Predictors of In-Stent Stenosis after Flow Diversion of Intracranial Aneurysms using the Flow Redirection Endoluminal Device-X (FRED-X): A Multicenter Analysis of 6 and 12-Month Outcomes

Introduction: In-stent stenosis (ISS) occurs in about 0-55.3% of cases after flow diversion and may require modifications in antiplatelet regimen or retreatment based on the severity of symptoms. The Flow Redirection Endoluminal Device-X (FRED-X) is a newer generation flow diverter with surface modifications. Our study identifies predictors of ISS after flow diversion using the FRED-X.

Methods: This was a retrospective study of patients who underwent flow diversion of an intracranial aneurysm at six institutions across the United States between February 2022- February 2024. ISS was categorized as mild (0-25%, moderate (51-75%) or severe (76-100%) based on digital subtraction angiography. Outcomes of interest were the presence of ISS at 6- or 12-month follow up.

Results: 154 patients with 161 aneurysms underwent flow diversion with 164 FRED-X devices. At 6-months, 15.1% cases (n= 21) developed ISS on angiographic follow up. 61.9% of patients (n= 13) developed mild ISS, 33.3% (n= 7) patients had moderate ISS and 4.7% (n= 1) patient had severe ISS. On multivariate regression, cardiovascular disease and FRED-X stent length were associated with 6.25-fold (95% CI: 1.19- 32.86) and 1.09-fold (95% CI: 1.00- 1.20) higher odds of developing ISS at 6-months, while aneurysm width was associated with decreased odds of developing ISS (OR: 0.61, 95% CI: 0.38- 0.88). At 12-months, 12.0% of cases (n= 10) developed ISS. 80% of this cohort (n= 8) developed mild ISS, while one patient each developed moderate and severe ISS. All patients who developed ISS were functionally independent.

Conclusion : Our study reports ISS at rates of 15.1% and 12% at 6- and 12-months after flow diversion using the FRED-X. However, these patients were functionally independent and did not require retreatment. Cardiovascular disease, smaller aneurysm width and stent length were independent predictors of ISS after flow diversion using the FRED-X. Further prospective studies are necessary to validate these findings.