Study Provides Guidance For Treating Patients With Brain Aneurysms

December 09, 1998

A new study will help physicians decide how to treat individuals with unruptured intracranial aneurysms (UIAs). The study, reported in the December 10, 1998, issue of The New England Journal of Medicine, found that the size and location of the aneurysm in the brain, as well as the patient's medical history, are the best predictors of future rupture.

"This study gives us more 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, Maryland.

An aneurysm is a weak spot on an artery wall that balloons out due to pressure from the blood. When a brain aneurysm bursts, it releases blood into the spaces of the brain, causing a hemorrhagic stroke. Although hemorrhagic strokes account for only about 20 percent of all strokes, they are much more severe than other strokes and are fatal more than 50 percent of the time. The standard treatment for UIAs at risk for rupture is surgery. But surgery to remove an aneurysm carries its own health risks, including stroke or infection that can lead to impaired mental ability, brain damage, or even death. Perhaps as many as 10-15 million Americans may have intracranial aneurysms at some point in their lifetimes. In contrast, the number of people who have a first subarachnoid hemorrhage, a specific type of brain hemorrhage, is low, only about 10 people in 100,000 per year. This means that most intracranial aneurysms do not rupture.

"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 David O. Wiebers, M.D., Chair of the Division of Cerebrovascular Diseases at the Mayo Clinic in Rochester, Minnesota, and lead author of the study. "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."

The study enrolled 2,621 patients at 53 centers throughout the U.S., Canada, and Europe, and is the first large, multicenter study to use retrospective and prospective data to determine the natural course of UIAs in patients without a history of subarachnoid hemorrhage (group I) and patients with a history of subarachnoid hemorrhage (group II). Advances in imaging technology have made it possible to detect intracranial aneurysms before they rupture. Subjects in the NEJM study were diagnosed with UIAs through arteriography, an imaging technique that uses X-rays to photograph the arteries of the head made visible by a dye injected into the blood flowing through the artery. CT scans and MRI scans also can detect a brain aneurysm.

Dr. Wiebers and his colleagues found that for patients who have not had a previous subarachnoid hemorrhage, the risk of rupture for aneurysms smaller than 10 millimeters (mm) or about 1/3 of an inch in diameter was very low, less than 1/20 of 1 percent per year. For patients with a history of subarachnoid hemorrhage, the risk of rupture for the same sized aneurysm is about 11 times higher, about 1/2 of 1 percent per year. For aneurysms between 10 and 25 mm, the risk of rupture is still quite low, slightly less than 1 percent per year for both groups. The risk of rupture for giant aneurysms (greater than 25 mm in diameter) was about 6 percent for the first year for both groups. The exact position of the aneurysm in the brain was also a predictor of rupture in both groups.

Of course, the risk of rupture for an aneurysm must be compared to the overall risk of surgery to repair an aneurysm. For patients without a history of subarachnoid hemorrhage (group I), the surgery-related morbidity and mortality combined was about 17.5 percent at 30 days and about 15.9 percent at 1 year. For patients with a history of subarachnoid hemorrhage (group II), the combined surgery-related morbidity and mortality was less, about 13.6 percent at 30 days and about 13.2 percent at 1 year. One reason for this may be the average age difference between the two groups. Younger patients had substantially less operative morbidity and mortality than older patients and group II patients were younger than group I patients (an average of 47 versus 53 years old).

The investigators concluded that the likelihood of rupture of aneurysms less than 10 mm in diameter is exceedingly low among group I patients and that the combined morbidity and mortality rate related to surgery greatly exceeds the 7 1/2 year risk of rupture in these patients. They therefore advise against surgery for most patients who have aneurysms less than 10 mm in diameter and are without a history of subarachnoid hemorrhage. Other risk factors that surgeons should take into account before performing aneurysm surgery are the patient's history of previous subarachnoid hemorrhage, and the size and location of the aneurysm.

Dr. Wiebers states that the study should not cause worry among individuals without a history of brain hemorrhage. "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," he says.

The NINDS is the nation's principal supporter of research on the brain and nervous system and a lead agency for the Congressionally designated Decade of the Brain. The Institute supports and conducts a broad program of basic and clinical neurological investigations and is part of the National Institutes of Health, located in Bethesda, Maryland.
This release will be posted on EurekAlert! at and on the NINDS home page at

The Mayo Clinic will hold a press conference in Rochester, Minnesota, on Wednesday, December 9, at 10:00 a.m. CT and a satellite media tour from 1:30 p.m. to 3:00 p.m. CT. Please call Jane Jacobs at 507-284-2387 or email her at for more information.

NIH/National Institute of Neurological Disorders and Stroke

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