International study sheds new light on yreatment of unruptured brain aneurysms

December 09, 1998

ROCHESTER, MINN. -- An international study spearheaded at Mayo Clinic has identified new information that will assist physicians in better caring for patients who have unruptured brain aneurysms, a condition that will affect five percent of people in North America and Europe (10-15 million Americans) in their lifetime.

The study, published in the December 10, 1998 issue of the New England Journal of Medicine, finds that small intracranial aneurysms, especially those located near the front of the brain, have a very low probability of rupture if the patient has no history of ruptured aneurysms. According to the study findings, the risk of rupture of these small aneurysms is 1/20 of one percent per year. Comparatively, the risk of impaired mental ability, other brain damage or death related to surgery for this group of patients is greater than 10 percent at one year.

"Historically, there has been little if any consensus on the issue of which aneurysms needed to be treated and which could be left alone and monitored," says Dr. David O. Wiebers, a Mayo Clinic neurologist and the study's principal investigator. "That lack of consensus was the basis for instigating this study seven years ago. This study sheds significant light on the natural history of unruptured intracranial aneurysms, and offers physicians and their patients a new, low-risk option. Physicians and their patients will need to consider each situation individually. However, in general, patients with small unruptured intracranial aneurysms and no history of other ruptured aneurysms should be comforted by the prospect of living a normal lifestyle with minimal risk while monitoring the aneurysm."

"This study will lead to a very significant change in the way these lesions are considered," says Richard Kerr, M.D., a neurosurgeon at The Radcliffe Infirmary and Oxford University in Oxford, England. "The risk of hemorrhage is clearly less than previously thought and will have a huge impact on the decision as to whether they should be treated conservatively and observed, as opposed to being actively dealt with by endovascular or surgical means."

"Physicians and their patients can now better weigh the risk of an aneurysm rupturing with the risks associated with surgery," says Dr. Wiebers. "We found that the overall risk associated with the natural history of unruptured intracranial aneurysms is lower than commonly recognized and the risk associated with the surgical repair of these aneurysms is higher than commonly recognized. There may be subgroups of patients which constitute exceptions to these findings, however, and that is the main reason the study will continue over the next few years."

"This study gives us important new data on which to base treatment decisions for patients with unruptured intracranial aneurysms," says John R. Marler, M.D., a neurologist with the Division of Stroke, Trauma and Neurodegenerative Disorders at the National Institute of Neurological Disorders and Stroke (NINDS), sponsor of the study and part of the National Institutes of Health, located in Bethesda, Md.

The study identifies patients for whom surgery may not be needed based on the size and location of the aneurysm in the brain as well as the patient's medical history. The study took place in 53 leading research centers in the United States, Canada and Europe and included 2,621 patients. Unruptured intracranial aneurysms are most common in women, especially in those who smoke.

An intracranial aneurysm occurs when a weak spot on the wall of an artery in the brain balloons out, forming a sac that fills with blood. When an intracranial aneurysm ruptures, it releases blood into the spaces around and sometimes into the brain causing a hemorrhagic stroke. Although hemorrhagic strokes account for only about 20 percent of all strokes, they are the cause of about 80 percent of stroke deaths. Specifically, subarachnoid hemorrhages (bleeding under the outer membrane around the brain) can lead to extensive brain damage and are the deadliest of all strokes.

The Study: A Summary
Patients for this study were divided into two groups. Group I patients had no history of ruptured aneurysms. Group II patients had previously experienced a ruptured aneurysm.

The study found that in Group I patients with unruptured intracranial aneurysms less than 10 millimeters in diameter the risk of rupture was 1/20 of one percent per year. Patients in this same group that had unruptured aneurysms which measured 10-24 millimeters in diameter had a higher risk of rupture, slightly less than one percent per year. Group I patients with giant aneurysms measuring more than 25 millimeters in diameter had a six percent chance of the aneurysm rupturing during the first year.

Group II patients with unruptured intracranial aneurysms less than 10 millimeters in diameter had a risk of rupture that was 11 times greater than Group I patients with the same size aneurysms. Group II patients with aneurysms measuring 10-24 millimeters in diameter had a rupture risk of slightly less than one percent, similar to Group I patients with the same size aneurysms.
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