Bigger brain aneurysms not more likely to burst

The size of a brain aneurysm does not play a major role in its risk of bursting, a new study finds.

A brain aneurysm occurs when a blood vessel in the brain weakens and balloons out. If it bursts, it causes a bleeding (hemorrhagic) stroke that typically results in brain damage or death.

Finnish researchers analysed data from aneurysm patients who were followed for their entire lives, and found that about one-third of all aneurysms burst, including about one-quarter of small aneurysms.

Low risk of rupture

The size of the aneurysm had little effect on its risk for rupture, particularly among men. Rupture risk was particularly high among women who smoked and had aneurysms that were 7 millimetres (mm) or more in diameter. The risk of rupture was exceptionally low among men who didn't smoke.

"This is not to say that aneurysms in non-smoking men never rupture, but that the risk is much lower than we previously thought. This means treating every unruptured aneurysm may be unnecessary if one is discovered in a non-smoking man with low blood pressure," study author Dr Seppo Juvela said in a University of Helsinki news release.

Previous short-term studies have concluded that the size of an aneurysm is the most important risk factor for rupture. This has led to small (less than 7 mm in diameter) aneurysms often being left untreated.

The study findings were published online in the journal Stroke.

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