A conversation with Dr. Tharani Thirugnanachandran, MBChB, stroke researcher, Monash University, Victoria, Australia.
Interviewed by Dr. Andy Lim, MBA, emergency physician, Monash Medical Centre, Victoria, Australia.
They will be discussing the article “Anterior Cerebral Artery Stroke: Role of Collateral Systems on Infarct Topography,” published in Stroke.
Dr. Lim: Dr. Thirugnanachandran, on behalf of the Blogging Stroke team, it is a pleasure to welcome you to this author interview regarding your publication in Stroke that explored the role of leptomeningeal anastomoses in influencing infarct topography after anterior cerebral artery stroke. Can I start by asking you to give us a brief summary of what you did?
Dr. Thirugnanachandran: Thank you, Dr Lim. Anterior cerebral artery stroke is far less common than middle cerebral artery stroke. So comparatively less attention has been given to it in the literature. Much of our current understanding about it has come from older works taken postmortem or poststroke. In contrast to prior studies, our study was able to give us an insight into what happens to this arterial territory at stroke onset with the use perfusion imaging and a computer model.
In this study, we explored the perfusion and infarct topography following occlusion of the anterior cerebral artery and its branches. We found that the perfusion topography extended further posteriorly than the infarct topography. We postulated that this difference is likely explained by leptomeningeal collaterals, which are formed between branches of the anterior cerebral artery with branches from the middle cerebral artery and posterior cerebral artery.
We also found that the regions with the highest probabilities of infarction occurred in areas that had poor collateral flow, such as the superior frontal gyrus (probability =0.26) and anterior cingulate gyrus (probability =0.24).
To confirm our suspicions regarding the importance of leptomeningeal anastomoses, we created a computer model of the cerebral circulation and simulated occlusion of the anterior cerebral artery and its branches.
Our experiments showed two important findings: Firstly, despite the Circle of Willis being regarded as the primary collateral system, the Circle of Willis was only helpful in redirecting blood flow following occlusion of the proximal anterior cerebral artery (pre-Anterior communicating artery). Secondly, following distal anterior cerebral artery occlusion, there remains residual flow in selected arteries. These selected arteries are the ones with known collaterals with the middle cerebral artery.
Dr. Lim: I see that previous work in 2014 has explored computer modelling of cerebrovascular occlusion in the anterior circulation, demonstrating the role of leptomeningeal anastomosis in infarct topography following middle cerebral artery occlusion. How did the present study draw inspiration and direction from these previous works?
Dr. Thirugnanachandran: Prof. Phan and his team’s prior work on the computational modelling of the middle cerebral artery and its branches was essential in inspiring this present study. The present model extends on his earlier work by incorporating different anatomical variants of the Circle of Willis in the simulated occlusion experiments. Prof. Phan has also developed a computer model to explore scenarios of clot extraction. Interested readers can review his model on the following website (see https://gntem3.shinyapps.io/ecrsim).
Dr. Lim: You state in your article the availability of the computational model experiments on https://gntem3.shinyapps.io/acasim. Can you let our readers know what to expect when they visit this online resource?
Dr. Thirugnanachandran: The app allows readers to change the location of the experimental occlusion and the configuration of the Circle of Willis variant to see how this impacts blood flow in different branches of the anterior cerebral artery.
Dr. Lim: What is your desired take-home message for clinicians who read your paper?
Dr. Thirugnanachandran: Our study has shown that there is a variability in infarct topography (namely the posterolateral extent) of the anterior cerebral artery territory after stroke. This finding suggests that collaterals modify the fate of penumbra in this region. The low risk of infarction in the posterolateral aspect (somatosensory and motor areas) implies that these areas are important sanctuary sites.
Dr. Lim: You mentioned that “the potential compensatory capacity of interterritorial leptomeningeal anastomoses may provide a therapeutic target in stroke management.” What do you think is the next step for researchers who are interested to further this direction?
Dr. Thirugnanachandran: The next step would be to identify the locations of all sanctuary sites in the brain and investigate how infarction of these regions impacts clinical outcome. Our group has taken a closer look at important fiber tracts that pass through the sanctuary sites in the anterior cerebral artery territory. We are in the process of publishing a paper looking specifically at corticofugal fiber tracts and motor outcome in anterior cerebral artery stroke.
Ultimately, we need to discover ways to improve blood flow through collaterals (to use as an adjunct to reperfusion therapies) and hence optimize the rescue of the ischemic penumbra.
Dr. Lim: Thank you for your time, and I look forward to seeing the outcome of your future work.
Dr. Thirugnanachandran: Thanks, Dr. Lim.