Role of stereotactic radiosurgery in meningiomas and vestibular schwannomas
Intracranial meningiomas and vestibular schwannomas (VS, aka acoustic neuromas) are typically benign, slow-growing, non-invasive neoplasms. The imaging and radiobiologic characteristics of these tumors make them good candidates for stereotactic radiosurgery (SRS), a technique that has been in use for over three decades. Patient selection is critical for successful SRS: small- to moderate-sized tumors can be effectively treated with SRS if the patient does not have symptoms related to mass effect. Factors related to tumor control in meningioma SRS include histology, history of prior surgery, and volume. Tumor control rates after SRS is significantly lower for patients with WHO grade II or III meningiomas compared to patients with WHO grade I meningiomas. The risk of radiation-related complications is higher for patients with larger tumors and tumors located over the convexities or along the falx. Patients with small-volume non-operated skull base or tentorial WHO grade I meningiomas typically have the best outcomes after SRS. Radiosurgery of sporadic VS provides a high tumor control rate (92-95 %), with less than a 5 % risk of facial weakness. Hearing preservation progressively declines for 10 years or more after SRS, and the primary factors related to long-term preservation of useful hearing are tumor size and pre-SRS hearing class. Radiosurgery remains an important option for patients with neurofibromatosis type 2, but tumor control is lower and the risk of cranial nerve deficits is greater when compared to patients with sporadic VS.