BACKGROUND: The pipeline embolization device with adjunctive coiling (PAC) for small- and medium-sized unruptured cerebral aneurysms (UCAs) has not yet been fully evaluated for promoting aneurysm occlusion and preventing delayed rupture. The present study investigated the efficacy and safety of the PAC for UCAs ≤10 mm in diameter. METHODS: Fifty consecutive UCAs (50 patients) ≤10 mm in diameter that underwent flow diversion with a single pipeline embolization device (PED) at three institutions between January 2019 and January 2024 were retrospectively reviewed. Patients were divided into PAC- (n = 23) and PED-alone (n = 27) groups. Data were compared regarding embolization results and complications. RESULTS: Aneurysms with bleb formation, medium-sized aneurysms (7-10 mm), and those treated via transfemoral access were significantly more frequently managed with PAC than PED alone. In the PAC group, Raymond-Roy Occlusion Classification scores immediately after treatment were class 1 in 1 case (4.3%) and class 3 in 22 cases (96%), with a mean volume embolization ratio of 20.6%. The PAC group had a significantly longer procedure time (184 vs. 117 minutes, P <
0.002) but showed no differences in ischemic or hemorrhagic complications, access site complications, or in-stent stenosis. Complete occlusion was significantly higher in the PAC group at 6 months (100% vs. 67%, P = 0.002) and 1 year (100% vs. 74%, P = 0.011). No delayed complications, including ischemic events, aneurysm rupture, or death, were observed in either group. CONCLUSIONS: PAC for UCAs ≤10 mm in diameter may enhance the rate of complete occlusion without increasing the risk of complications.