The spectrum of MR detectable cortical microinfarcts: a classification study with 7-tesla postmortem MRI and histopathology

Clinical Significance of Diffusion-Weighted Brain MRI Lesions After TAVR: Results of a Patient-Level Pooled Analysis

BACKGROUND

Acute brain infarction detected by diffusion-weighted magnetic resonance imaging (DW-MRI) is common after transcatheter aortic valve replacement (TAVR), but its clinical relevance is uncertain.

OBJECTIVES

The authors investigated the relationship between DW-MRI total lesion number (TLN), individual lesion volume (ILV), and total lesion volume (TLV) and clinical stroke outcomes after TAVR.

METHODS

Patient-level data were pooled from 4 prospective TAVR embolic protection studies, with consistent predischarge DW-MRI acquisition and core laboratory analysis. C-statistic was used to determine the best DW-MRI measure associated with clinical stroke.

RESULTS

A total of 495 of 603 patients undergoing TAVR completed the predischarge DW-MRI. At 30 days, the rate of clinical ischemic stroke was 6.9%. Acute ischemic brain injury was seen in 85% of patients with 5.5 ± 7.3 discrete lesions per patient, mean ILV of 78.2 ± 257.1 mm3, and mean TLV of 555 ± 1,039 mm3. The C-statistic was 0.84 for TLV, 0.81 for number of lesions, and 0.82 for maximum ILV in predicting ischemic stroke. On the basis of the TLV cutpoint as defined by receiver operating characteristic (ROC), patients with a TLV >500 mm3 (vs TLV ≤500 mm3) had more ischemic stroke (18.2% vs 2.3%; P < 0.0001), more disabling strokes (8.8% vs 0.9%; P < 0.0001), and less complete stroke recovery (44% vs 62.5%; P = 0.001) at 30 days.

CONCLUSIONS

Our study confirms that the number, size, and total volume of acute brain infarction defined by DW-MRI are each associated with clinical ischemic strokes, disabling strokes, and worse stroke recovery in patients undergoing TAVR and may have value as surrogate outcomes in stroke prevention trials. (A Prospective, Randomized Evaluation of the TriGuard™ HDH Embolic Deflection Device During TAVI [DEFLECT III]; NCT02070731) (A Study to Evaluate the Neuro-embolic Consequences of TAVR [NeuroTAVR]; NCT02073864) (The REFLECT Trial: Cerebral Protection to Reduce Cerebral Embolic Lesions After Transcatheter Aortic Valve Implantation [REFLECT I]; NCT02536196) (The REFLECT Trial: Cerebral Protection to Reduce Cerebral Embolic Lesions After Transcatheter Aortic Valve Implantation [REFLECT II]; NCT02536196).

Seven Tesla MRI in Alzheimer's disease research: State of the art and future directions: A narrative review

Seven tesla magnetic resonance imaging (7T MRI) is known to offer a superior spatial resolution and a signal-to-noise ratio relative to any other non-invasive imaging technique and provides the possibility for neuroimaging researchers to observe disease-related structural changes, which were previously only apparent on post-mortem tissue analyses. Alzheimer's disease is a natural and widely used subject for this technology since the 7T MRI allows for the anticipation of disease progression, the evaluation of secondary prevention measures thought to modify the disease trajectory, and the identification of surrogate markers for treatment outcome. In this editorial, we discuss the various neuroimaging biomarkers for Alzheimer's disease that have been studied using 7T MRI, which include morphological alterations, molecular characterization of cerebral T2*-weighted hypointensities, the evaluation of cerebral microbleeds and microinfarcts, biochemical changes studied with MR spectroscopy, as well as some other approaches. Finally, we discuss the limitations of the 7T MRI regarding imaging Alzheimer's disease and we provide our outlook for the future.

Neuroimaging in Dementia: More than Typical Alzheimer Disease

Alzheimer disease (AD) is the most common cause of dementia. The prevailing theory of the underlying pathology assumes amyloid accumulation followed by tau protein aggregation and neurodegeneration. However, the current antiamyloid and antitau treatments show only variable clinical efficacy. Three relevant points are important for the radiologic assessment of dementia. First, besides various dementing disorders (including AD, frontotemporal dementia, and dementia with Lewy bodies), clinical variants and imaging subtypes of AD include both typical and atypical AD. Second, atypical AD has overlapping radiologic and clinical findings with other disorders. Third, the diagnostic process should consider mixed pathologies in neurodegeneration, especially concurrent cerebrovascular disease, which is frequent in older age. Neuronal loss is often present at, or even before, the onset of cognitive decline. Thus, for effective emerging treatments, early diagnosis before the onset of clinical symptoms is essential to slow down or stop subsequent neuronal loss, requiring molecular imaging or plasma biomarkers. Neuroimaging, particularly MRI, provides multiple imaging parameters for neurodegenerative and cerebrovascular disease. With emerging treatments for AD, it is increasingly important to recognize AD variants and other disorders that mimic AD. Describing the individual composition of neurodegenerative and cerebrovascular disease markers while considering overlapping and mixed diseases is necessary to better understand AD and develop efficient individualized therapies.

Sex Differences in Alzheimer's Disease

Reviewing the research presented in this article, it is evident that from an epidemiological perspective, it is important to evaluate the extent to which findings of sex and gender differences in Alzheimer's dementia (AD) are due to differences in longevity, survival bias, and comorbidities. Medical, genetic, psychosocial, and behavioral factors, in addition to hormonal factors, can differentially affect the risk and progression of AD in women versus men. Further, evaluation of sex differences in AD progression and the trajectory of change in cognitive function, neuroimaging, cerebrospinal fluid (CSF), and blood-based biomarkers of AD is needed. Finally, identifying sex differences in AD biomarkers and change across the lifespan is critical for the planning of prevention trials to reduce the risk of developing AD.

Histopathology of Cerebral Microinfarcts and Microbleeds in Spontaneous Intracerebral Hemorrhage

In patients with spontaneous intracerebral hemorrhage caused by different vasculopathies, cerebral microinfarcts have the same aspect on MRI and the same applies to cerebral microbleeds. It is unclear what pathological changes underlie these cerebral microinfarcts and cerebral microbleeds. In the current study, we explored the histopathological substrate of these lesions by investigating the brain tissue of 20 patients (median age at death 77 years) who died from ICH (9 lobar, 11 non-lobar) with a combination of post-mortem 7-T MRI and histopathological analysis. We identified 132 CMIs and 204 CMBs in 15 patients on MRI, with higher numbers of CMIs in lobar ICH patients and similar numbers of CMBs. On histopathology, CMIs and CMBs were in lobar ICH more often located in the superficial than in the deep layers of the cortex, and in non-lobar ICH more often in the deeper layers. We found a tendency towards more severe CAA scores in lobar ICH patients. Other histopathological characteristics were comparable between lobar and non-lobar ICH patients. Although CMIs and CMBs were found in different segments of the cortex in lobar ICH compared to non-lobar ICH patients, otherwise similar histopathological features of cortical CMIs and CMBs distant from the ICH suggest shared pathophysiological mechanisms in lobar and non-lobar ICH caused by different vasculopathies.

Optimization of the fluid-attenuated inversion recovery (FLAIR) imaging for use in autopsy imaging of the brain region using synthetic MRI

BACKGROUND

The failure of cerebrospinal fluid (CSF) signal suppression in postmortem fluid-attenuated inversion recovery (FLAIR) of the brain is a problem.

OBJECTIVE

The present study was to clarify the relationship between the temperature of deceased persons and CSF T1, and to optimize the postmortem brain FLAIR imaging method using synthetic MRI.

METHODS

Forehead temperature was measured in 15 deceased persons. Next, synthetic MRI of the brain was performed, the CSF T1 was measured, and the optimal TI was calculated. Two types of FLAIR images were obtained with the clinical and optimal TI. The relationship between forehead temperature and the CSF T1 and optimal TI was evaluated. The optimized FLAIR images were physically and visually evaluated.

RESULTS

The CSF T1 and optimal TI were strongly correlated with forehead temperature. Comparing the average SNR and CNR ratios and visual evaluation scores of the two FLAIR images, those captured with the optimal TI showed statistically lower SNR, higher CNR, and higher visual evaluation scores (p< 0.01).

CONCLUSIONS

Synthetic MRI enables the quantification of the CSF T1 resulting from postmortem temperature decreases and calculation of the optimal TI, which could aid in improving the failure of CSF signal suppression and in optimizing postmortem brain FLAIR imaging.

The Impact of Cortical Cerebral Microinfarcts on Functional Outcomes in Patients With Ischemic Stroke

The present study examined cortical cerebral microinfarcts (CMIs) on a 3T magnetic resonance imaging and investigated the impact of CMIs on the comprehensive functional outcomes during the post-stroke rehabilitation period. Patients with acute phase of first-ever ischemic stroke were retrospectively recruited (n = 62) and divided into 2 groups with and without CMIs. Clinical parameters including age, sex, stroke lesion laterality, location, the National Institutes of Health Stroke Scale score, as well as history of hypertension, dyslipidemia, diabetes mellitus, and smoking were obtained. Functional outcomes were assessed twice at baseline and one month later with the Korean version of the Mini-Mental State Examination, the Berg balance scale (BBS), and the functional independence measure. Partial correlation and multiple linear regression analyses were used to examine the relationship between the presence of CMIs and the change in functional outcomes. At least one CMI was reported in 27 patients, who were older (p = 0.043). The presence of CMIs was significantly associated with functional impairment in all 3 functional outcomes, after controlling for confounding factors (p < 0.05). CMIs might contribute to poor functional outcomes during the post-stroke rehabilitation period. These results suggest that CMIs should be considered when establishing rehabilitation treatment strategies or making a prognosis.

Neuropathology of Vascular Brain Health: Insights From Ex Vivo Magnetic Resonance Imaging-Histopathology Studies in Cerebral Small Vessel Disease

Sporadic cerebral small vessel disease (SVD) is a major contributor to vascular cognitive impairment and dementia in the aging human brain. On neuropathology, sporadic SVD is characterized by abnormalities to the small vessels of the brain predominantly in the form of cerebral amyloid angiopathy and arteriolosclerosis. These pathologies frequently coexist with Alzheimer disease changes, such as plaques and tangles, in a single brain. Conversely, during life, magnetic resonance imaging (MRI) only captures the larger manifestations of SVD in the form of parenchymal brain abnormalities. There appears to be a major knowledge gap regarding the underlying neuropathology of individual MRI-detectable SVD abnormalities. Ex vivo MRI in postmortem human brain tissue is a powerful tool to bridge this gap. This review summarizes current insights into the histopathologic correlations of MRI manifestations of SVD, their underlying cause, presumed pathophysiology, and associated secondary tissue injury. Moreover, we discuss the advantages and limitations of ex vivo MRI-guided histopathologic investigations and make recommendations for future studies.

Assessing cortical cerebral microinfarcts on iron-sensitive MRI in cerebral small vessel disease

Recent studies suggest that a subset of cortical microinfarcts may be identifiable on T2* but invisible on T1 and T2 follow-up images. We aimed to investigate whether cortical microinfarcts are associated with iron accumulation after the acute stage. The RUN DMC - InTENse study is a serial MRI study including individuals with cerebral small vessel disease (SVD). 54 Participants underwent 10 monthly 3 T MRIs, including diffusion-weighted imaging, quantitative R1 (=1/T1), R2 (=1/T2), and R2* (=1/T2*) mapping, from which MRI parameters within areas corresponding to microinfarcts and control region of interests (ROIs) were retrieved within 16 participants. Finally, we compared pre- and post-lesional values with repeated measures ANOVA and post-hoc paired t-tests using the mean difference between lesion and control ROI values. We observed 21 acute cortical microinfarcts in 7 of the 54 participants (median age 69 years [IQR 66-74], 63% male). R2* maps demonstrated an increase in R2* values at the moment of the last available follow-up MRI (median [IQR], 5 [5-14] weeks after infarction) relative to prelesional values (p = .08), indicative of iron accumulation. Our data suggest that cortical microinfarcts are associated with increased R2* values, indicative of iron accumulation, possibly due to microhemorrhages, neuroinflammation or neurodegeneration, awaiting histopathological verification.

Correlations in post-mortem imaging-histopathology studies of sporadic human cerebral small vessel disease: A systematic review

AIMS

Sporadic human cerebral small vessel disease (SVD) commonly causes stroke and dementia but its pathogenesis is poorly understood. There are recognised neuroimaging and histopathological features. However, relatively few studies have examined the relationship between the radiological and pathological correlates of SVD; better correlation would promote greater insight into the underlying biological changes.

METHODS

We performed a systematic review to collate and appraise the information derived from studies that correlated histological with neuroimaging-defined SVD lesions. We searched for studies describing post-mortem imaging and histological tissue examination in adults, extracted data from published studies, categorised the information and compiled this narrative.

RESULTS

We identified 38 relevant studies, including at least 1146 subjects, 342 of these with SVD: 29 studies focussed on neuroradiological white matter lesions (WML), six on microinfarcts and three on dilated perivascular spaces (PVS) and lacunes. The histopathology terminology was diverse with few robust definitions. Reporting and methodology varied widely between studies, precluding formal meta-analysis. PVS and 'oedema' were frequent findings in WML, being described in at least 94 and 18 radiological WML, respectively, in addition to myelin pallor. Histopathological changes extended beyond the radiological lesion margins in at least 33 radiological WML. At least 43 radiological lesions not seen pathologically and at least 178 histological lesions were not identified on imaging.

CONCLUSIONS

Histopathological assessment of human SVD is hindered by inconsistent methodological approaches and unstandardised definitions. The data from this systematic review will help to develop standardised definitions to promote consistency in human SVD research.

A Review of Translational Magnetic Resonance Imaging in Human and Rodent Experimental Models of Small Vessel Disease

Cerebral small vessel disease (SVD) is a major health burden, yet the pathophysiology remains poorly understood with no effective treatment. Since much of SVD develops silently and insidiously, non-invasive neuroimaging such as MRI is fundamental to detecting and understanding SVD in humans. Several relevant SVD rodent models are established for which MRI can monitor in vivo changes over time prior to histological examination. Here, we critically review the MRI methods pertaining to salient rodent models and evaluate synergies with human SVD MRI methods. We found few relevant publications, but argue there is considerable scope for greater use of MRI in rodent models, and opportunities for harmonisation of the rodent-human methods to increase the translational potential of models to understand SVD in humans. We summarise current MR techniques used in SVD research, provide recommendations and examples and highlight practicalities for use of MRI SVD imaging protocols in pre-selected, relevant rodent models.

Histological correlates of postmortem ultra-high-resolution single-section MRI in cortical cerebral microinfarcts

The identification of cerebral microinfarctions with magnetic resonance imaging (MRI) and histological methods remains challenging in aging and dementia. Here, we matched pathological changes in the microvasculature of cortical cerebral microinfarcts to MRI signals using single 100 μm-thick histological sections scanned with ultra-high-resolution 11.7 T MRI. Histologically, microinfarcts were located in superficial or deep cortical layers or transcortically, compatible with the pattern of layer-specific arteriolar blood supply of the cerebral cortex. Contrary to acute microinfarcts, at chronic stages the core region of microinfarcts showed pallor with extracellular accumulation of lipofuscin and depletion of neurons, a dense meshwork of collagen 4-positive microvessels with numerous string vessels, CD68-positive macrophages and glial fibrillary acidic protein (GFAP)-positive astrocytes. In MRI scans, cortical microinfarcts at chronic stages, called chronic cortical microinfarcts here, gave hypointense signals in T1-weighted and hyperintense signals in T2-weighted images when thinning of the tissue and cavitation and/or prominent iron accumulation were present. Iron accumulation in chronic microinfarcts, histologically verified with Prussian blue staining, also produced strong hypointense T2*-weighted signals. In summary, the microinfarct core was occupied by a dense microvascular meshwork with string vessels, which was invaded by macrophages and astroglia and contained various degrees of iron accumulation. While postmortem ultra-high-resolution single-section imaging improved MRI-histological matching and the structural characterization of chronic cortical cerebral microinfarcts, miniscule microinfarcts without thinning or iron accumulation could not be detected with certainty in the MRI scans. Moreover, string vessels at the infarct margin indicate disturbances in the microcirculation in and around microinfarcts, which might be exploitable in the diagnostics of cortical cerebral microinfarcts with MRI in vivo.

Vascular Cognitive Impairment

PURPOSE OF REVIEW

This article provides an overview of vascular cognitive impairment; discusses its epidemiology, subtypes, and associations with other neurodegenerative diseases; and reviews the diagnostic evaluation and management of these disorders.

RECENT FINDINGS

Cerebrovascular disease is a common cause of dementia and frequently coexists with neurodegenerative causes. The heterogeneity of mechanisms leading to vascular cognitive impairment makes developing unifying clinical and research criteria difficult. Recognizing the neuroimaging hallmarks of different forms of vascular cognitive impairment can allow for individualized treatment and management. In individuals with mild vascular cognitive impairment, aerobic exercise appears to be a promising treatment but requires further investigation.

SUMMARY

Vascular cognitive impairment can be caused by several mechanisms. While treating vascular risk factors is rational to prevent worsening of cognitive impairment, well-designed studies are needed to demonstrate efficacy.

Cerebral Cortical Microinfarcts on Magnetic Resonance Imaging and Their Association With Cognition in Cerebral Amyloid Angiopathy

Background and Purpose- We aimed to explore the association between presence of cerebral cortical microinfarcts (CMIs) on magnetic resonance imaging and other small-vessel disease neuroimaging biomarkers in cerebral amyloid angiopathy (CAA) and to analyze the role of CMIs on individual cognitive domains and dementia conversion. Methods- Participants were recruited from an ongoing longitudinal research cohort of eligible CAA patients between March 2006 and October 2016. A total of 102 cases were included in the analysis that assessed the relationship of cortical CMIs to CAA neuroimaging markers. Ninety-five subjects had neuropsychological tests conducted within 1 month of magnetic resonance imaging scanning. Seventy-five nondemented CAA patients had cognitive evaluation data available during follow-up. Results- Among 102 patients enrolled, 40 patients had CMIs (39%) on magnetic resonance imaging. CMIs were uniformly distributed throughout the cortex without regional predilection ( P=0.971). The presence of CMIs was associated with lower total brain volume (odds ratio, 0.85; 95% CI, 0.74-0.98; P=0.025) and presence of cortical superficial siderosis (odds ratio, 2.66; 95% CI, 1.10-6.39; P=0.029). In 95 subjects with neuropsychological tests, presence of CMIs was associated with impaired executive function (β, -0.23; 95% CI, -0.44 to -0.02; P=0.036) and processing speed (β, -0.24; 95% CI, -0.45 to -0.04; P=0.020). Patients with CMIs had a higher cumulative dementia incidence compared with patients without CMIs ( P=0.043), whereas only baseline total brain volume (hazard ratio, 0.76; 95% CI, 0.62-0.92; P=0.006) independently predicted dementia conversion. Conclusions- Magnetic resonance imaging-detected CMIs in CAA correlated with greater overall disease burden. The presence of CMIs was associated with worse cognitive performance, whereas only total brain atrophy independently predicted dementia conversion.

Association Between Microinfarcts and Blood Pressure Trajectories

Importance

Cerebral microinfarcts are associated with increased risk of cognitive impairment and may have different risk factors than macroinfarcts. Subcortical microinfarcts are associated with declining blood pressure (BP) in elderly individuals.

Objective

To investigate BP slopes as a risk factor for microinfarcts.

Design, Setting, and Participants

From the population-based Mayo Clinic Study of Aging, 303 of 1158 individuals (26.2%) in this cohort study agreed to have an autopsy between November 1, 2004, and March 31, 2016. Cerebral microinfarcts were identified and classified as cortical or subcortical. Baseline and BP trajectories were compared for groups with no microinfarcts, subcortical microinfarcts, and cortical microinfarcts. A secondary logistic regression analysis was performed to assess associations of subcortical microinfarcts with midlife hypertension, as well as systolic and diastolic BP slopes.

Main Outcomes and Measures

The presence of cerebral microinfarcts using BP slopes.

Results

Of the 303 participants who underwent autopsy, 297 had antemortem BP measurements. Of these, 177 (59.6%) were men; mean (SD) age at death was 87.2 (5.3) years. The autopsied individuals and the group who died but were not autopsied were similar for all demographics except educational level with autopsied participants having a mean of 1 more year of education (1.06; 95% CI, 0.66-1.47 years; P < .01). Among 297 autopsied individuals with antemortem BP measurements, 47 (15.8%) had chronic microinfarcts; 30 (63.8%) of these participants were men. Thirty (63.8%) had cortical microinfarcts, 19 (40.4%) had subcortical microinfarcts, and 4 (8.5%) had only infratentorial microinfarcts. Participants with microinfarcts did not differ significantly on baseline systolic (mean difference, -1.48; 95% CI, -7.30 to 4.34; P = .62) and diastolic (mean difference of slope, -0.90; 95% CI, -3.93 to 2.13; P = .56) BP compared with those with no microinfarcts. However, participants with subcortical microinfarcts had a greater annual decline (negative slope) of systolic (mean difference of slope, 4.66; 95% CI, 0.13 to 9.19; P = .04) and diastolic (mean difference, 3.33; 95% CI, 0.61 to 6.06; P = .02) BP.

Conclusions and Relevance

Subcortical microinfarcts were associated with declining BP. Future studies should investigate whether declining BP leads to subcortical microinfarcts or whether subcortical microinfarcts are a factor leading to declining BP.

Neuroimaging of Small Vessel Disease in Late-Life Depression

Cerebral small vessel disease is associated with late-life depression, cognitive impairment, executive dysfunction, distress, and loss of life for older adults. Late-life depression is becoming a substantial public health burden, and a considerable number of older adults presenting to primary care have significant clinical depression. Even though white matter hyperintensities are linked with small vessel disease, white matter hyperintensities are nonspecific to small vessel disease and can co-occur with other brain diseases. Advanced neuroimaging techniques at the ultrahigh field magnetic resonance imaging are enabling improved characterization, identification of cerebral small vessel disease and are elucidating some of the mechanisms that associate small vessel disease with late-life depression.

Two histological methods for recognition and study of cortical microinfarcts in thick sections

Cortical microinfarcts are the most widespread form of brain infarction but frequently remain undetected by standard neuroimaging protocols. Moreover, microinfarcts are only partially detectable in hematoxylin- eosin-stained (H&E) 4-10 μm paraffin sections at routine neuropathological examination. In this short report, we provide two staining protocols for visualizing cortical microinfarcts in 100-300 μm sections. For low-power microscopy, the first protocol combines aldehyde fuchsine staining for detection of lipofuscin granules and macrophages with Darrow red counterstaining for Nissl material. The second protocol combines collagen IV immunohistochemistry with aldehyde fuchsine/Darrow red or with erythrosin-phosphotungstic acid-aniline blue staining for detailed study of the capillary network. In the first protocol, microinfarcts are recognizable as radially- oriented funnel-like accumulations of aldehyde fuchsine-positive macrophages. The second protocol recognizes microinfarcts and alterations of the capillary network, at whose center accumulations of dead neurons and aldehyde fuchsine-positive macrophages cluster. In addition, the second protocol permits visualization of abnormalities within the capillary network associated with more recent microinfarcts. Both protocols can be useful for comparing MRI datasets with cortical microinfarcts in corresponding whole brain sections of 100-300 μm thickness.

The choice of embedding media affects image quality, tissue R2 * , and susceptibility behaviors in post-mortem brain MR microscopy at 7.0T

PURPOSE

The quality and precision of post-mortem MRI microscopy may vary depending on the embedding medium used. To investigate this, our study evaluated the impact of 5 widely used media on: (1) image quality, (2) contrast of high spatial resolution gradient-echo (T₁ and T₂ ^* -weighted) MR images, (3) effective transverse relaxation rate (R₂ ^* ), and (4) quantitative susceptibility measurements (QSM) of post-mortem brain specimens.

METHODS

Five formaldehyde-fixed brain slices were scanned using 7.0T MRI in: (1) formaldehyde solution (formalin), (2) phosphate-buffered saline (PBS), (3) deuterium oxide (D₂ O), (4) perfluoropolyether (Galden), and (5) agarose gel. SNR and contrast-to-noise ratii (SNR/CNR) were calculated for cortex/white matter (WM) and basal ganglia/WM regions. In addition, median R₂ ^* and QSM values were extracted from caudate nucleus, putamen, globus pallidus, WM, and cortical regions.

RESULTS

PBS, Galden, and agarose returned higher SNR/CNR compared to formalin and D₂ O. Formalin fixation, and its use as embedding medium for scanning, increased tissue R₂ ^* . Imaging with agarose, D₂ O, and Galden returned lower R₂ ^* values than PBS (and formalin). No major QSM offsets were observed, although spatial variance was increased (with respect to R₂ ^* behaviors) for formalin and agarose.

CONCLUSIONS

Embedding media affect gradient-echo image quality, R₂ ^* , and QSM in differing ways. In this study, PBS embedding was identified as the most stable experimental setup, although by a small margin. Agarose and Galden were preferred to formalin or D₂ O embedding. Formalin significantly increased R₂ ^* causing noisier data and increased QSM variance.

Detection and characterization of small infarcts in the caudate nucleus on 7 Tesla MRI: The SMART-MR study

Small infarcts are among the key imaging features of cerebral small vessel disease (CSVD), but remain largely undetected on conventional MRI. We aimed to evaluate (1) imaging criteria for the detection of small infarcts in the caudate nucleus on 7T MRI, (2) intra- and inter-rater agreement, (3) frequency and (4) detection rate on 7T versus 1.5T MRI. In 90 patients (68 ± 8 years) with a history of vascular disease from the SMART-MR study, we defined 7T imaging criteria for cavitated and non-cavitated small infarcts in the caudate nucleus. In a separate set of 23 patients from the SMART study, intra-rater and inter-rater agreement was excellent for presence, number, and individual locations (Kappa's, ICCs, and Dice similarity coefficients ranged from 0.85 to 1.00). In the 90 patients, 21 infarcts (20 cavitated) in 12 patients were detected on 7T (13%) compared to 7 infarcts in 6 patients on 1.5T (7%). In conclusion, we established reproducible imaging criteria for the detection of small infarcts in the caudate nucleus on 7T MRI and showed that 7T MRI allows for a higher detection rate than conventional 1.5T MRI. These imaging criteria can be used in future studies to provide new insights into the pathophysiology of CSVD.

Signal Change of Acute Cortical and Juxtacortical Microinfarction on Follow-Up MRI

BACKGROUND AND PURPOSE

Although the clinical importance of cortical microinfarcts has become well-recognized recently, the evolution of cortical microinfarcts on MR imaging is not fully understood. The aim of this study was to examine the temporal changes in acute cortical microinfarcts using susceptibility-weighted imaging and conventional MR imaging.

MATERIALS AND METHODS

Patients with acute infarcts located in the cortical and/or juxtacortical region measuring ≤10 mm in axial diameter based on diffusion-weighted imaging who had a follow-up 3T MR imaging were retrospectively included in the study. All lesions did not show hypointensity on initial T2*WI. For cortical and/or juxtacortical microinfarcts detected on initial DWI, 2 neuroradiologists evaluated the follow-up MR imaging (T2WI, FLAIR, T2*WI, and SWI) and assessed lesion signal intensities and locations (cortical microinfarcts or microinfarcts with juxtacortical white matter involvement).

RESULTS

On initial DWI, 2 radiologists observed 180 cortical and/or juxtacortical microinfarcts in 35 MR imaging examinations in 25 patients; on follow-up, the neuroradiologists identified 29 cortical microinfarcts (16%) on T2WI, 9 (5%) on FLAIR, 4 (2%) on T2*, and 97 (54%) on SWI. All cortical microinfarcts detected with any follow-up MR imaging showed hyperintensity on T2WI/FLAIR and/or hypointensity on T2*WI and SWI.

CONCLUSIONS

SWI revealed conversion (paramagnetic susceptibility changes) of acute cortical microinfarcts, suggesting that a substantial number of cortical microinfarcts may contain hemorrhagic components.

Comparative Analysis of Cortical Microinfarcts and Microbleeds using 3.0-Tesla Postmortem Magnetic Resonance Images and Histopathology

Microvascular lesions including cortical microinfarctions (CMIs) and cerebral lobar microbleeds (CMBs) are usually caused by cerebral amyloid angiopathy (CAA) in the elderly and are correlated with cognitive decline. However, their radiological-histopathological coincidence has not been revealed systematically with widely used 3-Tesla (3T) magnetic resonance imaging (MRI). The purpose of the present study is to delineate the histopathological background corresponding to MR images of these lesions. We examined formalin-fixed 10-mm thick coronal brain blocks from 10 CAA patients (five were also diagnosed with Alzheimer's disease, three with dementia with Lewy bodies, and two with CAA only) with dementia and six non CAA patients with neurodegenerative disease. Using 3T MRI, both 3D-fluid attenuated inversion recovery (FLAIR) and 3D-double inversion recovery (DIR) were examined to identify CMIs, and T2* and susceptibility-weighted images (SWI) were examined to identify CMBs. These blocks were subsequently examined histologically and immunohistochemically. In CAA patients, 48 CMIs and 6 lobar CMBs were invariably observed in close proximity to degenerated Aβ-positive blood vessels. Moreover, 16 CMIs (33%) of 48 were detected with postmortem MRI, but none were seen when the lesion size was smaller than 1 mm. In contrast, only 1 undeniable CMI was founded with MRI and histopathology in 6 non CAA patients. Small, cortical high-intensity lesions seen on 3D-FLAIR and 3D-DIR images likely represent CMIs, and low-intensity lesions in T2* and SWI correspond to CMBs with in vivo MRI. Furthermore, a close association between amyloid-laden vessels and these microvascular lesions indicated the contribution of CAA to their pathogenesis.

An updated diagnostic approach to subtype definition of vascular parkinsonism - Recommendations from an expert working group

This expert working group report proposes an updated approach to subtype definition of vascular parkinsonism (VaP) based on a review of the existing literature. The persistent lack of consensus on clear terminology and inconsistent conceptual definition of VaP formed the impetus for the current expert recommendation report. The updated diagnostic approach intends to provide a comprehensive tool for clinical practice. The preamble for this initiative is that VaP can be diagnosed in individual patients with possible prognostic and therapeutic consequences and therefore should be recognized as a clinical entity. The diagnosis of VaP is based on the presence of clinical parkinsonism, with variable motor and non-motor signs that are corroborated by clinical, anatomic or imaging findings of cerebrovascular disease. Three VaP subtypes are presented: (1) The acute or subacute post-stroke VaP subtype presents with acute or subacute onset of parkinsonism, which is typically asymmetric and responds to dopaminergic drugs; (2) The more frequent insidious onset VaP subtype presents with progressive parkinsonism with prominent postural instability, gait impairment, corticospinal, cerebellar, pseudobulbar, cognitive and urinary symptoms and poor responsiveness to dopaminergic drugs. A higher-level gait disorder occurs frequently as a dominant manifestation in the clinical spectrum of insidious onset VaP, and (3) With the emergence of molecular imaging biomarkers in clinical practice, our diagnostic approach also allows for the recognition of mixed or overlapping syndromes of VaP with Parkinson's disease or other neurodegenerative parkinsonisms. Directions for future research are also discussed.

Clinical vascular imaging in the brain at 7T

Stroke and related cerebrovascular diseases are a major cause of mortality and disability. Even at standard-field-strengths (1.5T), MRI is by far the most sensitive imaging technique to detect acute brain infarctions and to characterize incidental cerebrovascular lesions, such as white matter hyperintensities, lacunes and microbleeds. Arterial time-of-flight (TOF) MR angiography (MRA) can depict luminal narrowing or occlusion of the major brain feeding arteries, and this without the need for contrast administration. Compared to 1.5T MRA, the use of high-field strength (3T) and even more so ultra-high-field strengths (7T), enables the visualization of the lumen of much smaller intracranial vessels, while adding a contrast agent to TOF MRA at 7T may enable the visualization of even more distal arteries in addition to veins and venules. Moreover, with 3T and 7T, the arterial vessel walls beyond the circle of Willis become visible with high-resolution vessel wall imaging. In addition, with 7T MRI, the brain parenchyma can now be visualized on a submillimeter scale. As a result, high-resolution imaging studies of the brain and its blood supply at 7T have generated new concepts of different cerebrovascular diseases. In the current article, we will discuss emerging clinical applications and future directions of vascular imaging in the brain at 7T MRI.

Only White Matter Hyperintensities Predicts Post-Stroke Cognitive Performances Among Cerebral Small Vessel Disease Markers: Results from the TABASCO Study

BACKGROUND

White matter hyperintensities (WMH) were shown to predict cognitive decline following stroke or transient ischemic attack (TIA). However, WMH are only one among other radiological markers of cerebral small vessel disease (SVD).

OBJECTIVE

The aim of this study was to determine whether adding other SVD markers to WMH improves prediction of post-stroke cognitive performances.

METHODS

Consecutive first-ever stroke or TIA patients (n = 266) from the Tel Aviv Acute Brain Stroke Cohort (TABASCO) study were enrolled. MRI scans were performed within seven days of stroke onset. We evaluated the relationship between cognitive performances one year following stroke, and previously suggested total SVD burden score including WMH, lacunes, cerebral microbleeds (CMB), and perivascular spaces (PVS).

RESULTS

Significant negative associations were found between WMH and cognition (p < 0.05). Adding other SVD markers (lacunes, CMB, PVS) to WMH did not improve predication of post-stroke cognitive performances. Negative correlations between SVD burden score and cognitive scores were observed for global cognitive, memory, and visual spatial scores (all p < 0.05). However, following an adjustment for confounders, no associations remained significant.

CONCLUSION

WMH score was associated with poor post-stroke cognitive performance. Adding other SVD markers or SVD burden score, however, did not improve prediction.

Postmortem magnetic resonance imaging

This chapter provides a brief overview of studies that combine postmortem magnetic resonance imaging (MRI) and histopathology. We touch upon the logistics of setting up a protocol that limits unwanted postmortem delays and explain how combining postmortem MRI and histopathology can elucidate the histologic substrate of signal changes that appear on MRI. This is demonstrated by exemplary studies in multiple sclerosis, and includes various histopathologic techniques and a wide range of conventional and advanced MRI sequences at various field strengths. We cover topics such as how to visualize white-matter pathology and repair with conventional and advanced MRI sequences, describe the history of visualizing pathology of the gray matter (with newly developed MRI and immunohistopathology techniques), and how advanced methods have aided research in other neurologic diseases. We conclude with several suggestions for future development, such as bridging the gap between postmortem and in vivo research and the importance of collecting non-neurological control tissue.

Evolution of DWI lesions in cerebral amyloid angiopathy: Evidence for ischemia

OBJECTIVE

To address the pathophysiologic nature of small diffusion-weighted imaging (DWI) lesions in patients with cerebral amyloid angiopathy (CAA) who underwent serial MRI. Specifically, we tested (1) whether DWI lesions occurred preferentially in individuals with prior DWI lesions, (2) the cross-sectional association with chronic cortical cerebral microinfarcts (CMIs), and (3) the evolution of DWI lesions over time.

METHODS

Patients with probable CAA (n = 79) who underwent at least 2 MRI sessions were included. DWI lesions were assessed at each available time point. Lesion appearance and characteristics were assessed on available structural follow-up images. Presence and burden of other neuroimaging markers of small vessel disease (white matter hyperintensities, cerebral microbleeds, cortical superficial siderosis, and chronic cortical CMIs) were assessed as well.

RESULTS

Among 221 DWI scans (79 patients with 2 DWI scans; 40 with ≥3), 60 DWI lesions were found in 28 patients. Patients with DWI lesions at baseline were not more likely to have additional DWI lesions on follow-up compared to patients without DWI lesions at baseline. DWI lesions were associated with chronic cortical CMIs and cortical superficial siderosis, but not with other markers. For 39/60 DWI lesions, >1 MRI sequence was available at follow-up to determine lesion evolution. Twenty-four (62%) were demarcated as chronic lesions on follow-up MRI. Five appeared as cavitations, 18 as noncavitated infarcts, and 1 underwent hemorrhagic transformation.

CONCLUSIONS

Based on their neuroimaging signature as well as their association with chronic cortical CMIs, DWI lesions appear to have an ischemic origin and represent one part of the CMI spectrum.

Functional deficits induced by cortical microinfarcts

Clinical studies have revealed a strong link between increased burden of cerebral microinfarcts and risk for cognitive impairment. Since the sum of tissue damage incurred by microinfarcts is a miniscule percentage of total brain volume, we hypothesized that microinfarcts disrupt brain function beyond the injury site visible to histological or radiological examination. We tested this idea using a mouse model of microinfarcts, where single penetrating vessels that supply mouse cortex were occluded by targeted photothrombosis. We found that in vivo structural and diffusion MRI reliably reported the acute microinfarct core, based on spatial co-registrations with post-mortem stains of neuronal viability. Consistent with our hypothesis, c-Fos assays for neuronal activity and in vivo imaging of single vessel hemodynamics both reported functional deficits in viable peri-lesional tissues beyond the microinfarct core. We estimated that the volume of tissue with functional deficit in cortex was at least 12-fold greater than the volume of the microinfarct core. Impaired hemodynamic responses in peri-lesional tissues persisted at least 14 days, and were attributed to lasting deficits in neuronal circuitry or neurovascular coupling. These data show how individually miniscule microinfarcts could contribute to broader brain dysfunction during vascular cognitive impairment and dementia.

A panel of clinical and neuropathological features of cerebrovascular disease through the novel neuroimaging methods

The last decade has witnessed substantial progress in acquiring diagnostic biomarkers for the diagnostic workup of cerebrovascular disease (CVD). Advanced neuroimaging methods not only provide a strategic contribution for the differential diagnosis of vascular dementia (VaD) and vascular cognitive impairment (VCI), but also help elucidate the pathophysiological mechanisms ultimately leading to small vessel disease (SVD) throughout its course.

OBJECTIVE

In this review, the novel imaging methods, both structural and metabolic, were summarized and their impact on the diagnostic workup of age-related CVD was analysed. Methods: An electronic search between January 2010 and 2017 was carried out on PubMed/MEDLINE, Institute for Scientific Information Web of Knowledge and EMBASE.

RESULTS

The use of full functional multimodality in simultaneous Magnetic Resonance (MR)/Positron emission tomography (PET) may potentially improve the clinical characterization of VCI-VaD; for structural imaging, MRI at 3.0 T enables higher-resolution scanning with greater imaging matrices, thinner slices and more detail on the anatomical structure of vascular lesions.

CONCLUSION

Although the importance of most of these techniques in the clinical setting has yet to be recognized, there is great expectancy in achieving earlier and more refined therapeutic interventions for the effective management of VCI-VaD.

Detection, risk factors, and functional consequences of cerebral microinfarcts

Cerebral microinfarcts are small lesions that are presumed to be ischaemic. Despite the small size of these lesions, affected individuals can have hundreds to thousands of cerebral microinfarcts, which cause measurable disruption to structural brain connections, and are associated with dementia that is independent of Alzheimer's disease pathology or larger infarcts (ie, lacunar infarcts, and large cortical and non-lacunar subcortical infarcts). Substantial progress has been made with regard to understanding risk factors and functional consequences of cerebral microinfarcts, partly driven by new in-vivo detection methods and the development of animal models that closely mimic multiple aspects of cerebral microinfarcts in human beings. Evidence from these advances suggests that cerebral microinfarcts can be manifestations of both small vessel and large vessel disease, that cerebral microinfarcts are independently associated with cognitive impairment, and that these lesions are likely to cause damage to brain structure and function that extends beyond their actual lesion boundaries. Criteria for the identification of cerebral microinfarcts with in-vivo MRI are provided to support further studies of the association between these lesions and cerebrovascular disease and dementia.

Focal Macroscopic Cortical Lesions in Cerebral Autosomal-Dominant Arteriopathy With Subcortical Infarcts and Leukoencephalopathy

Background and Purpose—

Cortical microinfarcts and secondary cortical degeneration have been demonstrated in cerebral autosomal-dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL), a severe monogenic cerebral small vessel disease. The aim of this study was to determine whether focal macroscopic cortical lesions can be detected using a specific in vivo magnetic resonance imaging approach.

Methods—

Three-dimensional T1 magnetic resonance imaging scans were obtained in 28 nondemented nondisabled CADASIL patients and 29 age- and sex-matched controls. The cortical mantle of patients and controls were extracted using Brainvisa by an experienced user and then evaluated during a dedicated reading session by a second reader after removing the white matter to stay blind to the clinical status. Thereafter, confirmed focal macroscopic cortical lesions were characterized using all available imaging data, including 7-T magnetic resonance imaging in some patients.

Results—

Three focal macroscopic cortical lesions were confirmed in 3 of 28 patients (11%) but none in controls. All lesions were observed in the close vicinity of severe signal changes in the underlying white matter.

Conclusions—

Focal macroscopic cortical lesions can be detected using specific magnetic resonance imaging approaches in CADASIL patients long before the end stage of the disorder. The underlying mechanisms and precise clinical consequences of these cortical changes still need to be determined.

Relationship between white matter connectivity loss and cortical thinning in cerebral amyloid angiopathy

Patients with cerebral amyloid angiopathy (CAA) show loss of white matter connectivity and cortical thinning on MRI, primarily in posterior brain regions. Here we examined whether a potential causal relationship exists between these markers of subcortical and cortical brain injury by examining whether changes in cortical thickness progress in tandem with changes in their underlying connections. Thirty-one patients with probable CAA with brain MRI at two time points were included (follow-up time: 1.3 ± 0.4 years). Brain networks were reconstructed using diffusion MRI-based fiber tractography. Of each network node, we calculated the change in fractional anisotropy-weighted connectivity strength over time and the change in cortical thickness. The association between change in connectivity strength and cortical thickness was assessed with (hierarchical) linear regression models. Our results showed that decline in posterior network connectivity over time was strongly related to thinning of the occipital cortex (β = 0.65 (0.35-0.94), P < 0.001), but not to thinning of the other posterior or frontal cortices. However, at the level of individual network nodes, we found no association between connectivity strength and cortical thinning of the corresponding node (β = 0.009 ± 0.04, P = 0.80). Associations were independent of age, sex, and other brain MRI markers of CAA. To conclude, CAA patients with greater progressive loss of posterior white matter connectivity also have greater progression of occipital cortical thinning, but our results do not support a direct causal relationship between them. The association can be better explained by a shared underlying mechanism, which may form a potential target for future treatments. Hum Brain Mapp 38:3723-3731, 2017. © 2017 Wiley Periodicals, Inc.

7-T MRI in Cerebrovascular Diseases: Challenges to Overcome and Initial Results

Magnetic resonance imaging (MRI) plays a key role in the investigation of cerebrovascular diseases. Compared with computed tomography (CT) and digital subtraction angiography (DSA), its advantages in diagnosing cerebrovascular pathology include its superior tissue contrast, its ability to visualize blood vessels without the use of a contrast agent, and its use of magnetic fields and radiofrequency pulses instead of ionizing radiation. In recent years, ultrahigh field MRI at 7 tesla (7 T) has shown promise in the diagnosis of many cerebrovascular diseases. The increased signal-to-noise ratio (SNR; 2.3x and 4.7x increase compared with 3 and 1.5 T, respectively) and contrast-to-noise ratio (CNR) at this higher field strength can be exploited to obtain a higher spatial resolution and higher lesion conspicuousness, enabling assessment of smaller brain structures and lesions. Cerebrovascular diseases can be assessed at different tissue levels; for instance, changes of the arteries feeding the brain can be visualized to determine the cause of ischemic stroke, regional changes in brain perfusion can be mapped to predict outcome after revascularization, and tissue damage, including old and recent ischemic infarcts, can be evaluated as a marker of ischemic burden. For the purpose of this review, we will discriminate 3 levels of assessment of cerebrovascular diseases using MRI: Pipes, Perfusion, and Parenchyma (3 Ps). The term Pipes refers to the brain-feeding arteries from the heart and aortic arch, upwards to the carotid arteries, vertebral arteries, circle of Willis, and smaller intracranial arterial branches. Perfusion is the amount of blood arriving at the brain tissue level, and includes the vascular reserve and perfusion territories. Parenchyma refers to the acute and chronic burden of brain tissue damage, which includes larger infarcts, smaller microinfarcts, and small vessel disease manifestations such as white matter lesions, lacunar infarcts, and microbleeds. In this review, we will describe the key developments in the last decade of 7-T MRI of cerebrovascular diseases, subdivided for these 3 levels of assessment.

Radiologic-Histopathologic Correlation of Cerebral Microbleeds Using Pre-Mortem and Post-Mortem MRI

Introduction

Cerebral microbleeds (CMB), also known as cerebral microhemorrhages, are small areas of susceptibility on brain magnetic resonance imaging (MRI), that are increasingly detected due to the higher availability of high-field MRI systems and dedicated pulse sequences. The prevalence of CMBs increases in cases with cognitive decline. The current investigation assessed the poorly investigated radiologic–histopathologic correlation of CMBs on MRI.

Methods

The local ethical committee approved the current investigation. We retrospectively assessed a consecutive series of 1303 autopsy cases hospitalized in Geneva University Hospitals between 2000–2014. Of 112 cases with pre-mortem T2* sequences, we included 25 cases (mean age 77.3 ± 9.6, 9 females) with at least one CMB. We compared pre-mortem CMBs with targeted histopathology and post-mortem MRI.

Results

25 cases had 31 CMB lesions detected by pre-mortem MRI. 25 additional CMB were detected on histopathology. 4 CMBs on pre-mortem MRI were false positives, resulting in a total of 52 CMBs. 27 CMBs on pre-mortem MRI were confirmed on histopathology, corresponding to a sensitivity or true positive rate of 51.9% (95% CI 37.6–66.0%). The false negative rate of pre-mortem MRI was 48.1% (95% CI 34.0–62.4%). Post-mortem MRI showed only 3 cases with additional CMBs. Overall, pre-mortem MRI significantly underestimated CMBs (p = 0.0001).

Conclusions

Routine clinical brain MRI underestimates the prevalence of CMBs by approximately 50%, and 12% of radiologic pre-mortem MRI CMBs were false positives. Post-mortem MRI confirmed that this discordance is not explained by microbleeds occurring after the pre-mortem MRI.

The concept of sporadic cerebral small vessel disease: A road map on key definitions and current concepts

Sporadic cerebral small vessel disease is considered to be among the most common known neuropathological processes and has an important role in stroke, cognitive impairment, and functional loss in elderly persons. The term is now commonly used to describe a range of neuroimaging, neuropathological, and associated clinical features, the pathogenesis of which is largely unclear but that are thought to arise from disease affecting the perforating cerebral arterioles, capillaries, and venules. Modern neuroimaging has revolutionized our understanding of the consequences of small vessels disease on the brain parenchyma, even though small arteries, arterioles, capillaries, and venules are difficult to be directly visualized with current techniques used in clinical practice. In this short review, we focus on histopathological and neuroimaging perspectives, basic definitions, and recent advances in the field.

Microbleed and microinfarct detection in amyloid angiopathy: a high-resolution MRI-histopathology study

Cerebral amyloid angiopathy is a common neuropathological finding in the ageing human brain, associated with cognitive impairment. Neuroimaging markers of severe cerebral amyloid angiopathy are cortical microbleeds and microinfarcts. These parenchymal brain lesions are considered key contributors to cognitive impairment. Therefore, they are important targets for therapeutic strategies and may serve as surrogate neuroimaging markers in clinical trials. We aimed to gain more insight into the pathological basis of magnetic resonance imaging-defined microbleeds and microinfarcts in cerebral amyloid angiopathy, and to explore the pathological burden that remains undetected, by using high and ultra-high resolution ex vivo magnetic resonance imaging, as well as detailed histological sampling. Brain samples from five cases (mean age 85 ± 6 years) with pathology-proven cerebral amyloid angiopathy and multiple microbleeds on in vivo clinical magnetic resonance imaging were subjected to high-resolution ex vivo 7 T magnetic resonance imaging. On the obtained high-resolution (200 μm isotropic voxels) ex vivo magnetic resonance images, 171 microbleeds were detected compared to 66 microbleeds on the corresponding in vivo magnetic resonance images. Of 13 sampled microbleeds that were matched on histology, five proved to be acute and eight old microhaemorrhages. The iron-positive old microhaemorrhages appeared approximately four times larger on magnetic resonance imaging compared to their size on histology. In addition, 48 microinfarcts were observed on ex vivo magnetic resonance imaging in three out of five cases (two cases exhibited no microinfarcts). None of them were visible on in vivo 1.5 T magnetic resonance imaging after a retrospective analysis. Of nine sampled microinfarcts that were matched on histology, five were confirmed as acute and four as old microinfarcts. Finally, we explored the proportion of microhaemorrhage and microinfarct burden that is beyond the detection limits of ex vivo magnetic resonance imaging, by scanning a smaller sample at ultra-high resolution, followed by serial sectioning. At ultra-high resolution (75 μm isotropic voxels) magnetic resonance imaging we observed an additional 48 microbleeds (compared to high resolution), which proved to correspond to vasculopathic changes (i.e. morphological changes to the small vessels) instead of frank haemorrhages on histology. After assessing the serial sections of this particular sample, no additional haemorrhages were observed that were missed on magnetic resonance imaging. In contrast, nine microinfarcts were found in these sections, of which six were only retrospectively visible at ultra-high resolution. In conclusion, these findings suggest that microbleeds on in vivo magnetic resonance imaging are specific for microhaemorrhages in cerebral amyloid angiopathy, and that increasing the resolution of magnetic resonance images results in the detection of more 'non-haemorrhagic' pathology. In contrast, the vast majority of microinfarcts currently remain under the detection limits of clinical in vivo magnetic resonance imaging.

Post-mortem assessment in vascular dementia: advances and aspirations

BACKGROUND

Cerebrovascular lesions are a frequent finding in the elderly population. However, the impact of these lesions on cognitive performance, the prevalence of vascular dementia, and the pathophysiology behind characteristic in vivo imaging findings are subject to controversy. Moreover, there are no standardised criteria for the neuropathological assessment of cerebrovascular disease or its related lesions in human post-mortem brains, and conventional histological techniques may indeed be insufficient to fully reflect the consequences of cerebrovascular disease.

DISCUSSION

Here, we review and discuss both the neuropathological and in vivo imaging characteristics of cerebrovascular disease, prevalence rates of vascular dementia, and clinico-pathological correlations. We also discuss the frequent comorbidity of cerebrovascular pathology and Alzheimer's disease pathology, as well as the difficult and controversial issue of clinically differentiating between Alzheimer's disease, vascular dementia and mixed Alzheimer's disease/vascular dementia. Finally, we consider additional novel approaches to complement and enhance current post-mortem assessment of cerebral human tissue.

CONCLUSION

Elucidation of the pathophysiology of cerebrovascular disease, clarification of characteristic findings of in vivo imaging and knowledge about the impact of combined pathologies are needed to improve the diagnostic accuracy of clinical diagnoses.

Calcineurin proteolysis in astrocytes: Implications for impaired synaptic function

Mounting evidence suggests that astrocyte activation, found in most forms of neural injury and disease, is linked to the hyperactivation of the protein phosphatase calcineurin. In many tissues and cell types, calcineurin hyperactivity is the direct result of limited proteolysis. However, little is known about the proteolytic status of calcineurin in activated astrocytes. Here, we developed a polyclonal antibody to a high activity calcineurin proteolytic fragment in the 45-48kDa range (ΔCN) for use in immunohistochemical applications. When applied to postmortem human brain sections, the ΔCN antibody intensely labeled cell clusters in close juxtaposition to amyloid deposits and microinfarcts. Many of these cells exhibited clear activated astrocyte morphology. The expression of ΔCN in astrocytes near areas of pathology was further confirmed using confocal microscopy. Multiple NeuN-positive cells, particularly those within microinfarct core regions, also labeled positively for ΔCN. This observation suggests that calcineurin proteolysis can also occur within damaged or dying neurons, as reported in other studies. When a similar ΔCN fragment was selectively expressed in hippocampal astrocytes of intact rats (using adeno-associated virus), we observed a significant reduction in the strength of CA3-CA1 excitatory synapses, indicating that the hyperactivation of astrocytic calcineurin is sufficient for disrupting synaptic function. Together, these results suggest that proteolytic activation of calcineurin in activated astrocytes may be a central mechanism for driving and/or exacerbating neural dysfunction during neurodegenerative disease and injury.

Brain structural connectivity in late-life major depressive disorder

Disrupted brain connectivity might explain both the pathogenesis and consequences of late-life major depressive disorder (LLD). However, it remains difficult to ascertain whether and how specific circuits are affected. We reviewed literature regarding brain connectivity in LLD, and we specifically focused on the role of structural pathology. LLD is associated with greater levels of cerebrovascular disease, and greater levels of cerebrovascular disease are associated with both depression development and treatment responsiveness. Cerebrovascular disease is most often measured as white matter hyperintensity (WMH) burden, and histopathology studies suggest WMH reflect myelin damage and fluid accumulation (among other underlying pathology). WMHs appear as confluent caps around the ventricles (periventricular), as well as isolated lesions in the deep white matter. The underlying tissue damage and implications for brain connectivity may differ by WMH location or severity. WMHs are associated with lower white matter microstructural integrity (measured with diffusion tensor imaging) and altered brain function (measured with functional MRI). LLD is also associated with lower white matter microstructural integrity and grey matter loss which may also alter the network properties and function of the brain. Damage to brain structure reflected by WMH, reduced white matter microstructural integrity, and atrophy may affect brain function, and are therefore likely pathophysiological mechanisms of LLD. Additional research is needed to fully characterize the developmental course and pathology underlying these imaging markers, and to understand how structural damage explains LLD's various clinical manifestations.

Vascular cognitive impairment and dementia

Vascular contributions to cognitive impairment are receiving heightened attention as potentially modifiable factors for dementias of later life. These factors have now been linked not only to vascular cognitive disorders but also Alzheimer's disease. In this chapter we review 3 related topics that address vascular contributions to cognitive impairment: 1. vascular pathogenesis and mechanisms; 2. neuropsychological and neuroimaging phenotypic manifestations of cerebrovascular disease; and 3. prospects for prevention of cognitive impairment of later life based on cardiovascular and stroke risk modification. This article is part of a Special Issue entitled: Vascular Contributions to Cognitive Impairment and Dementia edited by M. Paul Murphy, Roderick A. Corriveau and Donna M. Wilcock.

Interaction between cerebrovascular disease and Alzheimer pathology

PURPOSE OF REVIEW

Epidemiological investigations have proposed strict control of vascular risk factors as a strategy to overcome dementia, because of the close interaction between cerebrovascular disease (CVD) and Alzheimer's disease. In light of recent advances in basic, translational, and clinical research in the area, this review focuses on the significance of CVD in Alzheimer's disease pathogenesis.

RECENT FINDINGS

Alzheimer's disease and CVD share several risk factors, and the coexistence of both pathologies is frequently noted. CVD and subsequent cerebral blood flow reduction would increase amyloid β (Aβ) production by modulating β and γ-secretase. Furthermore, CVD impairs Aβ clearance, which is mainly driven by vascular mediated systems, including active transport across the blood-brain barrier, and perivascular lymphatic/paravascular glymphatic drainage systems. Thus, CVD may disturb homeostasis between Aβ production and clearance, thereby aggravating Alzheimer's disease. Recent translational researches in this field aim to facilitate Aβ clearance. Several candidate drugs are being tested in clinical trials.

SUMMARY

Compared with Aβ pathology, little is known about the relationship between tau pathology and CVD, although some studies have shown that CVD has an influence on tau pathology. The close interrelationship between Alzheimer's disease and CVD suggests the necessity of the maintenance of cerebrovascular integrity, which may herald a new generation of dementia treatment strategies.

Heterogeneous histopathology of cortical microbleeds in cerebral amyloid angiopathy

OBJECTIVE

To investigate the histopathologic substrate of microbleeds detected on 7T postmortem MRI in autopsy cases with severe cerebral amyloid angiopathy (CAA) and Alzheimer pathology.

METHODS

Five decedents (mean age at death 79.6 ± 5.7 years) with documented severe CAA and Alzheimer pathology on standard neuropathologic examination were selected from a local database. Formalin-fixed coronal brain slices were scanned at 7T MRI, including high-resolution T2- and T2*-weighted sequences. Representative microbleeds from each case were sampled for histopathologic analysis, including the presence of blood, blood breakdown products, and markers of ischemic tissue injury.

RESULTS

On MRI, we identified >300 cortical and 4 subcortical microbleeds. Two out of 15 sampled cortical microbleeds corresponded histologically to erythrocytes (suggestive of recent hemorrhages), 4 to vasculopathies (fibrinoid necrosis in 3 and a cavernoma) without substantial parenchymal tissue injury, and 9 to accumulations of iron-positive siderophages without erythrocytes (suggestive of old hemorrhages) combined with mild to moderate degrees of chronic ischemic tissue injury.

CONCLUSIONS

This study provides evidence for heterogeneous pathologic substrates and possibly different pathophysiologic mechanisms underlying MRI-observed cortical microbleeds in the context of advanced CAA and Alzheimer disease.

Ischemic brain injury in cerebral amyloid angiopathy

Cerebral amyloid angiopathy (CAA) is a common form of cerebral small vessel disease and an important risk factor for intracerebral hemorrhage and cognitive impairment. While the majority of research has focused on the hemorrhagic manifestation of CAA, its ischemic manifestations appear to have substantial clinical relevance as well. Findings from imaging and pathologic studies indicate that ischemic lesions are common in CAA, including white-matter hyperintensities, microinfarcts, and microstructural tissue abnormalities as detected with diffusion tensor imaging. Furthermore, imaging markers of ischemic disease show a robust association with cognition, independent of age, hemorrhagic lesions, and traditional vascular risk factors. Widespread ischemic tissue injury may affect cognition by disrupting white-matter connectivity, thereby hampering communication between brain regions. Challenges are to identify imaging markers that are able to capture widespread microvascular lesion burden in vivo and to further unravel the etiology of ischemic tissue injury by linking structural magnetic resonance imaging (MRI) abnormalities to their underlying pathophysiology and histopathology. A better understanding of the underlying mechanisms of ischemic brain injury in CAA will be a key step toward new interventions to improve long-term cognitive outcomes for patients with CAA.

Assessing Cortical Cerebral Microinfarcts on High Resolution MR Images

Cerebral microinfarcts are frequent findings in the post-mortem human brain, and are related to cognitive decline and dementia. Due to their small sizes it is challenging to study them on clinical MRI scans. It was recently demonstrated that cortical microinfarcts can be depicted with MRI scanners using high magnetic field strengths (7T). Based on this experience, a proportion of these lesions is also visible on lower resolution 3T MRI. These findings were corroborated with ex vivo imaging of post-mortem human brain tissue, accompanied by histopathological verification of possible cortical microinfarcts. Here an ex vivo imaging protocol is presented, for the purpose of validating MR observed cerebral microvascular pathology with histological evaluation. Furthermore, guidelines are provided for the assessment of cortical microinfarcts on both in vivo 7T and 3T MR images. These guidelines provide researchers with a tool to rate cortical microinfarcts on in vivo images of larger patient samples, to further unravel their clinical relevance in cognitive decline and dementia, and establish these lesions as a novel biomarker of cerebral small vessel disease.

Clinical-pathologic correlations in vascular cognitive impairment and dementia

The most common causes of cognitive impairment and dementia are Alzheimer's disease (AD) and vascular brain injury (VBI), either independently, in combination, or in conjunction with other neurodegenerative disorders. The contribution of VBI to cognitive impairment and dementia, particularly in the context of AD pathology, has been examined extensively yet remains difficult to characterize due to conflicting results. Describing the relative contribution and mechanisms of VBI in dementia is important because of the profound impact of dementia on individuals, caregivers, families, and society, particularly the stability of health care systems with the rapidly increasing age of our population. Here we discuss relationships between pathologic processes of VBI and clinical expression of dementia, specific subtypes of VBI including microvascular brain injury, and what is currently known regarding contributions of VBI to the development and pathogenesis of the dementia syndrome. This article is part of a Special Issue entitled: Vascular Contributions to Cognitive Impairment and Dementia edited by M. Paul Murphy, Roderick A. Corriveau and Donna M. Wilcock.