_{Published January 4, 2022}

Jeremy J. Heit

Assistant Professor Departments of Radiology and Neurosurgery
Center for Academic Medicine Stanford University

Acute ischemic stroke (AIS) results from occlusion of a cervical or cerebral artery, and it is the leading cause of disability in the US. The most severe forms of AIS result from thrombo- or thromboembolic occlusion of the internal carotid artery or proximal (M1 segment) of the middle cerebral artery, and these occlusions are termed large vessel occlusions (LVOs). LVOs are amenable to thrombectomy, which is a minimally invasive endovascular surgery that removes the thrombus from the affected artery (Fig. 1).

Thrombectomy treatment of AIS due to LVO has exploded, following the publication of multiple randomized trials that demonstrated superior outcomes with thrombectomy treatment in patients presenting in both early (0–6 hours from last known well) and late (6–24 hours from last known well) time windows. These studies not only found thrombectomy to be superior to medical treatment, but they also fundamentally changed the evaluation and treatment triage of AIS-LVO patients.

Previously, the best medical therapy for AIS was intravenous thrombolysis with tissue plasminogen activator (tPA), but tPA treatment was limited to patients who present within 3–4.5 hours from symptom onset. The time-sensitive nature of tPA treatment was a significant barrier, and it limited the number of patients eligible for treatment. The success of the thrombectomy trials has shattered the stopwatch that governs tPA treatment in LVO patients, and we have now entered an era in which imaging guides stroke treatment, rather than the time from symptom onset.

The imaging evaluation of AIS patients has moved beyond the non-contrast head CT (NCCT) that has guided intravenous thrombolysis treatment decisions since 1995. Thrombectomy has the greatest impact when it is performed in a patient with minimal ischemic brain injury and an LVO, and these patients are identified at a minimum with an NCCT and a CT angiogram (CTA). Most of the index randomized thrombectomy trials also used CT perfusion (CTP) to characterize brain tissue that was likely permanently injured (the ischemic core) and the presence of underperfused, but salvageable, brain tissue (the penumbra). Due to the success of these trials, there has been a marked increase in CTP utilization for the evaluation of AIS patients with LVO. The increased use of CTA and CTP is making a meaningful impact on stroke treatment, but this usage has the potential to significantly strain radiology practice resources, given that AIS LVO patients should be screened for thrombectomy candidacy up to 24 hours after they were last known to be well.

The need for timely evaluation of AIS patients and the increased utilization of CTA and CTP is being aided by the integration of automated image processing and artificial intelligence (AI) techniques that identify thrombectomy treatment candidates. The emergence and implementation of these disruptive software platforms has integrated into clinical practice at a pace seldom seen in medicine, demonstrating the potential value of AI to the practice of radiology.

The success of thrombectomy and the increased use of CTA and advanced brain imaging, such as CTP, requires that radiologists are well aware of AIS patient evaluation and treatment workflows. Apropos, A RRS is offering an exciting and timely Sunday Featured Session with leading stroke experts during the 2022 Annual Meeting in New Orleans, LA. Join us for “Code Stroke: What Every Radiologist Should Know Early.”