Arteriovenous malformations (also called high-flow AVMs) are vascular malformations, which consist of an abnormal tangle of interconnected arteries and veins in the brain. AVMs are thought to form during fetal development and occur in less than 1 percent of the population.
AVMs can cause seizures and stroke-like problems, but bleeding is the most common and feared symptom. Bleeding from AVMs usually takes the form of an intracerebral hemorrhage, but a subarachnoid hemorrhage can also result. When a patient's history or clinical presentation suggests an AVM, a CT or MRI scan will usually confirm the presence of the lesion and show its exact location. An angiogram will provide a more detailed structural understanding of the AVM, and is essential to planning any AVM treatment. Using an angiogram, doctors inject a local anesthetic into the groin and insert very thin tubing into the arteries. A dye is then injected into the tube. As the dye travels through the arteries, it makes them visible on X-rays, allowing doctors to see whether the arteries are blocked.
Microsurgery: Microsurgery uses precision surgical techniques, under high magnification, and sometimes with computerized guidance, to remove the AVM. One of the major advantages of microsurgery is that it can result in an immediate cure. However, some lesions may be too large, too deep, or located in an area of the brain that is not accessible to safe microsurgical excision. In such cases, other treatments may be necessary. Endovascular surgery: During endovascular surgery, specially designed microcatheters are navigated by means of an angiogram into the AVM. The lesion is then treated from the inside, with either particles or glue, using a process called embolization. Although very effective in reducing the size of an AVM, endovascular embolization cures only the smallest AVMs. Therefore, endovascular therapy is usually combined with either microsurgery or stereotactic radiosurgery to give the best chance of a cure. Stereotactic radiosurgery: Stereotactic radiosurgery delivers a highly focused beam of radiation to the AVM. The two most common forms of radiosurgery are linear accelerator-based radiosurgery (also known as LINAC or photon knife) and gamma ray-based radiosurgery (gamma knife). For patients with AVMs that are deep or located in important areas of the brain, radiosurgery may be less risky when compared to microsurgery. However, the ability of conventional radiosurgery to cure an AVM drops off sharply as the AVM diameter goes above 2.5 cm (1 inch). With radiosurgery, a cure is not immediate, and may take up to two or three years. During this time, the patient may require follow-up tests and will still be at risk for problems. For these reasons, radiosurgery is especially appropriate for small, deep lesions located in or near critical brain areas. Multidisciplinary Treatment Many AVMs treated at Lahey Clinic require more than one form of treatment, so our staff takes a multidisciplinary approach to the evaluation and treatment of patients with these lesions. Complex cases are reviewed at a conference with professionals from all the major treatment areas. After careful consideration, an individualized treatment plan is developed, often using a combination of microsurgery, endovascular surgery and stereotactic radiosurgery to achieve a complete cure.