Centrum Semiovale Perivascular Spaces Predict First Hemorrhagic Lesion in Asymptomatic Amyloid‐Positive Individuals

OBJECTIVE: Identification of cerebral amyloid angiopathy (CAA) before its hemorrhagic manifestations remains limited. We aimed to determine whether severe enlarged perivascular spaces in the centrum semiovale (EPVS-CSO) identify a prehemorrhagic stage of sporadic CAA by predicting the first appearance of CAA-related hemorrhagic lesions or incident cognitive decline in amyloid-positive, cognitively unimpaired, hemorrhage-free older adults. METHODS: We performed a secondary analysis of the Anti-Amyloid Treatment in Asymptomatic Alzheimer's Disease (A4) trial, a phase 3 randomized study in cognitively unimpaired, amyloid-positive older adults. Participants with baseline hemorrhagic lesions were excluded. Baseline EPVS-CSO severity was dichotomized as severe versus nonsevere. Severe basal ganglia EPVS, more closely associated with hypertensive small vessel disease, was evaluated as a topographical negative-control exposure. The primary outcome was incident strictly lobar cerebral microbleeds or cortical superficial siderosis. The secondary outcome was longitudinal cognitive trajectories measured by the Preclinical Alzheimer Cognitive Composite. RESULTS: Among 932 participants (mean age 71.7 ± 4.8 years; 61.3% female), 101 (10.8%) had severe EPVS-CSO at baseline. Over a median follow up of 5.1 years (IQR 3.3-5.5 years), 33.7% of those with severe EPVS-CSO developed incident CAA-related hemorrhagic lesions compared with 13.6% of those with nonsevere EPVS-CSO (adjusted HR 2.85, 95% CI 1.91-4.25; p < 0.0001). Severe basal ganglia EPVS was not associated with incident hemorrhagic lesions (adjusted HR 0.87, 95% CI 0.35-2.18; p = 0.77). Severe EPVS-CSO was not associated with early cognitive differences, and participants who developed incident hemorrhagic lesions showed more pronounced cognitive decline. INTERPRETATION: These findings identify severe EPVS-CSO as a strong predictor of first appearance of CAA-related hemorrhagic lesions in amyloid-positive individuals, supporting integration of amyloid biomarkers into magnetic resonance imaging-based Boston criteria. Identifying markers of the transition of CAA from a nonhemorrhagic to a hemorrhagic stage provides a potential foundation for approaching primary prevention of CAA-related hemorrhage. ANN NEUROL 2026.