One-third of all brain aneurysms rupture: The size is not a significant risk factor

May 22, 2014, University of Helsinki
Approximately one-third of all aneurysms and up to one fourth of small aneurysms will rupture during a patient's lifetime. Credit: Miikka Korja, University of Helsinki

The lifetime risk for rupture of a brain aneurysm depends heavily on the patient's overall load of risk factors. However, a recent study by researchers from the University of Helsinki and Helsinki University Central Hospital demonstrated that the size of an aneurysm has no great significance on the risk of rupture.

This is a unique study in that it monitored patients over their entire lifetimes, whereas typical follow-up studies last only between one and five years in duration. The study is also exceptionally broad in scope; Dr. Seppo Juvela points out that the only other place where a study of similar scope has been conducted is Japan.

"It is unlikely that another similar, non-selected lifetime follow-up study on aneurysm will ever be conducted again," he states.

Current care practices are based largely on the results of previous, shorter studies. Such studies have shown that the size of the aneurysm is the most significant factor predicting its risk for rupture. Consequently, small (<7mm) aneurysms have often been left untreated, even though such aneurysms have also been known to rupture and cause brain haemorrhages.

The new study established that approximately one third of all aneurysms and up to one fourth of small aneurysms will rupture during a patient's lifetime. The risk of rupture is particularly high for female smokers with brain aneurysms of seven millimetres or more in diameter. What surprised the researchers most was that the size of an aneurysm had little impact on its risk for rupture, particularly for men, despite a previously presumed correlation. In addition, the risk of rupture among non-smoking men was exceptionally low.

This video depicts microneurosurgical clipping of an unruptured intracranial aneurysm, which is arising from the bifurcation i.e. branching point of two right middle cerebral arteries. In brief, the aneurysm locates in this case between the frontal and temporal brain lobes, and therefore it can be reached by sharply cutting normal membranes between the frontal and temporal lobes. This microneurosurgical dissection opens a natural corridor leading to the aneurysm. One aneurysm clip occludes the neck of the aneurysm and the aneurysm cannot rupture anymore. The normal brain arteries are left patent. Operated by neurosurgeon, Associate Professor Miikka Korja Credit: Miikka Korja, University of Helsinki

"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," Juvela clarifies.

But why have previous studies not reached these same results if they are so obvious?

"It is difficult to conduct reliable epidemiological research in brain aneurysms. The past 10 years have seen a distortion in the field due to a very limited group of researchers determining the direction for research. Now the situation is clearly changing, and clinically reasonable, population-based studies using non-selected data are on the rise again," states Docent Miikka Korja of the HUCS neurosurgery clinic.

Finland has a strong tradition of studying the prevalence, risk factors and care of brain aneurysms, and the Helsinki University Central Hospital is one of the world's leading units to provide treatment for brain aneurysms. Major studies in the field published by Finnish researchers include the world's most extensive twin study on the hereditability of subarachnoid haemorrhage, the largest follow-up study on subarachnoid haemorrhages among diabetics, the most extensive study on the life expectancy of subarachnoid haemorrhage survivors and a study on the for subarachnoid haemorrhages using the most extensive population data.

Explore further: Growth in cerebral aneurysms increases risk of rupture

More information: The article will be published in Stroke 22 May, online. Juvela & al. "Lifelong rupture risk of intracranial aneurysms depends on risk factors - a prospective Finnish cohort study"

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sandbee54
not rated yet May 23, 2014
Being a female who had an aneurysm rupture when I was 42, just want to say that I never smoked. However I had headaches all of my life and tried to tell doctors that I had something wrong. No one would listen.

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