Thrombus Imaging in Acute Stroke: Are We Even Close?

Waldo R. Guerrero, MD; Dominika Golubczyk, MS; Piotr Walczak, MD, PhD


Stroke. 2019;50(8):1948-1949. 

Ischemic stroke remains a leading cause of serious, long-term disability.[1] Intravenous thrombolysis and endovascular thrombectomy, however, have fundamentally reshaped clinical management of stroke and brought significant improvements in the functional outcomes. One of the central elements in qualifying patients for endovascular thrombectomy is identification and characterization of the thrombus in the cerebral vasculature. This characterization is based on neuroimaging techniques, including noncontrast computed tomography, computed tomography angiography, or magnetic resonance angiography. Several studies attempted characterization of the thrombus[2–4] and various parameters and scoring systems have been developed, including thrombus permeability[2] or the Clot Burden Score;[5] however, predictive value of these measures has to date been controversial, and thrombus location is the only feature that is widely and routinely used in clinical practice.

In the current issue of Stroke, Dutra et al[6] present results of a large-scale multicenter study based on MR-CLEAN Registry, where imaging data of 408 stroke patients treated with endovascular thrombectomy were subjected to comprehensive analysis of the thrombus. Despite excluding a considerable number of patients, this study population is the largest sample to date about thrombus imaging characteristics in acute ischemic stroke treated by endovascular thrombectomy. Their imaging protocol consisted of noncontrast computed tomography, intracranial, and extracranial computed tomography angiography followed by interventional digital subtraction angiography. The objective of this study was to evaluate associations between imaging clot characteristics (site of occlusion, clot burden score, distance from the internal carotid artery terminus to the thrombus [DT], length, perviousness, absolute attenuation, and relative attenuation) and functional outcomes in the acute ischemic stroke after thrombectomy.

The main finding of this observational multicenter study was that distal occlusion, shorter clots, and higher Clot Burden Score values correlated with better functional outcomes. Endovascular procedure times in these cases were shorter. Dutra et al[6] report that clot density is not associated with revascularization success in acute ischemic stroke patients which is in line with a recent report by Jagani et al.[7]

The study still has some limitations. Most importantly, many patients were excluded mainly because of the unavailability of a thin-section noncontrast computed tomography. Furthermore, administration of intravenous alteplase before endovascular treatment may have affected perviousness evaluation results. Although this is a very informative study, there is still much to be desired in the realm of thrombus properties and their impact on endovascular treatment. Larger clots are more difficult to retrieve and might be associated with nonrecanalization.[3,5] Baek at al[8] demonstrated that measuring the thrombus volume was particularly predictive of first-pass recanalization, which was associated with a higher likelihood of a favorable outcome. Yet, in this article, the authors use thrombus length as an estimated measurement of thrombus size when, in fact, thrombus volume is more impactful. Thus, it is not surprising the authors of this study did not find an association between thrombus length and reperfusion. Thrombus length as a single entity is likely not a reliable measurement of thrombus size nor chance of recanalization. Furthermore, this study does not take into account thrombus composition. Previous studies have shown that erythrocyte-rich thrombi were associated with a smaller number of recanalization maneuvers, shorter procedure time, and shorter arrival-to-recanalization time interval.[9] Thrombus volume and composition are likely more critical when it comes to endovascular therapy and recanalization rates. Completely automated and clinically relevant imaging that assess thrombus volume and composition that might be able to guide our endovascular devices and techniques needs to be developed. Research evaluating the association between thrombus characteristics and endovascular devices and techniques is also lackluster. Further research to guide our selection of endovascular devices and techniques suited for specific thrombi volume and composition is imperative. This information might eventually guide initial endovascular approaches and devices in a manner that yields 100% complete recanalization and first-pass rates. In addition, clinical trial design of novel endovascular devices and techniques might, therefore, be optimized using factors like thrombus volume and composition.

In conclusion, this large-scale clinical study systematized imaging characteristics of thrombi and provide compelling evidence about their predictive value and useful hints for planning endovascular procedures. However, further studies need to be done analyzing endovascular device variables and techniques in relation to thrombus size and composition.