Chapter 16 - Imaging acute ischemic stroke

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Abstract

Acute ischemic stroke is common and often treatable, but treatment requires reliable information on the state of the brain that may be provided by modern neuroimaging. Critical information includes: the presence of hemorrhage; the site of arterial occlusion; the size of the early infarct “core”; and the size of underperfused, potentially threatened brain parenchyma, commonly referred to as the “penumbra.” In this chapter we review the major determinants of outcomes in ischemic stroke patients, and the clinical value of various advanced computed tomography and magnetic resonance imaging methods that may provide key physiologic information in these patients. The focus is on major strokes due to occlusions of large arteries of the anterior circulation, the most common cause of a severe stroke syndrome. The current evidence-based approach to imaging the acute stroke patient at the Massachusetts General Hospital is presented, which is applicable for all stroke types. We conclude with new information on time and stroke evolution that imaging has revealed, and how it may open the possibilities of treating many more patients.

Section snippets

Imaging acute ischemic stroke

Acute ischemic stroke is common and often treatable. But successful treatment of the stroke patient often requires reliable information on the state of the brain. Modern neuroimaging provides information on the physiologic basis for the patient's neurologic deficits including: the presence of hemorrhage; the site of arterial occlusion; the size of the early infarct “core”; and the size of underperfused, potentially threatened brain parenchyma, commonly referred to as the “penumbra.” However,

Neurologic status

The single most important factor that predicts outcome and guides management of patients that present with an acute ischemic stroke syndrome is the severity of the neurologic deficit, which may be reliably assessed using the National Institutes of Health Stroke Scale (NIHSS: Table 16.1). The neurologic exam provides critical diagnostic and prognostic information in stroke, and provides pretest probabilities on whether imaging will reveal a major artery occlusion and the size of territory at

Imaging stroke physiology by CT and MRI

Modern CT and MRI are powerful tools for interrogating the physiologic state of the brain during and after an ischemic insult. The choice of CT and/or MRI when the stroke patients first presents depends on the clinical state of the patient and the therapeutic options. Table 16.2 lists the relationships between neurologic status, treatment options, key physiologic parameters, and imaging options. The key parameters in ischemic stroke and the CT and MRI methods available to measure them are shown

Estimating the penumbra

The ischemic penumbra is generally defined as severely hypoperfused brain tissue that may eventually be recruited into the infarct core, in the absence of timely reperfusion (Baron, 1999). The diffusion/perfusion mismatch (as an operational penumbra) has been used to identify those patients with occlusion of the terminal ICA and/or proximal MCA who are most likely to benefit from therapy. Diffusion MRI is used to estimate the core infarct, and perfusion-weighted imaging (PWI) is used to

MGH acute stroke imaging algorithm

The MGH Neuroradiology Division and the Stroke Service undertook a critical evaluation of stroke imaging methods in order to develop a neuroimaging algorithm that optimizes outcomes in patients with severe ischemic strokes caused by anterior circulation occlusions (Gonzalez, 2013, Gonzalez et al., 2013a). Each method was assessed for its capability to provide reliable information on the presence of hemorrhage, the site of arterial occlusion, the extent of irreversibly injured tissue (“infarct

Time, imaging, and opportunities for expanding stroke therapy

The parameter that determines treatment decisions in most acute ischemic stroke patients is the time since stroke onset. The effect of time after ictus on the odds ratio of a good outcome was demonstrated in an analysis of the original National Institute of Neurological Disorders and Stroke t-PA trial (Marler et al., 2000) and has been validated (Jauch et al., 2013). Less well validated are guidelines for endovascular therapy, although a widely used guideline is that intervention should be

Conclusions

Imaging the acute ischemic stroke patient with CT and MRI provides valuable diagnostic and prognostic information. These technologies can inform on the presence of hemorrhage, vessel occlusion, irreversible injury, and tissue at risk, which are of great importance for making the most appropriate management decisions. CT and MRI provide complementary information, and the most comprehensive understanding of the state of the brain in the patient with a stroke syndrome is attained using both. It

Acknowledgment

The authors wish to thank Dr. Julian He for his many efforts in the preparation of this manuscript.

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