Background: Quantitative data on the impact of smok- ing on genesis of intracranial aneurysms (IA) is sparse. In this prospective observational cohort study (07/2016- 01/2023), we analyzed the association between lifetime and current smoking exposure and IA characteristics.

Methods: At inclusion, patients or next of kin filled out the questionnaire for assessment of smoking habits inclu- ding the status (no/former/current) and the consumption level (for current – heavy/light smoker [≥/<10 cigarettes/ day], and lifetime exposure in pack-years). The study endpoints were the ruptured status, size, and presence of multiple IA.

Results: In the final IA cohort (n=918), the distri- bution of non-, former, light, and heavy smokers was 23.2%, 25.6%, 11.2% and 40% respectively. The me- dian lifetime smoking exposure was 20 pack-years. Current smokers were at higher risk of presenting with ruptured (adjusted odds ratio [aOR]=1.71, 95% confi- dence interval [CI]=1.29-2.26, p<0.0001), large (≥7mm, aOR=1.41, 95% CI=1.05-1.89, p=0.022) and multiple IA (aOR=1.34, 95% CI=1.01-1.77, p=0.045). In the subgroup analysis among ever smokers, heavy smoking additionally increased the risk of IA rupture (aOR=1.83, 95% CI=1.33-2.50, p<0.0001) and larger size (aOR=1.65, 95% CI=1.19-2.30, p=0.003). Finally, longer history of smoking (>20 pack-years) was related to higher probabil- ity of multiple (aOR=1.61, 95% CI=1.21-2.13, p=0.001) and large IA (aOR=1.40, 95% CI=1.04-1.87, p=0.025).

Conclusions: Our data underline the role of smoking in IA genesis, and the importance of smoking cessation for rupture prevention. Current and particularly heavy smoking increases the risk of IA rupture, whereas the chronic exposure over years more likely results in the de- velopment of multiple and large IA.