We aimed to develop a model for predicting the probability of an intracranial aneurysm (IA) during follow-up screening in persons with a positive family history of aneurysmal subarachnoid hemorrhage (aSAH).

First-degree family members of patients with aSAH are at increased risk of aSAH. The risk of an IA at initial screening in these persons can be predicted, but knowledge on the risk at follow-up screening is lacking. 

We studied results from follow-up screening for IAs in 499 prospectively collected persons with ≥2 affected first-degree relatives screened at the University Medical Center Utrecht and the University Hospital of Nantes. Cox regression analysis was performed to study the association between potential predictors and IA presence. A risk prediction model was derived, and predictive performance around 5 and 10 years after initial screening was assessed with the c-statistic and a calibration plot, corrected for overfitting. 

IAs were present in 52 persons during 5,050 person-years of follow-up. The mean observed 5-year risk of an IA after initial screening was 5.2% (95% confidence interval [CI] 3.4-7.5) and the cumulative 10-year risk was 9.0% (95% CI 6.7-11.9). Predictors were female Sex, Previous IA/aSAH, and older Age (SPA). The SPA score had a c-statistic at 5 years of 0.70 (95% CI 0.61-0.78) and at 10 years of 0.71 (95% CI 0.64-0.78), and showed good calibration. The 5-year risk after initial screening ranged from 2% to 12% and the 10-year risk from 4% to 28%, depending on the presence of the three predictors. 

For persons with ≥2 affected first-degree relatives the SPA score provides risk estimates for IAs found around 5 and 10 years after initial screening based on three easily retrievable predictors.