What imaging can disclose about suspected stroke and its Tx

Best practices for stroke treatment are based on the cause of the event.³ To identify the likely cause, the aforementioned characteristics are incorporated into one of the scoring systems, which seek to clarify either the cause or the phenotypic appearance of the AIS, which helps direct further testing and treatment. (The ASCOD³⁶ and TOAST³⁷ classification schemes are commonly used phenotypic and causative classifications, respectively.) Several (not all) of the broad phenotypic imaging patterns, with myriad clinical manifestations, are reviewed below. They include:

• Embolic stroke, which, classically, involves end circulation and therefore has cortical involvement. Typically, these originate from the heart or large extracranial arteries, and higher rates of atrial fibrillation and hypercoagulable states are implicated.
• Thrombotic stroke, which, typically, is from large vessels or small vessels, and occurs as a result of atherosclerosis. These strokes are more common at the origins or bifurcations of vessels. Symptoms of thrombotic stroke classically wax and wane slightly more frequently. Lacunar strokes are typically from thrombotic causes, although there are rare episodes of an embolic source contributing to a lacunar stroke syndrome.³⁸

There is evidence for using MRI discrepancies between diffusion-weighted and FLAIR imaging to time AIS findings in so-called wake-up strokes.³⁹ The rationale is that strokes < 4.5 hours old can be identified because they would have abnormal diffusion imaging components but normal findings with FLAIR. When these criteria were utilized in considering whether to treat with thrombolysis, there was a statistically significant improvement in 90-day modified Rankin scale (odds ratio = 1.61; 95% confidence interval, 1.09-2.36), but also an increased probability of death and intracerebral hemorrhage.³⁹

This trial showed that thrombectomy could be performed as long as 16 hours after the patient was last well-appearing and still result in an improved outcome.

A recent multicenter, randomized, open-label trial, with blinded outcomes assessment, showcased the efficacy of thrombectomy as an adjunct when ischemic brain territory was identified without frank infarction, as ascertained by CT perfusion within the anterior circulation. This trial showed that thrombectomy could be performed as long as 16 hours after the patient was last well-appearing and still result in an improved outcome with favorable imaging characteristics (on the modified Rankin scale, an ordinal score of 4 with medical therapy and an ordinal score of 3 with EVT [odds ratio = 2.77; 95% confidence interval, 1.63-4.70]).²⁹ A 2018 multicenter, prospective, randomized trial with blinded assessment of endpoints extended this idea, demonstrating that, when there was mismatch of the clinical deficit (ie, high NIHSS score) and infarct volume (measured on diffusion-weighted MRI or CT perfusion), thrombectomy as late as 24 hours after the patient was last known to be well was beneficial for lesions in the anterior circulation—specifically, the intracranial internal carotid artery or the proximal middle cerebral artery.⁴⁰

^a Whether local emergency departments (EDs) should be bypassed in favor of a specialized stroke center is the subject of debate. The 2019 American Heart Association/American Stroke Association guidelines note the AHA’s Mission: Lifeline Stroke EMS algorithm, which bypasses the nearest ED in feared cases of large-vessel occlusion if travel to a comprehensive stroke center can be accomplished within 30 minutes of arrival at the scene. This is based on expert consensus.^3,12,13

CORRESPONDENCE
Brian Ford, MD, 4301 Jones Bridge Road, Bethesda, MD; brian.ford@usuhs.edu.