Brain bleed risk from unruptured arteriovenous malformations lower than previously thought

The annual incidence of intracranial haemorrhage from an unruptured arteriovenous malformation (AVM) appears to be lower than current clinical estimates, according to the Multicenter Arteriovenous Malformation Research Study.

Researchers used data from nine cohorts, with each cohort having at least 100 unruptured brain AVMs. Of the cohorts, two were population-based and seven were referral-based. The primary outcome was time to first ICH after diagnosis of unruptured brain AVM.

The analysis included 3,030 participants (median age 38 years, 50.3 percent female). Most of them presented with seizure (45 percent). The median maximal brain AVM diameter was 3.1 cm, and 10 percent of AVMs had exclusively deep venous drainage, 11 percent were in supratentorial deep or cerebellar locations, and 19 percent had associated arterial aneurysms. The mean follow-up duration was 3.74 years.

A first ICH was documented in 159 participants over 11,339 person-years of follow-up. The corresponding ICH rate was 1.40 (95 percent confidence interval [CI], 1.20–1.64) per 100 person-years.

Factors associated with ICH risk included increasing age at diagnosis (20–39 vs <20 years: hazard ratio [HR], 0.87, 95 percent CI, 0.53–1.41; 40–59 vs <20 years: HR, 1.23, 95 percent CI, 0.74–2.04; ≥60 vs <20 years: HR, 2.01, 95 percent CI, 1.14–3.57; p=0.008), presence of associated aneurysms (HR, 1.66, 95 percent CI, 1.06–2.59; p=0.03), and cerebellar or supratentorial deep location (HR, 1.87, 95 percent CI, 1.16–3.00; p=0.01).

These findings may be used to better inform patients about the natural history of unruptured brain AVMs, the researchers said.