An arteriovenous malformation (AVM) is an abnormal connection between arteries and veins that bypasses the usual method of connection, the capillary system. It can occur pretty much anywhere but is often observed in the Central Nervous System (usually as cerebral AVMs). The majority of people with an AVM are asymptomatic (i.e. they are carrying the disease or disorder but have not presented with any symptoms of the disease / disorder).
However, cerebral AVMs can present themselves in a number of different ways especially bleeding, severe headaches and a seizure or brain seizure. Bleeding from an AVM can be devastating and can cause severe, sometimes fatal, strokes.