A meningioma is a brain tumor, but not in the way most people picture one. It doesn’t grow from brain tissue itself. Instead, it grows from the meninges, the protective layers of tissue that surround the brain and spinal cord. Meningiomas account for 37% of all central nervous system tumors, making them the single most common type.
The distinction matters because meningiomas sit on the surface of the brain rather than inside it. They press inward as they grow, which affects both the symptoms they cause and how treatable they are. The majority are slow-growing and noncancerous, though a small percentage behave more aggressively.
Where Meningiomas Actually Grow
Your brain is wrapped in three protective layers called the meninges. The outermost layer (the dura) is tough, fibrous tissue. Beneath it sits a thin, web-like middle layer (the arachnoid), and the innermost layer (the pia) clings directly to the brain’s surface. Meningiomas typically arise from cells in the arachnoid layer.
Because they grow from these coverings rather than from brain cells, meningiomas are classified as extra-axial tumors. They push against the brain as they enlarge but don’t invade it the way gliomas or other intrinsic brain tumors do. This is one reason they’re often easier to remove surgically. However, they can still cause serious problems by compressing brain tissue, blood vessels, or nerves as they expand.
How Meningiomas Are Graded
The World Health Organization classifies meningiomas into three grades based on how quickly the cells are dividing and how abnormal they look under a microscope. There are 15 recognized subtypes, but they all fall into one of these three tiers:
- Grade 1 (low grade): The most common by far, accounting for roughly 80-85% of cases. These are slow-growing and considered benign.
- Grade 2 (atypical): These grow faster and are more likely to come back after removal. Certain subtypes, like chordoid and clear cell meningiomas, are automatically placed in this category because of their higher recurrence risk.
- Grade 3 (malignant): The rarest and most aggressive. These can invade surrounding tissue and grow rapidly.
The grade has a direct impact on treatment decisions and long-term outlook. A grade 1 meningioma discovered by accident may never need treatment at all, while a grade 3 tumor typically requires surgery followed by radiation.
Symptoms Depend on Location
Many meningiomas cause no symptoms at all and are found incidentally on brain scans done for unrelated reasons. When symptoms do appear, they depend almost entirely on where the tumor is sitting.
Meningiomas along the top of the brain (convexity meningiomas) tend to cause headaches, seizures, weakness, or numbness. Those growing near the midline between the brain’s two hemispheres can lead to leg weakness as they press on the motor areas that control the lower body. Tumors at the base of the skull produce a different set of problems: a meningioma near the eye socket can cause the eye to bulge or affect vision, while one growing near the ear can interfere with hearing, facial sensation, or facial movement.
Symptoms usually develop gradually over months or years because most meningiomas grow slowly. A sudden onset of seizures or neurological changes is less typical but can happen if the tumor reaches a size where it creates significant pressure.
Risk Factors
Meningiomas are roughly twice as common in women as in men, and they occur more frequently after age 40. Hormonal factors play a role: many meningiomas have progesterone receptors, which may partly explain the higher rates in women.
Ionizing radiation is the strongest confirmed environmental risk factor. People who received radiation to the scalp or head during childhood, whether for skin conditions or childhood brain tumors, have a significantly elevated risk of developing meningiomas later in life. The radiation damages DNA strands in meningeal cells, and a loss of genetic material on chromosome 22 has been observed in about 80% of meningiomas, suggesting a common pathway in how these tumors form.
How Meningiomas Are Diagnosed
MRI with contrast dye is the primary tool. Meningiomas typically appear as well-defined, round masses attached to the dura. One classic sign radiologists look for is the “dural tail,” a thickening of the surrounding membrane that flares out from the tumor’s edges. This sign has a sensitivity of about 59% and a specificity of 94% for meningioma, meaning it’s not always present but when it is, it strongly suggests meningioma rather than something else. That said, other conditions (including lymphoma, metastases, and even pituitary tumors) can occasionally mimic this appearance, so imaging alone isn’t always definitive.
A definitive diagnosis requires examining tumor tissue, which happens either through a biopsy or after surgical removal. This is when the WHO grade is determined.
Treatment Options
Not every meningioma needs immediate treatment. For small, asymptomatic tumors (generally under 3 centimeters), the preferred approach recommended by major neuro-oncology guidelines is watchful waiting with periodic MRI scans. A study following 64 patients with incidentally discovered meningiomas over five years found that none developed tumor-related symptoms, and about 61% of the tumors showed a self-limiting growth pattern. Monitoring lets doctors confirm whether a tumor is actually growing before committing to intervention.
When treatment is needed, surgery is the primary option. The goal is to remove as much of the tumor as possible, including any affected membrane and bone. The extent of removal matters for recurrence: in one foundational study, tumors that were completely removed along with their dural attachment recurred about 9% of the time, while those where only the visible tumor was taken out (leaving behind involved membrane) recurred around 19% of the time. For skull base tumors, complete removal is sometimes impossible because of nearby critical structures, and surgeons balance aggressiveness against the risk of neurological damage.
Radiation therapy is used for tumors that can’t be fully removed, that recur after surgery, or that are grade 2 or 3. Focused techniques like stereotactic radiosurgery can target the tumor precisely while limiting exposure to surrounding brain tissue.
Long-Term Outlook
For grade 1 meningiomas, the prognosis is generally excellent. Most people do well after treatment, and five-year recurrence-free survival rates exceed 85-95% when the tumor is fully removed. Many people with small, monitored tumors live their entire lives without ever needing intervention.
Higher-grade tumors are more challenging. In a 25-year study of patients with grade 2 and 3 meningiomas, the overall five-year survival rate was about 68%, and the ten-year rate was roughly 44%. The median progression-free survival for grade 2 tumors was 3.2 years, meaning about half of patients saw their tumor return within that time frame. These tumors often require multiple rounds of treatment over the years.
Regardless of grade, long-term follow-up with regular imaging is standard. Even benign meningiomas can recur years or decades after treatment, so ongoing monitoring remains an important part of care.