In patients with occlusion of the internal carotid artery (ICA), the presence of internal borderzone (IBZ) infarcts has been associated with impaired perfusion to the brain [1, 2]. We assessed vasomotor reactivity and collateral flow patterns in 36 patients with recent transient ischemic attack or minor ischemic stroke associated with ICA occlusion and studied whether presence of IBZ infarcts would predict recurrent stroke. All patients underwent magnetic resonance imaging (MRI), digital subtraction angiography, and transcranial Doppler CO2-reactivity examination. We assessed whether collateral flow was present via the ophthalmic artery, via the anterior and posterior communicating artery, or via leptomeningeal arteries defined as pial branches from the posterior cerebral artery extending as far as the vascular territory of the middle or anterior cerebral artery. Fifteen patients (42%) had IBZ infarcts on their MRI. No differences in collateral flow patterns on angiograms were found between patients with and without IBZ infarcts. Mean CO2-reactivity was lower in patients with IBZ infarcts [6%, standard deviation (SD) 9%] than in patients without IBZ infarcts [20%, SD 14%; mean difference 14%, 95% confidence interval (CI) 5–23]. During follow-up (mean 2·4 years, SD 1·3), three (20%) patients with IBZ infarcts had a recurrent stroke vs. four (19%) patients without IBZ infarcts [hazard ratio: 1·0 (95% CI 0·2–4·6)]. Six of the seven recurrent infarcts occurred in the hemisphere ipsilateral to the ICA occlusion.
This study shows that in patients with symptomatic ICA occlusion, IBZ infarcts are associated with low CO2-reactivity but cannot be utilized to identify patients who are at high risk of future ischemic stroke.