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 <5 mm (median size 3.2 mm) and located in the anterior circulation (88%). The median PHASES (Population, Hypertension, Age, Size, Earlier SAH, Site) score was 3 (IQR 2–4). The median follow-up was 11.8 years (IQR 8.8–15.7 years) with no loss to follow-up. During follow-up 107 patients (25%) underwent elective repair, most with >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 <5 mm; overall 44% of ruptures were fatal. The 10-year cumulative incidence of aSAH was 2.2% (95% CI 1.1– 4.0%; Figure 1). The 10-year all-cause mortality risk was 13% (95% CI 10–17%). Conclusions: In patients with small UIAs selected for conservative management, the long-term aSAH risk was low. These findings support conservative management in appropriately selected patients and provide evidence to guide patient-centered decision-making and guideline recommendations.