Computed tomography (CT) angiogram scan of the head of a 38 year old male patient who has an arteriovenous malformation (AVM, upper centre) in his brain. An AVM is an abnormal blood vessel arrangement. This AVM is supplied by one or more branches of the left sylvian artery and drains to the superior sagittal sinus. Most AVMs are asymptomatic, but some can bleed causing symptoms including headache, visual disturbance, muscle weakness or seizures.