Arteriovenous malformations (AVM)
Arteriovenous malformations (AVMs) are defects of the circulatory system that are generally believed to arise during fetal development or soon after birth. Although AVMs can develop in many different sites, those located in the brain or spinal cord can have especially widespread effects on the body.
Dural AVMs occur in the covering (dura) of the brain and are an acquired disorder that may be triggered by an injury. AVMs can sometimes develop after head or spine trauma, and are referred to as AV fistulas.
The incidence of AVM is estimated at 1 in 100,000. An estimated two-thirds of AVMs occur before the age of 40. Every year, approximately four out of every 100 people with an AVM experience a hemorrhage. AVMs are the second most identifiable cause of subarachnoid hemorrhage (SAH) after cerebral aneurysms, accounting for 10 percent of all cases of SAH.
Most people with neurological AVMs experience few, if any, significant symptoms. The malformations tend to be discovered only incidentally, usually either at autopsy or during treatment for an unrelated disorder. But for about 12 percent of the affected population (about 36,000 of the estimated 300,000 Americans with AVMs), the abnormalities cause symptoms that vary greatly in severity. The most common symptom is brain hemorrhage.
Other symptoms include:
- New-onset seizures
- Muscle weakness or paralysis
- Loss of coordination
- Difficulties carrying out organizational tasks
- Visual disturbances
- Language problems
- Abnormal sensations such as numbness, tingling or spontaneous pain
- Memory deficits
- Mental confusion
AVMs are usually diagnosed through a combination of MRI and angiography. Your neurosurgeon may repeat the tests to check for a change in the size of the AVM, recent bleeding or the appearance of new lesions.
Left untreated, AVMs can enlarge and rupture, causing intracerebral hemorrhage or subarachnoid hemorrhage and permanent brain damage. If you have an AVM, you will be carefully monitored for any sign of instability that may indicate an increased risk of hemorrhage.
Medication can often alleviate general symptoms such as headache, back pain and seizures caused by AVMs and other vascular lesions. However, the definitive treatment for AVMs is either surgery or stereotactic radiosurgery. The decision to perform surgery on anyone with an AVM requires a careful consideration of possible benefits versus risks.
Your neurosurgeon will devise a treatment plan with the lowest risk and highest chance of eliminating the lesion. Three types of treatment are available: direct removal using microsurgical techniques, stereotactic radiosurgery, and embolization using neuroendovascular techniques. Some AVMs are best treated with a combination of therapies.
Microsurgery allows for removal of the AVM with minimal disruption of normal brain tissue. Your neurosurgeon will perform a craniotomy and use microsurgical techniques to gain access to the AVM. The use of an operating microscope and image-guided surgical navigation helps enable safer surgery with as little disruption as possible to normal brain activity. Once the skull is opened, your surgeon will close off the AVM with special clips and remove it. The skull is secured into place with mini-plates.
Stereotactic radiosurgery is a minimally invasive treatment that uses computer guidance to concentrate radiation on the malformed vessels of the brain, causing them to close off. The procedure is usually limited to lesions less than 3.5 centimeters in diameter.
Embolization uses specially designed microcatheters, which are guided directly into the AVM using angiography. The lesion is blocked from the inside during the process of embolization, which seals the abnormal blood vessels in the AVM. Once the catheter reaches the core of the AVM, liquid glue or particles are injected to close of portions of the AVM or its feeding arteries. Although the method may be effective in reducing the size of an AVM, it rarely completely eliminates it. Neuroendovascular therapy can make subsequent surgical removal of an AVM safer, or can reduce an AVM to a size that may improve the outcome of stereotactic radiosurgery.
Source: American Association of Neurological Surgeons and the National Institute for Neurological Disorders and Stroke