CONCLUSIONS: Antegrade collateral internal carotid artery flow was found in 60% of patients with common carotid artery occlusion and was mainly supplied by retrograde external carotid artery flow. It contributes to maintenance of middle cerebral artery territory regional cerebral blood flow.he regional cerebral blood flow ipsilateral to the occlusion at rest was higher in patients with common carotid artery occlusion than those with internal carotid artery occlusion (mean ± SD, 40.4 ± 8.5 versus 34.3 ± 6.2 mL/100 g/min; P = .02).