Researchers Tease Out Risk And Benefits Of Treating Brain Blood Vessel "Tangle"

May 07, 1998

DALLAS, May 8 -- Treating a condition that causes bleeding in the brain, called cerebral arteriovenous malformation (AVM), may pose a greater danger than the condition itself, according to researchers, whose study is in this month's Stroke: Journal of the American Heart Association.

AVM is a tangle of arteries and veins in the brain that become disconnected from the capillaries, a web of smaller blood vessels that circulate blood to and from tissues. Blood from the arteries, which normally flows into the capillaries, is forced into the veins, often at high velocity. The pressure in the veins increases, and the blood vessel ruptures, causing a hemorrhagic (bleeding) stroke. Bleeding can also occur from the arteries feeding into the tangle. Most AVMs are congenital, meaning that individuals are born with the condition.

"Having AVM was thought to be like having an explosive time bomb in the brain," says J.P. Mohr, M.D., a co-investigator of the study. However, the new research finds that the "bomb" sometimes goes off with a "poof."

The damage to the brain from a bleeding AVM is not as serious as once thought and most surviving individuals will have their brain functions intact. "Severe consequences from bleeding appear to occur less frequently than assumed and because treatment of AVM is associated with an eight percent complication risk, physicians should re-evaluate the risk and benefits of treatment," says Mohr, professor of clinical neurology at Columbia-Presbyterian Medical Center, New York.

According to the researchers, about 250,000 individuals in the United States carry an AVM and about 10 percent hemorrhage a year. Individuals often have no way of knowing they have the condition, unless the AVM leaks blood, or a person develops neurological symptoms, such as seizure or headache. Magnetic resonance imaging (MRI) and computed tomography (CT scan) provide an image of the brain to detect the AVM. When AVM is detected, physicians typically have used surgery, embolization, which reduces the size of the AVM, or radiation to remove the tangled vessels to prevent a bleeding stroke from occurring.

This current approach is being questioned by results of the study designed to determine how often individuals with bleeding AVM suffer disabilities. Researchers gave study participants a series of mental and physical tests, which rated them on a scale of 0 to 6 based on their level of disability. Of the 115 people in the study, 54 (47 percent) had no neurological damage; 43 (37 percent) had a score of one, indicating they were able to do daily activities without assistance. Fifteen individuals (13 percent) had scores of two or three, indicating they were moderately disabled and three (about three percent) were severely disabled with scores above four. None of the individuals died during the 16-month study.

Andreas Hartmann, M.D., research scientist in the stroke unit at the Neurological Institute at Columbia University in New York City, and lead author of the study, says the findings surprised him because previous research on AVM had found higher rates of complications and death. Furthermore, other conditions, such as aneurysm, that cause blood vessels to leak blood in the brain, can result in severe disabilities. About 50 percent of individuals who have a burst blood vessel, or aneurysm, will either die or will be disabled, says Hartmann.

"It was common practice to assume that the rates of complications were similar for a bleeding aneurysm, but we didn't find that in our study," says Hartmann. An aneurysm is a pouch that forms from the blood vessel at a weak point. If it ruptures, it can be fatal.

"We can't draw conclusions about who should or should not be treated, but the physician may want to use this information to refine their decision-making process," says Hartmann.

Researchers don't know why bleeding from an AVM poses less danger than a bleeding aneurysm. But they suspect that type and the extent of the AVM bleed may lead to a more favorable outcome.

Further research will be directed at teasing out which blood vessel tangles are most dangerous, and which should be treated.

Co-authors are Henning Mast, M.D.; Hans Christian Koennecke, M.D.; Andrei Osipov, M.D.; John Pile-Spellman, M.D.; D. Hoang Duong, M.D.; and Williams L. Young, M.D.
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NR 98-4892
Media advisory: Drs. Hartmann and Mohr can be reached by calling (212) 305-8033. (Please do not publish telephone number.)
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American Heart Association

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