STEREOTACTIC RADIOSURGERY OF ANGIOGRAPHICALLY OCCULT VASCULAR MALFORMATIONS - 14-YEAR EXPERIENCE

OBJECTIVE: Radiosurgery is generally effective in obliterating true ar teriovenous malformations, but less is known about its effects on angi ographically occult vascular malformations (AOVMs). Since July 1983, 5 7 patients with surgically inaccessible AOVMs of the brain were treate d using helium ion (47 patients) or linear accelerator (10 patients) r adiosurgery. This study retrospectively evaluates the response of thes e AOVMs to treatment. METHODS: All patients presented with previous he morrhage. The mean patient age was 35.6 years (range, 13-71 yr). The m ean AOVM volume was 2.25 cm(3) (range, 0.080-15.2 cm(3)), treated with a mean of 18.0 Gy equivalent (physical dose x relative biological eff ectiveness, 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). Th e mean follow-up period was 7.5 years (range, 9 mo-13.8 yr). RESULTS: Eighteen patients (32%) bled symptomatically (20 hemorrhages) after ra diosurgery. Sixteen hemorrhages occurred within 36 months after radios urgery (9.4% annual bleed rate; 16 hemorrhages/171 patient yr); 4 hemo rrhages occurred more than 36 months after treatment (1.6% annual blee d rate; 4 hemorrhages/257 patient yr) (P < 0.001). Complications inclu ded symptomatic radiation edema (four patients, 7%), necrosis (one pat ient, 2%), and increased seizure frequency (one patient, 2%). Eight pa tients underwent surgical resection of their AOVMs 8 to 59 months afte r radiosurgery because of subsequent hemorrhage. The Drake scale score s after treatment were as follows: excellent (25 patients), good (24 p atients), 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 inaccessib le regions of the brain. A significant decrease in bleed rate exists m ore 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 le sions, longer term clinical follow-up is required.