Arteriovenous malformations, also known as AVMs, are deficiencies of the cardiovascular system. In a normal functioning human body, arteries carry oxygen-rich blood away from the heart to the rest of the body, and veins return oxygen-depleted blood to the lungs and heart. An AVM interferes with this cyclical process. Instead of the gradual transition through the capillaries from arteries to veins that is typical of normal functioning vasculature, AVMs cause direct associations of the arteries and veins. AVMs can cause intense pain and lead to serious medical problems. Although AVMs are often associated with the brain and spinal cord, they can develop in any part of the body.
Symptoms of arteriovenous malformations, known as AVMs vary according to the location of the malformation. Roughly 88% of people affected with AVM are asymptomatic; often the malformation is discovered as part of an autopsy or during treatment of an unrelated disorder (called in medicine "an incidental finding"); in rare cases its expansion or a micro-bleed from an AVM in the brain can cause epilepsy, deficit or pain.
The most general symptoms of a cerebral AVM include headache and epilepsy, with more specific symptoms occurring that normally depend on the location of the malformation and the individual. Such possible symptoms include.
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CAUSES & RISK FACTORS
Arteries and veins are part of the human cardiovascular system. Normally, the arteries in the vascular system carry oxygen-rich blood, except in the case of the pulmonary artery. Structurally, arteries divide and sub-divide repeatedly, eventually forming a sponge-like capillary bed. Blood moves through the capillaries, giving up oxygen and taking up waste products, including CO2, from the surrounding cells. Capillaries in turn successively join together to form veins that carry blood away. The heart acts to pump blood through arteries and uptake the venous blood.
An AVM lacks the dampening effect of capillaries on the blood flow; it also causes the surrounding area to be deprived of the functions of the capillaries - removal of CO2 and delivery of nutrients to the cells. The resulting tangle of blood vessels, often called a nidus (Latin for "nest") has no capillaries and abnormally direct connections between high-pressure arteries and low-pressure veins. It can be extremely fragile and prone to bleeding. The resultant sign, audible via stethoscope, is a rhythmic, whooshing sound caused by excessively rapid blood flow through the arteries and veins. It has been given the term "bruit", French for noise. On some occasions a patient with a brain AVM may become aware of the noise, which can compromise hearing and interfere with sleep in addition to causing psychological distress.
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AVMs can occur in various parts of the body, including:
- Brain, causing a cerebral arteriovenous malformation
- Spinal cord
- Intercostal space
- Spermatic cord
AVMs may occur in isolation or as a part of another disease, e.g. Von Hippel-Lindau disease or hereditary hemorrhagic telangiectasia. AVM's have also been associated with Aortic Stenosis.
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Treatment can be symptomatic, or it can involve surgery or radiation therapy. Embolization, that is, cutting off the blood supply to the AVM with coils or particles or glue introduced by a radiographically guided catheter, can be used in addition to either, but is rarely successful in isolation except for in smaller AVMs.
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