Stereotactic radiosurgery is a well established treatment option for arteriovenous malformations (AVMs). The potential complications related to radiosurgery are well documented and are predominately related to radiation effects to the surrounding brain parenchyma. These risks increase with larger lesions, requiring a concommitant reduction in the amount of radiation that can be delivered. This reduction in radiation dose decreases the efficacy of treatment. The broad, long-term objectives of this proposal are 1) to determine the role of fractionated stereotactic radiosurgery in the treatment of large (>10cc) AVMs; 2) to evaluate the complication rates related to fractionating these doses compared to conventional stereotactic treatment 3) to evaluate the success rate of treating large AVMs with this protocol.

This research project will involve performing a preoperative MRI and angiogram on patients harboring an AVM to determine the feasibility of treating the lesion with gamma knife radiosurgery. Patient with lesions greater than 10 cc will be studied.

Each patient will have a Magnetic resonance angiography (MRA) with gadolinium and an angiogram immediately before each radiation treatment. If there is a contraindication for MRI examination (pacemaker or any other implanted ferromagnetic material), a CT angiogram will be obtained instead. Each treatment will be spaced at least 3 months apart. Follow-up MRIs or CT scans will be obtained at 6 month intervals. A follow-up angiogram will be obtained when there is radiographic evidence of complete occlusion based on the MRI images, or at 3 years after the procedure, whichever occurs first.

Inclusion Criteria:

• All patients age 18 or older
• Inpatients and outpatients, referred for radiosurgical treatment of an arteriovenous malformation
• Patients with lesions greater than 10 cc, who are currently symptomatic from the AVM (hemorrhage, seizure, or ischemia from steal phenomenon)

Exclusion Criteria:

• Patients without symptoms related to AVM