Reversed flow in the CB. Ultrasound vector flow imaging shows high‐velocity red vectors moving forward along the flow divider in the internal carotid artery (ICA; arrow). Some low‐velocity green vectors move back on the opposite wall to the flow divider in the ICA sinus (asterisk). Wall shear stress measurements (blue dots) at that level gave about normal maximum values (0.90–1.53 Pa) in 5 of the 6 samples and abnormal mean values (0.03–0.20 Pa) in all of the sample points as a consequence of the unsteady shear stress. CCA indicates common carotid artery; and ECA, external carotid artery.