Reduced Hypoxic Tissue and Cognitive Improvement after Revascularization Surgery for Chronic Cerebral Ischemia

Abstract

Background: Hypoxic but viable neural tissue is seen on 1-(2–¹⁸F-fluoro-1-[hydroxymethyl]ethoxy) methyl-2-nitroimidazole (¹⁸F-FRP170) positron emission tomography (PET) in patients with chronic cerebral ischemia with a combination of misery perfusion and moderately reduced oxygen metabolism. Cognitive function sometimes improves after revascularization surgery in patients with chronic cerebral ischemia. Objectives: We used brain perfusion single-photon emission computed tomography (SPECT) and ¹⁸F-FRP170 PET to determine whether hypoxic tissue was reduced following the restoration of cerebral perfusion after carotid endarterectomy (CEA) in patients with severe stenosis of the cervical internal carotid artery (ICA) and whether the reduction in hypoxic tissue was associated with cognitive improvement. Method: Eighteen patients with abnormally reduced cerebral blood flow (CBF) in the affected cerebral hemispheres on preoperative brain perfusion SPECT ­underwent CEA. They underwent ¹⁸F-FRP170 PET and neuropsychological tests preoperatively and 6 months postoperatively. Brain perfusion SPECT was also performed 6 months postoperatively. Regions of interest were placed in the bilateral middle cerebral artery territories on SPECT and PET images, and the ratio of values in the affected versus contralateral hemispheres was calculated. Results: The CBF ratio (p = 0.0006) and ¹⁸F-FRP170 ratio (p = 0.0084) were significantly increased and reduced, respectively, after surgery compared to the corresponding ratios before surgery. The difference in the ¹⁸F-FRP170 ratio (postoperative – preoperative value) was negatively correlated with the difference in the CBF ratio (ρ = –0.695; p = 0.0009). The difference in the ¹⁸F-FRP170 ratio was significantly lower in patients with postoperative improved cognition compared to that in those without (p = 0.0007). The area under the receiver operating characteristics curve for the difference in the ¹⁸F-FRP170 ratio for detecting postoperative improved cognition was significantly greater than that for the difference in the CBF ratio (difference between areas, 0.278; p = 0.0248). Conclusions: Hypoxic tissue is reduced following the restoration of cerebral perfusion with revascularization surgery in patients with severe atherosclerotic stenosis of the cervical ICA. The reduction in hypoxic tissue is associated with cognitive improvement in such patients.