Although the underlying cause of Mike Patterson's seizure and subsequent collapse on Wednesday morning has come under dispute by his agent, if in fact it was due to an arteriovenous malformation (AVM) of the brain as has been reported by the team, with the proper care his long-term prognosis is promising.

An AVM is a tangle of abnormal and poorly formed blood vessels (arteries and veins) that, due to their anatomy, have a higher rate of bleeding than normal vessels. They are thought to be due to abnormal formation of vessels during development and may be present since birth. Brain AVMs are rare, occurring in less than 1 percent of the general population, and the typical time of discovery is between the ages of 20 and 40 years.

AVMs can occur anywhere in the body, but brain AVMs are of special concern because of the damage they cause when they bleed. Typically, oxygenated blood travels through arteries to the lungs and heart and then to the rest of the body. Blood from the arteries travels at high pressures, and after supplying oxygen to the organs and other parts of the body, deoxygenated blood travels back to the lungs and heart through veins. Veins are far more susceptible to damage from pressure than are arteries. To this end, a system of tiny vessels called capillaries rests between the arteries and veins to diffuse some of the pressure and lessen the force on the veins, preventing rupture.





Brain AVMs are made up of arteries and veins which are connected in such a way that there is no capillary bed at all. This causes the pressure of the arteries to be transmitted directly into the veins within the AVM. This unusual flow of blood creates an area of high pressure and high turbulence that causes the AVM to become larger over time, and to affect the function of the surrounding brain tissue. In the grand majority of patients, an AVM isn't discovered until they suffer symptoms from the extreme stretching or bursting of the vessels.

Due to the abnormal anatomy, a variety of symptoms may be produced which depend on the location and size of the AVM. Common problems include:

1. Seizures: An AVM in the brain may act as an irritant, resulting in abnormal electrical activity. Seizures may devleop as a result of this hyperactivity.

2. Headaches: Headaches may be caused by the high blood flow through the AVM . These headaches may be similar to a migraine, and often are described as the worst headache of one's life. These headaches are often followed by nausea , vomiting , neurological problems or a decreasing level of consciousness.

3. Stroke-like symptoms: Brain AVMs may cause stroke-like symptoms by depriving the nearby brain tissue of oxygen and nutrients. The symptoms vary with the location of the AVM and include:

Weakness or paralysis on one side of the body

Numbness and tingling

Problems with vision, hearing, balance, memory and personality changes

4. Bleeding: This is the most serious complication of an AVM and is the main reason for treatment. Sometimes, a bleed may be small and produce no noticeable symptoms. Approximately 50 percent of the bleeds are significant with permanent disability in half of these cases and death in the other half.

After showing symptoms suggestive of an AVM, diagnosis is made with a number of imaging studies of the brain, which may include MRI, CT scan, or a cerebral angiogram. Once the diagnosis is made, treatment is primarily to minimize the risk of future bleeding. Untreated, the risk of bleeding over one's lifetime may be high, especially if the AVM is discovered in a young person. For example, over 80 percent of patients in their 20s at the time of their diagnosis, like Patterson, are likely to experience a bleed at some point in their life if not treated.

Treatment is determined by the size of the AVM and also the location. It is not uncommon to recommend a combination of treatments, which may include:

Embolization: Under general anesthesia a small catheter (plastic tube) is advanced from the groin, into the brain vessels and then into the AVM. A liquid glue or a metal "coil" is injected into the vessels which form the AVM to block the AVM off. There is a small risk to this procedure and the chances of completely curing the AVM using this technique depend on the size of the AVM. It is frequently combined with the other treatments such as radiation or surgery.

Radiation treatment: A narrow x-ray beam is focused on the AVM such that a high dose is concentrated on the AVM with a much lower dose delivered to the rest of the brain. This radiation causes the AVM to shrivel up and close off over a period of 2-3 years in up to 80 percent of patients. The risk of complications is low. Until the AVM is completely closed off, the risk of bleeding still persists.

Surgery: The AVM is surgically removed in an operating room under general anesthesia. Since AVMs do not grow back, the cure is immediate and permanent if the AVM is removed completely. The risks of surgery are considered to be high for AVMs that are located in deep parts of the brain with very important functions.

Eagles trainer Rick Buckholder indicated yesterday that -- assuming the diagnosis of an AVM is correct -- doctors plan to embolize Patterson's AVM with a coil as treatment. If in fact this is pursued, Patterson's course of recovery will depend on the degree to which the AVM is repaired, as it is possible he may need a combination of therapies over time. Furthermore, those patients who present with seizures often require long-term treatment with medications to prevent future recurrence.

Nonetheless, with proper care, Patterson's long-term prognosis is quite good, although his return to the playing field depends on a number of factors related to the outcomes of his treatment. Ultimately, the most important prognostic factor may be whether the diagnosis is, indeed, an arteriovenous malformation, in the first place.