Comparative Outcomes of Endovascular Therapy Versus Microsurgery for Ruptured Internal Carotid Blood Blister-Like Aneurysms: A Nationwide Propensity Score–Matched Study

BACKGROUND: Ruptured internal carotid artery blood blister-like aneurysms (IC-BBAs) are rare, fragile lesions, with an uncertain optimal treatment strategy. Comparative real-world evidence between endovascular therapy (EVT) and microsurgery is limited, and the timing and risk of pretreatment rerupture remain poorly characterized. METHODS: A nationwide multicenter retrospective cohort study was conducted across 95 Japanese centers from April 2015 to March 2025. Patients with ruptured IC-BBAs were included. Outcomes between EVT and microsurgery were compared using propensity score matching among treated patients. The primary endpoint was 90-day functional independence, defined as modified Rankin Scale score 0–2. RESULTS: Of 395 patients, 387 underwent definitive treatment, including EVT in 228 and microsurgery in 159. Flow diverters were used in 13.1% of stented EVT cases. Propensity score matching generated 141 matched pairs. In the matched cohort, 90-day functional independence was more frequent after EVT (68.1% vs 55.3%; p = 0.036). Functional independence at 30 days was more frequent after EVT (54.6% vs 35.5%; p = 0.003). EVT was associated with fewer intraprocedural ruptures, ischemic complications, procedure-related morbidity, shunt-dependent hydrocephalus, and delayed cerebral ischemia, but with more frequent retreatment and post-treatment rerupture. In a sensitivity matched analysis incorporating treatment timing, the 90-day outcome difference was attenuated. Pretreatment rerupture occurred in 27 patients (6.8%), with more than half occurring within 2 days. CONCLUSIONS: In this nationwide propensity score–matched study of ruptured IC-BBAs, EVT and microsurgery showed distinct trade-off profiles. EVT was associated with favorable early functional recovery and fewer procedure-related complications, but with more frequent retreatment and post-treatment rerupture. Differences in 90-day recovery should be interpreted cautiously considering treatment-timing–related selection factors.