Multiple mechanisms are postulated regarding the pathogenesis of stroke in these cases, including artery-to-artery emboli, in situ thromboembolism, and hemodynamic impairment 6 ( Fig. 7 Proximal intracranial vascular disease is also under the purview of large artery atherosclerosis.
The anterior cerebral artery (ACA) territory is frequently spared, because of an intact circle of Willis. Such infarcts typically involve the central portion of the brain, including the anterior parietal lobe, the posterior frontal lobe, and the superior temporal lobe ( Fig. 6Īnterior circulation infarcts from carotid atherosclerosis most commonly involve the middle cerebral artery (MCA), 5 resulting in a territorial infarction that involves the deep gray matter and cortex. The mechanism of infarction secondary to atherosclerosis of the extracranial vasculature is a combination of low-flow states and artery-to-artery emboli, with the latter thought to be the greater contributing factor. 5 Evaluation of the cervical and intracranial vasculature is critical when large vessel atherosclerosis is suspected as the cause of acute infarction. Infarctions larger than 15 to 20 mm, involving the cortex, cerebellum, brainstem, and subcortical regions, are usually caused by large vessel disease arising from atherosclerosis of cervical or proximal intracranial vessels, 3– 5 comprising a major cause of acute stroke, ranging from 30% to 43%. This article reviews imaging patterns and secondary findings that can assist in determining the cause of acute stroke. It is important to recognize these patterns to better guide image evaluation, recommend appropriate additional imaging as necessary, and ultimately arrive at the underlying cause. In addition to aiding in diagnosis of acute stroke, patterns of infarction on imaging can suggest a cause, which not only influences immediate management strategies, but also informs optimal secondary prevention therapies to prevent stroke recurrence. Therefore, imaging has a critical role in early diagnosis of stroke. 1, 2 In the United States, patients who arrive at a hospital emergency department with acute stroke symptoms often undergo immediate computed tomography (CT) scanning, often before detailed clinical evaluation. Acute stroke is a leading cause of morbidity and mortality in the United States and worldwide, with more than 750,000 cases and 140,000 deaths in the United States each year.
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