Hyperintense acute reperfusion marker is associated with higher contrast agent dosage in acute ischaemic stroke

Ipsilateral blooming of microbleeds after Hyperintense Acute Reperfusion Marker sign in an ischemic Stroke patient, a case report

Background

Hyperintense Acute Reperfusion Marker (HARM) is a hyperintense subarachnoid signal on FLAIR MRI sequence caused by gadolinium contrast leakage into the subpial space. While, on FLAIR, HARM may mimic subarachnoid hemorrhage, it is differentiated from it on computed tomography (CT) and SWAN MRI sequences. Cerebral microbleeds are black, rounded spots on SWAN caused by blood-products deposition following red blood cell leakage from small cerebral vessels brain. Both microbleeds and HARM carry important prognostic implication as they are associated with blood-brain barrier disruption and an increased risk of intracerebral hemorrhage.

Case presentation

A 79-year-old man presented with aphasia and right hemiparesis due to ischemic stroke with left middle cerebral artery occlusion. Admission NIHSS score was 7, and he was successfully treated by intravenous thrombolysis and mechanical thrombectomy. On day 1, his clinical condition worsened, and he had an urgent gadolinium-enhanced MRI. There was no evidence of early recurrence, nor of hemorrhage on SWAN or on FLAIR. Left middle cerebral artery was permeable. The patient was anticoagulated for newly diagnosed atrial fibrillation, and a second MRI following a generalized tonic-clonic seizure showed multiple left hemispheric diffusion-weighted imaging (DWI) hyperintense spots and a left hemispheric sub-arachnoid hyperintensity on FLAIR, compatible with a subarachnoid hemorrhage. This diagnosis was excluded by SWAN MRI sequence and a normal cerebral CT the same day. The diagnosis of HARM was retained. At day 9, patient’s condition improved, and a control MRI did not show evidence of HARM. However, numerous microbleeds were detected in the left hemisphere only (ipsilateral with HARM and stroke).

Conclusions

This case highlights first of all the importance of differentiating HARM and subarachnoid hemorrhage, especially in an anticoagulated patient with clinical aggravation. Secondly, it is crucial to identify microbleeds and understand their pathophysiology, as they are associated with higher risk of hemorrhage and stroke recurrence in ischemic stroke patients. Finally, the mono-hemispheric appearance of microbleeds in this case suggests for the first time that, in some acute ischemic stroke patients, a relationship between HARM and cerebral microbleeds may exist.

Contrast-Enhanced Fluid-Attenuated Inversion Recovery in Neuroimaging: A Narrative Review on Clinical Applications and Technical Advances

While contrast-enhanced fluid-attenuated inversion recovery (FLAIR) has long been regarded as an adjunct sequence to evaluate leptomeningeal disease in addition to contrast-enhanced T1-weighted imaging, it is gradually being used for more diverse pathologies beyond leptomeningeal disease. Contrast-enhanced FLAIR is known to be highly sensitive to low concentrations of gadolinium within the fluid. Accordingly, recent research has suggested the potential utility of contrast-enhanced FLAIR in various kinds of disease, such as Meniere's disease, seizure, stroke, traumatic brain injury, and brain metastasis, in addition to being used for visualizing glymphatic dysfunction. However, its potential applications have been reported sporadically in an unorganized manner. Furthermore, the exact mechanism for its superior sensitivity to low concentrations of gadolinium has not been fully understood. Rapidly developing magnetic resonance technology and unoptimized parameters for FLAIR may challenge its accurate application in clinical practice. This review provides the fundamental mechanism of contrast-enhanced FLAIR, systematically describes its current and potential clinical application, and elaborates on technical considerations for its optimization. LEVEL OF EVIDENCE: 3 TECHNICAL EFFICACY STAGE: 5.

Hyperintense acute reperfusion marker associated with hemorrhagic transformation in the WAKE-UP trial

Introduction

Hyperintense acute reperfusion marker (HARM) is an indicator of early disruption of the blood-brain-barrier. Our aim was to investigate the incidence of HARM in patients with a diffusion weighted imaging (DWI) - fluid attenuated inversion recovery (FLAIR) mismatch and determine the association between this marker and hemorrhagic complications as well as clinical outcome.

Patients and Methods

We included patients from the Efficacy and Safety of MRI-Based Thrombolysis in Wake-Up Stroke (WAKE-UP) trial who underwent baseline perfusion weighted imaging (PWI). HARM was defined as a hyperintense signal in the cerebrospinal fluid space on FLAIR imaging at 24 h after baseline imaging. We compared baseline characteristics in patients with and without HARM and investigated the association between HARM and any hemorrhagic transformation (HT) and parenchymal hematoma (PH) in a multivariate logistic regression. We also explored HARM as an independent predictor of poor outcome, defined as a modified Rankin Scale of 3-6 at 90 days.

Results

HARM was present in 14 of 223 (6%) patients with a DWI-FLAIR mismatch and baseline characteristics were similar in patients with vs without HARM. HARM showed an independent relationship with any HT (OR 6.67; 95%CI 1.72-26.58) and any PH (OR 6.92; 95%CI 1.34-29.49). The rate of HARM was similar in patients with good and poor outcome (5%, p = 0.90).

Conclusion

In the WAKE-UP trial, the incidence of HARM was only 6% at 24 h. An association was present between HARM and hemorrhagic complications, but no relationship with functional outcome was observed.

GLOS and HARM in patients with transient neurovascular symptoms with and without ischemic infarction

BACKGROUND AND PURPOSE

Gadolinium leakage in ocular structures (GLOS) on fluid attenuated inversion recovery images (FLAIR) is a novel imaging marker in acute ischemic stroke and other neurological disorders.

METHODS

In patients with transient neurovascular symptoms who underwent repeated MRI with intravenous contrast agent administration, the presence of acute ischemic lesions on diffusion-weighted images (DWI) as well as the frequency and pattern of blood-brain barrier and blood-retina barrier impairment as demonstrated by the hyperintense acute reperfusion marker (HARM) and GLOS respectively on postcontrast FLAIR were evaluated.

RESULTS

Overall 28 patients with transient neurovascular symptoms (median age 70.5 years; 18 (64.3%) male) were included. Follow-up MRI was performed within 35 (IQR 21-47) hours after the initial MRI. On DWI, acute ischemic lesions were observed in 22 (78.6%). On contrast-enhanced FLAIR, GLOS was observed in 12 (42.9%) patients: in 1 (3.6%) only in the anterior chamber, and in 11 (39.3%) in the anterior chamber and vitreous body. HARM was observed in 3 (10.7%) patients. In one patient without ischemic lesion on DWI or HARM on FLAIR, GLOS was observed in the anterior chamber and vitreous body. Presence of GLOS was associated with higher age (p = 0.04) and detection of HARM (p = 0.03).

CONCLUSIONS

In patients with transient neurovascular symptoms, GLOS is a frequent finding and associated with HARM on contrast-enhanced FLAIR. As GLOS was observed in one patient without an ischemic lesion or HARM, it might be useful as an additional imaging marker.

Pathophysiology of Blood-Brain Barrier Permeability Throughout the Different Stages of Ischemic Stroke and Its Implication on Hemorrhagic Transformation and Recovery

The blood-brain barrier (BBB) is a dynamic interface responsible for maintaining the central nervous system homeostasis. Its unique characteristics allow protecting the brain from unwanted compounds, but its impairment is involved in a vast number of pathological conditions. Disruption of the BBB and increase in its permeability are key in the development of several neurological diseases and have been extensively studied in stroke. Ischemic stroke is the most prevalent type of stroke and is characterized by a myriad of pathological events triggered by an arterial occlusion that can eventually lead to fatal outcomes such as hemorrhagic transformation (HT). BBB permeability seems to follow a multiphasic pattern throughout the different stroke stages that have been associated with distinct biological substrates. In the hyperacute stage, sudden hypoxia damages the BBB, leading to cytotoxic edema and increased permeability; in the acute stage, the neuroinflammatory response aggravates the BBB injury, leading to higher permeability and a consequent risk of HT that can be motivated by reperfusion therapy; in the subacute stage (1-3 weeks), repair mechanisms take place, especially neoangiogenesis. Immature vessels show leaky BBB, but this permeability has been associated with improved clinical recovery. In the chronic stage (>6 weeks), an increase of BBB restoration factors leads the barrier to start decreasing its permeability. Nonetheless, permeability will persist to some degree several weeks after injury. Understanding the mechanisms behind BBB dysregulation and HT pathophysiology could potentially help guide acute stroke care decisions and the development of new therapeutic targets; however, effective translation into clinical practice is still lacking. In this review, we will address the different pathological and physiological repair mechanisms involved in BBB permeability through the different stages of ischemic stroke and their role in the development of HT and stroke recovery.

CSF enhancement on post-contrast fluid-attenuated inversion recovery images; a systematic review

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CSF enhancement on post-contrast FLAIR images is a novel marker for BBB leakage.

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This neuroradiological marker is frequently observed in neurological diseases.

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Post-contrast FLAIR CSF enhancement is associated with higher age and brain atrophy.

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There is large methodological heterogeneity between studies that use this technique.

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We provide recommendations for future methodological standardization.

Cerebrospinal fluid (CSF) enhancement on T2-weighted post-contrast fluid-attenuated inversion recovery (pcT2wFLAIR) images is a relatively unknown neuroradiological marker for gadolinium-based contrast agent extravasation due to blood–brain barrier (BBB) disruption. We systematically reviewed human studies reporting on CSF enhancement on pcT2wFLAIR images to provide a comprehensive overview of prevalence of this new biomarker in healthy and diseased populations as well as its etiology and optimal detection methodology. We extracted information on the prevalence of CSF enhancement, its vascular risk factor and neuroimaging correlates, and methodological attributes of each study. Forty-four eligible studies were identified. By pooling data, we found that the prevalence of CSF enhancement was 82% (95% confidence interval (CI) 80–89) in meningitis (4 studies, 65 patients), 73% (95%CI 62–81) in cases with (post-) acute intracerebral hemorrhage (2 studies, 77 cases), 64% (95% CI 54–73) in cases who underwent surgery for aneurysm treatment (2 studies, 99 patients), 40% (95% CI 30–51) in cases who underwent surgery for carotid artery disease treatment (3 studies, 76 patients), 27% (95% CI 25–30) in cases with acute ischemic stroke (9 studies, 1148 patients), 21% (95% CI 17–23) in multiple sclerosis (6 studies, 897 patients), and 13% (95% CI 7–21) in adult controls (4 studies, 112 cases). Presence of CSF enhancement was associated with higher age in eleven studies, with lobar cerebral microbleeds in one study, and with cerebral atrophy in four studies. PcT2wFLAIR imaging represents a promising method that can provide novel perspectives on BBB leakage into CSF compartments, with the potential to reveal important new insights into the pathophysiological mechanisms of varying neurological diseases.

Effect of contrast agent dosage on longitudinal relaxation time, signal and apparent tumor volume in glioblastoma at 9.4T

INTRODUCTION

Glioblastoma multiforme is the most frequent innate brain tumor and still yields an unfavorable prognosis of 15 months of survival after diagnosis. Animal models play an important role in the investigation of therapeutic strategies of brain tumors. Thereby, MRI is substantial to individual follow-up examination for therapeutic response. Contrast agent dosage at 1.5 and 3T MRI has been thoroughly tested, while there is hardly any data for 9.4T. Therefore, the aim of this study was to find the optimal contrast agent dosage at 9.4T for examination of T1 relaxation time and apparent tumor volume in an animal model.

MATERIAL AND METHODS

Six animals with a U-87 glioblastoma were part of this study. Scans were performed on a 9.4T MRI. The MRI protocol contained a standard T1w sequence, which was employed for tumor volumetry and signal intensity measurement after single, double and triple contrast agent dosage injections and a T2w sequence for volumetry of tumor and edema. From a T1 map, T1 relaxation times and tumor area were measured. Histologic tumor size measurements were also performed for two animals.

RESULTS

The mean apparent tumor volume in T1w MRI increased significantly with each additional contrast agent injection, mainly due to the increase of the hyperintense tumor rim. Volumetry based on T2w MRI resulted in a higher tumor volume than in T1w volumetry, whereas the tumor volume in T1w MRI approached the volume in T2w MRI with increasing contrast agent dosage. Histology revealed an apparent tumor volume that corresponded to the volume of the hypointense center in T1w MRI. In contrast, T1 time decrease and T1w signal increase occurred mainly in the tumor rim.

CONCLUSION

Increasing the contrast agent dosage led to an increase in apparent tumor volume. High-dose T1 MRI, however, overestimated the tumor volume that was determined by histology. Thereby, it can be concluded that standard contrast agent dosage is sufficient to visualize the core tumor volume in T1w MRI. Measurement of tumor volume after increasing contrast agent dosage depicts tumor core and edema, which can be due to diffusion or accumulation or both. Tumor core and edema, however, can be visualized by T2w MRI without need of additional contrast agent.

Role of Hyperintense Acute Reperfusion Marker for Classifying the Stroke Etiology

Purpose

The hyperintense acute reperfusion marker (HARM) is a delayed enhancement of the subarachnoid or subpial space observed on post-contrast fluid-attenuated inversion recovery (FLAIR) images and is associated with permeability changes to the blood–brain barrier in acute stroke. We investigated the relationship between HARM and stroke etiology based on the Trial of ORG 10172 in Acute Stroke Treatment (TOAST) classification. In addition, we evaluated the relationship between HARM and stroke locations with respect to vascular territories and anatomic compartments.

Materials and methods

We recruited 264 consecutive patients (109 women; mean age 68.63 years) who were diagnosed with acute ischemic stroke and underwent brain magnetic resonance imaging (MRI) including post-contrast FLAIR and DWI within 7 days of symptom onset from May 2015 to March 2016 for this retrospective study. Post-contrast FLAIR images were obtained 5 min after gadolinium administration. The mean time interval between the onset of stroke symptoms and MRI acquisition in total included patients was 18 h and 7 min (median 12 h and 57 min, range 2–127 h). We analyzed the overall incidence and distribution patterns of HARM in acute ischemic stroke cases and compared the relative incidence and distribution patterns of HARM between the subgroups of stroke etiology based on conventional TOAST classification. We obtained odds ratio (OR) of HARM in different stroke locations based on vascular territories and anatomical compartments. This study was approved by our institutional review board.

Results

Among the 264 patients, 67 (25.38%) patients were HARM positive and 197 (74.62%) patients were HARM negative. There was significant difference in HARM incidence among the stroke subgroups (p < 0.001). Small vessel occlusion (SVO) was associated with the HARM-negative group (p < 0.001), while large artery atherosclerosis (LAA) and cardioembolism (CE) were associated with the HARM-positive group (p = 0.001). Also, regional pattern of HARM on the same vascular territory as the acute infarction was dominantly demonstrated regardless of stroke etiology. The OR for HARM from middle cerebral artery (MCA) infarction was 1.868 [95% confidence interval (CI): 1.025–3.401]. The OR for HARM from cortical infarction was 9.475 (95% CI: 4.754–18.883) compared to other anatomic compartments.

Conclusion

The presence of the HARM was significantly associated with embolic infarctions including LAA and CE. Conversely, SVO was exclusively associated with the absence of the HARM. Second, MCA and cortical infarction showed a more pronounced HARM compared to infarctions at other vascular territories and anatomic compartments. According to the results in the current study, we speculate that the presence of HARM on post-contrast FLAIR images was associated with specific stroke causes especially in embolic causes.

Triglyceride-rich lipoprotein lipolysis products increase blood-brain barrier transfer coefficient and induce astrocyte lipid droplets and cell stress

Elevation of blood triglycerides, primarily as triglyceride-rich lipoproteins (TGRL), has been linked to cerebrovascular inflammation, vascular dementia, and Alzheimer's disease (AD). Brain microvascular endothelial cells and astrocytes, two cell components of the neurovascular unit, participate in controlling blood-brain barrier (BBB) permeability and regulating neurovascular unit homeostasis. Our studies showed that infusion of high physiological concentrations of TGRL lipolysis products (TGRL + lipoprotein lipase) activate and injure brain endothelial cells and transiently increase the BBB transfer coefficient (K_i = permeability × surface area/volume) in vivo. However, little is known about how blood lipids affect astrocyte lipid accumulation and inflammation. To address this, we first demonstrated TGRL lipolysis products increased lipid droplet formation in cultured normal human astrocytes. We then evaluated the transcriptional pathways activated in astrocytes by TGRL lipolysis products and found upregulated stress and inflammatory-related genes including activating transcription factor 3 (ATF3), macrophage inflammatory protein-3α (MIP-3α), growth differentiation factor-15 (GDF15), and prostaglandin-endoperoxide synthase 2 (COX2). TGRL lipolysis products also activated the JNK/cJUN/ATF3 pathway, induced endoplasmic reticulum stress protein C/EBP homologous protein (CHOP), and the NF-κB pathway, while increasing secretion of MIP-3α, GDF15, and IL-8. Thus our results demonstrate TGRL lipolysis products increase the BBB transfer coefficient (K_i), induce astrocyte lipid droplet formation, activate cell stress pathways, and induce secretion of inflammatory cytokines. Our observations are consistent with evidence for lipid-induced neurovascular injury and inflammation, and we, therefore, speculate that lipid-induced astrocyte injury could play a role in cognitive decline.

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.

Importance of Contrast-Enhanced Fluid-Attenuated Inversion Recovery Magnetic Resonance Imaging in Various Intracranial Pathologic Conditions

Intracranial lesions may show contrast enhancement through various mechanisms that are closely associated with the disease process. The preferred magnetic resonance sequence in contrast imaging is T1-weighted imaging (T1WI) at most institutions. However, lesion enhancement is occasionally inconspicuous on T1WI. Although fluid-attenuated inversion recovery (FLAIR) sequences are commonly considered as T2-weighted imaging with dark cerebrospinal fluid, they also show mild T1-weighted contrast, which is responsible for the contrast enhancement. For several years, FLAIR imaging has been successfully incorporated as a routine sequence at our institution for contrast-enhanced (CE) brain imaging in detecting various intracranial diseases. In this pictorial essay, we describe and illustrate the diagnostic importance of CE-FLAIR imaging in various intracranial pathologic conditions.