LAUSR

BACKGROUND Formation and rupture of saccular intracranial aneurysms (sIAs) may have different pathobiologies in patients with younger age at first diagnosis of sIA disease. OBJECTIVE To study the phenotype of sIA disease and formation of new (de novo) sIAs in patients below 40 yr. METHODS A population‐based cohort study was conducted in 613 young (<40 yr) sIA patients with first diagnosis between 1980 and 2014 and total angiographic follow‐up of 3768 yr. RESULTS Of the 613 sIA patients <40 yr, 508 had aneurysmal subarachnoid hemorrhage (sIA‐SAH) and 105 unruptured sIA(s) at first sIA diagnosis. Hypertension was 2 times less common among <40 than >40‐yr‐old patients (unruptured and ruptured). Smoking was very prevalent in <40‐yr‐old patients (33% in SAH, 68% unruptured). SAH patients <40 yr more often had family history of sIA, and lower PHASES scores (age omitted, P < .001). Ruptured sIAs were small (<7 mm) in 33% of 39 to 30 yr patients, in 44% of 29 to 20 yr patients, and 57% of <19 yr patients. Their shape was irregular in 90% 94% and 95% respectively. Smoking history (hazard ratio [HR] 2.8, 95% confidence interval [CI] 1.2‐7.0) family history for sIAs (HR 3.1, 95% CI 1.3‐7.7) and age at presentation (HR .91 per year, 95% CI .85‐.98) were risk factors for de novo sIA formation, diagnosed in 4% even after 20 yr (median 11.8 yr). CONCLUSION Smoking and family history are risk factors for sIA formation and aneurysmal SAH at young age. Young aneurysmal SAH patients had lower PHASES scores and often rupture from a small sIA, suggesting need for more aggressive management.