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

Abstract

Background and Purpose-The purpose of the present study was to assess whether 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 internal carotid artery (ICA) who did not experience recurrent cerebral ischemic symptoms. Methods-Sixty-two patients with a symptomatic ICA occlusion were investigated within 6 months after symptoms occurred. The investigations were repeated after 6 and 12 months. The directions of flow in the A1 segment and the posterior communicating artery (PCoA), both on the side of the symptomatic ICA 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 A1 segment only, via the PCoA only, via the A1 segment plus the PCoA, or no collateral flow via the circle of Willis. The direction of flow in the OphA was investigated with transcranial Doppler sonography. CO 2 reactivity was determined with transcranial Doppler sonography to investigate whether changes in flow patterns were accompanied by changes in cerebrovascular reactivity. Results-There were no statistically significant changes over time in the direction of blood flow in the A1 segment and the PCoA or in the pattern of collateral flow via the circle of Willis. On average, 72% of patients with a unilateral ICA occlusion (nϭ41) had willisian collateral flow compared with 37% of patients with a bilateral ICA occlusion (nϭ21; PϽ0.05). Patients with a unilateral ICA occlusion tended to a lower prevalence of reversed flow via the OphA over time. CO 2 reactivity did not change significantly in any patient group. In patients with a unilateral ICA occlusion, decreased CO 2 reactivity was associated with a higher prevalence of absent willisian collateral flow and a lower prevalence of collateral flow via the A1 segment plus 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.

Effect of Collateral Blood Flow and Cerebral Vasomotor Reactivity on the Outcome of Carotid Artery Occlusion

“…17 Finally, a recent study suggested that patients with ICA occlusion who had a decreased CO 2 reactivity more often showed absent willisian collateral flow and less often showed collateral flow via both primary pathways compared with patients who had a normal CO 2 reactivity. 40 A study with MRA and TCD 18 demonstrated that in symptomatic patients with ICA occlusions, different collateral flow patterns via the ACoA, PCoA, or OA have no effect on hemodynamic and metabolic parameters as long as 1 of these pathways is present. The absence of collateral flow via ACoA, ipsilateral PCoA, and ipsilateral OA can result in severely deteriorated hemodynamic and metabolic status, presumably increasing the risk of stroke.…”

Time Course of Vascular Reactivity Using Repeated Phase-Contrast MR Angiography in Patients With Carotid Artery Stenosis

“…Collateral circulation in the circle of Willis was determined according to a previously published imaging protocol with 2 consecutive 2-dimensional phase-contrast measurements, of which 1 was phase-encoded in the anteroposterior direction and 1 in the right-left direction. 13 …”

Arterial Spin-Labeling MR Imaging Measurements of Timing Parameters in Patients with a Carotid Artery Occlusion

“…The presence of collateral flow was assessed with intra-arterial DSA and MR angiography (MRA). The direction of blood flow in the circle of Willis was assessed according to a previously published imaging protocol, 13 with 2 consecutive 2D phase-contrast MR imaging measurements, of which 1 was phase-encoded in the left-right direction and 1, in the anteroposterior direction. Anterior collateral flow was defined as flow across the anterior communicating artery with retrograde flow in the precommunicating part (A1 segment) of the anterior cerebral artery (ACA).…”