When brain aneurysms are most likely to rupture

A new international collaborative study led by Mayo Clinic found that the risk of a brain aneurysm rupturing over time depends on the location and size of the aneurysm. This study was presented at the 6th World Stroke Congress meeting in Vienna, Austria, on 25 September 2008.

A brain aneurysm, also known as an intracranial or cerebral aneurysm, is an abnormal sac or tiny balloon on a blood vessel to the brain. Aneurysms can rupture and bleed into the area between the brain and the surrounding membrane, leading to stroke and death. An estimated 2 percent of Americans, approximately 6 million people, have brain aneurysms. These aneurysms rupture in about 25,000 people each year.

"This study provides us with very useful information that will allow us to better guide our patients with unruptured aneurysms regarding the risk of aneurysm rupture during a very long period of follow-up," says Robert Brown, MD, a Mayo Clinic neurologist and the study’s lead investigator.

This study was part of the International Study of Unruptured Intracranial Aneurysms, which includes 4,059 patients with unruptured brain aneurysms at 61 different medical centres in North America and Europe. These patients have been followed for an average of more than nine years.

Dr Brown and his team found that rupture risk was somewhat higher among patients with aneurysms in the back of the brain or in the posterior communicating artery, also in the back of the brain, compared to those in the front of the brain. Additionally, patients whose aneurysms were more than 13 millimetres (mm) in diameter were at least twice as likely to experience rupture, compared to those whose aneurysms were 7–12 mm in diameter.

"When one compares the risk of rupture determined in this study to the risk of treatment for an aneurysm, it appears that these risks are similar for small aneurysms less than 10–12 mm in size. It is unclear whether these aneurysms need to be treated in all patients, and this will be clarified with further research," says Dr Brown.

(Source: 6th World Stroke Congress: Mayo Clinic: October 2008)