Differences in risk factors according to the site of intracranial aneurysms

Background and purpose: Several risk factors for aneurysmal subarachnoid haemorrhage have been identified but it is not known whether some sites of aneurysms are linked to a specific risk factor. In a series of patients with aneurysmal subarachnoid haemorrhage, we compared risk factors according to the site of the ruptured aneurysm at the circle of Willis. Methods: From our prospectively collected database of patients with aneurysmal subarachnoid haemorrhage admitted to our hospital between 2003 and 2007, we retrieved 304 patients with saccular aneurysms on the anterior communicating artery, middle cerebral artery, posterior communicating artery, basilar artery and vertebral artery. Risk factors (age, gender, smoking, no or excessive alcohol intake, hypertension and familial preponderance) were assessed per aneurysm location and compared with the anterior communicating artery as reference. We calculated odds ratios (ORs) and corresponding 95% CI. Results: In comparison with aneurysms at the anterior communicating artery, those at the middle cerebral artery were less associated with age >55 years (OR 0.4; 95% CI 0.2 to 0.8), those at the posterior communicating artery were less associated with male gender (OR 0.4; 95% CI 0.2 to 0.9) and those at the basilar artery were more associated with no alcohol consumption (OR 5.8; 95% CI 1.1 to 29.9). Conclusion: Risk factors differ according to the site of aneurysm. This heterogeneity should be kept in mind in studies on the aetiology of aneurysms, such as genetic studies.