Non-linear association between aneurysm size ratio and in-stent stenosis after flow diverter treatment: A retrospective cohort study of patients with unruptured aneurysms.

Background And Purpose: Flow diversion (FD) treatment has emerged as an effective endovascular therapy for intracranial aneurysms, but in-stent stenosis remains a significant complication affecting patient outcomes. The size ratio (SR) of aneurysms may influence this outcome, but their relationship remains unclear. We investigate the association between intracranial aneurysm SR and in-stent stenosis after FD treatment.

Methods: This retrospective cohort study included 217 patients with unruptured aneurysms who underwent with flow-diversion treatment from January 2020 to January 2022. SR was the exposure variable, and in-stent stenosis within one year was the outcome. Covariates included demographic, clinical, and procedural factors. Binary logistic regression and two-piecewise linear models were used for analysis.

Results: Using binary logistic regression, we found that for every increase in SR by 1, there was on average an associated with a 37 % reduction in stenosis risk (RR = 0.63, 95 %CI: 0.40-0.99, P = 0.046). Further two-piecewise linear regression analysis identified a piecewise linear relationship between SR and in-stent stenosis with a threshold effect at SR = 3.50 (P for log likelihood ratio test = 0.037). In the low SR range (≤3.50), each unit increase in SR was significantly associated with a 54 % lower risk of in-stent stenosis (adjusted RR = 0.46, 95 % CI: 0.25-0.85, P = 0.013) after adjusting for potential confounders. However, in the high SR range (>3.50), this association became non-significant (adjusted RR = 1.56, 95 % CI: 0.51-4.77, P = 0.438).

Conclusion: The relationship between aneurysm SR and in-stent stenosis risk demonstrates a piecewise linear pattern with a threshold effect at SR = 3.50. Among aneurysms with SR values of 3.50 or less, each unit increase in SR corresponded to a 54 % decrease in stenosis risk.