Stroke Awareness Month: The Expanding Role of Neuroimaging in Stroke Intervention

Advanced neuroimaging has become increasingly central to patient selection for mechanical thrombectomy in acute ischemic stroke, particularly following the DAWN (NCT02142283) and DEFUSE 3 (NCT02586415) trials.¹ Current stroke workflows frequently incorporate noncontrast CT, CT angiography, CT perfusion, and MRI to evaluate infarct core size, salvageable penumbra, hemorrhagic transformation, and collateral circulation. These imaging modalities help clinicians estimate tissue viability and balance the potential benefits of reperfusion against procedural risks. Investigators are continuing to evaluate the role of thrombectomy beyond the traditional 24-hour window from symptom onset.

In recognition of Stroke Awareness Month, held annually in May, NeurologyLive^® spoke with Firas Bounni, MD, a vascular neurologist at the Miami Neuroscience Institute, part of Baptist Health South Florida. In the interview, Bounni discussed the growing role of neuroimaging in thrombectomy decision-making and personalized stroke management. He highlighted how imaging biomarkers can inform treatment selection in both standard and extended thrombectomy windows. Furthermore, Bounni also addressed recent data on medium vessel occlusions, patient-specific treatment considerations, and ongoing clinical trials evaluating thrombectomy beyond 24 hours from last known well.

NeurologyLive: How is advanced neuroimaging shaping modern stroke care and thrombectomy decision-making in clinical practice?

Firas Bounni, MD: The treatment window for thrombectomy got pushed further up to 24 hours from time of symptom onset or last known well, thanks to 2 clinical trials, specifically DAWN and DEFUSE 3. DEFUSE 3 pushed it to 16 hours, and DAWN pushed it to 24 hours. Since the DAWN trial, that has basically been the classic timeframe for thrombectomy. Beyond that, we really don't have any guidelines or body of prospective data to guide us, at this time. We really have to be careful when selecting these patients because we don't want to introduce harm with a procedure. Just like any other procedure, thrombectomy has the potential to harm. Even though it could be very effective, it could also be harmful. So, we want to be cautious with which patients to select beyond the 24-hour window, of course.

This is not evidence-based or guideline-based but rather based on experience and common sense, but things that would encourage me to pursue thrombectomy is a high ASPECTS score. By that, I mean not too many areas that are hypodense on the noncontrast head CT, which would potentially indicate that there's a larger area of the brain that we could potentially save with thrombectomy. On the CT perfusion, I would be looking for what we call a small ischemic core, which is defined by relative cerebral blood flow less than 30% of normal brain tissue. An ischemic core is basically the part of the brain that we think has been irreversibly injured or damaged because ischemia. So, the smaller that area is, the better thrombectomy is likely to be helpful for these patients.

Of course, we would be looking at patients that do not have any hemorrhagic transformation, especially if we're doing it beyond the 24-hour window. We do not want to treat patients that have bleeding in the stroke bed. We also do not want to treat patients that have mass effect because dead brain tissue tends to swell with time, and if we're seeing that on head CT, then probably a lot of that brain tissue is already dead, and thrombectomy would likely make things worse. Obviously, we're looking for patients that have a good functional baseline. I probably would not treat someone beyond 24 hours who's coming from a nursing home or who's dependent. I would probably also not treat patients that are older, like 90 years old or something.

But again, just to recap, this is not technically standard of care beyond 24 hours, and it's based on clinician judgment. It's actually a topic of ongoing research, and I'm specifically referring to the SELECT Late trial that is being led by one of our colleagues from University Hospitals in Cleveland, Dr. Al Sarraj. We will be part of that trial here at Baptist. We haven't enrolled any patients yet. The trial will basically randomize patients presenting with large vessel occlusion, specifically anterior circulation large vessel occlusions, with a last known well from 24 to 72 hours to either medical therapy or thrombectomy. There are other inclusion and exclusion criteria, but to summarize, this is an area of ongoing research too.

Which neuroimaging biomarkers and stroke imaging profiles are most informative for guiding personalized treatment strategies in stroke?

One thing that, as far as imaging is concerned, is of interest to us early on is the location of the occlusion. First is the presence or absence of occlusion in the first place, but if you're having a large vessel occlusion, most commonly occlusion of the M1 segment of the middle cerebral artery, versus what we call a medium vessel occlusion, and that involves locations like the M2 segment of the middle cerebral artery.

The standard of care for large vessel occlusions in 24 hours is thrombectomy. If it's a medium vessel occlusion, we have 3 clinical trials that came out recently—ESCAPE-MeVO, DISTAL, and DISCOUNT—that showed no benefit of thrombectomy in these patients. One thing to keep in mind for these trials is that the median NIH Stroke Scale was somewhere between 6 to 7. So, we're talking about medium vessel occlusion patients with a low NIH Stroke Scale.

Other imaging markers that would influence my decision, for example not to pursue reperfusion therapy, is the presence of hemorrhage. If you have hyperdensity on a noncontrast head CT, obviously that's a contraindication for thrombolysis with alteplase and tenecteplase, and would probably make us hesitant in pursuing thrombectomy, especially if the hemorrhage is large or if it carries any mass effect. Similarly, cytotoxic edema, mass effect, or herniation are typically indicative of an older stroke and typically would discourage us from performing reperfusion therapies.

On CT perfusion specifically, if we have a very large ischemic core, which is our approximation of the part of the brain that is irreversibly damaged by ischemia. If that area is large or comprises most of the territory distal to the site of the occlusion, then that's also typically a finding that would potentially discourage us from pursuing reperfusion therapies. Another subtype of stroke presentation is large core infarcts, as estimated by the noncontrast head CT, specifically the ASPECTS score. If the ASPECTS score is less than 3, meaning there are a lot of areas that look hypodense on the noncontrast head CT, that would also be discouraging when it comes to thrombectomy.

How do you see advanced neuroimaging and imaging-guided personalized treatment strategies evolving in stroke care?

When it comes to stroke therapy, we typically like to treat symptoms that we consider to be disabling. That's more of a patient-centric, vaguely defined criterion. If we think that the symptoms are disabling for a patient, let's say they can't make use of their hands or they can't talk, then we usually like to be aggressive. If the patient presents with mild symptoms, let's say isolated sensory symptoms, then we're usually less aggressive when it comes to treatment.

Again, there are some subtleties. If you're dealing with large vessel occlusion, the standard of care is typically thrombectomy. If we're dealing with medium vessel occlusion with a low NIH Stroke Scale, we now have 3 clinical trials that show no benefit, so we tend to be a little bit more conservative and prioritize medical management.

Transcript edited for clarity. Click here to view more of our stroke coverage.

REFERENCES
1. Baron JC. Selection of Patients for Thrombectomy in the Extended Time Window. JAMA Neurol. 2021;78(9):1051-1053. doi:10.1001/jamaneurol.2021.1825