A meningioma is a tumor that develops from the meninges, the protective layers of tissue surrounding the brain and spinal cord. As the most common primary tumor originating in the central nervous system, meningiomas account for approximately 37% of all such diagnoses in adults. The vast majority (80 to 90%) are classified as benign and grow very slowly. Because these tumors grow within the confined space of the skull, mortality, while uncommon, remains a possibility.
Distinguishing Benign from Malignant Tumors
Most meningiomas are designated as World Health Organization (WHO) Grade I, which reflects their benign status and slow cellular growth rate. These tumors are distinct from true malignant cancers because they do not typically metastasize, or spread, to other parts of the body. For the large population of patients with an asymptomatic Grade I meningioma, the prognosis is generally favorable, with many individuals living a normal lifespan. However, the designation “benign” can be misleading, as a tumor’s behavior is dictated more by its immediate surroundings than its cellular makeup.
Mechanisms of Life-Threatening Complications
A meningioma can become life-threatening not by spreading like cancer, but by the mechanical pressure it exerts on sensitive brain structures. The skull is a fixed space, and any growing mass within it increases the intracranial pressure (ICP). This pressure can lead to severe neurological symptoms and, ultimately, brain herniation, which is frequently fatal.
Compression of the brainstem, which controls involuntary functions like breathing and heart rate, is a particularly dangerous consequence of tumor growth. Tumors located at the skull base or near the brainstem pose an inherently higher risk because there is little margin for error in these functionally dense areas. The tumor mass can also disrupt the normal flow of cerebrospinal fluid (CSF), causing a buildup of fluid known as hydrocephalus, which further increases pressure inside the skull. A meningioma can also cause surrounding brain tissue to swell, a condition called cerebral edema. Additionally, a tumor may sometimes cause a fatal hemorrhage or precipitate intractable seizures that lead to death, even if the tumor itself is Grade I.
Classifying the Risk of Aggressive Growth
Not all meningiomas are slow-growing, and the risk of death increases significantly with higher grades assigned by the WHO classification system. The grading system predicts the tumor’s biological behavior and its likelihood of recurring after treatment. Grade I tumors are the most common and present the lowest risk of recurrence.
Atypical meningiomas, classified as Grade II, account for about 15 to 20% of cases and exhibit a faster growth rate and a greater chance of returning after initial removal. These tumors may also show evidence of brain invasion, indicating a more aggressive biological potential. The most concerning tumors are the rare Grade III, or anaplastic, meningiomas, representing only 1 to 4% of cases. Grade III tumors are considered malignant, behaving much like true cancers with rapid cell division and a high probability of invading the surrounding brain tissue. Patients diagnosed with an anaplastic meningioma face the highest risk of death due to the tumor’s aggressive nature and high propensity for recurrence.
Treatment Strategies for Risk Mitigation
The primary strategy for mitigating the risk posed by a meningioma is intervention tailored to the tumor’s size, grade, and location. For small, asymptomatic Grade I tumors, a strategy of “watchful waiting” with regular Magnetic Resonance Imaging (MRI) surveillance is often employed.
Surgical resection remains the optimal treatment for symptomatic or growing tumors, aiming for the complete removal of the mass to reduce pressure and minimize the chance of recurrence. Achieving a Gross Total Resection is particularly important for Grade I tumors, as the rate of recurrence is closely tied to the amount of tumor left behind. When a tumor is located near sensitive structures, such as at the skull base, a subtotal resection may be performed to decompress the brain while preserving neurological function. For tumors that cannot be fully removed or for higher-grade tumors (Grade II and Grade III), radiation therapy is used to stop or slow the growth of any remaining cells. Long-term follow-up with neuroimaging is necessary for all patients, as early detection of recurrence is paramount to effectively controlling the tumor and preventing life-threatening complications.