Natural history of brain arteriovenous malformations: systematic review

INTRODUCTION: The appropriate interpretation of natural history of brain arteriovenous malformations (bAVMs) and of factors that negatively affect the risk of future hemorrhage are important when recommending management pathways. With the present systematic review, we aim to provide an overview of the available evidence on natural history of brain arteriovenous malformations (bAVMs), focusing on hemorrhage rates and risk factors for future hemorrhage. EVIDENCE ACQUISITION: We performed a systematic literature analysis using the Ovid Medline database, encompassing English language studies (published between 1980 and 2018) reporting the natural history of untreated bAVMs. Annual hemorrhage rates in both unruptured and previously ruptured bAVMs, as well as risk factors for future hemorrhage were extracted for analysis. EVIDENCE SYNTHESIS: Eighteen studies with a total of 8418 bAVM-cases could be extracted from the literature. Seventeen studies reported annual hemorrhage rates and ten studies reported risk factors for future hemorrhage. The average annualized hemorrhage rate was 2.2% for unruptured bAVMs and 4.3%, for bAVMs that presented with hemorrhage. Prior hemorrhage and deep AVM location could be identified as most consistently reported risk factors for future hemorrhage. CONCLUSIONS: Previously ruptured bAVMs have a higher annual hemorrhage rate than unruptured bAVMs. Deep bAVM location and prior hemorrhage may increase the risk for subsequent hemorrhage.