Imaging acute ischemic stroke patients in the era of endovascular thrombectomy

Stroke is the second most common cause of death in the world and the third leading cause of disability. Because an estimated 1.9 million brain cells die for each minute of an ischemic stroke, rapid treatment is critical. In 2015, results from five clinical trial findings showed that endovascular thrombectomy was effective as a treatment for patients whose stroke was caused by large-vessel proximal anterior circulation occlusion. This new standard of care requires diagnosis by imaging procedures and the ability of radiology departments and radiologists to work at the highest possible levels of workflow efficiency.

Neuroradiologists from the QEII Health Sciences Center and Dalhousie University in Halifax, Nova Scotia, provide a concise overview of appropriate imaging procedures and imaging selection criteria in an article published in the Canadian Association of Radiologists Journal. The article is intended to aid general radiologists.

The five multi-center randomized, controlled clinical trials investigated various aspects of the utilization of endovascular thrombectomy. These determined that patients with acute ischemic stroke caused by large-vessel thrombus occlusion of the proximal anterior circulation had significantly reduced disability 90 days following the stroke when treated with rapid endovascular thrombectomy and usual stroke care compared to usual stroke care alone. The usual stroke care included the administration of alteplase, a tissue plasminogen activator.

Diagnostic imaging is essential to determine if endovascular thrombectomy is appropriate for a patient. The commonly accepted cut-off time from symptom onset to endovascular thrombectomy consideration is 6 hours. However, some findings suggest there may be benefit up to 7 hours. Patients with National Institutes of Health Stroke Scale (NIHSS) equal to or greater than 11 had corresponding common odds ratio (cOR) that were significant. Patients with minor strokes as well as alteplase-ineligible patients should be evaluated on a case-by-case basis.

Patient-level data from the five randomized clinical trials involving 1,287 patients were also pooled in a research project entitled Highly Effective Reperfusion evaluated in Multiple Endovascular Stroke Trials (HERMES). These researchers assessed the primary outcome of reduced disability on the modified Rankin Scale (mRS) at 90 days in the pooled population and examined heterogeneity of this treatment effect across pre-specified subgroups. They also concluded that endovascular thrombectomy is of benefit to most patients with acute ischemic stroke caused by occlusion of the proximal anterior circulation, irrespective of patient characteristics. They recommended that the decision to perform endovascular therapy for stroke be based on specific clinical and radiological features of the individual patient, and not be withheld solely on the basis of advanced age, moderately extensive early ischemic changes on basely CT, and moderate or severe clinical deficit.¹

A noncontrast CT head scan is the initial imaging test recommended by both North American and European stroke guidelines. It has the ability to identify the presence of early ischemic changes and plays a significant role in the assessment of alteplase eligibility. The Alberta Stroke Program Early CT score (ASPECTS) is a 10 point quantitative topographic CT score. Lower ASPECTS scores indicate more extensive and irreversible early ischemic changes. Patients with scores higher than 5 are more likely candidates for endovascular thrombectomy.

The second imaging examination recommended by North American and European stroke guidelines is a multiphase CT angiography of the intracranial and neck vasculature for thrombus localization and collateral scoring. Authors Elizabeth H.Y. Du, MD, and Jai J. S. Shankar, DM, advise that perfusion parameters are useful for predicting functional outcome, but that existing data cannot reliably predict who should be excluded from endovascular thrombectomy. They advise that based on their experience, cerebral blood volume on CT perfusion can reliably predict the infarct volume on 24-hour CT scan and is very helpful in patient selection.

Radiologists in Australia recommend that patients who are alterplase-ineligible have a CT perfusion scan and that CT angiography images of the intracranial vessels be extracted from the perfusion study. At the Sir Charles Gairdner Hospital in Perth, endovascular thrombectomy is offered as adjunctive treatment to alteplase if the CT angiographic image identifies a LV0 in the anterior circulation, and if the CT perfusion scan identifies a salvageable penumbra surrounding any decreased cerebral blood flow.²

“The adoption of endovascular thrombectomy relies on diagnostic imaging to identify ischemic stroke patients who will benefit from this treatment. Radiology departments need to maintain imaging protocols for stroke patients at the highest level of workflow efficiency and quality. The indirect impact that a radiologist can have on the quality of the life of a stroke patient cannot be underestimated,” Dr. Shankar told Applied Radiology.

REFERENCES

1. Goyal M, Menon BK, van Zwam WH, et al. Endovascular thrombectomy after large-vessel ischaemic stroke: a meta-analysis of individual patient data from five randomised trials. Lancet 2016 23; 387 (10029): 1723-1731.
2. Wee C-K, McAuliffe W, Phatouros CC, et al. Outcomes of Endovascular Thrombectomy with and without Thrombolysis for Acute Large Artery ischaemic Stroke at a Tertiary Stroke Centre. Cerebrovasc Dis Extra 2017 7: 95-102.
3. Du EHY, Shankar JJS. Rapid Endovascular Treatment of Acute Ischemic Stroke: What a General Radiologist Should Know. Can Assoc Radiol J. 2017 68;2: 154-160.