Neuroimaging of Acute Stroke PDF

Neuroimaging of acute stroke - UpToDate https://www.uptodate.com/contents/neuroimaging-of-acute-stroke/print Official reprint from UpToDate® www.uptodate.com © 2025...

Neuroimaging of acute stroke - UpToDate https://www.uptodate.com/contents/neuroimaging-of-acute-stroke/print Official reprint from UpToDate® www.uptodate.com © 2025 UpToDate, Inc. and/or its affiliates. All Rights Reserved. Neuroimaging of acute stroke authors: Jamary Oliveira-Filho, MD, MSc, PhD, Maarten G Lansberg, MD, PhD section editors: Scott E Kasner, MD, Glenn A Tung, MD, FACR deputy editor: John F Dashe, MD, PhD All topics are updated as new evidence becomes available and our peer review process is complete. Literature review current through: Dec 2024. This topic last updated: Jun 13, 2024. INTRODUCTION Neuroimaging in the evaluation of acute stroke is used to differentiate hemorrhage from ischemic stroke, to assess the degree of brain injury, and to identify the vascular lesion responsible for the stroke. Multimodal computed tomography (CT) and magnetic resonance imaging (MRI), including perfusion imaging, can distinguish between brain tissue that is irreversibly infarcted and that which is potentially salvageable, thereby allowing selection of patients who are likely to benefit from reperfusion therapy. The use of this technology is dependent upon availability. Neuroimaging during the acute phase (first 24 hours) of stroke will be reviewed here. Other aspects of the acute evaluation of stroke, the clinical diagnosis of different types of stroke, and the subacute and long-term assessment of patients who have had a stroke are discussed separately: Initial assessment and management of acute stroke Clinical diagnosis of stroke subtypes Overview of the evaluation of stroke Approach to reperfusion therapy for acute ischemic stroke Spontaneous intracerebral hemorrhage: Pathogenesis, clinical features, and diagnosis Aneurysmal subarachnoid hemorrhage: Clinical manifestations and diagnosis Nonaneurysmal subarachnoid hemorrhage Ischemic stroke in children: Clinical presentation, evaluation, and diagnosis 1 z 44 14/01/2025, 12:40 Neuroimaging of acute stroke - UpToDate https://www.uptodate.com/contents/neuroimaging-of-acute-stroke/print Hemorrhagic stroke in children Stroke in the newborn: Classification, manifestations, and diagnosis APPROACH TO IMAGING Goals of imaging — Neuroimaging should be obtained for all patients suspected of having acute stroke or transient ischemic attack (TIA). Brain and neurovascular imaging plays an essential role in acute stroke by [2-4]: Differentiating ischemia from hemorrhage Excluding stroke mimics, such as tumor Assessing the status of large cervical and intracranial arteries Estimating the volume of brain tissue that is irreversibly infarcted (ie, infarction core) Estimating the extent of potentially salvageable brain tissue that is at risk for infarction (ie, ischemic penumbra) Guiding acute interventions, including patient selection for reperfusion therapies (ie, intravenous thrombolysis and mechanical thrombectomy) Urgency and scope of imaging — Because "time is brain" and because imaging provides essential information for selecting treatment, immediate imaging of patients with acute stroke is a priority. Brain imaging is required to exclude the presence of acute hemorrhage, because the management of patients with hemorrhagic stroke is very different from that of patients with acute ischemic stroke. Neurovascular imaging with CT angiography (CTA) or MR angiography (MRA) is necessary for confirming the presence of large artery occlusion in patients who are potential candidates for mechanical thrombectomy. Neurovascular imaging should evaluate the extracranial (internal carotid and vertebral) and intracranial (internal carotid, vertebral, basilar, and Circle of Willis) large vessels. (See "Approach to reperfusion therapy for acute ischemic stroke".) Multimodal CT and MRI can identify acute infarction, large vessel occlusion, infarct core, and salvageable brain tissue and are used to select patients for intravenous thrombolysis and mechanical thrombectomy in later time windows. (See 'Multimodal imaging' below and "Approach to reperfusion therapy for acute ischemic stroke".) Brain imaging should not be considered in isolation but rather as one part of the acute stroke evaluation. The approach to imaging may differ according to individual patient characteristics (eg, time from stroke onset or time last known well, potential candidate for 2 z 44 14/01/2025, 12:40 Neuroimaging of acute stroke - UpToDate https://www.uptodate.com/contents/neuroimaging-of-acute-stroke/print reperfusion therapies) and local availability of stroke expertise and imaging capabilities. CT or MRI for initial imaging? — While CT and MRI can both be used for the initial evaluation of patients suspected of an acute stroke, CT with CTA is the standard imaging modality at most centers. Advantages of CT – CT is used more often than MRI in acute stroke because of its widespread availability, the rapid scan times, and lower cost [6,7]. The noncontrast CT has excellent test performance characteristics for differentiating ischemic from hemorrhagic stroke. Disadvantage of CT – Although the noncontrast CT can show signs of early acute ischemic stroke, these signs are very subtle and are often absent in the first hours after ischemic stroke onset (see 'Parenchymal changes on CT' below). Because of that, both the sensitivity and interrater agreement for the assessment of early infarct signs on CT are suboptimal. In one report of 786 patients with ischemic stroke, the sensitivity of noncontrast CT during the first six hours of cerebral ischemia was 64 percent. Advantages of MRI – A major advantage of MRI is that DWI is much more sensitive than noncontrast CT for detection of acute ischemic stroke and the exclusion of some stroke mimics. This can be particularly helpful when the diagnosis of stroke is in doubt. For example, the absence of a lesion on DWI can suggest that symptoms are caused by a stroke mimic. In addition, MRI does not expose the patient to radiation. Standard brain MRI protocols that include conventional T1-weighted, T2-weighted, fluid-attenuated inversion recovery (FLAIR), and T2*-weighted gradient-recalled echo (GRE) sequences along with DWI can reliably diagnose both acute ischemic stroke and acute hemorrhagic stroke in emergency settings. MRI with T2*-weighted GRE and susceptibility-weighted imaging (SWI) is equivalent to noncontrast CT for the detection of acute intraparenchymal hemorrhage and is better than noncontrast CT for the detection of chronic hemorrhage [9-11]. (See "Spontaneous intracerebral hemorrhage: Pathogenesis, clinical features, and diagnosis", section on 'Brain MRI'.) Disadvantages of MRI – Compared with CT, shortcomings of MRI are higher cost, limited availability and access (particularly in the emergency setting), patient intolerance or incompatibility, and longer scan completion time. There are numerous potential contraindications to MRI including metallic or electrical implants, devices, and foreign bodies. This issue is reviewed in detail separately. (See "Patient evaluation for metallic or electrical implants, devices, or foreign bodies before magnetic resonance 3 z 44 14/01/2025, 12:40 Neuroimaging of acute stroke - UpToDate https://www.uptodate.com/contents/neuroimaging-of-acute-stroke/print imaging" and "Patient evaluation before gadolinium contrast administration for magnetic resonance imaging".) Despite these drawbacks, a trial of patients with a large vessel occlusion found that 88 percent were able to undergo MRI , and a few reports have demonstrated that it is possible to use MRI routinely as the sole neuroimaging screening method prior to intravenous thrombolytic therapy [13,14] or endovascular therapy. In one such study of 135 patients screened with MRI and treated with intravenous thrombolysis, quality improvement processes led to reduced door-to-needle times of ≤60 minutes. These data suggest that MRI can be used as the only imaging method in select centers with sufficient MRI availability for the evaluation of patients with suspected acute ischemic stroke. Multimodal imaging — Assessment of ischemic brain injury and brain perfusion can be performed with either multimodal CT or multimodal MRI if results are likely to influence treatment decisions, such as mechanical thrombectomy in the late time window (ie, >6 hours from stroke onset or from the time of last known well). Multimodal CT includes noncontrast head CT with CTA of the head and neck and CT perfusion (CTP). Multimodal CT improves detection of acute ischemic stroke when compared with noncontrast CT alone [16-19]. In addition, multimodal CT can diagnose large vessel occlusion and estimate the core and penumbra of an acute ischemic stroke [20,21]. After endovascular intervention, both hemorrhage and contrast staining of infarcted tissue can occur. Both conditions have the same appearance on standard noncontrast CT. Dual-energy CT can be used to differentiate the two. Multimodal MRI includes MRI of the brain without contrast, high-susceptibility imaging (to exclude hemorrhage), MRA of the head and neck, DWI, and perfusion-weighted imaging (PWI). Multimodal MRI can identify acute infarction, emergent large vessel occlusion, infarct core, and salvageable penumbral brain tissue [23-25]. Time-based selection of imaging — It is vitally important to determine the time the patient was last known to be well (ie, at neurologic baseline), because the use of reperfusion therapies for ischemic stroke (intravenous thrombolysis and mechanical thrombectomy) are time- and imaging-dependent. (See "Approach to reperfusion therapy for acute ischemic stroke".) Time last known well