Magnetic resonance imaging in acute ischemic stroke treatment

Abstract

Although intravenous administration of tissue plasminogen activator is the only proven treatment after acute ischemic stroke, there is always a concern of hemorrhagic risk after thrombolysis. Therefore, selection of patients with potential benefits in overcoming potential harms of thrombolysis is of great importance. Despite the practical issues in using magnetic resonance imaging (MRI) for acute stroke treatment, multimodal MRI can provide useful information for accurate diagnosis of stroke, evaluation of the risks and benefits of thrombolysis, and prediction of outcomes. For example, the high sensitivity and specificity of diffusion-weighted image (DWI) can help distinguish acute ischemic stroke from stroke-mimics. Additionally, the lesion mismatch between perfusion-weighted image (PWI) and DWI is thought to represent potential salvageable tissue by reperfusion therapy. However, the optimal threshold to discriminate between benign oligemic areas and the penumbra is still debatable. Signal changes of fluid-attenuated inversion recovery image within DWI lesions may be a surrogate marker for ischemic lesion age and might indicate risks of hemorrhage after thrombolysis. Clot sign on gradient echo image may reflect the nature of clot, and their location, length and morphology may provide predictive information on recanalization by reperfusion therapy. However, previous clinical trials which solely or mainly relied on perfusion-diffusion mismatch for patient selection, failed to show benefits of MRI-based thrombolysis. Therefore, understanding the clinical implication of various useful MRI findings and comprehensively incorporating those variables into therapeutic decision-making may be a more reasonable approach for expanding the indication of acute stroke thrombolysis.

Keywords: Acute ischemic stroke; Magnetic resonance image; Thrombolysis.

Figure 1

Common stroke mimics, identified in a systematic review and meta-analysis of case series.

Figure 2

DWI lesion patterns according to stroke subtypes. (A) Intracranial atherosclerotic stenosis, (B) extracranial atherosclerotic stenosis, (C) cardioembolism, and (D) aortic arch embolism.

Figure 3

PWI-DWI mismatch (A), time-concentration curves (B and C) and various PWI parameters (D).

Figure 4

Types of hemorrhagic transformation according to ECASS criteria.

Figure 5

MRI markers predicting hemorrhagic transformation (A) Delayed gadolinium enhancement of the CSF space (arrows); (B) Parenchymal enhancement at post contrast T1-weighted image (arrow) and hemorrhagic transformation at the corresponding area at follow-up (arrow).

Figure 6

Clot presented on gradient echo image (arrow) with long segment (A) and tortuous vessel (B).

Figure 7

DWI-FLAIR mismatch: positive (A) and negative (B).