Neuroanatomical study
A multidetector CT angiography study of variations in the circle of Willis in a Chinese population

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Abstract

The circle of Willis is a major collateral circulation that has an important role in ischemic events. The purpose of our study was to investigate the collateral circulation in a Chinese population with 64-section multidetector CT angiography (CTA). A total of 170 patients who underwent 64-section CT angiography at The First Affiliated Hospital of Chongqing Medical University were included in our study. The morphological variations in the anterior and posterior circle of Willis were assessed in each patient. A total of 160 patients were included in the final analysis, of whom 126 (79%) demonstrated a complete anterior circle of Willis, and 50 (31%) had a complete posterior circle of Willis. A complete circle of Willis was seen in 43 of 160 participants (27%). A fetal-type posterior circle of Willis was seen in 15 (9.4%) patients. This is the first report of a CTA study of collateral circulation in a Chinese population. A higher prevalence of compromised posterior collaterals was observed in this Chinese population compared to Western and Japanese populations.

Introduction

The cerebral collateral circulation in the circle of Willis is an important potential pathway that maintains adequate blood flow in various ischemic conditions.[1], [2], [3] In patients with severe carotid artery stenosis or occlusion, redistribution of blood flow through the cerebral collateral pathways improves cerebral perfusion in ischemic areas and may protect against ischemic events.[4], [5] The recruitment of circle of Willis collateral flow to any ischemic area depends on the presence and patency of its component vessels.

Because of prior limitations in non-invasive evaluation methods, current knowledge of the morphologic variations in the circle of Willis is mainly based on postmortem autopsy studies. Recent technical advance in CT angiography (CTA) technology have made direct visualization of the circle of Willis collaterals possible in large patient populations.6

The morphological characteristics of the circle of Willis have been documented in various studies of patients with cerebrovascular disorders.[7], [8] In previous reports, the absence of cerebral collateral function has been regarded as a risk factor for ischemic stroke.9 Recently, correlations between certain types of variations in the circle of Willis and development of intracranial aneurysms have been proposed.[10], [11] In previous studies, it has been noted that considerable cerebral collateral variations exist in patients with cerebrovascular disorders. However, previous studies have only documented the variations of the collateral circulation in Western populations, and the configuration of the collateral circulation in a Chinese population remains largely unknown. We hypothesized that the collateral circulation may differ in different ethic groups. Thus, the purpose of our study was to investigate the morphologic variations in the circle of Willis in a Chinese population using 64-section CTA and to compare our findings with previous reports from Western countries.

Section snippets

Participants

This study was approved by the Ethics Committee of Chongqing Medical University. Informed consent was obtained from all participants. A total of 170 healthy participants (86 men, 84 women; mean age, 46 years) who underwent 64-section CTA at The First Affiliated Hospital of Chongqing Medical University were retrospectively reviewed for evaluation of the circle of Willis configurations. Inclusion criteria were as follows: (i) no past history of transient ischemic attack, acute ischemic stroke or

Participants

All participants underwent a 64-section CTA examination at our institution. There were no technical failures or complications. Of the 170 participants who underwent CTA examination, seven were excluded because of incidental aneurysms (n = 5), an arteriovenous malformation (n = 1) and moyamoya disease (n = 1) on CT angiograms. Thus, the circle of Willis configurations were evaluated in 163 participants. However, another three participants were excluded from the final analysis because assessment of

Discussion

The collateral circulation in the circle of Willis has been widely investigated since Sir Thomas Willis first described the circle in 1664. In early studies, knowledge about the circle of Willis was mainly based on dissection and measurement of autopsy brains.[12], [13] In early autopsy studies, the diameters of arterial segments in the circle of Willis were usually assessed after formalin fixation or using injection methods. A limitation of these studies is that the documentation of vessel

Conclusion

This is the first study to investigate cerebral collateral circulation in a normal Chinese population with a multidetector CTA. A substantially higher prevalence of compromised posterior collaterals was observed in a normal Chinese population compared to reports of Western and Japanese populations. The anatomical variations of cerebral collaterals reported here may contribute to our understanding of collaterals as well as to various underlying mechanisms of cerebrovascular diseases.

Acknowledgements

This work was supported by Grants from the National Basic Research Program of China (973 Program No. 2009CB918300) and the Cerebrovascular Research Funding of Chongqing Neurological Society (200901).

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