The Natural History of Hemorrhage in Brain Arteriovenous Malformations—Poisson Regression Analysis of 1066 Patients in a Single Institution

BACKGROUND AND OBJECTIVES: Natural history of hemorrhage in brain arteriovenous malformations (bAVM) is reported at 2%–4% per year. Published studies using survival analysis fail to account for recurrent hemorrhagic events. In this study, we present a large, single institution series to elucidate the natural history of bAVM using multivariable Poisson regression. METHODS: This is a retrospective cohort study. All patients with bAVM seen at our institution from 1990 to 2021 were included. Hemorrhages after detection of bAVM during the untreated interval were recorded. Natural history of hemorrhage was calculated by dividing number of hemorrhages by untreated interval. The frequency of hemorrhages followed a Poisson distribution. Multivariable Poisson regression with an offset variable of untreated interval in patient-years was constructed. Model selection was through a stepwise Akaike information criterion method. Stratified hemorrhagic rate was presented using different combinations of significant factors. RESULTS: A total of 1066 patients with nonhereditary hemorrhagic telangiectasia harboring a single bAVM were included. Ninety (8.44%) patients had 101 hemorrhages during an untreated interval of 3596.3344 patient-years, translating to an overall hemorrhagic rate of 2.81% per year. Significant factors increasing hemorrhage risk included ruptured presentation ( P < .001), increasing age ( P < .001), female sex ( P = .043), and deep location ( P = .040). Adult male patients with ruptured presentation and deep bAVMs sustained the highest annual risk at 10.81%, whereas no hemorrhages occurred in unruptured pediatric male patients or ruptured pediatric (younger than 18 years) male patients with superficial bAVMs. CONCLUSION: Hemorrhage after bAVM detection occurs in 8.41% of all patients, and the rate averages 2.81% per year. However, this risk varies from 0.00% to 10.81% per year depending on various risk factor combinations. Efforts should be made to stratify bAVM hemorrhage rate by risk factors for more precise estimation of bleeding risk if left untreated.