diagnosis and imaging

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.

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.

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.

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.