Arterial supply of the temporo-medial region of the brain: significance for preoperative vascular occlusion testing

Ipsilateral foetal-type posterior cerebral artery is associated with cognitive decline after carotid revascularisation

Background

Stenosis of the internal carotid artery has been associated with cognitive impairment and decline. However, studies testing the effect of carotid revascularisation on cognition have had conflicting results. This may in part be explained by variation in the flow territory of the carotid artery. In 12 to 36% of the patients, the posterior cerebral artery is mainly or exclusively supplied by the internal carotid artery via a foetal-type posterior cerebral artery. In these patients, ipsilateral carotid artery stenosis is likely to result in a larger area with hypoperfusion than in case of a normal posterior cerebral artery. Patients with a foetal-type posterior cerebral artery could therefore benefit more from revascularisation. We compared the effects of carotid revascularisation on cognition between patients with a foetal-type and those with a normal posterior cerebral artery.

Methods

Patients with symptomatic internal carotid artery stenosis ≥ 50%, enrolled in the International Carotid Stenting Study (ICSS) at a single centre, underwent detailed neuropsychological examinations before and 6 months after revascularisation. Cognitive test results were standardized into z-scores, from which a cognitive sumscore was calculated. The primary outcome was the change in cognitive sumscore between baseline and follow-up. Changes in cognitive sumscore were compared between patients with an ipsilateral foetal-type and those with a normal posterior cerebral artery, as assessed with CT or MR angiography.

Results

Of 145 patients enrolled in ICSS at the centre during the study period, 98 had both angiography at baseline and neuropsychological examination at baseline and at 6-months follow-up. 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). This did not change essentially after adjustment for baseline factors.

Conclusion

An ipsilateral foetal-type posterior cerebral artery appears to increase cognitive decline after carotid revascularisation. Our findings have to be reproduced in an independent study before further implications can be made.

The contribution of posterior circulation to memory function during the intracarotid amobarbital procedure

The purpose of this study was to evaluate the contribution of posterior circulation to memory function by comparing memory scores between patients with and without a foetal-type posterior cerebral artery (FTP) during the intracarotid amobarbital procedure (IAP) in epilepsy patients. Patients undergoing bilateral IAP between January 2004 and January 2010 were retrospectively included. Pre-test angiograms were assessed for the presence of a FTP. Memory function scores (% correct) after right and left injections were obtained. Functional significance of FTP was affirmed by relative occipital versus parietal EEG slow-wave increase during IAP. Memory and EEG scores were compared between patients with and without FTP (Mann-Whitney U test). A total of 106 patients were included, 73 with posterior cerebral arteries (PCA) without FTP ('non-FTP'), 28 patients with unilateral FTP and 5 with a bilateral FTP. Memory scores were lower when amytal was injected to the hemisphere contralateral to the presumed seizure focus (on the right decreasing from 98.3 to 59.1, and on the left decreasing from 89.1 to 72.4; p < 0.001). When IAP was performed on the side of FTP memory scores were significantly lower (70.8) compared to non-FTP (82.0; p = 0.02). Relative occipital EEG changes were 0.44 for FTP cases and 0.36 for non-FTP patients (p = 0.01). A relationship between vasculature and brain function was demonstrated by lower memory scores and more slow-wave activity on occipital EEG during IAP in patients with foetal-type PCA compared to patients with non-FTP. This suggests an important contribution of brain areas supplied by the PCA to memory function.