Meningioma: The Brain Tumor That Is Often Found by Accident
When 68-year-old Patricia hit her head in a minor car accident, her doctor ordered a precautionary brain CT scan. The scan showed no injury from the accident—but revealed something unexpected: a 2-centimeter mass attached to the membranes covering her brain. “I was terrified when they said ‘brain tumor,'” Patricia recalled. “But then the neurosurgeon explained it was a meningioma, probably been there for years, causing no problems. He recommended just watching it with periodic scans rather than rushing into surgery.”
Incidental discovery accounts for 30% of newly-diagnosed intracranial meningiomas. With the widespread access and use of brain imaging, incidental asymptomatic meningiomas are fast becoming a modern medical issue. Meningioma comprise 15% of incidental findings on brain MRI and have a prevalence of 5 per 1000 persons. With an increasing population age, their prevalence is likely to increase PubMed Central. Patricia’s experience reflects a modern medical reality: meningiomas are often discovered not because they’re causing problems, but because brain imaging done for entirely unrelated reasons happens to detect them.
What Meningiomas Are
Meningiomas arise from the meninges—the protective membranes covering the brain and spinal cord, specifically from arachnoid cap cells. They represent the most common primary brain tumor, accounting for about 40% of all brain tumors. Meningioma is the most common intracranial primary neoplasm and is often discovered accidentally. A 5-year prospective study with 64 patients showed that although 75% of incidental meningiomas increased in volume, none of the patients developed tumor-related symptoms. This suggests that incidental meningiomas are not only asymptomatic at diagnosis, but that they also tend to remain asymptomatic despite that the majority will grow during a 5-year period The JNS.
Most meningiomas are benign (grade 1), growing slowly and rarely spreading. About 80-85% fall into this category. Approximately 15-20% are atypical (grade 2), with higher recurrence rates after treatment. Only 1-3% are malignant (grade 3), behaving aggressively. The vast majority of incidentally discovered meningiomas are grade 1 tumors that may never require treatment.
Meningiomas predominantly affect older adults, with median age at diagnosis around 66 years, and show striking female predominance—occurring about twice as often in women as men, likely due to hormonal influences. In the group aged 75 years and older, the incidence rate of meningiomas was 42 per 100,000 person years. An autopsy study reported a prevalence of undiagnosed asymptomatic meningiomas of 2–3%, whereas studies demonstrated a prevalence of asymptomatic meningiomas of 1.0% in the age group 60–74 years The JNS. Autopsy studies reveal that about 2-3% of people have meningiomas they never knew about during life—silent tumors that never caused problems.
Why Many Remain Asymptomatic
Meningiomas grow extremely slowly—typically millimeters per year—allowing the brain time to compensate and adjust. Because they arise from the covering membranes rather than brain tissue itself, they push the brain aside rather than infiltrating it. Small tumors in “quiet” brain regions—areas not controlling critical functions—may never cause symptoms even if they grow moderately.
Location profoundly influences whether meningiomas cause symptoms. A small tumor near the optic nerve can cause vision problems while much larger tumors in the frontal lobe remain asymptomatic for years. Skull base meningiomas, while challenging to remove surgically, often grow more slowly than those in other locations.
One study found that the majority of incidental meningiomas followed a self-limiting curve, either sigmoid, parabolic, or continuous reduction. Incidental asymptomatic meningiomas grow according to an S-shaped, or Gompertzian curve, rather than a linear growth model, taking the often self-limiting growth pattern over time into account Taylor & Francis Online. This S-shaped growth pattern—early exponential growth, then linear growth, eventually reaching a plateau—explains why many meningiomas discovered in elderly patients remain stable; they’ve already reached their growth plateau.
The Watch-And-Wait Approach
For most incidentally discovered meningiomas, observation rather than immediate treatment represents the safest strategy. Initial management strategies at diagnosis were: surgery (27.3%), stereotactic radiosurgery (22.0%) and active monitoring (50.7%). The pooled risk of symptom development in patients actively monitored was 8.1%. Most patients who clinically or radiologically progressed did so within 5 years of diagnosis. Intervention at diagnosis may lead to unnecessary overtreatment Springer.
Only about 8% of patients under observation develop symptoms requiring treatment. The first five years are critical—if a meningioma remains stable during this period, the likelihood of future problems decreases substantially. Serial MRI scans, typically every 6-12 months initially, monitor for growth or concerning changes.
Imaging features help predict which tumors might grow: absence of calcium, T2-hyperintensity on MRI, peritumoral edema (brain swelling around the tumor), and larger initial size all increase growth risk. Conversely, heavily calcified tumors rarely grow. Patient factors matter too—younger patients’ tumors are more likely to grow than those in elderly patients.
When Treatment Becomes Necessary
Twenty-five percent of the patients operated for incidental meningiomas acquired postoperative complications requiring treatment. In a recent study of asymptomatic meningiomas, the risk of new neurological deficits was 8% and new seizures developed in 4%. Also, 2% of the patients were re-operated due to complications and 0.3% died within 30 days of surgery Taylor & Francis Online.
Surgery carries real risks—neurologic deficits, seizures, infection, bleeding—making the decision to operate significant. Treatment is warranted when: tumors cause symptoms (headaches, seizures, neurologic deficits); imaging shows rapid or progressive growth; the tumor approaches critical structures (optic nerve, brainstem); or younger patients have growing tumors likely to eventually cause problems.
Surgery aims for complete removal when feasible. Stereotactic radiosurgery (focused radiation in 1-5 sessions) treats small to medium tumors in surgically challenging locations. Conventional radiation therapy may follow incomplete surgery.
Despite the often small size and indolent behavior of incidental meningiomas during follow-up, a systematic review found that surgery was performed in 27.3%, stereotactic radiosurgery in 22%, and active monitoring in 50.7%. They concluded that there is a lack of consensus on how meningioma growth should be defined The JNS. The lack of standardized growth definitions and management guidelines means treatment decisions remain highly individualized, balancing tumor characteristics, patient age and health, and personal preferences.
Living With An Incidental Meningioma
Discovering you have a brain tumor—even a benign one unlikely to cause problems—creates anxiety. Many patients struggle with “scanxiety”—worry before each follow-up scan. Understanding that most incidental meningiomas never require treatment helps, but the uncertainty of not knowing whether your tumor will be among the minority that grows can be distressing.
Quality of life studies show that most patients with incidental meningiomas lead normal lives. The meningioma itself rarely impacts daily function. However, the knowledge of having a brain tumor and undergoing periodic monitoring can affect psychological wellbeing. Some patients experience headaches or other symptoms they attribute to the meningioma when these symptoms likely existed before discovery or have unrelated causes.
References
- Expert Review of Anticancer Therapy. Overview and recent advances in incidental meningioma. https://www.tandfonline.com/doi/full/10.1080/14737140.2023.2193333
- PMC. The management of incidental meningioma: An unresolved clinical conundrum. https://pmc.ncbi.nlm.nih.gov/articles/PMC10243855/
- Springer. Incidental intracranial meningiomas: a systematic review and meta-analysis. https://link.springer.com/article/10.1007/s11060-019-03104-3
- PMC. Prevalence and symptoms of incidental meningiomas: a population-based study. https://pmc.ncbi.nlm.nih.gov/articles/PMC11968542/
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