Elsevier

World Neurosurgery

Volume 154, October 2021, Pages e443-e457
World Neurosurgery

Original Article
Turbulence Intensity as an Indicator for Ischemic Stroke in the Carotid Web

https://doi.org/10.1016/j.wneu.2021.07.049Get rights and content

Objective

Carotid web (CaW) is reported as one of the causes of cryptogenic strokes. However, its pathophysiology is not known, which makes clinicians debate CaW treatment. The current study presents the mechanism of ischemic stroke in CaW and finds a potential indicator for ischemic stroke in CaW.

Methods

Computational fluid dynamics (CFD) was applied to computer-aided artificial human CaW models to investigate the correlation between stenosis rate and CaW angle. The CFD results were compared with stroke or symptomatic CaW including adequate reported images for anatomic analysis of the stenosis rate and CaW angle.

Results

The CFD result of the CaW models shows that the velocity decreases and the turbulence generation of blood flow increases in the area under CaW (AuCaW). In AuCaW, turbulence intensity (TI) is high in the high stenosis rate and small angle conditions. Moreover, TI remained high in the AuCaW throughout the cardiac cycles. The analysis of 67 anatomic figures appeared in 36 articles merged with CFD results, and a CaW scoring system was introduced for clinicians to determine patients with CaW with a high risk of ischemic stroke.

Conclusions

This study is believed to be the first to apply TI to CaW. Because most ischemic strokes in CaW occurred at a high stenosis rate and small angle, TI may be used as a potential indicator of ischemic stroke in CaW. Furthermore, TI is easily used in the daily clinical field by applying CaW scores.

Introduction

Carotid web (CaW) is one of the intimal fibromuscular dysplasias characterized by fibroelastic thickening of the arterial intima forming a membrane with an orifice structure occurring at the most proximal portion of the internal carotid artery (ICA).1, 2, 3, 4, 5 Unlike atherosclerosis, CaW does not contain thrombogenic disease. However, it has been reported as one of the causes of cryptogenic strokes (9.4%–37%).1,5, 6, 7, 8

However, CaW treatment methods have been debated among clinicians.9 Moreover, >50% and 23% of responders chose to use antiplatelet drugs and observe for asymptomatic patients with CaW, respectively. However, no responders chose to use anticoagulants. For patients with acute stroke with CaW, >50%, 7%, and 21% of responders chose to use antiplatelet drugs and anticoagulant drugs and perform stent deployment or endarterectomy for CaW. For CaW with recurrent stroke, >50% of responders chose to perform stent deployment or endarterectomy.

This study assumed that the debate on CaW treatment is caused by a lack of knowledge of CaW pathophysiology. According to the pathologic findings and clinical presentations, the current study focused on the blood flow around the CaW as the cause of ischemic strokes. Hence, a series of computational fluid dynamics (CFD) simulations was conducted and compared with reported CaW ischemic strokes, the pathophysiology of which it has not yet been possible to find in vivo.

Section snippets

Review of Literature

A literature search was performed using PubMed with literature from 1968 to July 2020 using combinations of the following terms: (“Carotid web” OR “Carotid bulb web” OR “Carotid artery web” OR “Carotid artery stenosis” OR “Atypical fibromuscular hyperplasia” OR “Fibromuscular dysplasia” OR “Fibromuscular hyperplasia”) AND (“Ischemic” OR “Ischemia” OR “Recurrent” OR “Embolic” OR “Thromboembolism” OR “Stroke” OR “Symptom” OR “Cryptogenic” OR “Silent”). Two conditions were required for these

Results

The current study found 3866 articles from a PubMed search. Among these articles, 67 figures from 36 articles met the requirements of this study.1, 2, 3,5, 6, 7, 8,14,20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47 The stenosis rate and CaW angle were independently measured from these figures by 2 neurosurgeons (J.C. and J.K.). Moreover, the interobserver agreement of these values was represented by the Bland-Altman plots, where the

Discussion

High stenosis rate and the nature of atherosclerosis plaque are 2 important factors of ischemic stroke in carotid bulb atherosclerosis.48 High stenosis rate is usually related to hemodynamic stroke because blood flow is altered by atherosclerosis. Moreover, the nature of atherosclerosis plaque is usually engaged with an embolic stroke, especially in hyperechoic plaque.49 Unlike carotid bulb atherosclerosis, histologic CaW evidence shows that it does not contain atherosclerotic change, which is

Conclusions

CFD has been conducted to analyze the CaW pathophysiology. The result of CFD represents various aspects of the hemodynamics around CaW. TI is applied to the CaW, for what is believed to be the first time. Furthermore, TI gives more information on the nature of the hemodynamics for the AuCaW than does WSS and velocity. Moreover, it gives a logical explanation of the clinical data obtained from previous studies. Furthermore, using it in the daily clinical field will be easy by introducing the CaW

CRediT authorship contribution statement

Taewoong Bae: Writing – original draft, Data curation. Jung Ho Ko: Conceptualization, Writing – review & editing. Jaewoo Chung: Conceptualization, Writing – review & editing, Visualization, Supervision.

Acknowledgments

The authors would like to express sincere gratitude to Dr. Sang K. Chung, Professor Emeritus of Department of Mathematics Education, Seoul National University, for his invaluable comments and suggestions on the mathematics of CFD. Our thanks also go to SimFlow Technologies, developer of the computational fluid dynamics (CFD) software SimFlow (https://sim-flow.com/), for courtesy of the SimFlow software.

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    Conflict of interest statement: The authors declare that the article content was composed in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

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