Introducing the Caliber-Flow Status Scale (CFSS): a novel tool for assessing covered cortical branch status after flow diverter treatment of middle cerebral artery aneurysms

Background This study assessed caliber and flow changes of covered cortical middle cerebral artery (MCA) branches using the new Caliber-Flow Status Scale (CFSS), postoperative diffusion-weighted imaging (DWI) lesions, and clinical outcome following flow diverter (FD) treatment of MCA aneurysms. Methods This single-center retrospective study collected data from patients treated with FD between January 2016 and March 2024, including patient characteristics, aneurysm features, postoperative DWI lesions, and clinical outcomes. Vessel status was assessed using CFSS: 1a (normal caliber and flow), 1b (normal caliber, reduced flow), 2a (reduced caliber, normal flow), 2b (reduced caliber and flow), and 3 (occlusion). Results Thirty-nine patients with 41 aneurysms with 63 covered MCA branches were included. Immediately after FD deployment, 63.5% of covered branches retained normal caliber and flow (CFSS 1a) while the remaining branches with compromised caliber and flow (CFSS >1a) showed significant improvement following tirofiban administration. Intraoperative thromboembolic complications led to occlusion in three branches, all restored after tirofiban without clinical symptoms (P=0.003). At 6 months, 79% of covered branches showed normal flow with or without caliber reduction (CFSS 1a/2a). DWI lesions showed no significant correlation with caliber and flow changes and clinical symptoms. Conclusions FD treatment for MCA aneurysms leads to significant but primarily asymptomatic CFSS changes in covered cortical branches within the first 6 months. Intra-arterial tirofiban effectively improves vessel status in branches with higher CFSS (>1a). CFSS is valuable for tracking these changes and underscores the importance of long-term follow-up.