J Neurosurg / Volume 121 / August 2014 J Neurosurg 121:457–467, 2014 457 ©AANS, 2014 A rteriovenous malformations (AVMs) are among the most complex intracranial vascular patholo- gies and are associated with wide variations in clinical presentation, location, size, and angioarchitec- ture. 5 There is a paucity of prospective, multicenter data regarding the natural history of and long-term treatment outcomes for AVMs, owing to their rarity. Therefore, AVMs continue to represent a signifcant challenge to the cerebrovascular community, and opinions differ regarding the optimal management of these lesions. 6,9,41,42 A num- ber of AVM grading systems have been developed over the years with the ultimate goal of predicting treatment outcomes based on AVM subgroup. 19,30,40,43,49 For surgical planning, however, no classifcation is more widely used than the Spetzler-Martin (SM) grading scale because of its simplicity and reliability in predicting microsurgical AVM outcomes. 40 Based on the composition of the Spetzler-Martin grad- ing scale, Grade I and II, or low-grade, AVMs are typically small, drain into the superfcial venous system, and are lo- cated in noneloquent cortex. Despite having decreased rates of microsurgical morbidity compared with their higher- grade counterparts, low-grade AVMs have not been defni- tively shown to have more benign natural histories. 12,23 In fact, small AVMs may be more prone to hemorrhage than larger ones as a result of higher pressures in the feeding Radiosurgery for low-grade intracranial arteriovenous malformations Clinical article Dale Ding, M.D., Chun-Po Yen, M.D., ZhiYuan Xu, M.D., RobeRt M. StaRke, M.D., M.SC., anD JaSon P. Sheehan, M.D., Ph.D. Department of Neurological Surgery, University of Virginia, Charlottesville, Virginia Object. Low-grade, or Spetzler-Martin (SM) Grades I and II, arteriovenous malformations (AVMs) are associ- ated with lower surgical morbidity rates than higher-grade lesions. While radiosurgery is now widely accepted as an effective treatment approach for AVMs, the risks and benefts of the procedure for low-grade AVMs, as compared with microsurgery, remain poorly understood. The authors of this study present the outcomes for a large cohort of low-grade AVMs treated with radiosurgery. Methods. From an institutional radiosurgery database comprising approximately 1450 AVM cases, all patients with SM Grade I and II lesions were identifed. Patients with less than 2 years of radiological follow-up, except those with complete AVM obliteration, were excluded from analysis. Univariate and multivariate Cox proportional-hazards and logistic regression analyses were used to determine factors associated with obliteration, radiation-induced chang- es (RICs), and hemorrhage following radiosurgery. Results. Five hundred two patients harboring low-grade AVMs were eligible for analysis. The median age was 35 years, 50% of patients were male, and the most common presentation was hemorrhage (47%). The median AVM volume and prescription dose were 2.4 cm 3 and 23 Gy, respectively. The median radiological and clinical follow- up intervals were 48 and 62 months, respectively. The cumulative obliteration rate was 76%. The median time to obliteration was 40 months, and the actuarial obliteration rates were 66% and 80% at 5 and 10 years, respectively. Independent predictors of obliteration were no preradiosurgery embolization (p < 0.001), decreased AVM volume (p = 0.005), single draining vein (p = 0.013), lower radiosurgery-based AVM scale score (p = 0.016), and lower Vir- ginia Radiosurgery AVM Scale (Virginia RAS) score (p = 0.001). The annual postradiosurgery hemorrhage rate was 1.4% with increased AVM volume (p = 0.034) and lower prescription dose (p = 0.006) as independent predictors. Symptomatic and permanent RICs were observed in 8.2% and 1.4% of patients, respectively. No preradiosurgery hemorrhage (p = 0.011), a decreased prescription dose (p = 0.038), and a higher Virginia RAS score (p = 0.001) were independently associated with postradiosurgery RICs. Conclusions. Spetzler-Martin Grade I and II AVMs are very amenable to successful treatment with stereotactic radiosurgery. While patient, physician, and institutional preferences frequently dictate the fnal course of treatment, radiosurgery offers a favorable risk-to-beneft profle for the management of low-grade AVMs. (http://thejns.org/doi/abs/10.3171/2014.1.JNS131713) keY WoRDS • intracranial arteriovenous malformation • stroke • low Spetzler-Martin grade • Gamma Knife • vascular malformation • vascular disorders • stereotactic radiosurgery 457 Abbreviations used in this paper: AVM = arteriovenous mal- formation; DSA = digital subtraction angiography; RBAS = radio- surgery-based AVM scale; RIC = radiation-induced change; SM = Spetzler-Martin; Virginia RAS = Virginia Radiosurgery AVM Scale.