Background Indications for flow diversion stent (FDS) treatment are expanding. However, there is still a lack of evidence for the long-term outcome in distally located aneurysms in the M2 segment of the middle cerebral artery (MCA) and beyond.

Methods Consecutive subjects (from June 2013 to August 2020) with MCA aneurysms in the M2 segment or beyond treated with FDS were reviewed retrospectively. The primary endpoints for clinical safety were the absence of mortality, stroke event, re-rupture of the aneurysm, and worsening of clinical symptoms. The primary endpoint for treatment efficacy was complete/near-complete occlusion at follow-up after 12 months.

Results 23 patients were identified: 7 aneurysms were located in the M2 segment of the MCA, 4 in the M2-M3 bifurcation, 2 in M3, 3 in M3-4 branching, and 2 in M4; 5 aneurysms were located in M2 with extension into the M1-M2 bifurcation. 13 aneurysms were of fusiform morphology, 8 sacculofusiform, and 2 saccular. 16 aneurysms were of highly suspected dissecting etiology. The median diameter of the parent vessel was 2.1 mm proximally and 2 mm distally. The median time of the follow-up was 30 months (range 16 months to 6 years). Complete/near complete occlusion was observed in 14/20 patients (70%) and one stable remodeling (5%) was seen at 12 months. 22 patients (95.6%) had an excellent clinical outcome (mRS 0–1) at 6 months. Technical challenges associated with the deployment of FDS occurred in 8.7% of cases. Severe complications, intraparenchymal hemorrhage and re-rupture of the aneurysm occurred in 2 patients (8.7%).

Conclusion Flow diversion of distally located aneurysms is technically feasible with low morbidity and mortality.