Flow Patterns in Carotid Webs: A Patient-Based Computational Fluid Dynamics Study

Abstract

Background and purpose: Carotid webs are increasingly recognized as an important cause of (recurrent) ischemic stroke in patients without other cardiovascular risk factors. Hemodynamic flow patterns induced by these lesions might be associated with thrombus formation. The aim of our study was to evaluate flow patterns of carotid webs using computational fluid dynamics.

Materials and methods: Patients with a carotid web in the Multicenter Randomized Clinical Trial of Endovascular Treatment of Acute Ischemic Stroke in the Netherlands (MR CLEAN) were selected for hemodynamic evaluation with computational fluid dynamics models based on lumen segmentations obtained from CT angiography scans. Hemodynamic parameters, including the area of recirculation zone, time-averaged wall shear stress, transverse wall shear stress, and the oscillatory shear index, were assessed and compared with the contralateral carotid bifurcation.

Results: In our study, 9 patients were evaluated. Distal to the carotid webs, recirculation zones were significantly larger compared with the contralateral bifurcation (63 versus 43 mm², P = .02). In the recirculation zones of the carotid webs and the contralateral carotid bifurcation, time-averaged wall shear stress values were comparable (both: median, 0.27 Pa; P = .30), while transverse wall shear stress and oscillatory shear index values were significantly higher in the recirculation zone of carotid webs (median, 0.25 versus 0.21 Pa; P = .02 and 0.39 versus 0.30 Pa; P = .04). At the minimal lumen area, simulations showed a significantly higher time-averaged wall shear stress in the web compared with the contralateral bifurcation (median, 0.58 versus 0.45 Pa; P = .01).

Conclusions: Carotid webs are associated with increased recirculation zones and regional increased wall shear stress metrics that are associated with disturbed flow. These findings suggest that a carotid web might stimulate thrombus formation, which increases the risk of acute ischemic stroke.

Fig 1.

A case with a carotid web in the ipsilateral carotid bifurcation of a patient with ischemic stroke. Images of CTA (A1) and CFD simulations (A2, streamlines; A3, wall shear stress). Focused on the region distal from the carotid web, a large recirculation zone is observed with low time-averaged WSS values. At the minimal lumen area at the location of the web, a high TAWSS is observed. Streamlines were based on the time-averaged velocity field.

Fig 2.

Boxplots showing the distribution of the total surface of the recirculation zone, TransWSS, OSI, and TAWSS for the carotid bifurcation with a web and the contralateral bifurcation. P values were obtained from a paired Wilcoxon signed rank test. A, Distribution of the total surface of the recirculation area, which was statistically significant (P = .02) larger in carotid bifurcations with a web compared with the contralateral carotid bifurcation (control group) within patients. B, Distribution of TransWSS in the recirculation zone, which was statistically significant (P = .02) larger in carotid bifurcations with a web compared with the contralateral carotid bifurcation (control group) within patients. C, Distribution of maximum OSI in the recirculation zone, which was statistically significant (P = .04) larger in carotid bifurcations with a web compared with the contralateral carotid bifurcation (control group) within patients. D, Distribution of maximum time-averaged wall shear stress (Pascal) at the level of the carotid bulb, which was statistically significant (P = .01) larger in carotid bifurcations with a web compared with the contralateral carotid bifurcation (control group) within patients.