Thromboembolic events remain a periprocedural concern despite latest-generation flow diverters (FDs), including the Pipeline Embolization Device-Flex with Shield technology (PEDS). We examined the association between FD-to-parent artery (PA) diameter mismatch and postoperative diffusion-weighted imaging–positive lesions (DPLs) after PEDS treatment.

This retrospective cohort study included patients with unruptured intracranial aneurysms who underwent PEDS treatment and postoperative MRI within 48 h at a single center (June 2019–February 2026). We evaluated the nonlinear association between the stent-to-distal PA diameter ratio (RDd) and DPL count.

Overall, 58 patients with 61 aneurysms undergoing 64 procedures were analyzed. Segmented negative binomial regression demonstrated a nonlinear association between RDd and DPL count, with an exploratory breakpoint estimated at 1.25 (Davies test, P = 0.01). Procedures were classified into high (RDd ≥1.25; n = 23) and low (RDd <1.25; n = 41) ratio groups. The high-ratio group had more DPLs (median, 10 vs. 2; P < 0.001). After adjustment for sex and percutaneous transluminal angioplasty (PTA), RDd ≥1.25 was associated with higher DPL counts (adjusted incidence rate ratio, 4.12; 95% confidence interval [CI], 2.53–6.80; P < 0.001), whereas PTA was associated with fewer DPLs (adjusted incidence rate ratio, 0.59; 95% CI, 0.34–0.99; P = 0.05). RDd association remained consistent in sensitivity analyses excluding PTA from adjustment.

A higher stent-to-distal PA diameter ratio was associated with greater postoperative DPL burden after PEDS treatment, with an exploratory breakpoint near 1.25. Assessment of diameter mismatch may inform procedural risk evaluation, although the estimated breakpoint requires external validation.