- Progressive or disabling signs and symptoms as determined by the study investigators. In the case of sporadic bAVM, these would be referable to the lesion, e.g., progressive neurological deficits, refractory headaches and seizures; for HHT patients, bAVM may be asymptomatic, but patient must have one progressively symptomatic manifestation of HHT that is referable to a vascular lesion, e.g., epistaxis, GI bleeding; or another solid organ AVM