Advanced Imaging Not Needed for Late-Stroke Thrombectomy?

November 10, 2021

Simple noncontrast CT alone may be just as good as advanced imaging in selecting stroke patients with late-presenting large-vessel occlusion for mechanical thrombectomy, a new study suggests.

The CLEAR cohort study showed that in patients with a proximal anterior ischemic stroke undergoing mechanical thrombectomy in the late time window (6-24 hours after symptom onset), there were no significant differences in the clinical outcomes of patients selected with simple noncontrast CT imaging compared with those selected with advanced imaging.

"These findings have the potential to widen the indication for treating patients in the extended window using the simpler, less costly, and easier to implement noncontrast CT imaging," the authors conclude.

The study was published online November 8 in JAMA Neurology.

Dr Thanh Nguyen

"Stroke patients are mostly selected for late-window thrombectomy with advanced imaging such as CT perfusion (CTP) or MRI, as these technologies were used to identify patients with salvageable brain tissue in the randomized trials which showed late thrombectomy to be beneficial. Clinical guidelines therefore recommend advanced imaging is performed to identify patients who could benefit from this approach," lead author Thanh Nguyen, MD, explained to | Medscape Cardiology.

"But advanced imaging can be prohibitively expensive and is not widely available across the world, so many patients will be prevented from being considered for late thrombectomy if we require them to be selected with this technology," she commented.

Nguyen, who is professor of neurology, neurosurgery, and radiology at Boston University School of Medicine, Boston, Massachusetts, noted that some stroke physicians do not believe advanced imaging is necessary, as the area of the brain impacted by the stroke can be seen on a regular noncontrast CT. Clinicians use the ASPECTS score — a 10-point scale which measures how much of the brain is infarcted — to help guide this decision. 

"We make a visual estimate. There are automated software programs which calculate the ASPECTS score, but you can read it with experience," she said.

For the current study, Nguyen and colleagues wanted to look at how regular noncontrast CT imaging compared with advanced imaging in identifying patients who would achieve a good outcome after late thrombectomy.

"If we just use advanced imaging to select patients for late thrombectomy we run the risk of excluding patients from a very effective treatment. Advanced imaging also takes more time to perform. If, as our study suggests, patients can be selected with a regular CT scan, this could make a difference for centers which don't have the advanced imaging technology and will open up this treatment to a broader population," Nguyen said.

"Although this was not a randomized trial, we had a large sample size, and conducted a complete case analysis. I believe these data are robust," she said. "These results should make clinicians more comfortable to make the decision on whether a patient should receive late thrombectomy just with the regular CT scan," she added.  

CLEAR study

The multinational cohort CLEAR study, conducted at 15 sites across 5 countries in Europe and North America from January 2014 to December 2020, included 1604 consecutive patients with proximal anterior circulation occlusion stroke presenting within 6 to 24 hours of time last seen well and who underwent thrombectomy.

Of the 1604 patients, 534 were selected to undergo mechanical thrombectomy by noncontrast CT, 752 by CTP, and 318 by MRI.

Results showed that after adjustment for confounders, there was no difference in the primary endpoint — distribution of modified Rankin Scale (mRS) score at 90 days — between patients selected by noncontrast CT vs CTP (adjusted odds ratio 0.95; P = .64) or noncontrast CT vs MRI (aOR, 0.95; P = .55).

The rates of 90-day functional independence (mRS scores 0-2) were similar between patients selected by noncontrast CT vs CTP (aOR, 0.90; P = .42) but lower in patients selected by MRI than noncontrast CT (aOR, 0.79; P = .03).

Successful reperfusion was more common in the noncontrast CT and CTP groups compared with the MRI group (88.9% and 89.5% vs 78.9%; P < .001). No significant differences in symptomatic intracranial hemorrhage or 90-day mortality were observed.

The researchers note that the rate of functional independence at 90 days among patients in the current study who were selected using noncontrast CT was comparable with that of patients treated in the two late thrombectomy trials (DAWN and DEFUSE-3) which used advanced imaging to select patients.

They also point out that the time from patient presentation to thrombectomy was shorter in patients selected by noncontrast CT than those selected by advanced imaging.

"To our knowledge, this is the largest multicenter study to date assessing selection of patients in the extended time window with noncontrast CT compared with CTP or MRI," the authors write.

"These findings have the potential to support the adoption of a more pragmatic selection of patients for mechanical thrombectomy in the extended window, simply based on noncontrast CT and proximal anterior circulation large-vessel occlusion," the researchers conclude.

The authors explain that although this study did not specify patient inclusion based on a particular ASPECTS score, most sites used an ASPECTS score of 6 or more to treat patients in the extended window, and the median noncontrast CT ASPECTS score was 8.

"As the interquartile range for ASPECTS score ranged from 7 to 9 in this cohort, this suggests an ASPECTS of 7 or more may be considered if one were to select patients with noncontrast CT for thrombectomy in the extended window," they say.

They note that two randomized trials are in progress to provide more definitive evidence of a simplified imaging protocol in the extended window: the MR CLEAN LATE trial and the RESILIENT-Extended trial.

More Evidence Needed

Commenting on the current study for | Medscape Cardiology, Michael Hill, MD, president of the Canadian Neurological Sciences Federation and professor of neurology at University of Calgary, said he agreed with the idea that only simple imaging is required to select patients for late thrombectomy, but he does not believe this study provides enough evidence for this to be proven.

"This is a cohort study, defined by the treatment modality — endovascular thrombectomy. The methodology issue is that patients were selected by the treatment. Patients who were not treated are not included in the study," he said. "Therefore, we have no idea what kinds of patients and their imaging characteristics were excluded from treatment. Thus, the best we can say from this study is that some patients, selected by simple imaging, can have outcomes that are equivalent regardless of imaging modality used," Hill said.

"This suggests that there is a common characteristic (a latent variable that we could call 'favorable imaging profile') that is common among treated patients. We still need to know whether there is a common 'unfavorable imaging profile' that defines patients who were not treated, and this study does not tell us that," he added.

Hill notes that in many parts of the world where advanced imaging is not routinely available, treating physicians are using what they have.

He says he rarely uses CTP and MRI. "I use noncontrast CT and multiphase CT angiography to make acute decisions. This approach is fast and simple and adequate for nearly all treatment decisions. When CTP is done before I get to the hospital, I find that it does not change the treatment decision," Hill added.

Nguyen reports research support from Medtronic and the Society of Vascular and Interventional Neurology with data safety monitoring board involvement for the TESLA, ENDOLOW, SELECT 2, PROST, CREST-2, WE-TRUST trials.

JAMA Neurol. Published online November 8, 2021.  Full text

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