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Background: Hyperintensity of distal vessels on FLAIR-MRI has been associated with a higher grade of arterial collaterals and a smaller infarct volume in acute stroke patients. No studies analyze the influence of the hyperintense vessel (HV) sign on the speed of the ischemia progression during the first hours. Our aim was to study the association of the HV sign with progression of infarction in acute stroke patients. Methods: From a prospectively derived stroke database, we retrospectively selected acute stroke patients with a large artery occlusion of the anterior circulation admitted to our comprehensive stroke center with available baseline CT scan and a multimodal MRI carried out thereafter to make a decision about endovascular treatment. Progression of the ischemic area was calculated as the difference in the Alberta Stroke Program Early CT Scan (ASPECTS) score between CT scan and diffusion-weighted imaging (DWI). Slow progression was considered as no change or 1 point decrease on the ASPECTS score between both exams. The presence of HV on FLAIR sequence was graded as absent, subtle or prominent by two readers. Results: A total of 70 patients were included in the study. Mean time between baseline CT and MRI was 124 ± 82 min. ASPECTS score on baseline CT was 10 in 34% of patients, 9 in 49% and 8 or less in 17%. ASPECTS score was 2 (1–3) points lower in the DWI and this decrease did not correlate with the time elapsed between the two exams. Distal HV sign was observed in 57/70 (81%) patients (subtle in 33 and prominent in 24). HV was more frequently observed in patients with proximal artery occlusion. There were no differences regarding stroke severity, stroke subtype and ASPECTS score on baseline CT between groups. Patients with prominent HV showed a lower progression of the ischemic area [median ASPECTS score decrease, 1 (1–0)] compared with patients with subtle HV [median ASPECTS score decrease, 2 (2–1)] and patients with absence of HV [median ASPECTS score decrease, 3 (4–3)] (p < 0.001). Prominent HV was independently associated with slow progression of ischemia in a multivariate logistic regression analysis adjusted by systolic blood pressure on admission, site of occlusion and time elapsed between both neuroimaging exams compared to the absence of HV (OR, 16.2; 95% CI, 2.1–123.1) and to subtle HV sign (OR, 6.1; 95% CI, 1.5–23.9). Conclusion: HV sign on FLAIR, especially if prominent, is associated with a slow progression of the ischemic area in acute stroke patients with cerebral artery occlusion of the anterior circulation. This radiological sign may predict the speed of the ischemia progression, opening an opportunity for reperfusion therapies in longer time windows.