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diagnosis and imaging

Infarct Distribution Following Endovascular Therapy in Large Vessel Occlusion Stroke

Christopher Wilkins, MD

Al-Dasuqi K, Payabvash S, Torres-Flores GA, Strander SM, Nguyen CK, Peshwe KU, Kodali S, Silverman A, Malhotra A, Johnson MH, et al. Effects of Collateral Status on Infarct Distribution Following Endovascular Therapy in Large Vessel Occlusion Stroke. Stroke. 2020;51:e193–e202.

Endovascular therapy has become an invaluable tool in the treatment of acute ischemic stroke as it can provide significant improvement in the functional outcome of selected patients. Since its reception, studies have broadened the time window for endovascular therapy by using perfusion imaging during acute ischemic strokes to determine how much cerebral tissue is, or close to be, infarcted (i.e., the core) and comparing it to tissue which has reduced blood flow but is likely salvageable with reperfusion (i.e., the penumbra). The volume of the core, as well as ratio between core and penumbra, ultimately determines which patients are appropriate for endovascular therapy. Studies have shown that cerebral collateral circulation can be a major determinant of final infarct volume and can thus impact who would be deemed appropriate for thrombectomy. However, data on whether the status of collateral circulation impacts final clinical outcome in those undergoing thrombectomy remains discrepant.

In this retrospective study, Al-Dasuqi et al. investigated how collateral status impacts final infarct size, as well as functional outcomes, in those with successful and unsuccessful recanalization following endovascular therapy with either mechanical thrombectomy or intra-arterial thrombolytic drug delivery.  The authors selected patients who: had evidence of large vessel occlusion on CTA in the ICA or MCA at the M1 or proximal M2 segment; underwent mechanical thrombectomy or intraarterial thrombolysis, with or without IV-tPA before intervention; had follow up MRI obtained within 24 hours to 7 days post endovascular treatment.  The collateral status of patients was defined using a grading system designed by Miteff et al.1 There are 3 grades which include: “good,” where the entire MCA distal to the occluded segment reconstitutes with contrast; “moderate,” where some MCA branches distal to the occluded segment reconstituted in the sylvian fissure; and “poor,” where only distal superficial MCA branches reconstituted distal to the occlusion. Though many different grading systems for collateralization have been created, Al-Dasuqi et al. used the grading system by Miteff et al. because this grading system showed to be reliable in predicting favorable and poor outcomes in patients treated with IV-tPA while other collateral grading systems were of limited value. Successful recanalization was defined by mTICI score of 2b-3. A summation map of all infarct lesions detected on MRI was created to identify regions of infarct associated with mTICI scores and collateral grading. Early functional outcome was measured using the modified Rankin Scale (mRS) at discharge with a favorable outcome defined as mRS score of 0 to 2.

Multimodal Stroke CT in the COVID-19 Era: More With Less

Elena Zapata-Arriaza, MD
@ElenaZaps

Esenwa C, Lee J-A, Nisar T, Shmukler A, Goldman I, Zampolin R, Hsu K, Labovitz D, Altschul D, Haramati LB. Utility of Apical Lung Assessment on Computed Tomography Angiography as a COVID-19 Screen in Acute Stroke. Stroke. 2020.

Acute ischemic stroke (AIS) management has changed since the beginning of the COVID-19 pandemic. Chart flows and assessment protocols have evolved with the aim of redirecting stroke and COVID-19 patients to places prepared for their management. The use of thorax CT has been implemented in patients with ischemic stroke, to identify patients infected with SARS-Cov-2, regardless of respiratory symptoms.

At the beginning of 2020, it was difficult for a vascular neurologist to imagine how essential it is to perform an accurate thoracic imaging test in those patients with ischemic stroke. Although these measures have improved patient management circuits, they have also led to an increase in the time to revascularization treatments with the impact that this entails. Taking advantage of the CT angiography protocols performed in stroke codes, evaluating the diagnostic accuracy of apical lung exam to identify patients with COVID-19, has been the authors’ aim.

Author Interview: Prof. Marc Ribo on “Deep Learning Based Software to Identify Large Vessel Occlusion on Noncontrast Computed Tomography”

Prof. Marc Ribo
Prof. Marc Ribo

An interview with Prof. Marc Ribo, MD, PhD, Assistant Professor at the Stroke Unit/Department of Neurology at the Hospital Vall d’Hebron, Barcelona, Spain.

Interviewed by Dr. Vera Sharashidze, MD, Vascular Neurology Fellow, University of Miami.

They will be discussing the article “Deep Learning Based Software to Identify Large Vessel Occlusion on Noncontrast Computed Tomography,” published in the October 2020 issue of Stroke.

Dr. Sharashidze: First of all, thank you for taking time to discuss this very interesting article. What led you to become interested in this topic?

Prof. Ribo: My first interest in AI analysis of acute stroke imaging began when I met by coincidence with an expert engineer who wanted to use his skills to help stroke patients.

Author Interview: Dr. Mayank Goyal on “Challenging the Ischemic Core Concept in Acute Ischemic Stroke Imaging”

Dr. Mayank Goyal and Dr. Saurav Das
Dr. Mayank Goyal, left, and Dr. Saurav Das

A conversation with Mayank Goyal, MD, PhD, Professor of Radiology and Clinical Neurosciences, University of Calgary.

Interviewed by Saurav Das, MD, Fellow in Vascular Neurology, Washington University School of Medicine, St. Louis.

They will be discussing the topical review “Challenging the Ischemic Core Concept in Acute Ischemic Stroke Imaging,” published in October 2020 issue of Stroke

Dr. Das: Dr. Goyal, the Blogging Stroke team is happy to have you for an author interview today. Thanks for this provocative paper, which disrupts several currently accepted ideas that guide decision-making in stroke patients to make way for new innovation.

Let’s start by discussing the context in which this paper was conceptualized. The paper has a line-up of great authors, many considered visionaries in vascular neurology, across countries. Please tell us more about how this collaboration came into being.

Dr. Goyal: I have been thinking about the problem of defining ischemic core on baseline imaging for a long time. I noticed patients with a really bad-looking baseline CT, patients in which you would be inclined to call the whole MCA territory “core.” But when these patients went on to endovascular treatment and we managed to re-open the occluded vessel quickly, many of those did well, and their follow-up MRI scans showed that much of the parenchyma thought to be “core” was not actually damaged. More importantly, many of these patients did well clinically, resulting in a clinical-imaging mismatch. In addition, I was quite convinced that the so called “core” on CT perfusion was quite an exaggeration of the truth. In some ways, when many of the trials were being designed, they came in the aftermath of the Interventional Management of Stroke (IMS) 3 trial, and hence, people were over-conservative in their selection criteria. I then started talking to several of my collaborators and friends from all over the world, to see whether they felt the same way. This is when this collaboration was formed.

On Brains and Machines: Artificial Intelligence and Stroke

Raffaele Ornello, MD

Mouridsen K, Thurner P, and Zaharchuk G. Artificial Intelligence Applications in Stroke. Stroke. 2020.

Artificial intelligence (AI) is increasingly used in several aspects of everyday life and in medicine, as well. Stroke medicine, in which rapid decisions are required, can benefit from the implementation of AI in terms of decision making and patient safety.

This review by Mouridsen et al. focuses on AI applications in stroke imaging. Machine algorithms can be trained to improve the quality of imaging techniques and sparing radiations for diagnostic tools such as CT perfusion imaging; they can also date stroke onset and differentiate the ischemic stroke core from the ischemic penumbra, thus identifying the patients that can benefit the most from revascularization procedures. Machines can also help clinicians in selecting patients with large vessel occlusion, who benefit from endovascular treatments, and in predicting stroke outcomes, such as hemorrhagic transformation and 3-month outcomes.

Article Commentary: “Early Brain Imaging Shows Increased Severity of Acute Ischemic Strokes With Large Vessel Occlusion in COVID-19 Patients”

Burton J. Tabaac, MD
@burtontabaac

Escalard S, Chalumeau, Escalard C, Redjem H, Delvoye F, Hébert S, Smajda S, Ciccio G, Desilles J-P, Mazighi M, et al. Early Brain Imaging Shows Increased Severity of Acute Ischemic Strokes With Large Vessel Occlusion in COVID-19 Patients. Stroke. 2020.

In May of this year, amidst the sweeping COVID-19 global pandemic, the New England Journal of Medicine published a paper detailing how large vessel occlusive disease might be a presenting feature in patients with strokes secondary to the infection.1 The authors of this particular paper, cited above, build upon the NEJM observation with imaging evidence to posit that strokes secondary to COVID-19 are also more severe in nature.

Patients were selected and included to be a part of the comparative cohort if COVID-19 was diagnosed (via real-time PCR) and had documented acute large vessel occlusion between the observation and recruitment timeframe between March 15 and April 30, 2020. Two of the authors of the study were blinded to the COVID-19 status of the patient and were asked to quantify the infarct core volume for all patients with large vessel occlusion during the time period. During the study, fifteen patients with large vessel occlusion and confirmed COVID-19 infection were treated.

Looking Beyond the Primary Infarction: Remote Regional Brain Atrophy After Stroke

Lin Kooi Ong, PhD
@DrLinOng

Brodtmann A, Khlif MS, Egorova N, Veldsman M, Bird LJ, Werden E. Dynamic Regional Brain Atrophy Rates in the First Year After Ischemic Stroke. Stroke. 2020;51:e183–e192.

Brain atrophy refers to a loss of brain cells or a loss in the networks between brain cells, and is a common feature for many neurodegenerative diseases. Ischemic stroke is usually viewed as an acute cerebrovascular injury, and not as a neurodegenerative condition. Nevertheless, there is now emerging evidence demonstrating that stroke can cause persistent regional brain atrophy for months and even years after the initial event. Further, this regional brain atrophy after stroke has been linked to several late phase functional disturbances, including cognitive impairment. Notably, stroke increases the risk of developing vascular dementia.

The CANVAS study (Cognition and Neocortical Volume After Stroke) is a longitudinal study in people recruited from Melbourne hospitals, Australia, following ischemic stroke, comparing brain volume and cognitive function over 3 years with a group of healthy age- and sex-matched control participants.(1) In this article, Brodtmann and colleagues examined the trajectories of total and regional brain volume changes in the first year following stroke. Specifically, brain magnetic resonance imaging (MRI) was performed on stroke and healthy control participants, with 86 stroke participants completing testing at baseline, 125 at 3 months, and 113 participants at 12 months, as well as 40 healthy control participants. Five brain measures — hippocampal volume, thalamic volume, total brain and hemispheric brain volume, and cortical thickness — were examined to evaluate whether brain atrophy rates differed between time points and groups.

Article Commentary: “Clot-Based Radiomics Predict a Mechanical Thrombectomy Strategy for Successful Recanalization in Acute Ischemic Stroke”

Aurora Semerano, MD
@semerano_aurora

Hofmeister J, Bernava G, Rosi A, Vargas MI, Carrera E, Montet X, Burgermeister S, Poletti P-A, Platon A, Lovblad K-O, Machi P. Clot-Based Radiomics Predict a Mechanical Thrombectomy Strategy for Successful Recanalization in Acute Ischemic Stroke. Stroke. 2020;51:2488–2494.

Tools for predicting the success or the failure of reperfusion treatments in the acute setting of ischemic stroke are useful both to assist treatment decision-making and to guide the selection of the best device and reperfusion strategy. Multiple biomarkers and models, including clinical, biochemical, and radiological parameters, are currently under investigations with this purpose. Recently, multimodal analyses of the occlusive clot are receiving growing interest for the potential predictive value on reperfusion outcomes.

Hofmeister et al.(1) addressed this important issue in their recent article in Stroke. More specifically, the authors aimed at identifying the radiomic features of the occlusive clot on pre-treatment non-contrast CT scan, which may predict both first-attempt successful reperfusion with thromboaspiration (defined by modified Treatment in Cerebral Ischemia, mTICI 2b-3) and the number of maneuvers required to achieve successful reperfusion.

More Than Meets the Eye: Widespread White Matter Changes After Ischemic Stroke

Charlotte Zerna, MD, MSc
@CharlotteZerna

Egorova N, Dhollander T, Khlif SM, Khan W, Werden E, Brodtmann. Pervasive White Matter Fiber Degeneration in Ischemic Stroke. Stroke. 2020;51:1507–1513.

Studies have shown that ischemic stroke does not only lead to focal tissue destruction, but can also result in the remote loss of gray matter and disruption of functional connectivity. However, less is known about the remote and regional white matter degeneration after ischemic stroke. Prior studies have been limited by using diffusion-tensor imaging metrics that are non-specific voxel-averaged measures and can lead to erroneous interpretations in locations where white matter fibers are crossing. The objective of the study by Egorova et al. was, therefore, to examine white matter degeneration in a cohort of participants at 3 months post-infarct using a novel fixel-based analysis (fiber population within an MRI voxel). This method allowed the authors to assess complex microstructural fiber geometry in greater detail.

Participants with ischemic stroke (confirmed both clinically and radiologically) were recruited within 6 weeks of their index event at 3 hospitals in Melbourne, Australia. Both patients with first ever (85.6%) and recurrent ischemic stroke (14.4%) in any vascular territory and of any etiology were considered. Age-matched controls (that were also comparable in sex and education status) were selected from a database of volunteers who had previously undertaken MRI research at one of the recruiting hospitals. Of the 165 recruited participants who completed scanning at 3 months, complete usable MRI diffusion data were available for 104 stroke and 40 control participants and could be used for analysis after successfully undergoing pre-processing.

Article Commentary: “Cerebral Blood Flow Predicts the Infarct Core”

Adeola Olowu, MD

Amukotuwa S, Straka M, Aksoy D, Fischbein N, Desmond P, Albers G, et al. Cerebral Blood Flow Predicts the Infarct Core: New Insights From Contemporaneous Diffusion and Perfusion Imaging. Stroke. 2019;50:2783–2789.

The purpose of this study was to assess if cerebral blood flow (CBF) from perfusion studies could accurately estimate infarct core size in ischemic stroke patients during acute stroke management for appropriate thrombectomy triage. Relative cerebral blood flow (rCBF) accuracy would be determined by comparing infarct size to DWI of MRI.

Imaging data was assessed from the DEFUSE 2 and SENSE 3 studies. DEFUSE 2 (Diffusion and Perfusion Imaging Evaluation for Understanding Stroke Evaluation) evaluated if MRI can be used to determine which patients would most likely benefit from endovascular reperfusion. SENSE 3 (Sensitivity Encoding) compared DWI and CT perfusion to reliably detect ischemic core tissue, at risk tissue, and tissue at risk of hemorrhagic transformation. Between the two studies, 119 patients had both DWI and perfusion studies within 24 hours of symptoms onset. 

Relative CBF (rCBF) was divided into 12 thresholds (0.20-0.44), and each of those thresholds were compared to the corresponding DWI. rCBF threshold of 0.32 provided the best prediction of infarct core estimate with DWI. When applying an infarct core limit of 70 mL for thrombectomy, approximately 94% of patients were correctly triaged to the appropriate therapy.

Figure 1. Coregistered diffusion-weighted imaging (DWI) and processed perfusion-weighted imaging (PWI) images from a 66-year old man who had an acute right MCA M1 segment occlusion.
Figure 1. Coregistered diffusion-weighted imaging (DWI) and processed perfusion-weighted imaging (PWI) images from a 66-year old man who had an acute right MCA M1 segment occlusion.