Young survivors of aneurysmal subarachnoid hemorrhage (aSAH) are at risk of de novo aneurysm formation. However, evidence on its cumulative incidence, risk factors, and rupture rate remains limited. To address this gap, a study evaluated the lifetime cumulative incidence, risk factors, and rupture rate of radiologically detected de novo aneurysm formation in 544 young survivors of aSAH, with a median age of 33 years. Over 13,738 person-years of follow-up, 106 patients (19.5%) developed 158 de novo aneurysms, of which 23 ruptured.

The Fine-Gray cumulative incidence reached 30.2% at 40 years, without a plateau. Independent risk factors included female sex (HR, 1.76), smoking (HR, 1.75), and family history (HR, 2.17). Smoking cessation was associated with a lower risk of de novo aneurysm formation, with the risk decreasing in a dose-dependent manner. The annual rupture rate was 153 per…