Background

Stroke is the leading cause of disability and the third‐leading cause of death in the United States. Rapid bedside and radiological evaluation of cases of suspected acute stroke within 4.5–6 hours of symptom onset are critical in the assessment of patients potentially eligible for intravenous (IV) and intra‐arterial thrombolysis. In acute ischemic stroke (Figure 47.1), the central event is an acute vascular occlusion; however, 15% of strokes are hemorrhagic (Figure 47.2). Hemorrhagic strokes do not benefit from thrombolysis, as it can worsen bleeding and increase mortality. While this chapter focuses on the diagnosis of stroke, it is important to consider why the diagnosis of stroke is clinically important. Importantly, when the correct diagnosis of stroke is made in a timely way, early interventions such as tissue plasminogen activator (tPA) and endovascular treatment (i.e., mechanical thrombectomy) have been shown to improve outcomes.¹

The approach to diagnostic imaging depends on patient characteristics, time since symptoms onset, and local availability of imaging and stroke expertise. Traditionally, noncontrast head computed tomography (NCHCT) has been the first imaging modality in acute stroke in the emergency department (ED) (Figure 47.1). NCHCT can rule out hemorrhagic stroke, completed stroke, and also exclude other potential causes of acute neurological symptoms. NCHCT is widely available, easier, and faster to perform with shorter scan times and fewer patient exclusions/contraindications, has lower cost compared to MRI, and is a cost‐effective strategy.² In cases where a large vessel occlusion (LVO) is suggested on exam, computed tomography angiogram (CTA) head and neck can also be performed to demonstrate large clots that are best treated with IV or arterial tPA or mechanical clot retrieval. A LVO is defined as the occlusion of the internal carotid artery and of the proximal segments (M1, M2) of the middle cerebral artery. In cases where the deficit is equivocal or the timing of last known normal is uncertain more advanced imaging technique, multimodal magnetic resonance imaging (MRI) with diffusion‐weighted imaging (dwMRI) and perfusion MRI, or computed tomography perfusion (CTP) can be performed after computed tomography (CT) because these advanced imaging methods are considered a more accurate diagnostic test for demonstrating acute ischemia. CTP is particularly useful in selecting patients amenable to mechanical thrombectomy, particularly those within 24 hours of symptoms including those with unknown symptoms onset (wake‐up strokes). Diffusion‐weighted magnetic resonance imaging (dwMRI) is sensitive for acute ischemia, however the primary clinical concerns regarding the use of dwMRI as a solitary test are (i) reduced ability to detect intracranial hemorrhage in the setting of acute stroke, (ii) less clinical access to potentially unstable patients, (iii) longer testing times, and (iv) poor availability of rapid MRI.