Differential Effect of Baseline Computed Tomographic Angiography Collaterals on Clinical Outcome in Patients Enrolled in the Interventional Management of Stroke III Trial

Association Between CT Angiogram Collaterals and CT Perfusion in the Interventional Management of Stroke III Trial

BACKGROUND AND PURPOSE

Collateral flow can determine ischemic core and tissue at risk. Using the Interventional Management of Stroke (IMS) III trial data, we explored the relationship between computed tomography angiogram (CTA) collateral status and CT perfusion (CTP) parameters.

METHODS

Baseline CTA collaterals were trichotomized as good, intermediate, and poor, and CTP studies were analyzed to quantify ischemic core, tissue at risk, and mismatch ratios. Kruskal-Wallis and Spearman tests were used to measure the strength of association and correlation between CTA collaterals and CTP parameters.

RESULTS

A total of 95 patients had diagnostic CTP studies in the IMS III trial. Of these, 53 patients had M1/M2 middle cerebral artery±intracranial internal carotid artery occlusion, where baseline CTA collateral grading was performed. CTA collaterals were associated with smaller CTP measured ischemic core volume (P=0.0078) and higher mismatch (P=0.0004). There was moderate negative correlation between collaterals and core (rs=-0.45; 95% confidence interval, -0.64 to -0.20) and moderate positive correlation between collaterals and mismatch (rs=0.53; 95% confidence interval, 0.29-0.71).

CONCLUSION

Better collaterals were associated with smaller ischemic core and higher mismatch in the IMS III trial. Collateral assessment and perfusion imaging identify the same biological construct about ischemic tissue sustenance.

[Endovascular stroke treatment following recent positive clinical trials]

Recently, five independent randomized controlled clinical trials demonstrated the efficacy and safety of endovascular stroke treatment in stroke patients with occlusion of proximal intracranial arteries. The five trials MR CLEAN, ESCAPE, EXTEND-IA, SWIFT-PRIME and REVASCAT randomized a total of 1287 stroke patients to either standard treatment, which in the majority of patients consisted of intravenous thrombolysis within 4.5 h of symptom onset or additional endovascular stroke treatment. In all the studies endovascular treatment resulted in a better clinical outcome with an odds ratio for a better clinical outcome 90 days after stroke ranging between 1.7 and 3.1 and an absolute increase in the proportion of patients with functionally independent outcome between 14% and 31%. The overwhelming benefit of endovascular treatment mainly results from mechanical thrombectomy using stent retriever devices and starting endovascular treatment within 6 h of symptom onset in stroke patients.

Comparison of four different collateral scores in acute ischemic stroke by CT angiography

Purpose

Multiple scores have been described for the assessment of collateralization in acute ischemic stroke. Currently, there is no gold standard for collateral assessment by CT angiography (CTA). This study compared four frequently used collateral scores with regard to their correlation with early infarct core and mismatch ratio.

Methods

30 consecutive patients with acute occlusion of the M1 segment or terminal carotid artery were reviewed retrospectively. Collaterals were assessed using dynamic and also single-phase CTA according to grading systems by the American Society of Interventional and Therapeutic Neuroradiology/Society of Interventional Radiology (ASITN/SIR), Alberta Stroke Program Early CT Score (ASPECTS) (on collaterals), Christoforidis et al and Miteff et al. The Christoforidis and ASITN/SIR scores, which were initially designed for conventional angiography, were adapted to be applicable to CTA. The scores were compared with respect to early infarct core and mismatch ratio in perfusion CT estimated by RAPID software using Spearman correlation.

Results

ASITN/SIR and ASPECTS collateral scores showed good correlation with early infarct core (rho=−0.696, p<0.001 and rho=−0.677, p<0.001) and mismatch ratio (rho=0.609, p<0.001 and rho=0.581, p<0.001). In contrast, the Christoforidis and Miteff scores correlated less well with infarct core (rho=0.245, p=0.191 and rho=−0.272, p=0.145, respectively) and mismatch ratio (rho=−0.329, p=0.075 and rho=0.279, p=0.135, respectively). ASPECTS and ASITN/SIR showed excellent cross-correlation (rho=0.901, p<0.001).

Conclusions

Compared with the Christoforidis and Miteff scores, the modified ASITN/SIR and ASPECTS collateral scores showed consistently higher correlation with the extent of early infarct core and mismatch volume. This is probably because these scores evaluate the extent and delay of vascular enhancement in the affected territory rather than the backflow of contrast medium to the occlusion.

The emerging age of endovascular treatment of acute ischaemic stroke and the role of CT angiography in patient work-up: a guide for the radiologist

Recent trial evidence suggests that for patients suffering large-vessel occlusive stroke, endovascular therapy based on the stent-retriever technique is associated with superior clinical outcomes when compared to intravenous thrombolysis alone. The challenge now is how this service is to be delivered. This may involve both centralisation of services around large cities and development of robust networks to receive patients from district general hospitals situated further afield. Both diagnostic and interventional neuroradiology will need to expand. Furthermore, we suggest that it would be advantageous for radiology departments in those hospitals receiving hyperacute stroke patients to perform computed tomography (CT) angiography in addition to non-contrast CT, which also has implications for service delivery in these units. This could swiftly aid identification of patients who might benefit from thrombectomy and improve decision-making through demonstration of occlusive thrombus and of collateral status.

Choosing a Hyperacute Stroke Imaging Protocol for Proper Patient Selection and Time Efficient Endovascular Treatment: Lessons from Recent Trials

Recently, several prospective randomized control trials regarding endovascular treatment for patients with intracranial large artery occlusions causing acute ischemic stroke have been successfully reported. Effort to minimize time delays to endovascular treatment, patient selection and the use of retrievable stent were important factors for the success of these trials. The inclusion and exclusion criteria for each of these trials did include differences in imaging protocols. In this review, we focus on the importance of baseline non-invasive angiography prior to deciding endovascular treatment. Then imaging protocols are described for each trial according to measurement of infarct volume and collateral grading.

Mechanical Thrombectomy Is Now the Gold Standard for Acute Ischemic Stroke: Implications for Routine Clinical Practice

BACKGROUND

This review aims to summarize the findings of the recently published randomized controlled studies which provide overwhelming evidence in support of mechanical thrombectomy for acute ischemic stroke with large artery occlusion. The five studies, Multicenter Randomized Clinical Trial of Endovascular Treatment for Acute Ischemic Stroke in the Netherlands (MR CLEAN), Endovascular Revascularization with Solitaire Device versus Best Medical Therapy in Anterior Circulation Stroke within 8 h (REVASCAT), Endovascular Treatment for Small Core and Proximal Occlusion Ischemic Stroke (ESCAPE), Solitaire™ FR as Primary Treatment for Acute Ischemic Stroke (SWIFT PRIME) and Extending the Time for Thrombolysis in Emergency Neurological Deficits with Intra-Arterial Therapy (EXTEND IA) have demonstrated the critical role of selecting patients by advanced neuroimaging, the superior recanalization capacity of stent retrievers and the effects of minimization of work processes delay.

SUMMARY

This review outlines lessons gained from the 5 positive studies which assessed mechanical thrombectomy as part of endovascular therapy for patients with proximal artery occlusion in the internal carotid and middle cerebral arteries. It discusses the role of age and stroke severity on treatment while also comparing the unique trial designs and selection criteria used amongst the 5 studies. In addition to examining the importance of unique imaging parameters such as collateral circulation, mismatch ratio and ischemic core volume, the review outlines differences in workflow parameters within the context of outcome. Finally the benefit of neuroimaging to broaden treatment eligibility and the issues associated with general anesthesia will be discussed in this review.

KEY MESSAGES

Questions remain over the applicability of mechanical thrombectomy to stroke subgroups including wake-up strokes and basilar artery thrombosis. The role of imaging is integral to this process and can lead to broadening eligibility criteria in the future. Workflow practices have been streamlined in the 5 positive randomized controlled studies, but guidelines will need to be revised accordingly if similar patient outcomes are to be replicated in a wider population.

[Imaging-based indications for interventional treatment of stroke]

The indications for mechanical thrombectomy are based on a proximal vessel occlusion in the absence of extensive ischemic damage in the corresponding dependent vascular territory. The maximum extent of early ischemic edema for which endovascular treatment is still useful is not clear from the studies. A benefit of mechanical thrombectomy can be safely assumed with an ASPECT score of 6-10, possibly also with lower scores. A more complex imaging with assessment of the status of collateral vessels or perfusion abnormality is scientifically interesting but usually not necessary for clinical decision-making for endovascular stroke treatment within the first 6 h after symptom onset.

Role of imaging in current acute ischemic stroke workflow for endovascular therapy

Ischemic stroke is caused by a thrombus that blocks an intracranial artery. Brain tissue beyond the blocked artery survives for a variable period of time because of blood and nutrients received through tiny vessels called collaterals. Imaging the brain and the vasculature that supplies it is therefore a vital first step in treating patients with acute ischemic stroke. In this review, we focus on current evidence for imaging selection of patients for endovascular therapy in the context of the recently positive clinical trials, such as Multicenter Randomized Clinical Trial of Endovascular Treatment for Acute Ischemic Stroke in the Netherlands (MR CLEAN), Endovascular Treatment for Small Core and Anterior Circulation Proximal Occlusion With Emphasis on Minimizing Computed Tomography to Recanalization Times (ESCAPE), Solitaire With the Intention for Thrombectomy as Primary Endovascular Treatment (SWIFT PRIME), and Extending the Time for Thrombolysis in Emergency Neurological Deficits-Intra-Arterial (EXTEND-IA). We discuss evidence for and use of the various imaging paradigms available. We discuss how to set up quick and efficient imaging protocols for patient selection and address common concerns about the use of imaging, including time spent, contrast, radiation, and other advantages and disadvantages. Finally, we briefly comment on how imaging can integrate itself within various health systems of care in the future, thereby potentially improving patient outcomes further.