MRA evaluation of aneurysms treated with woven endobridge (WEB) devices or coils: an inter- and intra-observer reliability study.

Background: Magnetic resonance angiography (MRA) is a commonly used non-invasive imaging modality for the follow-up of treated intracranial aneurysms. The 3-category Montreal classification system is widely used to evaluate treatment outcomes, including aneurysms treated with Woven EndoBridge (WEB) devices or coils. This study aimed to assess the reliability and clinical implications of the Montreal scale for aneurysms imaged with MRA.

Methods: An electronic portfolio of 60 aneurysms (30 treated with WEB devices and 30 with coils) was evaluated by 30 raters from diverse clinical backgrounds. Raters graded aneurysm occlusion using the Montreal classification system and provided management recommendations (delayed follow-up, close follow-up, or re-treatment). Twenty-three raters completed a second evaluation of permuted cases after one month. Reliability was assessed using Gwet's AC2 (κG) coefficients, and the correlation between occlusion grade and management recommendation was analyzed with Cramer's V.

Results: Inter-rater agreement for occlusion grades was substantial (κG = 0.70; 95% CI: 0.66-0.75) and similar for WEB-treated (κG = 0.66; 95% CI: 0.59-0.74) and coiled aneurysms (κG = 0.75; 95% CI: 0.68-0.82). Management decisions showed substantial agreement overall (κG = 0.68; 95% CI: 0.60-0.76). Mean intra-rater agreement was almost perfect (κG = 0.84 ± 0.06). Strong correlations were observed between occlusion grades and management recommendations (mean Cramer's V = 0.78 ± 0.13), with consistent management strategies across treatment modalities.

Conclusion: The Montreal scale demonstrated substantial reliability and clinical relevance for evaluating aneurysms treated with WEB or coils using MRA, supporting its use in non-invasive follow-up protocols.