Arteriovenous Malformations
What is an Arteriovenous Malformation?
An arteriovenous malformation is an abnormal cluster of blood vessels in the brain or spine. The abnormal condition occurs when arteries in the brain connect directly to nearby veins without using the normal vessels (capillaries) between them. Arteriovenous malformations vary in size and location in the brain. cause of cerebral arteriovenous malformations (AVMs) is unknown, according to the National Institutes of Health (NIH). Dural AVMs occur in the covering of the brain, and are an acquired disorder that may be triggered by an injury.
What are the symptoms of AVMs?
Those with an AVM run the risk of it rupturing at a rate of 2 to 4% per year cumulatively, which can occur for a variety of reasons. Approximately half of those with AVMs will experience a hemorrhagic stroke as their first symptom; other symptoms may also occur when large AVMs that have not bled press on the surrounding brain tissue. These symptoms include terrible headaches and dizziness, ear buzzing, difficulty walking, and all kinds of seizures. Symptoms caused by pressure on one part or area of the brain include blurred, decreased, or double vision, dizziness, muscle weakness in any part of the body or face, or numbness at any part of the body or face. Cerebral AVMs occur in less than 1% of the population, and while the condition is present at birth, symptoms may occur at any age. For example, hemorrhages occur most often in people ages 15 to 20, but can also occur later in life.
How is an AVM diagnosed?
AVMs can be detected with a cranial MRI, an electroencephalogram (EEG), head CT scan, magnetic resonance angiography (MRA), and by cerebral angiographies. Physicians use the Spetzler-Martin grading system to classify AVMs into six types based on size, pattern of venous drainage, and the neurological eloquence of the adjacent brain. The Spetzler-Martin grading system is widely accepted worldwide as a simple, useful tool for assessing the pre-treatment risks and predicting the potential outcome of surgery for patients with intracranial AVMs. According to the classification, “[g]rade I malformations are small, superficial, and located in non-eloquent cortex; Grade V lesions are large, deep, and situated in neurologically critical areas; and Grade VI lesions are essentially inoperable AVMs.” Thus, the higher the grade an AVM is, the more difficult it is to operate, and the higher the general risk is associated with it.
How is an AVM treated?
Your doctor will select the appropriate treatment according to the classification of AVM based on a variety of factors, such as location, size, and drainage of the AVM, as well as the patient’s age, risk for complications, and overall health. There are three treatment options for AVMs: surgery, stereotactic radiosurgery (CyberKnife, Gamma Knife), and endovascular therapy; some AVMs require combined therapies.
Surgical removal (or resection) entails a highly skilled surgeon physically removing the AVM through an opening made in the skull.The patient may undergo the operation while unconscious, or the doctor may opt to keep the patient awake (but anesthetized, of course!). The doctor will ask the patient questions to ensure that he or she is not cutting into very important areas of the brain that might control speech or movement.
Stereotactic Radiosurgery (SRS) is the recommended treatment for a specific number of AVMs that are difficult to reach due to their location in the brain, particularly for those small AVMs located deep in the brain. CyberKnife and Gamma Knife deliver radiation directly to the AVM, occluding (or blocking off) the vessels, causing scarring and shrinkage, and eventually stopping the blood flow. When the AVM is 3 cm or less in diameter, Dr. Berti may opt for radiosurgery, depending on the position in the brain. SRS will deliver rays through the volumes treated and will change the nature of the DNA by the cells within target, and in the case of tumors not allow to them to grow any more. In the case of AVMs, CyberKnife and Gamma Knife produce an increase in the number of cells within the vessels, also known as hyperplasia, to the point that they become occluded, stopping the blood flow through them. SRS protects patients from hemorrhages that occur from AVMs once all the AVM is occluded. Children and youth may have a recurrence of AVMs under the age of nineteen. A hemorrhaging AVM is a medical emergency, and between 2 to 4% of malformations bleed every year.
Endovascular therapy is a very good treatment option for certain grades of AVMs, if surgery cannot be performed. In endovascular therapy, a catheter (or long, thin tube) is guided through an artery and then into the blood vessels in your brain that are feeding the AVM, using X-ray imaging to help locate the appropriate artery. Your surgeon then injects a glue-like substance into the abnormal vessel to stop the blood flow into the AVM. Surgeons may perform this embolization before surgery to reduce bleeding during an operation to remove the AVM, or even to reduce the size of the AVM so the other forms of treatment, like stereotactic radiosurgery, can be more effective.
Sources:
Aldo Berti, M.D., F.A.C.S., F.A.A.P.
http://www.nlm.nih.gov/medlineplus/ency/article/000779.htm
http://thejns.org/doi/abs/10.3171/jns.1986.65.4.0476
http://emedicine.medscape.com/article/252426-overview
http://www.mayoclinic.org/arteriovenous-malformation/treatment.html