A longitudinal study of collateral flow patterns in the circle of willis and the ophthalmic artery in patients with a symptomatic internal carotid artery occlusion

Background and Purpose-The purpose of the present study was to assess wheth er the direction of flow via the circle of Willis and the ophthalmic artery (OphA) changed over time in patients with a symptomatic occlusion of the i nternal carotid artery (ICA) who did not experience recurrent cerebral isch emic symptoms. Methods-Sixty-two patients with a symptomatic ICA occlusion were investigat ed within 6 months after symptoms occurred. The investigations were repeate d after 6 and 12 months. The directions of flow in the Al segment and the p osterior communicating artery (PCoA), both on the side of the symptomatic I CA occlusion, were assessed with the use of magnetic resonance angiography. The pattern of collateral flow via the circle of Willis was categorized as via the Al segment only, via the PCoA only, via the Al segment plus the PC oA, or no collateral flow via the circle of Willis. The direction of flow i n the OphA was investigated with transcranial Doppler sonography. CO2 react ivity was determined with transcranial Doppler sonography to investigate wh ether changes in flow patterns were accompanied by changes in cerebrovascul ar reactivity. Results-There were no statistically significant changes over time in the di rection of blood flow in the Al segment and the PCoA or in the pattern of c ollateral flow via the circle of Willis. On average, 72% of patients with a unilateral ICA occlusion (n=41) had willisian collateral flow compared wit h 37% of patients with a bilateral ICA occlusion (n=21; P<0.05). Patients w ith a unilateral ICA occlusion tended to a lower prevalence of reversed flo w via the OphA over time. CO2 reactivity did not change significantly in an y patient group. In patients with a unilateral ICA occlusion, decreased CO2 reactivity was associated with a higher prevalence of absent willisian col lateral flow and a lower prevalence of collateral flow via the Al segment p lus the PCoA. Conclusions-The absence of recurrent cerebral ischemic symptoms in patients with a symptomatic ICA occlusion is not associated with an improvement in collateral flow via the circle of Willis or the OphA during 1.5-year follow -up.