When followed up on magnetic resonance im- aging, larger aneurysms ( 8 mm in diameter) tended to grow more over time,45 which implies a higher risk of rupture. Several characteristics of aneurysm morphology (such as a bottleneck shape46 and the ratio of size of aneurysm to parent vessel47,48) have been associated with rupture status, but how these might be applied to individual patients to predict future aneurysmal rupture is still unclear.33 Variability within each patient is unpredictable at this time, but such intraindividual variability markedly changes the risk of aneurysm detection and rupture and may attenuate the benefits of routine screen- ing in high-risk patients.49 Given such uncertainties, younger age, longer life expec- tancy, and higher rate of rupture all make treatment of unruptured aneurysms more likely to be cost-effective and reduce morbidity and mortality.50 Two large observational studies of familial aneurysms suggest that screening these patients may also be cost-effective in preventing aSAH and improving quality of life.26,27 Smaller studies have suggested that screening of those with 1 first-degree relative with aSAH may be justified as well, but it is far less clear whether patients who underwent treatment for a previous aSAH require ongoing screening.51,52 In the Cerebral Aneurysm Rerupture After Treatment (CARAT) study, recurrent aSAH was predicted by incomplete obliteration of the aneurysm and occurred a median of 3 days after treatment but rarely after 1 year.53 Repeated noninvasive screening at later times may not be cost-effective, increase life expectancy, or improve quality of life in unselected patients.54 Patients with adequately obliterated aneurysms after aSAH have a low risk of recurrent aSAH for at least 5 years,55,56 although some coiled aneu- rysms require retreatment.57 Risk Factors for and Prevention of aSAH: Recommendations 1. 