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Arteriovenous Malformation (AVM) 

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What is It?
 An arteriovenous malformation (AVM) is a tangle of abnormal and poorly formed blood vessels (arteries and veins), with an innate propensity to bleed. An arteriovenous malformation can cause headaches, seizures and aneurysms.

An arteriovenous malformation can occur anywhere in the body, but brain and spinal arteriovenous malformations present substantial risks when they bleed.

Dural AVMs occur in the covering (dura) of the brain, and are an acquired disorder that may be triggered by an injury. An arteriovenous malformation can sometimes develop after a head or spine trauma

What are the symptoms?
 A person with an arteriovenous malformation may experience no symptoms. AVMs tend to be discovered only incidentally, usually either at autopsy or during treatment for an unrelated disorder. However, about 12 percent of people with an arteriovenous malformation will experience symptoms, varying in severity. AVMs can irritate the surrounding brain and cause seizures or headaches. The most common symptom is brain hemorrhage.

Any of the following symptoms may occur with an arteriovenous malformation:
- Seizures, new onset
- Muscle weakness or paralysis
- Loss of coordination
- Difficulties carrying out organizational tasks
- Dizziness
- Headaches
- Visual disturbances
- Language problems
- Abnormal sensations such as numbness, tingling, or spontaneous pain
- Memory deficits
- Mental confusion
- Hallucinations
- Dementia

How is it diagnosed?
An arteriovenous malformation is usually diagnosed through a combination of MRIs and angiography. These tests may need to be repeated to analyze a change in the size of the AVM, recent bleeding or the appearance of new lesions.

Left untreated, an arteriovenous malformation can enlarge and rupture, causing a hemorrhage and permanent brain damage. Bleeding from AVMs located deep inside the brain tissues generally causes more severe neurological damage than bleeding from lesions located on the surface of the brain or spinal cord.

What treatments are offered?
The location of an arteriovenous malformation is an important factor when weighing the risks of surgical versus nonsurgical treatment. Preventing the rupture or rerupture of an arteriovenous malformation is one of the major reasons that early neurosurgical treatment is recommended.

The three types of treatment available include: direct removal using microsurgical techniques, stereotactic radiosurgery, and embolization using neuroendovascular techniques. Although microsurgical treatment affords the opportunity for immediate removal of the arteriovenous malformation, some may best be treated with a combination of therapies.

In some patients, the AVM is monitored on a regular basis with the understanding that there may be some risk of hemorrhage or other neurological symptoms including seizures or focal deficit. This strategy depends on the type of the arteriovenous malformation and cannot be used to predict when a hemorrhage may occur.

Microsurgery
Because an arteriovenous malformation often is congenital, and, therefore, associated with abnormal brain tissue, it may be removed with minimal disruption of normal brain tissue. The recommendation for surgery is typically elective, except in the case of large, life-threatening blood accumulations (hematomas) caused by bleeding of the arteriovenous malformation.

Stereotactic radiosurgery
Stereotactic radiosurgery is a minimally invasive treatment that uses computer guidance to concentrate radiation to the arteriovenous malformation. This radiation causes abnormal vessels to close off. Stereotactic radiosurgery is usually limited to lesions less than 3.5 cm in diameter, and may take up to two years to completely obliterate the lesion. This method is not ideally suited for an arteriovenous malformation that has already bled, unless it is surgically inaccessible. Ionizing radiation is also harmful to normal tissue and must be used judiciously.

Embolization
Endovascular embolization uses specially designed microcatheters, which are guided directly into the arteriovenous malformation via angiography. The lesion is blocked from the inside using the process of embolization, which occludes the abnormal blood vessels in the arteriovenous malformation. Once the catheter reaches the core of the AVM, liquid glue or other particles can be injected to close off portions of the AVM or its feeding arteries.

Although this method may be effective in reducing the size of an arteriovenous malformation, it is rarely able to eliminate it. Neuroendovascular therapy can make subsequent surgical removal of an arteriovenous malformation safer, or can reduce the size of an AVM to a size that may inevitably improve the outcome of stereotactic radiosurgery. This procedure is also associated with substantial risk, since the path taken by such embolic materials can be difficult to predict, and blockage of normal vessels may occur.

Outcome
Patient outcome depends on the location of the arteriovenous malformation and severity of the bleeding, as well as the extent of neurological symptoms. Many patients undergoing microsurgery make an excellent and quick recovery after several days of hospitalization. Following or during surgery, an angiogram is performed to assure complete removal of the arteriovenous malformation. If the AVM is completely removed, the patient is considered cured.

Sources:
-- The Aneurysm and AVM Foundation
-- International Radiosurgery Association
-- MedlinePlus
-- National Institute of Neurological Disorders and Stroke


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