Imaging stroke patients with unclear onset times

Follow-up infarct volume on fluid attenuated inversion recovery (FLAIR) imaging in distal medium vessel occlusions: the role of cerebral blood volume index

BACKGROUND

Distal medium vessel occlusions (DMVOs) contribute substantially to the incidence of acute ischemic strokes (AIS) and pose distinct challenges in clinical management and prognosis. Neuroimaging techniques, such as Fluid Attenuation Inversion Recovery (FLAIR) imaging and cerebral blood volume (CBV) index derived from perfusion imaging, have significantly improved our ability to assess the impact of strokes and predict their outcomes. The primary objective of this study was to investigate relationship between follow-up infarct volume (FIV) as assessed by FLAIR imaging in patients with DMVOs.

METHODS

This prospectively collected, retrospective reviewed cohort study included patients from two comprehensive stroke centers within the Johns Hopkins Medical Enterprise, spanning August 2018-October 2022. The cohort consisted of adults with AIS attributable to DMVO. Detailed imaging analyses were conducted, encompassing non-contrast CT, CT angiography (CTA), CT perfusion (CTP), and FLAIR imaging. Univariable and multivariable linear regression models were employed to assess the association between different factors and FIV.

RESULTS

The study included 79 patients with DMVO stroke with a median age of 69 years (IQR, 62-77 years), and 57% (n = 45) were female. There was a negative correlation between the CBV index and FIV in a univariable linear regression analysis (Beta =  - 16; 95% CI,  - 23 to  - 8.3; p < 0.001) and a multivariable linear regression model (Beta =  - 9.1 per 0.1 change; 95% CI,  - 15 to  - 2.7; p = 0.006). Diabetes was independently associated with larger FIV (Beta = 46; 95% CI, 16 to 75; p = 0.003). Additionally, a higher baseline ASPECTS was associated with lower FIV (Beta =  - 30; 95% CI,  - 41 to  - 20; p < 0.001).

CONCLUSION

Our findings underscore the CBV index as an independent association with FIV in DMVOs, which highlights the critical role of collateral circulation in determining stroke outcomes in this patient population. In addition, our study confirms a negative association of ASPECTS with FLAIR FIV and identifies diabetes as independent factor associated with larger FIV. These insights pave the way for further large-scale, prospective studies to corroborate these findings, thereby refining the strategies for stroke prognostication and management.

Hematoma Expansion in Intracerebral Hemorrhage With Unclear Onset

OBJECTIVE

To investigate the prevalence, predictors, and prognostic effect of hematoma expansion (HE) in patients with intracerebral hemorrhage (ICH) with unclear symptom onset (USO).

METHODS

We performed a retrospective analysis of patients with primary spontaneous ICH admitted at 5 academic medical centers in the United States and Italy. HE (volume increase >6 mL or >33% from baseline to follow-up noncontrast CT [NCCT]) and mortality at 30 days were the outcomes of interest. Baseline NCCT was also analyzed for presence of hypodensities (any hypodense region within the hematoma margins). Predictors of HE and mortality were explored with multivariable logistic regression.

RESULTS

We enrolled 2,165 participants, 1,022 in the development cohort and 1,143 in the replication cohort, of whom 352 (34.4%) and 407 (35.6%) had ICH with USO, respectively. When compared with participants having a clear symptom onset, patients with USO had a similar frequency of HE (25.0% vs 21.9%, p = 0.269 and 29.9% vs 31.5%, p = 0.423). Among patients with USO, HE was independently associated with mortality after adjustment for confounders (odds ratio [OR] 2.64, 95% confidence interval [CI] 1.43-4.89, p = 0.002). This finding was similar in the replication cohort (OR 3.46, 95% CI 1.86-6.44, p < 0.001). The presence of NCCT hypodensities in patients with USO was an independent predictor of HE in the development (OR 2.59, 95% CI 1.27-5.28, p = 0.009) and replication (OR 2.43, 95% CI 1.42-4.17, p = 0.001) population.

CONCLUSION

HE is common in patients with USO and independently associated with worse outcome. These findings suggest that patients with USO may be enrolled in clinical trials of medical treatments targeting HE.

Thrombolysis beyond 4.5 h in Acute Ischemic Stroke

PURPOSE OF REVIEW

The purpose of this article is to review the current approaches using neuroimaging techniques to expand eligibility for intravenous thrombolytic therapy in acute ischemic stroke patients with stroke of unknown symptom onset.

RECENT FINDINGS

In recent years, several randomized, placebo-controlled trials have shown neuroimaging-guided approaches to be feasible in determining eligibility for alteplase beyond 4.5 h from last known well, and efficacious for reducing disability. DWI-FLAIR mismatch on MRI is an effective tool to identify stroke lesions less than 4.5 h in onset in patients with stroke of unknown symptom onset. Additionally, an automated perfusion-based approach, assessing for a disproportionate amount of salvageable tissue, is effective in identifying patients likely to benefit from late window alteplase treatment. In patients with stroke of unknown symptom onset, an individualized approach using neuroimaging to determine time of stroke onset or presence of salvageable brain tissue is feasible in the acute setting and associated with improved long-term outcomes.

Individualized quantification of the benefit from reperfusion therapy using stroke predictive models

PURPOSE

Recent imaging developments have shown the potential of voxel-based models in assessing infarct growth after stroke. Many models have been proposed but their relevance in predicting the benefit of a reperfusion therapy remains unclear. We searched for a predictive model whose volumetric predictions would identify stroke patients who are to benefit from tissue plasminogen activator (t-PA)-induced reperfusion.

MATERIAL AND METHODS

Forty-five cases were used to study retrospectively stroke progression from admission to end of follow-up. Predictive approaches based on various statistical models, predictive variables and spatial filtering methods were compared. The optimal approach was chosen according to the area under the precision-recall curve (AUPRC). The final lesion volume was then predicted assuming that the patient would or would not reperfuse. Patients, with an acute lesion of ≤50 ml and a predicted reduction in the presence of reperfusion >6 ml and >25% of the acute lesion, were classified as responders.

RESULTS

The optimal model was a logistic regression using the voxel distance to the acute lesion, the volume of the acute lesion and Gaussian-filtered MRI contrast parameters as predictive variables. The predictions gave a median AUPRC of 0.655, a median AUC of 0.976 and a median volumetric error of 8.29 ml. Nineteen patients matched the responder profile. A non-significant trend of improved reduction in NIHSS score (-42.8%, p = .09) and in lesion volume (-78.1%, p = 0.21) following reperfusion was observed for responder patients.

CONCLUSION

Despite limited volumetric accuracy, predictive stroke models can be used to quantify the benefit of reperfusion therapies.

Synergistic role of susceptibility-weighted imaging with diffusion-weighted imaging and magnetic resonance angiography in the evaluation of acute arterial stroke

Objective

This study was performed to investigate whether diffusion-weighted imaging (DWI) and susceptibility-weighted imaging (SWI) are more effective than conventional imaging modalities for evaluation of stroke and selection of candidates for thrombolytic therapy.

Methods

Eighty patients who presented within 12 hours of onset of symptoms of brain ischemia underwent 1.5T magnetic resonance imaging. DWI and SWI were compared with conventional sequences (T1, T2, and fluid-attenuated inversion recovery [FLAIR]) and time-of-flight magnetic resonance angiography (TOF-MRA) to assess factors that affect stroke management and prognosis.

Results

The volume of brain tissue showing hyperintensity was significantly greater than that showing diffusion restriction in patients with a >6-hour symptom onset. The hypointensity sign (susceptibility sign) on SWI showed a sensitivity of 66.7%, specificity of 87.5%, positive predictive value of 88.9, and negative predictive value of 63.6 compared with TOF-MRA. Micro-hemorrhagic foci were significantly associated with 27-mL infarcts on DWI (sensitivity, 71.4%; specificity, 85.0%). Patients with DWI–SWI mismatch showed better responses to thrombolytics. FLAIR–DWI mismatch helped to assess the time of stroke onset.

Conclusion

DWI and SWI should be part of the routine imaging protocol in patients with acute stroke and serve as a decision-making tool for selection of patients for thrombolytic therapy.

Infarct topography and functional outcomes

Acute ischemic stroke represents a major cause of long-term adult disability. Accurate prognostication of post-stroke functional outcomes is invaluable in guiding patient care, targeting early rehabilitation efforts, selecting patients for clinical research, and conveying realistic expectations to families. The involvement of specific brain regions by acute ischemia can alter post-stroke recovery potential. Understanding the influences of infarct topography on neurologic outcomes holds significant promise in prognosis of functional recovery. In this review, we discuss the recent evidence of the contribution of infarct location to patient management decisions and functional outcomes after acute ischemic stroke.

Neuroimaging Paradigms to Identify Patients for Reperfusion Therapy in Stroke of Unknown Onset

Despite the proven efficacy of intravenous alteplase or endovascular thrombectomy for the treatment of patients with acute ischemic stroke, only a minority receive these treatments. This low treatment rate is due in large part to delay in hospital arrival or uncertainty as to the exact time of onset of ischemic stroke, which renders patients outside the current guideline-recommended window of eligibility for receiving these therapeutics. However, recent pivotal clinical trials of late-window thrombectomy now force us to rethink the value of a simplistic chronological formulation that “time is brain.” We must recognize a more nuanced concept that the rate of tissue death as a function of time is not invariant, that still salvageable tissue at risk of infarction may be present up to 24 h after last-known well, and that those patients may strongly benefit from reperfusion. Multiple studies have sought to address this clinical dilemma using neuroimaging methods to identify a radiographic time-stamp of stroke onset or evidence of salvageable ischemic tissue and thereby increase the number of patients eligible for reperfusion therapies. In this review, we provide a critical analysis of the current state of neuroimaging techniques to select patients with unwitnessed stroke for revascularization therapies and speculate on the future direction of this clinically relevant area of stroke research.

Imaging of Ischemic Stroke

PURPOSE OF REVIEW

This article provides an overview of cerebrovascular hemodynamics, acute stroke pathophysiology, and collateral circulation, which are pivotal in the modern imaging of ischemic stroke that guides the care of the patient with stroke.

RECENT FINDINGS

Neuroimaging provides extensive information on the brain and vascular health. Multimodal CT and MRI delineate the hemodynamics of ischemic stroke that may be used to guide treatment decisions and prognosticate regarding expected outcomes. Mismatch imaging with either CT or MRI may identify patients with salvageable regions who are at risk and likely to benefit from reperfusion therapy, even if they are outside the standard time window. Imaging of collateral circulation and determination of collateral grade may predict greater reperfusion, lower hemorrhage risk, and better functional outcome. Current neuroimaging technology also enables the identification of patients at high risk of hemorrhagic transformation or those who may be harmed by treatment or unlikely to benefit from it.

SUMMARY

This article reviews the use and impact of imaging for the patient with ischemic stroke, emphasizing how imaging builds upon clinical evaluation to establish diagnosis or etiology, reveal key pathophysiology, and guide therapeutic decisions.

Translational MR Neuroimaging of Stroke and Recovery

Multiparametric magnetic resonance imaging (MRI) has become a critical clinical tool for diagnosing focal ischemic stroke severity, staging treatment, and predicting outcome. Imaging during the acute phase focuses on tissue viability in the stroke vicinity, while imaging during recovery requires the evaluation of distributed structural and functional connectivity. Preclinical MRI of experimental stroke models provides validation of non-invasive biomarkers in terms of cellular and molecular mechanisms, while also providing a translational platform for evaluation of prospective therapies. This brief review of translational stroke imaging discusses the acute to chronic imaging transition, the principles underlying common MRI methods employed in stroke research, and the experimental results obtained by clinical and preclinical imaging to determine tissue viability, vascular remodeling, structural connectivity of major white matter tracts, and functional connectivity using task-based and resting-state fMRI during the stroke recovery process.

Determining Stroke Onset Time Using Quantitative MRI: High Accuracy, Sensitivity and Specificity Obtained from Magnetic Resonance Relaxation Times

Many ischaemic stroke patients are ineligible for thrombolytic therapy due to unknown onset time. Quantitative MRI (qMRI) is a potential surrogate for stroke timing. Rats were subjected to permanent middle cerebral artery occlusion and qMRI parameters including hemispheric differences in apparent diffusion coefficient, T₂-weighted signal intensities, T₁ and T₂ relaxation times (qT₁, qT₂) and f₁, f₂ and V_overlap were measured at hourly intervals at 4.7 or 9.4 T. Accuracy and sensitivity for identifying strokes scanned within and beyond 3 h of onset was determined. Accuracy for V_overlap, f₂ and qT₂ (>90%) was significantly higher than other parameters. At a specificity of 1, sensitivity was highest for V_overlap (0.90) and f₂ (0.80), indicating promise of these qMRI indices in the clinical assessment of stroke onset time.

Diffusion-weighted imaging–fluid-attenuated inversion recovery mismatch is associated with better neurologic response to intravenous thrombolytic therapy in acute ischemic stroke patients

Objective

To investigate differences in the effect of intravenous (IV) thrombolysis regarding the mismatch of diffusion-weighted imaging–fluid-attenuated inversion recovery (DWI-FLAIR) among acute ischemic stroke patients who visited the emergency department (ED) within 3 hours from the onset of symptoms.

Methods

Among ED patients presenting with an acute ischemic stroke between January 2011 and May 2013 at a tertiary hospital, those who underwent magnetic resonance imaging before IV thrombolytic therapy were included in this retrospective study. Patients were divided into DWI-FLAIR mismatch and match groups. National Institutes of Health Stroke Scale (NIHSS) scores obtained initially, 24 hours after thrombolytic therapy, and on discharge, and early neurologic improvement (ENI) and major neurologic improvement (MNI) were compared.

Results

During the study period, 50 of the 213 acute ischemic stroke patients who presented to the ED were included. The DWI-FLAIR mismatch group showed a statistically significantly greater reduction in NIHSS both at 24 hours after thrombolytic therapy and upon discharge than did the match group (5.5 vs. 1.2, P<0.001; 6.0 vs. 2.3, P<0.01, respectively). Moreover, ENI and MNI were significantly greater for the DWI-FLAIR mismatch group than for the match group (27/36 vs. 2/14, P<0.001; 12/36 vs. 0/14, P=0.012, respectively).

Conclusion

Among acute ischemic stroke patients who visited the ED within 3 hours from the onset of symptoms, patients who showed DWI-FLAIR mismatch showed a significantly better response to IV thrombolytic therapy than did the DWI-FLAIR match group in terms of neurologic outcome.

The usefulness of diffusion-weighted/fluid-attenuated inversion recovery imaging in the diagnostics and timing of lacunar and nonlacunar stroke

INTRODUCTION

The DWI/FLAIR mismatch is a potential radiological marker for the timing of stroke onset. The aim of the study was to assess if the DWI/FLAIR mismatch can help to identify patients with both lacunar and nonlacunar acute ischemic stroke within 4.5 h of onset.

METHODS

A retrospective study was performed in which the authors analysed data from 86 ischemic lacunar and nonlacunar stroke patients with a known time of symptom onset, imaged within the first 24 h from stroke onset (36 patients <4.5 h, 14 patients 4.5-6 h, 15 patients 6-12 h, and 21 patients 12-24 h). Patients underwent the admission CT and MR scan. The presence of lesions was assessed in correlation with the duration of the stroke.

RESULTS

The time from stroke onset to neuroimaging was significantly shorter in patients with an ischemic lesion visible only in the DWI (mean 2.78 h, n = 24) as compared to patients with signs of ischemia also in other modalities (mean 8.6 h, n = 62) (p = 0.0001, Kruskal-Wallis ANOVA). The DWI/FLAIR mismatch was characterised by a global sensitivity of 58%, specificity 94%, PPV 87.5%, and NPV 76% in identifying patients in the 4.5 h thrombolysis time window. For lacunar strokes (n = 20), these parameters were as follows: sensitivity 50%, specificity 92.8%, PPV 75 %, and NPV 81.2%.

CONCLUSIONS

The presence of acute ischemic lesions only in DWI can help to identify both lacunar and nonlacunar stroke patients who are in the 4.5 h time window for intravenous thrombolysis with high specificity.

Thrombolysis and reperfusion: advanced understanding of early management strategies in acute ischemic stroke

Currently, intravenous (IV) thrombolysis within 3 hours from stroke onset is the only approved treatment in acute ischemic stroke (AIS). Although effective, the definition of therapeutic time window and appropriate patient selection still remains controversial. Notably, early endovascular treatment strategies may serve as an adjunct therapy for time window extension in AIS. In this article, we review the safety and efficacy of IV thrombolysis in AIS as it pertains to the optimal time window, the selection of eligible patients, and in combination with endovascular treatment. Combined clinical application of IV thrombolysis and endovascular therapy may improve the therapeutic outcomes for AIS patients.

MR perfusion imaging in acute ischemic stroke

Magnetic resonance (MR) perfusion imaging offers the potential for measuring brain perfusion in acute stroke patients, at a time when treatment decisions based on these measurements may affect outcomes dramatically. Rapid advancements in both acute stroke therapy and perfusion imaging techniques have resulted in continuing redefinition of the role that perfusion imaging should play in patient management. This review discusses the basic pathophysiology of acute stroke, the utility of different kinds of perfusion images, and research on the continually evolving role of MR perfusion imaging in acute stroke care.