Arteriovenous malformations vary greatly from person to person. The size varies, from massive lesions involving multiple vessels to lesions so small they are difficult to distinguish on testing. Large malformations may have enough blood flow through them to stress the pumping ability of the heart. There are often no symptoms until complications occur. In many cases, symptoms are related to bleeding from the abnormal vessels, which are often fragile and lack the normal supportive structure of arteries and veins.
Small lesions are more likely to bleed than large lesions.
If a lesion bleeds once, the risk is increased that it will bleed again in the future. Intracerebral hemorrhage and subarachnoid hemorrhage are the most common results of cerebral arteriovenous malformation. There may be a progressive loss of nerve cells in the brain caused by mechanical and ischemic factors. Hydrocephalus may develop and lead to symptoms. Cerebral arteriovenous malformations occur in approximately 3 out of 10,000 people.