Collateral Pattern on CT Angiography May Help Identify Candidates for Delayed Endovascular Thrombectomy

In patients with large vessel occlusion not treated with reperfusion therapies, researchers have noted a common symmetric collateral pattern via computed tomography (CT) angiography, according to a study recently published in Radiology. Moreover, this pattern was highly specific for low ischemic core growth rate and small 24-hour ischemic core volume as assessed at diffusion-weighted magnetic resonance imaging (MRI).

“Understanding ischemic core growth rate is key in identifying patients with slow-progressing large vessel occlusion stroke who may benefit from delayed endovascular thrombectomy,” wrote Aneesh B. Singhal, M.D., vice-chair of the Department of Neurology at Massachusetts General Hospital in Boston, and colleagues. “After further outcome studies, collateral status at presentation may prove useful in triage for endovascular thrombectomy, especially when MRI and CT perfusion are unavailable.”

In this retrospective study, researchers evaluated clinical trial data from January 2007 to June 2009, prior to the emergence of endovascular thrombectomy as the standard of care. The secondary analysis included 31 patients (median age of 71 years) with anterior proximal large vessel occlusion stroke not treated with reperfusion therapies. Patients underwent admission CT angiography and at least three MRI examinations at four time points over 48 hours. At presentation, the arterial phase CT angiography collaterals were categorized as symmetric, malignant or other. Diffusion-weighted MRI ischemic core volume and ischemic core growth rate were determined at multiple time points.

The median ischemic core volume and growth rate were significantly different in comparing collateral patterns at CT angiography at nearly all time points. At diffusion-weighted MRI, median 24-hour ischemic core volumes were 28 cm³ (symmetric), 156 cm³ (other) and 176 cm³ (malignant). Symmetric collateral pattern at CT angiography was common at 45%, with high sensitivity and specificity, at 87% and 94%, respectively, or 24-hour ischemic core volume less than 50 cm³.

“Our data set characterized the natural history of ischemic core growth in the setting of large vessel occlusion over 48 hours,” the authors wrote. “Comparison of collateral patterns showed that there were different ischemic core volumes and ischemic core growth rates at multiple points.”

The study authors conceded limitations of the study, including a small sample size and single center design, which could limit generalizability.

In an accompanying editorial, Steven A. Messina, M.D. noted that multivariable analyses of this research demonstrated independent associations between severe National Institutes of Health Stroke Scale scores and worse collateral pattern at presentation with greater ischemic core volume and growth rate.

“These data alone indicate that there are potentially more patients who may benefit from endovascular thrombectomy whom we are not identifying currently, and therefore a more thorough investigation is needed beyond the 24-hour mark,” wrote Dr. Messina, an assistant professor of radiology at the Mayo Clinic in Rochester, Minnesota.

Dr. Messina emphasized arterial collaterals as a key factor when assessing patients with large vessel occlusion.

“This work provides further evidence of the crucial role of arterial collaterals regarding infarct evolution in patients who present with large vessel occlusion, with intriguing data extending beyond the 24-hour point.” Dr. Messina wrote. “Importantly, these data highlight that it is necessary for radiologists to continue to add needed value regarding collateral status to CT angiography interpretations in these patients.”