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

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 aneurysm 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 patients 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 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 risk factors for subarachnoid haemorrhages using the most extensive population data.