Stereotactic radiosurgery of angiographically occult vascular malformations: 14-year experience.

OBJECTIVE: Radiosurgery is generally effective in obliterating true arteriovenous malformations, but less is known about its effects on angiographically occult vascular malformations (AOVMs). Since July 1983, 57 patients with surgically inaccessible AOVMs of the brain were treated using helium ion (47 patients) or linear accelerator (10 patients) radiosurgery. This study retrospectively evaluates the response of these AOVMs to treatment. METHODS: All patients presented with previous hemorrhage. The mean patient age was 35.6 years (range, 13-71 yr). The mean AOVM volume was 2.25 cm3 (range, 0.080-15.2 cm3), treated with a mean of 18.0 Gy equivalent (physical dose x relative biological effectiveness, which is 1.3 for helium ion Bragg peak) (range, 7.0-40 Gy equivalent). The Drake scale scores before treatment were as follows: excellent (25 patients), good (26 patients), and poor (6 patients). The mean follow-up period was 7.5 years (range, 9 mo-13.8 yr). RESULTS: Eighteen patients (32%) bled symptomatically (20 hemorrhages) after radiosurgery. Sixteen hemorrhages occurred within 36 months after radiosurgery (9.4% annual bleed rate; 16 hemorrhages/171 patient yr); 4 hemorrhages occurred more than 36 months after treatment (1.6% annual bleed rate; 4 hemorrhages/257 patient yr) (P < 0.001). Complications included symptomatic radiation edema (four patients, 7%), necrosis (one patient, 2%), and increased seizure frequency (one patient, 2%). Eight patients underwent surgical resection of their AOVMs 8 to 59 months after radiosurgery because of subsequent hemorrhage. The Drake scale scores after treatment were as follows: excellent (25 patients), good (24 patients), poor (3 patients), and dead (5 patients, 3 of whom died as a result of causes unrelated to the AOVMs or radiosurgery). CONCLUSION: Radiosurgery may be useful for AOVMs located in surgically inaccessible regions of the brain. A significant decrease in bleed rate exists more than 3 years after treatment compared with the bleed rate within 3 years of treatment. Because current neuroradiological techniques are not able to image obliterative response in these slow-flow vascular lesions, longer term clinical follow-up is required.