Arteriovenous malformations (AVMs) are defects of the circulatory system that are generally believed to arise during embryonic or fetal development or soon after birth. Although AVMs can develop in many different sites, those located in the brain or spinal cord can have especially widespread effects on the body. Most people with neurological AVMs experience few, if any, significant symptoms. The malformations tend to be discovered only incidentally, usually either at autopsy or during treatment for an unrelated disorder. But for about 12 percent of the affected population (about 36,000 of the estimated 300,000 Americans with AVMs), these abnormalities cause symptoms that vary greatly in severity.
AVMs are lesions of the vasculature that develop such that blood flows directly from the arterial system to the venous system without passing through a capillary system.
An Arterio-Venous Malformation, or AVM, is an abnormal collection of blood vessels. Normally, oxygenated blood is pumped by the heart through branching tubes called arteries to the brain, where it enters a fine network of tiny vessels called capillaries. It is in these capillary beds where the blood nourishes the tissues. The “used” (deoxygenated) blood then passes back to the heart through branching thin walled tubes called veins. Arterial-Venous Malformations are areas that lack the tiny capillaries. The location of the connection between the artery and the vein is called the shunt. The area of tissue is called a nidus of the AVM. An AVM can be thought of as a “Short Circuit” where the blood does not go to the tissues but is pumped through the shunt and back to the heart without ever giving nutrients to the tissues.