Hassanain Toma, MD
Studying the natural history of UIA is difficult because of the temptation to treat these aneurysms before they rupture. Fortuitously, in Finland, UIAs were left untreated until 1979. This provided Korja et al. a population to study the lifelong natural course of unruptured intracranial aneurysms and identify high-risk and low-risk patients for the rupture.
They prospectively evaluated 118 patients with UIA diagnosed between 1956 and 1978. They were followed until death or subarachnoid hemorrhage (SAH). They demonstrated that the annual UIA rupture rate ranges from 0% to 6.5% (average 1.6%), depending on individual risk factors. These risk factor were found to be female sex, current smoking and aneurysm size of >7 mm in diameter.
In their discussion, the authors focused on a very important concept. Large UIA (>7mm) are associated higher rupture rates, but they must start off as small aneurysms before they reach their critical rupture size. In their cohort 77% of small aneurysms grew to >7 mm before rupturing. That subgroup mainly involved women who are current smokers, whereas none of the non-smoking men developed aneurysmal rupture. This finding is important because it better stratifies UIA that are at risk of rupturing.
My neurosurgical colleagues often dismiss small aneurysms based on their size. Although underpowered, this study highlights the importance of considering patient’s sex and smoking status to inform patients of their UIA rupture risk, and empower physicians with data to better educate their patients about the risk of smoking and aneurysmal rupture.