The cognitive sum score decreased by 0.28 ( 95 % confidence interval , 0.10 to 0.45 ) in 13 patients with an ipsilateral foetal-type posterior cerebral artery and by 0.07 ( 95 % CI , 0.002 to 0.15 ) in 85 patients with a normal posterior cerebral artery ( mean difference , -0.20 ; 95 % CI , -0.40 to -0.01 ) .