Meningioma
A meningioma is a tumor that arises from the meninges—the protective membranes covering the brain and spinal cord. These are the most common primary brain tumors in adults, accounting for approximately 30-40% of all intracranial tumors. While the vast majority of meningiomas are benign (non-cancerous) and slow-growing, they can cause significant symptoms by compressing adjacent brain structures. They occur more frequently in women and their incidence increases with age, particularly after age 40.
What is it?
Meningiomas originate from arachnoid cap cells within the arachnoid layer of the meninges, the three-layered membrane system (dura mater, arachnoid mater, and pia mater) that envelops the brain and spinal cord. These tumors grow slowly outward from the meningeal surface and typically remain attached to the dura. While they arise from the coverings rather than from brain tissue itself, they are considered intracranial tumors because they grow within the skull. Approximately 90% of meningiomas are classified as WHO Grade I (benign), 5-7% as Grade II (atypical), and 1-3% as Grade III (anaplastic or malignant).
Meningiomas can occur anywhere along the brain or spinal cord where meninges are present, but are most commonly found along the convexity of the brain (the outer surface), at the skull base, along the falx cerebri (the membrane between the two hemispheres), or near the optic nerve sheath. Spinal meningiomas, which account for about 25% of all spinal tumors, most often occur in the thoracic spine. Risk factors include prior radiation exposure to the head, certain genetic conditions such as neurofibromatosis type 2 (NF2), and female gender—the female-to-male ratio is approximately 2:1, possibly related to hormonal factors including progesterone receptors on tumor cells.
Important to Know
Many meningiomas are discovered incidentally during brain imaging performed for other reasons and may never cause symptoms, particularly if they are small and slow-growing. When symptoms do occur, they result from compression of adjacent brain structures rather than invasion, and vary depending on location. Common symptoms include headaches, seizures (especially with convexity meningiomas), vision changes (with optic nerve or cavernous sinus meningiomas), hearing loss or facial numbness (with cerebellopontine angle meningiomas), and weakness or numbness (with parasagittal or falx meningiomas). Diagnosis is typically made with contrast-enhanced MRI, which shows characteristic features including a well-defined, extra-axial mass with a “dural tail” (thickening of the adjacent dura). Treatment options depend on tumor size, location, growth rate, and symptoms. Small, asymptomatic meningiomas may be monitored with serial imaging. Symptomatic or growing tumors are typically treated with surgical resection when feasible, with the goal of complete removal to minimize recurrence risk. Radiation therapy, including stereotactic radiosurgery, may be used for tumors in surgically inaccessible locations, for incomplete resections, or for atypical/malignant variants. The prognosis for benign meningiomas is generally excellent, with 5-year recurrence rates of approximately 5-15% after complete surgical resection.