by Steven Seung, M.D., Ph.D.
Generally benign tumors that only rarely undergo malignant transformation, meningiomas account for approximately 15% of all brain tumors. These tumors arise from the leptomeninges (tissue that serves as the lining of the brain). Because these tumors grow so slowly, they can sometimes become extremely large before being detected. MRI scanning is currently the best diagnostic tool for detecting and defining meningiomas.
Meningiomas are often diagnosed when a physician orders an MRI scan based on a patient's symptoms – such as seizures, focal weakness, sensory loss, or cranial nerve (including visual) disturbance. Because of the wide availability of advanced diagnostic imaging technology, many meningiomas are today discovered as "incidental" findings. It is not uncommon, for example, for a patient to be diagnosed with a meningioma following a CT scan for an unrelated brain trauma. If the tumor is small, it may be left untreated but followed with serial MRI or CT scans.
While open surgery has long been the standard treatment for large or symptomatic meningiomas, interest has recently surged in the use of stereotactic radiosurgery for this condition. Radiosurgery refers to the use of a single fraction of high dose radiation to precisely treat a target within the brain. No surgical incision is required, and therefore surgical risks such as hemorrhage, infection, cerebrospinal fluid leakage, etc., are markedly reduced. Radiation can control the growth of tumors by impairing cellular reproduction. Additionally, radiosurgery produces changes within the walls of the blood vessels that feed the tumor, and so the tumor's blood supply may be decreased over time.
Indications for treatment of meningiomas with radiosurgery continue to evolve. Most experts agree that smaller tumors (less than 3.0 to 3.5 cm average diameters) respond best to this form of treatment. Radiosurgery is the treatment of choice for small tumors involving the skull base (including those within the cavernous sinus) and those closely associated with the venous sinuses. Radiosurgery has proved to be a highly successful treatment for meningiomas with local control in the range of 90%. Thousands of meningioma patients have been treated with Gamma Knife radiosurgery worldwide. Larger tumors and those that can be resected easily, completely and with low morbidity (such as convexity meningiomas) are generally candidates for microsurgical resection. Of course, patient age, medical status and patient preference are important factors in any treatment decision. Additionally, observation may be recommended in elderly patients with asymptomatic tumors.
Meningiomas carry an excellent prognosis for many patients. Both radiosurgery and microsurgery represent acceptable treatment options for patients with meningiomas who require intervention.
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