A brain arteriovenous malformation (AVM) is a tangle of abnormal blood vessels connecting arteries and veins in the brain. The arteries are responsible for taking oxygen-rich blood from the heart to the brain. Veins carry the oxygen-depleted blood back to the lungs and heart. A brain AVM disrupts this vital process. This may not cause any signs or symptoms until the AVM ruptures, resulting in bleeding in the brain (haemorrhage). In about half of all brain AVMs, haemorrhage is the first signs. Some people may experience signs and symptoms other than bleeding signs; these may include, seizures, headache or pain in one area of the head, muscle weakness or numbness in one part of the body. Some people may experience more-serious neurological signs and symptoms, depending on the location of the AVM, including, severe headache, weakness, numbness or paralysis, vision loss, difficulty speaking, confusion or inability to understand others and severe unsteadiness.