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Arteriovenous malformations
Background
An arteriovenous malformation (AVM) is a tangled web of abnormal arteries and veins connected by fistulas (abnormal corridors). AVMs are thought to be present from birth and most commonly occur in the brain. AVMs can also occur in the spine, lungs, kidney, skin and, very rarely, limbs. Because some AVMs do not result in symptoms, the exact incidence is not known. AVMs of the brain that are detected are found in about 1 in 100,000 of the general population per year. AVMs affect both sexes and all ethnic groups.
Normally, oxygenated blood is carried by arteries to body tissues through ever smaller blood vessels. The smallest blood vessels are called capillaries and form the capillary bed which is where the exchange of oxygen and nutrients for carbon dioxide and other waste products produced by the body cells (cellular wastes) takes place. Following this exchange, the blood is carried away by progressively larger blood vessels, the veins. Because AVMs lack a capillary bed, arterial blood is shunted directly from the arteries into the veins via direct communications called fistulas.
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