Multimodal Diagnostic Imaging for Hyperacute Stroke

Differentiation of Acute Internal Carotid Artery Occlusion Etiology on Computed Tomography Angiography: Diagnostic Tree for Preparing Endovascular Treatment

BACKGROUND AND PURPOSE

This study aimed to identify the imaging characteristics and discriminate the etiology of acute internal carotid artery occlusion (ICAO) on computed tomography angiography (CTA) in patients with acute ischemic stroke.

MATERIALS AND METHODS

We retrospectively evaluated consecutive patients who underwent endovascular thrombectomy for acute ICAO. Contrast filling of the extracranial ICA in preprocedural CTA was considered apparent ICAO. Non-contrast filling of the extracranial ICA was evaluated according to the contrast-filled lumen configuration, lumen margin and location, Hounsfield units of the non-attenuating segment, and presence of calcification or an intimal flap. Digital subtraction angiography findings were the reference standard for ICAO etiology and the occlusion site. A diagnostic tree was derived using significant variables according to pseudo-occlusion, atherosclerotic vascular disease (ASVD), thrombotic occlusion, and dissection.

RESULTS

A total of 114 patients showed apparent ICAO (n = 21), pseudo-occlusion (n = 51), ASVD (n = 27), thrombotic occlusion (n = 9), or dissection (n = 6). Most pseudo-occlusions (50/51, 98.0%) showed dependent locations with ill-defined contrast column margins and classic flame or beak shapes. The most common occlusion site of pseudo-occlusion was the petro-cavernous ICA (n = 32, 62.7%). Apparent ICAO mainly appeared in cases with occlusion distal to the posterior communicating artery orifice. ASVD showed beak or blunt shapes in the presence of low-density plaques or dense calcifications. Dissection revealed flame- or beak-shaped appearances with circumscribed margins. Thrombotic occlusions tended to appear blunt-shaped. The decision-tree model showed a 92.5% overall accuracy.

CONCLUSIONS

CTA characteristics may help diagnose ICAO etiology. We provide a simple and easy decision-making model to inform endovascular thrombectomy.

Update on imaging in Code Stroke

"Code Stroke" is a multidisciplinary procedure designed to detect acute ischemic strokes and transfer patients for early reperfusion. Selecting these patients requires multimodal imaging with either CT or MRI. 1) Conventional studies without contrast material are obligatory to detect bleeding. Applying the ASPECTS scale, these studies can also identify and quantify areas of early infarction. 2) In candidates for mechanical thrombectomy, angiographic studies are necessary to identify stenoses and obstructions and to evaluate the collateral circulation. 3) Patients with known onset between 6 and 24h or with unknown onset require perfusion studies to distinguish between infracted tissue and recoverable ischemic tissue. Semi-automatic software facilitates diagnosis, but radiologists must interpret its output.

Current approaches and advances in the imaging of stroke

A stroke occurs when the blood flow to the brain is suddenly interrupted, depriving brain cells of oxygen and glucose and leading to further cell death. Neuroimaging techniques, such as computed tomography and magnetic resonance imaging, have greatly improved our ability to visualise brain structures and are routinely used to diagnose the affected vascular region of a stroke patient's brain and to inform decisions about clinical care. Currently, these multimodal imaging techniques are the backbone of the clinical management of stroke patients and have immensely improved our ability to visualise brain structures. Here, we review recent developments in the field of neuroimaging and discuss how different imaging techniques are used in the diagnosis, prognosis and treatment of stroke.

Summary: Stroke imaging has undergone seismic shifts in the past decade. Although magnetic resonance imaging (MRI) is superior to computed tomography in providing vital information, further research on MRI is still required to bring its full potential into clinical practice.

Imaging assessment of acute ischaemic stroke: a review of radiological methods

Acute ischaemic stroke is the second largest cause of death worldwide and a cause of major physical and psychological morbidity. Current evidence based treatment includes intravenous thrombolysis (IVT) and mechanical thrombectomy (MT), both requiring careful patient selection and to be administered as quickly as possible within a limited time window from symptom onset. Imaging plays a crucial role identifying patients who may benefit from MT or IVT whilst excluding those that may be harmed. For IVT, imaging must as a minimum exclude haemorrhage, stroke mimics and provide an estimate of non-viable brain. For MT, imaging must in addition detect and characterize intra-arterial thrombus and assess the intra and extracranial arterial architecture. More advanced imaging techniques may be used to assess more accurately the volume of non-viable and potentially salvageable brain tissue. It is highly likely that further research will identify patients who would benefit from treatment beyond currently accepted time windows for IVT (4.5 h) and MT (6 h) and patients with an unknown time of symptom onset. Current evidence indicates that best outcomes are achieved when treatment is instituted as soon as possible after symptom onset. A rapid, efficient imaging pathway including interpretation is fundamental to achieving the best outcomes. This review summarizes current techniques for imaging assessment of acute stroke, highlighting strengths and limitations of each. The optimum pathway is a balance between diagnostic information, local resources, specialization and the time taken to acquire, process and interpret the data. As new evidence emerges, it is likely that the minimum required imaging data will change.

Cognitive Function and Prognosis of Multimodal Neuroimage-Guided Thrombectomy on Mild to Moderate Anterior Circulation Infarction Patients with Broadened Therapeutic Window: A Prospective Study

BACKGROUND AND OBJECTIVES

Endovascular mechanical thrombectomy is an important approach for acute ischemic stroke (AIS) treatment. Multimodal neuroimaging methods ideally provide the exact localization, extent, and metabolic activity of target tissues. Post-stroke cognitive impairment has recently been realized to be another major concern except for neurological function impairment. The aim of our study was to carry out a prospective study to compare neurological and cognitive functions after thrombectomy in mild to moderate anterior circulation infarction patients selected by multimodal neuroimaging.

METHODS

Ninety patients were recruited from January 2016 to March 2017 consecutively. Neurological function was assessed by NIHSS before thrombectomy, and 6 h, 24 h, 7 days, 90 days after mechanical thrombectomy. Cognitive functions were evaluated by Mini-Mental State Examination (MMSE), Montreal Cognitive Assessment (MoCA) and Hachinski Ischemic Scale.

RESULTS

Patients who received mechanical thrombectomy had significantly better neurological functions at 6 h (p < 0.001), 24 h (p < 0.001), 7 days (p < 0.001), and 90 days (p < 0.001), as well as cognitive functions evaluated by MoCA (26.23 ± 3.85 vs. 24.62 ± 2.25, p = 0.022, n = 85) and MMSE (26.65 ± 2.77 vs. 25.10 ± 2.36, p = 0.023, n = 85) compared to the standard therapy group.

CONCLUSIONS

The current prospective study demonstrated that mechanical thrombectomy can significantly improve neurological and cognitive functions in patients with mild to moderate AIS at broadened therapeutic window under multimodal CT and multimodal MRI imaging.