Predictors of complete occlusion in endovascular coiling of very small intracranial aneurysms

Background Very small intracranial aneurysms (VSAs ≤ 3 mm) are increasingly treated endovascularly, yet procedural fragility and long-term durability remain disputed. Device miniaturization and adjunctive balloon- or stent assistance have improved immediate occlusion, but contemporary single-center outcome data with multivariable modeling are sparse. Methods We retrospectively analyzed a prospectively maintained database (2013–2024) for all VSAs treated endovascularly. Demographics, aneurysm morphology, and procedural details were abstracted from digital subtraction angiography (DSA). At the last follow-up, the primary endpoint was complete occlusion; secondary endpoints were favorable functional outcomes, retreatment, and procedural complications. Multivariable logistic regression was adjusted for rupture status, aneurysm width, location, adjunct use, and immediate occlusion. Results One-hundred-eighty-five very small intracranial aneurysms (VSAs ≤ 3 mm) (median dome 2.6 mm, 21% < 2 mm) were treated in 185 patients (median age 57.9 years, 71.9% female). 34% presented ruptured; 56% were bifurcation lesions, most commonly at the anterior communicating complex (34.6%). Balloon-assist, stent-assist, and flow diversion were used in 32.4%, 42.7%, and 4.9%, respectively. Immediate complete occlusion was achieved in 53%; at a median 12-month imaging follow-up, complete occlusion was 74.6%, and the retreatment rate was 9.7%. Procedural complications occurred in 10.8% overall, comprising major complications 2.2% (intra-operative rupture 1.1%, thromboembolism 1.1%) and other complications 8.6% ; there were no procedure-related deaths. 93% of patients had a favorable clinical outcome at 13.6-month clinical follow-up. On multivariable analysis, predictors of complete occlusion at last follow-up were complete occlusion at the end of the procedure (OR 3.53), whereas rupture, posterior-circulation location, width, and diameter < 2 mm independently reduced obliteration odds. Conclusions Endovascular coiling of VSAs provides high occlusion and excellent clinical outcomes with minimal morbidity. Anatomical complexity (ultra-small size, posterior circulation) and incomplete initial packing remain targets for technical optimization and prospective evaluation.