HEMORRHAGE RISK AFTER STEREOTAXIC RADIOSURGERY OF CEREBRAL ARTERIOVENOUS-MALFORMATIONS

TO ANALYZE THE effect of stereotactic radiosurgery on the hemorrhage r ate of arteriovenous malformations (AVMs), we reviewed the clinical an d angiographic characteristics of 315 patients with AVMs before and af ter radiosurgery. One hundred ninety-six patients sustained 263 bleeds in 10,939 patient-years before radiosurgery, for an annual nonfatal h emorrhage rate of 2.4%. Clinical follow-up after radiosurgery was avai lable in 312 patients (mean, 47 +/- 20 mo); follow-up greater than or equal to 24 months was obtained in 295 patients (94%). Twenty-one pati ents had AVM bleeds at a median of 8 months (range, 1-60 mo) after rad iosurgery. Two additional patients had three aneurysmal bleeds (at 5, 27, and 32 mo, respectively) for a 7.4% total risk of hemorrhage per p atient. The actuarial hemorrhage rate until AVM obliteration was 4.8% per year (95% confidence interval, 2.4-7.0%) during the first 2 years after radiosurgery and 5.0% per year (95% confidence interval, 2.3-7.3 %) for the third to fifth years after radiosurgery. Multivariate analy sis of clinical and angiographic factors demonstrated that the presenc e of an unsecured proximal aneurysm was associated with an increased r isk of postradiosurgical hemorrhage (relative risk, 4.56; 95% confiden ce interval, 1.77-11.70%; P < 0.001). No AVM hemorrhages were observed after radiosurgery in seven patients with intranidal aneurysms. No pr otective effect against hemorrhage was observed in patients who receiv ed an ''optimal'' radiation dose (greater than or equal to 25 Cy to th e AVM margin) compared with patients who received <25 Gy to the AVM ma rgin (P = 0.36). No patient suffered a hemorrhage after angiography ha d confirmed complete obliteration (n = 140) or suffered from an early draining vein without residual nidus (n = 19). Stereotactic radiosurge ry was not associated with a significant change in the hemorrhage rate of AVMs during the latency interval before obliteration. No protectiv e benefit was conferred on patients who had incomplete nidus obliterat ion in early (<60 mo) follow-up after radiosurgery. AVM patients with unsecured proximal aneurysms should have aneurysms obliterated either before radiosurgery or at the time of surgical resection of their AVMs .