Natural history, epidemiology and screening of unruptured intracranial aneurysms

The prevalence of unruptured intracranial aneurysms is around 2%; most of these aneurysms are small and located in the anterior circulation. Unruptured intracranial aneurysms may give rise to subarachnoid hemorrhage in the near or distant future and sometimes, these lesions warrant preventive intervention.

Most studies, on risk of rupture, have methodological weaknesses; the overall risk of rupture found in follow-up studies is around 1% per year. Size is the most important risk factor for rupture, with smaller risks for smaller aneurysms. Other risk factors are site of the aneurysm (higher risk for posterior-circulation aneurysms), age, female gender, population (higher risks in Finland and Japan) and probably also smoking. For aneurysms smaller than 10mm, treatment carries a risk of around 5% of complications leading to death or dependence on help for activities of daily living.

There are no good comparisons between clipping and coiling of unruptured aneurysms. The efficacy of coiling in the long-term is unsettled. Good-quality data are urgently needed to settle these questions.

In deciding whether or not to treat an aneurysm, life expectancy is a pivotal factor; other important factors are size and site of the aneurysm.