Focal Cerebral Arteriopathy Severity Score Validation and Temporal Dynamics in Korean Pediatric Stroke: Distinguishing Inflammatory Arteriopathy From Unilateral Moyamoya Disease

BACKGROUND AND PURPOSE: Focal cerebral arteriopathy-inflammatory type (FCA-i) is a leading cause of pediatric arterial ischemic stroke, but diagnostic challenges persist, particularly in East Asian populations where moyamoya disease (MMD) prevalence is high. The Focal Cerebral Arteriopathy Severity Score (FCASS) quantifies arteriopathy severity but has not been validated in East Asian cohorts. We aimed to validate FCASS in Korean pediatric patients with FCA-i and compare temporal progression patterns with unilateral moyamoya disease. METHODS: We conducted a retrospective cohort study of children with arterial ischemic stroke presenting to Seoul National University Hospital between January 2002 and December 2024. Patients were classified according to Childhood Arterial Ischemic Stroke Standardized Classification and Diagnostic Evaluation criteria. The FCASS was applied to serial magnetic resonance angiograms at baseline, peak severity, and final follow-up. Clinical outcomes were assessed using the Pediatric Stroke Outcome Measure at 12 months. RESULTS: Among 216 children with arterial ischemic stroke, 132 patients (61.1%) demonstrated arteriopathy, including 49 with FCA-i and 60 with MMD. In FCA-i patients, the severity score correlated significantly with baseline infarct burden (ρ=0.42, P =0.0069) and exhibited characteristic monophasic evolution with early peak at 2 months followed by gradual recovery reaching lowest values at 11 months. Unilateral MMDpatients demonstrated consistently higher severity scores at all timepoints compared with FCA-i (baseline: 6.0 vs 2.0; final: 8.0 vs 3.0, P