Meningioma Diagnosis, Risks, and Grades

So far as I know, there is no such thing as a good brain tumor. That said, most of the time a meningioma is about as good a brain tumor as you can get. In fact, in some ways, it doesn't even count as a brain tumor.

What Is a Meningioma? 

Although meningiomas often considered a primary brain tumor, I used quotes above because technically a meningioma is not a tumor of brain tissue at all. Instead, a meningioma grows from the meninges, the protective tissue surrounding the brain. Specifically, meningiomas usually stem from the arachnoid mater. 

The meninges follow the brain's major curves. For example, the meninges dive towards the middle of the brain where the left and right hemisphere are separated, and also wrap around the base of the skull and the optic nerves. The symptoms and treatment of meningioma partially depend on the tumor’s location. 

How Often Are Meningiomas Diagnosed?

While a study of over 2000 people on autopsy has suggested that about 1 percent of people may have a meningioma, they are not as commonly diagnosed in the living. The tumors may grow slowly, sometimes hardly at all. 

According to the Central Brain Tumor Registry in the United States (CBTRUS), the estimated prevalence of meningioma in the United States is about 170,000 people.  Based on these statistics, meningiomas are among the most common of all brain tumors, accounting for about one-third of cases.

If meningiomas do cause problems, they are often treated surgically with relative ease. That said, meningiomas can sometimes be serious or even life-threatening. The difference lies in the type and location of the meningioma, as well as unique characteristics of individual people. 

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Risks

Some risks for meningioma cannot be helped. For example, meningiomas are at least twice as common in women compared to men. The incidence of meningiomas increases with age. They are relatively rare in children but are likely the most common type of brain tumor diagnosed in people over the age of 85. 

There are also genetic risk factors for meningioma. The best known is neurofibromatosis type II, which increases the chances of someone getting many neoplasms. This syndrome is due to a mutation in the NF2 gene, which normally helps suppress tumors. Other genes implicated in meningioma are DAL1, AKT1, and TRAF7.

Radiation is the most definitive modifiable risk factor for meningioma. This is best studied in cases where the brain has been irradiated in the treatment of different cancer. Since there can be a long time between the time of radiation and the discovery of a meningioma, the risk is highest for children. For example, in a study of 49 people who had childhood leukemia treated with radiation, 11 had meningiomas after an average time of 25 years. Radiation by medical techniques such as dental X-rays is much lower, though studies have shown a connection between frequent X-ray use and later meningioma growth.

Other potential risk factors for meningioma have been studied with conflicting results, including obesity, hormone replacement, and head trauma. 

What Makes a Meningioma Serious?

While most meningiomas are so benign as to perhaps avoid detection, they may become quite serious. The World Health Organization has categorized meningiomas into three grades based on their appearance under a microscope. The more advanced the grade, the more dangerous the meningioma.

• WHO Grade 1: Grade I meningiomas are relatively benign. While they may still require surgery to avoid compression of important brain structures, often nothing more is necessary than periodic neuroimaging studies to ensure it is not getting significantly larger.
• WHO Grade 2: These meningiomas have more signs of active cell division. More caution needs to be taken with these tumors. Subtypes include chordoid, clear cell, and atypical meningiomas.
• WHO Grade 3: These tumors have several signs of active cell division. The tumor may even be infiltrating underlying brain or show areas of cell death. Subtypes include papillary, rhabdoid and anaplastic meningiomas. Only 2 to 3 percent of all meningiomas are Grade 3. 

Patients with advanced grades of meningiomas are more likely to have a recurrence of the meningioma after treatment and are more likely to have a higher risk of death overall. The five-year recurrence-free survival in grade II meningioma has been described at 87 percent compared to 29 percent for grade III.

Regardless of the type of meningioma, location and size can be very important in determining the need and urgency of treatment. Most important, however, is how the person with the meningioma is doing in their daily life.