Introduction: Liquid embolic agents are extensively used in the endovascular treatment of brain arteriovenous malformations (AVM). Yet, little is known regarding their effectiveness, particularly occlusion rates and factors affecting these rates following embolization. We conducted a systematic review of the literature to answer these questions.

Methods: We systematically reviewed PubMed and Cochrane databases. We included articles reporting on primary endovascular treatment of AVMs with embolic agents in adults. We excluded articles covering other endovascular treatments of brain arteriovenous malformations and those reporting on embolization of arteriovenous fistulae. We also excluded reviews, case reports, technical notes and animal studies. We stratified collected data by level of evidence as defined by the American Heart Association. The primary outcome was the total occlusion rate. Secondary outcomes were morbidity, mortality and hemorrhage rates related to embolization.

Results: A total of 2994 articles were retrieved. Of those, 829 met the inclusion criteria and were screened by title and abstract. We identified 2 meta-analyses (level I), 2 randomized controlled trials (level II), and 25 case series (level III). Occlusion rates for embolization ranged from 16 to 100% in the Onyx group and from 7.4 to 77% in the n-BCA group. AVM size was the single most determining factor of occlusion after embolization with smaller AVMs demonstrating higher occlusion rates for both embolic agents. Other factors that were associated with higher occlusion rates include superficial venous drainage, compact nidus and large arterial feeders. Mortality and morbidity data varied considerably between studies.

Conclusions: Smaller AVMs are associated with higher occlusion rate for both embolic agents. Morbidity, mortality and hemorrhage rates vary considerably between the studies. Comparison among studies was hindered by methodological heterogeneity.

Patient Care: The goal of this study is to determine factors that enhance occlusion rates in AVMs treated using endovascular embolization. Quantifying these factors would allow to better direct treatment,

Learning Objectives: AVM size, superficial venous drainage, compact nidus and large arterial feeders lead to enhanced occlusion rates after AVM embolization.

References: 1. Gibbons RJ, Smith S, Antman E, American College of C, American Heart A. American College of Cardiology/American Heart Association clinical practice guidelines: Part I: where do they come from? Circulation. 2003;107(23):2979-86. 2. Panagiotopoulos V, Gizewski E, Asgari S, Regel J, Forsting M, Wanke I. Embolization of intracranial arteriovenous malformations with ethylene-vinyl alcohol copolymer (Onyx). AJNR American journal of neuroradiology. 2009;30(1):99-106. 3. Frizzel RT, Fisher WS, 3rd. Cure, morbidity, and mortality associated with embolization of brain arteriovenous malformations: a review of 1246 patients in 32 series over a 35-year period. Neurosurgery. 1995;37(6):1031-9; discussion 9-40.