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Arteriovenous malformations are abnormal collections of blood vessels, where arteries are directly connected to veins. Normally blood flows through arteries under high pressure to supply all of the organs of the body including the brain. From the arteries, blood passes through thin-walled capillaries to supply oxygen and nutrients to the tissue of the brain and then enters the veins under low pressure to be carried back to the heart and lungs.
In an AVM, the blood flows from the arteries directly to the veins. There is no capillary bed. Without a capillary bed, the AVM blood vessels have an increase in flow and blood pressure. Over the years this causes them to dilate and become thin-walled, and more likely to break and bleed. Also, because there are no capillaries in AVMs, these abnormal blood vessels are not supplying oxygen and nutrients to normal brain tissue. AVMs are thought to be present at birth, but become symptomatic when blood pressure and flow increases. AVMs are usually not inherited and other members of the family are generally not at increased risk for having an AVM.
An AVM can cause headache, weakness, numbness, visual problems, or seizures. Patients often first show symptoms when there is a bleed or rupture from one of the blood vessels making up the AVM.
An AVM is often diagnosed with a CT (computed tomography) scan or MRI (magnetic resonance imaging). A patient usually requires an angiogram to then fully identify the anatomy of the AVM and make decisions about treatment.
AVMs may be treated using three different treatment methods. These methods are embolization, surgery and radiation therapy or radiosurgery. Often more than one method or modality is used to treat the same AVM because the combination of techniques may prove safer or more successful than one technique alone.
Surgery is done by opening the skull and removing the blood vessels that make up the AVM. This is done using an operating microscope and is called microsurgery. Radiosurgery uses beams of focused radiation to injure the blood vessels of the AVM and cause them to close off over time. Embolization is performed by placing a tiny catheter directly into the AVM vessels within the brain. A glue-type (embolic) material is then injected into the abnormal blood vessel to block them up.
The embolic material leaves the catheter as liquid and solidifies within the AVM blood vessel to block it up. Embolization of an AVM is often done before microsurgery or radiosurgery to help improve the likelihood these techniques will be successful.
Angiogram from a patient with an AVM (pointed out by blue arrows). The patient had suffered a bleed from this AVM. A decision was made to use embolization followed by radiosurgery to treat the patient's AVM.
Angiogram performed after the patient had both embolization and radiosurgery, showing the AVM has been completely eradicated.