Abstract TP361: Long-Term Aneurysmal Subarachnoid Haemorrhage and Mortality Risk in Small Unruptured Intracranial Aneurysms: An Individual-Level Data-Linked Cohort Study

Introduction: Long-term outcomes in patients with small unruptured intracranial aneurysms (UIAs) remain uncertain. We evaluated aneurysmal subarachnoid haemorrhage (aSAH) and mortality risk in patients with UIAs managed without repair. Methods: We conducted a single-center observational cohort study at a tertiary academic neurovascular centre in Melbourne, Australia. Adults with asymptomatic, non-cavernous, intradural, saccular UIA measuring 1.5–10 mm, managed conservatively without repair for more than 30-days between January 2005 and December 2018 were included; patients undergoing elective UIA treatment within 6-months of neurovascular imaging were excluded. Outcomes were obtained through individual-level data linkage to statewide hospital admission and mortality datasets. Cumulative incidence of aSAH was estimated using the cumulative incidence function with non-aSAH death and elective aneurysm treatment as competing events; overall survival was estimated using Kaplan–Meier methods. Results: We included 429 patients with 600 UIAs (73% female; median age 58 years). Most aneurysms (83%) were 1 mm growth (30%) or baseline size >5 mm (29%). Two patients (1.9%) died within 1 year of elective repair, one from periprocedural aSAH. Nine spontaneous ruptures occurred, six in UIAs