Neuroimaging of Acute Ischemic Stroke: Multimodal Imaging Approach for Acute Endovascular Therapy

Abstract

Advances in acute ischemic stroke (AIS) treatment have been contingent on innovations in neuroimaging. Neuroimaging plays a pivotal role in the diagnosis and prognosis of ischemic stroke and large vessel occlusion, enabling triage decisions in the emergent care of the stroke patient. Current imaging protocols for acute stroke are dependent on the available resources and clinicians' preferences and experiences. In addition, differential application of neuroimaging in medical decision-making, and the rapidly growing evidence to support varying paradigms have outpaced guideline-based recommendations for selecting patients to receive intravenous or endovascular treatment. In this review, we aimed to discuss the various imaging modalities and approaches used in the diagnosis and treatment of AIS.

Keywords: Acute stroke; Endovascular treatment; Neuroimaging.

Figure 1.

Early ischemic changes seen on (A) axial non-contrast head computed tomography (CT) as loss of the grey matter density of the right insula, part of the lenticular nucleus, and the right fronto-temporal regions. These changes are better seen on (B) the axial CT angiogram (CTA) source images and (C) the diffusion-weighted magnetic resonance imaging images as areas of reduced diffusion. Scarce collaterals are noted in the right middle cerebral artery territory on (B) the CTA source images.

Figure 2.

The Alberta Stroke Program Early CT Score (ASPECTS) consists of 10 specific regions of the middle cerebral artery (MCA) territory on a non-contrast axial head computed tomography at two levels: (A) the basal ganglia level and (B) the body of the lateral ventricles level. At the basal ganglia level, the following regions are assessed: caudate (C), internal capsule (IC), lentiform nucleus (L), insula (I), frontal MCA cortex (M1), anterior temporal MCA cortex (M2), and posterior temporal MCA cortex (M3). At the supraganglionic level, the following regions are assessed: anterior frontal MCA cortex (M4), lateral frontal MCA cortex (M5), and posterior frontal MCA cortex (M6).

Figure 3.

The posterior circulation Acute Stroke Prognosis Early Computed Tomography Score (pc-ASPECTS) is a score derived from evaluating eight distinct regions for evidence of early ischemic changes in the posterior circulation territories as shown on (A-C) three axial slices of a non-contrast head computed tomography. The superimposed numbers indicate the point values assigned to each region. Specifically, the midbrain and pons each account for two points in the scoring system, while the bilateral cerebellar hemispheres, bilateral thalami, and bilateral occipital lobes account for one point each.

Figure 4.

Examples of hyperdense vessel signs (white circles) on non-contrast axial head computed tomography in (A) the M1 segment of the right middle cerebral artery, (B) M2 segment of the left middle cerebral artery, (C) the basilar artery, and (D) the anterior cerebral artery.

Figure 5.

Collateral circulation in acute ischemic stroke. (A) CT angiograpy source images in a patient with left M1 occlusion showing dark left middle cerebral artery (MCA) territory due to lack of collaterals that were confirmed on (B) angiogram. Despite (C) complete recanalization, (D) there was progression to large left MCA infarct. Paucity of collaterals indicates a high probability of tissue infarction despite successful recanalization, and correlates strongly with hypoperfusion estimates on advanced neuroimaging. (E) Anteroposterior angiogram of a right internal carotid artery injection showing an abrupt cut-off of the M1 segment of the right MCA. There are significant leptomeningeal collaterals (white circle) from the right anterior cerebral artery to the right MCA territory. (F) Complete reperfusion was achieved with (G) very small infarction of the lenticular nucleus.

Figure 6.

Patient presented with an acute occlusion of the middle cerebral artery (arrowheads on A and C). There is also a shelf-like filling defect of the posterior aspect of the carotid bifurcation (white arrows on A and B), consistent with a carotid web which is an underappreciated cause of embolic stroke. Image on (A) is a 3D volume rendering reconstruction of a CT angiogram of the neck. Images on (B), (C), and (D) consist of cerebral angiograms.

Figure 7.

A patient presented with slurred speech, right arm and leg plegia and numbness. (A) Coronal computed tomography angiogram of the head and (C) anteroposterior angiogram showing an occlusion of the A2 segment of the left anterior cerebral artery (ACA) (white arrows) and critical stenosis of the M1 segment of the left middle cerebral artery (MCA) (white circle). (B) Magnetic resonance imaging (MRI) perfusion images with mean transient time (MTT), cerebral blood flow (CBF), and cerebral blood volume (CBV) showing a core infarct (prolonged MTT with significantly reduced CBF and CBV) in the left ACA territory and an area of penumbra (prolonged MTT with mildly reduced CBF and preserved CBV) in the left MCA territory. (D) Based on the patient’s clinical presentation and perfusion images, decision was to proceed with MCA recanalization to salvage the left MCA territory at risk. Intracranial stenting was performed with restoration of flow of the left MCA territory. No endovascular treatment was performed of the A2 occlusion because of the complete irreversible infarction of the ACA territory. (E and F) Follow-up MRI with diffusion-weighted imaging showing an infarction of the left ACA territory with a small focus of infarction of the lenticular nucleus.

Figure 8.

Magnetic resonance imaging findings in acute ischemic stroke. (A) Axial susceptibility-weighted images showing blooming (white circle) in the right Sylvian fissure due to (D) an M2 occlusion (white arrow) that was confirmed on the cerebral angiogram. (B) Axial diffusion-weighted images (DWI) showing areas of restricted diffusion with (C) no significant fluid-attenuated inversion recovery (FLAIR) hyperintensities (DWI-FLAIR mismatch). (C) Note of “hyperintense vessels sign” seen on FLAIR as a result of slow or retrograde flow (arrowheads). (E) Mechanical thrombectomy was performed with recanalization of the distal M2 occlusion.