A sterile, non-bioabsorbable, material (e.g., gel, liquid) intended to be implanted in a neurovascular blood vessel, to obstruct blood flow to treat a brain arteriovenous malformation (bAVM). It may be supplied as a liquid [e.g., ethylene vinyl alcohol (EVOH)], gel or powder intended to solidify or expand in situ to create a barrier to blood flow (embolus); it contains no pharmaceutical agents. It may be supplied with dedicated instruments for implantation.