Non-Contrast CT Is Effective for Selecting Patients for Late-Window Thrombectomy

Your definition of effective is totally wrong.  mRS of 1 and 2 are not 100% recovery. GET THERE! Stop using your tyranny of low expectations to justify your failures in stroke.

Non-Contrast CT Is Effective for Selecting Patients for Late-Window Thrombectomy

By Kurt Samson

January 6, 2022

Article In Brief

Non-contrast CT was as effective as CT perfusion or MRI in triaging late-window patients diagnosed with proximal large vessel occlusion stroke. The more accessible use of non-contrast CT could help expand the selection of candidates for mechanical thrombectomy, the study authors and independent experts said.

Distribution of 90-Day modified Rankin Scale Score (mRS) in patients presenting in the window 6 to 24 Hours after time last seen well with internal carotid artery and middle cerebral artery M1/M2 occlusions, by imaging modality: Scores range from 0 to 6, with 0 indicating no symptoms; 1, no clinically significant disability; 2, slight disability (the patient is able to look after their own affairs without assistance but unable to carry out all previous activities); 3, moderate disability (patient requires some help but is able to walk unassisted); 4, moderately severe disability (patient is unable to attend to bodily needs without assistance and unable to walk unassisted); 5, severe disability (patient requires constant nursing care and attention); and 6, death. After adjustment of confounders, there was no difference in 90-day ordinal mRS shift between patients selected by CT vs CT perfusion.

Non-contrast CT appears to be as effective as CT perfusion (CTP) or MRI in selecting thrombectomy candidates among patients with proximal occlusion anterior circulation stroke who present within an extended treatment window of 24 hours, according to a multinational study of 90-day outcomes published November 8 in JAMA Neurology.

The CT for Late EndovasculAr Reperfusion (CLEAR) study questioned whether non-contrast CT is sufficient in the triage of late-window patients diagnosed with proximal large vessel occlusion stroke by CT angiography, as compared with the standard comparator of CTP or MRI.

The Findings

The sites across five countries in Europe and a multicenter cohort study involved 1,604 patients who presented within the extended window of six to 24 hours with large-vessel occlusion. Those selected by CT had comparable clinical and safety outcomes with patients chosen by CTP or MRI.

Most patients who were selected had little evidence of infarction, as quantified by the Alberta Stroke Program Early CT Score (ASPECTS), which determines middle cerebral arterial stroke severity using available CT data. The 90-day clinical outcomes of patients were not significantly different whether they were selected by CT, CTP, or MRI. Safety outcomes, including intracerebral hemorrhage and mortality, were also not different across the three modalities.

“Because advanced imaging is not widely available, the possible utility of non-contrast CT alone is a viable alternative to advanced imaging in selecting patients with late-presenting occlusion for mechanical thrombectomy,” said lead author Thanh N. Nguyen, MD, FRCPc, FSVIN, FAHA, professor of neurology, neurosurgery, and radiology at Boston University School of Medicine and director of interventional neurology/neuroradiology at Boston Medical Center.

Imaging studies are used to exclude hemorrhage in the acute stroke patient, to assess the degree of brain injury, and to identify the vascular lesion responsible for the ischemic deficit, Dr. Nguyen explained.

“The CLEAR study has the potential to broaden access of patients presenting with proximal anterior circulation large vessel occlusion in the late window to mechanical thrombectomy, especially in centers where there is no available CT perfusion or MRI,” she told Neurology Today.

“After this study, we received feedback from colleagues around the world, including Honduras, Colombia, Mexico, China, and the UK,” Dr. Nguyen added. “There are many patients who are not being offered any endovascular treatment when presenting in the late window, for lack of availability of advanced imaging. Or they are being delayed from treatment because of a standard-of-care step, or the perceived necessity of the patient undergoing an advanced imaging study to offer treatment.”

This disparity of access to advanced imaging exists not only in most low-to-middle-income countries, but also in well-developed countries such as the United States, Canada, the UK, and Germany, Dr. Nguyen explained. “Of note, we found faster times to treatment in patients selected with NCCT compared with CTP or MRI.”

Study Details

Study subjects were recruited at 15 sites in Europe and North America between January 1, 2014, and December 31, 2020. The primary endpoint was the distribution of modified Rankin Scale (mRS) scores at 90 days. Secondary outcomes included the rates of 90-day functional independence (indicated by mRS scores of 0-2), symptomatic intracranial hemorrhage, and 90-day mortality.

The median age of the patients was 70 years old and 52.9 percent were women. A total of 534 patients were selected to undergo mechanical thrombectomy by CT, 752 by CTP, and 318 by MRI. After adjustment of confounders, there was no difference in the 90-day ordinal mRS shift between patients selected by CT versus CTP.

The rates of 90-day functional independence (mRS scores 0-2 versus 3-6) were similar between patients selected by CT versus CTP, but lower in patients selected by MRI than CT. Successful reperfusion was more common in the CT and CTP groups compared with the MRI group, and symptomatic intracranial hemorrhage or 90-day mortality was not significantly different.

Expert Commentary

“Overall, this is an important and compelling study,” said Steven R. Messé, MD, FAAN, FAHA, professor of neurology at the Hospital of the University of Pennsylvania, who was not involved with the study.

“Early on, CT is not sensitive to acute infarct, whereas the areas of irreversible injury should be more conspicuous in this late window. In combination with a CTA to confirm that there is a proximal large vessel occlusion, the information on the volume of irreversible injury on non-contrast CT should allow for reasonable patient selection for thrombectomy beyond six hours. This study suggests that this relatively ‘low-tech’ approach works, at least as well as MRI or CT perfusion,” he told Neurology Today.

Asked if the findings might change emergency stroke practices, Dr. Messé said that he thinks that the findings allow centers that do not yet have ready access to MRI or CT perfusion to still pursue thrombectomy for patients presenting in the late window.

“It is not clear how many centers might benefit in the US, but I would imagine that in some regions or countries it will have an impact,” he said. “Additionally, for patients who are transferred for consideration of thrombectomy from centers that do not have perfusion imaging, there may be some centers that will feel comfortable skipping a CTP on arrival and going directly to angiogram, as this will clearly save time, and faster time to recanalization is key to achieving the best outcomes possible.”

Importantly, he continued, the study was an observational non-randomized retrospective cohort, and there are possible confounders and biases that may impact the validity of the results. For example, sites that used a specific modality likely were different than sites that used a different modality. Another issue is that it is not known what explicit criteria were used to select patients for thrombectomy, only that they used each modality, he said.

“It is also not clear if non-contrast CT excludes more or less patients than the other modalities who may also benefit from treatment,” he added. “We only know that the patients who were selected using CT did at least as well as patients selected using the other modalities.”

Hesham Masoud, MD, assistant professor of neurology, neurosurgery, and radiology at Upstate Medical University in Syracuse, NY, told Neurology Today that MRI/CTP provide certain advantages that non-contrast CT does not.

Increased sensitivity and sophistication of images, such as different MRI sequences and CT-perfusion maps, are advantages, and MRI-DWI and perfusion maps are sensitive for detecting stroke in ways that are superior to the basic non-contrast CT images currently obtained in practice, he said.

“Also, there can be issues with any imaging modality that employs post processing, which is a major consideration in stroke CT-perfusion imaging and the basic non-contrast head CT ‘purist’ approach has value in clean cut clinical-imaging (as determined by favorable ASPECTS scores) mismatch,” Dr. Masoud added.

He said that the biggest winners with CT imaging are stroke centers operating around the world with limited imaging resources but capability to perform life-saving mechanical thrombectomy. “Due to the wide availability of CT technology in lower and medium income regions of the world, this data can assist when engaging policymakers for resource allocation to expand access to this important stroke therapy,” Dr. Masoud said.