Arteriovenous Malformations (AVM's)

Arteriovenous malformations are groups of abnormal vessels which may occur within the brain and other parts of the body. Arteries are the vessels that supply oxygen-rich blood to the brain and all other organs in the body. There are four major arteries that supply blood to the brain, the two carotid arteries in the front of the neck and the two vertebral arteries in the back of the neck. Blood is pumped from the heart to the brain through these four major arteries at a relatively high pressure. As the blood flow reaches the smaller vessels within the brain, called capillaries, it exchanges the oxygen and nutrients for carbon dioxide and other waste products, and then returns to the heart and lungs at a much lower level of pressure. Because of this lower pressure, veins have characteristically thinner walls and are much more delicate than arteries.

AVM's develop when there are abnormal communications that directly connect relatively large arteries to veins; thus, the blood is exchanged at a relatively higher pressure with more rapid flow directly into the veins. This unusual connection between arteries and veins is called a nidus. The anatomy of the vein is not designed to take the higher pressures and flow; thus, it expands and pushes against the normal brain tissue. This may damage the normal brain causing weakness, numbness, loss of vision, or seizures. Often there is a rupture in the supplying arteries, the AVM itself, or the enlarged veins which results in an intracranial hemorrhage, which is a type of stroke.

Reference material courtesy of the American Society of Interventional & Therapeutic Neuroradiology

The goal of treating an AVM is to occlude the communicating channels of the nidus to prevent the enlargement of the collateral circulation from supplying the nidus with blood flow. The process to occlude an AVM's blood flow is called embolization. Multiple embolizations may be required to fully treat an AVM. AVM's affect only a small percentage of the general population, about .02% - .05%, but early treatment is critical in pursuing positive patient outcomes.

Embolization of cerebral AVM's is usually done by an Interventional Neuroradiologist (INR) who uses small catheters and guide wires within the blood vessels to approach the location of the AVM. The IR is able to use X-ray imaging as the "map" to guide him/her to the AVM. Once the IR has located the area of the AVM, small spheres are injected through the microcatheter into the blood flow directly feeding the AVM. The microspheres block the arteries to the nidus, which may prevent the AVM from rupturing.

Vascular Malformations of the Head and Neck
Vascular malformations are not tumors but rather abnormal vessels that allow direct communication between arteries and veins. Vascular malformations can be found in many different locations in the body, including the brain, head and neck. These malformations are usually present at birth but may grow over time and typically produce symptoms due to bleeding or pressure on normal adjacent structures (seizures, pain, deformity of the face including the tongue, lips and eyelids). Vascular malformations are often embolized prior to surgery. In some cases vascular malformations are embolized prior to radiation therapy in order to reduce the malformation to a treatable size. Some types of vascular malformations may also be cured by embolization alone.

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Other Brain AVM Information for Patients and Families