A recent study published in the Journal of the American Medical Association found that the risk of a first intracranial hemorrhage (ICH) from unruptured brain arteriovenous malformations (AVMs) is significantly lower than traditionally believed. The Multicenter Arteriovenous Malformation Research Study (MARS) from 2017 to 2023 across 9 major international cohorts, reports an annual hemorrhage rate of just 1.4%, challenging the widely cited 2–4% figure used in clinical settings for decades.

AVMs are often detected incidentally or following neurological symptoms such as seizures. While rupture can lead to life-threatening bleeding, treatment decisions have long been hampered by uncertainty over the natural risk of bleeding in unruptured cases.

The MARS project combined data from 2 popula

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