The cause of cerebral arteriovenous malformation (AVM) is unknown. The condition occurs when, in the brain, one or more blood vessels develop in which the arteries connect directly to the veins, without having the normal capillaries between them.
Arteriovenous malformations vary in their size and location within the brain.
There are often no symptoms until complications occur, which involve rupture of the AVM and a resulting sudden bleed in the brain. Sudden bleeding in the brain is known as a hemorrhagic stroke, which is essentially what occurs when an AVM breaks. In more than half of patients with AVM, hemorrhage from the malformation is the first symptom. Depending on the location and the severity of the bleed, the hemorrhage can be profoundly disabling or fatal. The risk of bleeding from an AVM is approximately 2-4% per year. The first symptoms often include headache, seizure, or other sudden problems, such as vision problems, weakness, inability to move a limb or a side of the body, lack of sensation in part of the body, or abnormal sensations. Symptoms are the same as for stroke. After a hemorrhage, there is a risk of developing epilepsy. If an AVM bleeds once, the risk might be greater that it will bleed again. Intracerebral (in the brain) or subarachnoid (around the brain) hemorrhages are common with cerebral arteriovenous malformation.
In some cases, symptoms may also occur because of lack of blood flow to an area of the brain (ischemia), compression or distortion of brain tissue by large AVMs, or abnormal brain development in the area of the malformation. There may be a progressive loss of nerve cells in the brain caused by mechanical (pressure) and ischemic (lack of blood supply) factors. Cerebral arteriovenous malformations occurs in less than 1% of people. Although the condition is present at birth, symptoms may occur at any age. Hemorrhages occur most often in people aged 15-20, but can also occur later in life. Some patients harboring an AVM also have a cerebral aneurysm.
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