Introduction:Collateral circulation sustains cerebral perfusion in patients with arterial occlusion. Extensive arterial occlusion may redirect cerebral blood flow to compensate for insufficient perfusion. Cerebral artery occlusion can be observed in computed tomography perfusion imaging with increased mean transit time (MTT). However, in some cases, MTT delay occurs contralateral to the site of stenosis or occlusion. This delay cannot be explained simply by the collateral blood supply. Therefore, the authors considered the similarity of the perfusion delay observed at the normal site to that observed in subclavian steal syndrome.Case presentation:Three patients were reviewed: the first had severe stenosis in the left proximal internal carotid artery (ICA), and the second had left common carotid artery occlusion and diffusion restriction of the ICA-middle carotid artery border zone. The third patient had total occlusion of the left common carotid artery and right proximal ICA, with multifocal infarctions in the right frontal, occipital, left frontal, and parietal lobes. All 3 patients had a contralateral MTT delay on perfusion imaging.Conclusion:The site of stenosis or occlusion did not correlate with ipsilateral perfusion delay in these 3 cases. Based on the precedent relationship between infarction and perfusion delay, we developed 2 hypotheses to explain why perfusion decreases on the contralateral side of the occlusion or stenosis. However, this study was limited because we could not identify events, like volume loss or decreased blood pressure, before stroke development.