that an age over 70 to 75 is an independent risk factor, that can be said of just about any disease or condition. Recent research also points to other possible risk factors including the chronic use of NSAIDs (i.e. Aleve, Advil) or aspirin, the use of medications to lower blood pressure, and obesity (research points to a BMI over 30 as being a risk factor). Interestingly enough, there are two factors that negatively correlate with, or lower, meningioma risk. They include chronic severe anxiety and coronary artery disease. Just how these two conditions lower the risk has yet to be determined.
If a meningioma reaches a size where it causes symptoms, neurosurgical evaluation is warranted. Meningiomas may be surgically removed or treated with radiation therapy. Thankfully, the need to treat one is rare as most meningiomas never cause any symptoms.
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