Incidental Cerebral Microbleeds and Cerebral Blood Flow in Elderly Individuals

Impact of spontaneous intracerebral hemorrhage on cognitive functioning: An update

Intracerebral hemorrhage (ICH) accounts for 15% of all strokes and approximately 50% of stroke-related mortality and disability worldwide. Patients who have experienced ICH are at high risk of negative outcome, including stroke and cognitive disorders. Vascular cognitive impairment are frequently seen after brain hemorrhage, yet little is known about them, as most studies have focused on neuropsychological outcome in ischemic stroke survivors, using well-documented acute and chronic cognitive scores. However, recent evidence supports the notion that ICH and dementia are closely related and each increases the risk of the other. The location of the lesion also plays a significant role as regards the neuropsychological profile, while the pathophysiology of ICH can indicate a specific pattern of dysfunction. Several cognitive domains may be affected, such as language, memory, executive function, processing speed and gnosis.

Neuropsychological Effects of Cerebral Amyloid Angiopathy

Cerebral amyloid angiopathy is a condition of the cerebral arterioles and to a lesser extent capillaries and veins, wherein beta-amyloid is deposited. In arterioles, this preferentially targets vascular smooth muscle cells and in the later stages undermines the stability of the vessel. This condition is frequently comorbid with Alzheimer's disease and its role in cognitive impairment and dementia is a topic of considerable recent research. This article reviews recent literature which confirms that CAA independently contributes to cognitive impairment by potentiating the neurodegeneration of Alzheimer's disease, by predisposing to microhemorrhagic and microischemic injury to the brain parenchyma, and by interfering with the autoregulation of CNS blood flow. In this review, we discuss the clinical presentation of cerebral amyloid angiopathy, with a focus on the neuropsychological manifestations of this vasculopathy.

Cerebral Perfusion and the Risk of Dementia: A Population-Based Study

BACKGROUND

Cerebral hypoperfusion has previously been associated with mild cognitive impairment and dementia in various cross-sectional studies, but whether hypoperfusion precedes neurodegeneration is unknown. We prospectively determined the association of cerebral perfusion with subsequent cognitive decline and development of dementia.

METHODS

Between 2005 and 2012, we measured cerebral blood flow by 2-dimensional phase-contrast magnetic resonance imaging in participants of the population-based Rotterdam Study without dementia. We determined the association of cerebral perfusion (mL/100mL/min) with risk of dementia (until 2015) using a Cox model, adjusting for age, sex, demographics, cardiovascular risk factors, and apolipoprotein E genotype. We repeated analyses for Alzheimer disease and accounting for stroke. We used linear regression to determine change in cognitive performance during 2 consecutive examination rounds in relation to perfusion. Finally, we investigated whether associations were modified by baseline severity of white matter hyperintensities.

RESULTS

Of 4759 participants (median age 61.3 years, 55.2% women) with a median follow-up of 6.9 years, 123 participants developed dementia (97 Alzheimer disease). Lower cerebral perfusion was associated with higher risk of dementia (adjusted hazard ratio, 1.31; 95% confidence interval per standard deviation decrease, 1.07-1.61), similar for Alzheimer disease only, and unaltered by accounting for stroke. Risk of dementia with hypoperfusion was higher with increasing severity of white matter hyperintensities (with severe white matter hyperintensities; hazard ratio, 1.54; 95% confidence interval, 1.11-2.14). At cognitive reexamination after on average 5.7 years, lower baseline perfusion was associated with accelerated decline in cognition (global cognition: β=-0.029, P=0.003), which was similar after excluding those with incident dementia, and again most profound in individuals with higher volume of white matter hyperintensities (P value for interaction=0.019).

CONCLUSIONS

Cerebral hypoperfusion is associated with accelerated cognitive decline and an increased risk of dementia in the general population.

Susceptibility-weighted imaging: current status and future directions

Susceptibility-weighted imaging (SWI) is a method that uses the intrinsic nature of local magnetic fields to enhance image contrast in order to improve the visibility of various susceptibility sources and to facilitate diagnostic interpretation. It is also the precursor to the concept of the use of phase for quantitative susceptibility mapping (QSM). Nowadays, SWI has become a widely used clinical tool to image deoxyhemoglobin in veins, iron deposition in the brain, hemorrhages, microbleeds and calcification. In this article, we review the basics of SWI, including data acquisition, data reconstruction and post-processing. In particular, the source of cusp artifacts in phase images is investigated in detail and an improved multi-channel phase data combination algorithm is provided. In addition, we show a few clinical applications of SWI for the imaging of stroke, traumatic brain injury, carotid vessel wall, siderotic nodules in cirrhotic liver, prostate cancer, prostatic calcification, spinal cord injury and intervertebral disc degeneration. As the clinical applications of SWI continue to expand both in and outside the brain, the improvement of SWI in conjunction with QSM is an important future direction of this technology. Copyright © 2016 John Wiley & Sons, Ltd.

Association between large artery atherosclerosis and cerebral microbleeds: a systematic review and meta-analysis

OBJECTIVE

The aim of this systematic review and meta-analysis was to provide evidence that biomarkers of large artery atherosclerosis, including arterial stenosis and greater carotid intima-media thickness (cIMT), may serve as clinical markers of subclinical haemorrhage-prone cerebral small vessel disease, reflected by cerebral microbleeds (CMBs).

METHODS

We searched PubMed, MEDLINE, Web of Science, EMBASE and the Cochrane Library to identify relevant studies published before 1 July 2016. The association between arterial stenosis and CMBs was estimated by the OR and 95% CI. The association of cIMT and CMBs was calculated using the standardised mean difference (SMD). Heterogeneity and publication bias were explored.

RESULTS

8 studies including a total of 7160 participants were pooled in the meta-analysis. 6 of the included studies were cross-sectional, except that 2 were prospective. We found a significant association between arterial stenosis >50% and the presence of CMBs (OR 1.95, 95% CI 1.13 to 3.36, I²=56.1%). A fixed-effects model suggested that patients with CMBs were more likely to have a greater cIMT (SMD 0.20, 95% CI 0.11 to 0.28, I²=24.7%).

CONCLUSIONS

This systematic review and meta-analysis found that there is a relationship between large artery atherosclerosis and CMBs. Future studies are needed to confirm the impact of atherosclerosis on the CMBs, which may have potential therapeutic implications.

Kidney dysfunction and cerebral microbleeds in neurologically healthy adults

INTRODUCTION

Cerebral microbleed (CMB) is a potent risk factor for overt cerebrovascular disease. Although some studies indicated the possible role of renal dysfunction as a risk factor of CMB, the findings could not be generalized. This study aimed to investigate the association between renal dysfunction and cerebral microbleed (CMB) in neurologically healthy adults.

MATERIALS AND METHODS

A total of 2,518 subjects who underwent brain MRI as part of health screening were involved in the study. CMBs were defined as well-demarcated focal areas of low signal intensity with associated blooming on the T2-weighted MRI measuring less than 5mm in diameter. The glomerular filtration rate (GFR) was estimated using the Modification of Diet in Renal Disease formula. Kidney function was classified as normal (≥90), mild (60 to 89.9), moderate (30 to 59.9), and severe (<30 mL/min/1.73 m2) renal dysfunction according to the GFR.

RESULTS

The mean age of the participants was 57.5 ± 8.3 years (ranged 40 to 79), and 1,367 subjects (54.3%) were male. The mean GFR level was 81.5 ± 15.5, and the prevalence of CMB was 4.1% (n = 103). Subjects with CMB demonstrated a higher proportion of moderate-to-severe renal dysfunction than those without CMB (15.5% vs. 5.0%, p < 0.001). In the multivariate logistic regression analysis, moderate-to-severe renal dysfunction showed a significant association with CMB (adjusted odd ratio = 2.63; p = 0.008). Furthermore, a decrease in the GFR level was associated with an increasing trend of the presence of CMB (p for trend = 0.031) and number of CMB lesions (p for trend = 0.003).

CONCLUSIONS

Renal dysfunction was significantly associated with the presence of CMB in neurologically healthy adults. More studies are needed to evaluate if treatment of kidney disease and risk factor modification may prevent further progress of CMB.

Microbleeds in Alzheimer's Disease: A Neuropsychological Overview and Meta-Analysis

The current literature on the role of brain microbleeds (MB) on the neuropsychological outcomes of Alzheimer's disease (AD) is heterogeneous. We therefore meta-analytically examined the neuropsychological literature pertaining to MBs in AD. Using a priori selected criteria, studies with cross-sectional neuropsychological assessment on MBs and AD were reviewed. Six of 122 studies met selection criteria and provided neuropsychological data on either AD with MB and without MB, or in contrast to healthy controls. The global neuropsychological difference between AD with MB and AD without MB based on random effect model was nonsignificant, heterogeneous, and small (Effect Size =-0.155; 95% confidence interval =-0.465 to 0.155; p value =0.326; Heterogenity: Q-value =12.744; degrees of freedom =5; p =0.026; I2 =61%). The contribution of MBs to cognitive deficits in AD remains unclear. Future studies of MB in AD should strive to use standardized neuroimaging techniques with high sensitivity for MB, a common standard for MB definition, and neuropsychological tests sensitive for detecting subtle cognitive impairment.

Apolipoprotein E and Sex Bias in Cerebrovascular Aging of Men and Mice

Alzheimer disease (AD) research has mainly focused on neurodegenerative processes associated with the classic neuropathologic markers of senile plaques and neurofibrillary tangles. Additionally, cerebrovascular contributions to dementia are increasingly recognized, particularly from cerebral small vessel disease (SVD). Remarkably, in AD brains, the apolipoprotein E (ApoE) ɛ4 allele shows male excess for cerebral microbleeds (CMBs), a marker of SVD, which is opposite to the female excess of plaques and tangles. Mouse transgenic models add further complexities to sex-ApoE ɛ4 allele interactions, with female excess of both CMBs and brain amyloid. We conclude that brain aging and AD pathogenesis cannot be understood in humans without addressing major gaps in the extent of sex differences in cerebrovascular pathology.

Cortical atrophy in patients with cerebral amyloid angiopathy: a case-control study

BACKGROUND

Loss of cortical grey matter is a diagnostic marker of many neurodegenerative diseases, and is a key mediator of cognitive impairment. We postulated that cerebral amyloid angiopathy (CAA), characterised by cortical vascular amyloid deposits, is associated with cortical tissue loss independent of parenchymal Alzheimer's disease pathology. We tested this hypothesis in patients with hereditary cerebral haemorrhage with amyloidosis-Dutch type (HCHWA-D), a monogenetic disease with minimal or no concomitant Alzheimer's disease pathology, as well as in patients with sporadic CAA and healthy and Alzheimer's disease controls.

METHODS

In this observational case-control study, we included six groups of participants: patients diagnosed with HCHWA-D using genetic testing; healthy controls age-matched to the HCHWA-D group; patients with probable sporadic CAA without dementia; two independent cohorts of healthy controls age-matched to the CAA group; and patients with Alzheimer's disease age-matched to the CAA group. De-identified (but unmasked) demographic, clinical, radiological, and genetic data were collected at Massachusetts General Hospital (Boston, MA, USA), at Leiden University (Leiden, Netherlands), and at sites contributing to Alzheimer's Disease Neuroimaging Initiative (ADNI). The primary outcome measure was cortical thickness. The correlations between cortical thickness and structural lesions, and blood-oxygen-level-dependent time-to-peak (BOLD-TTP; a physiological measure of vascular dysfunction) were analysed to understand the potential mechanistic link between vascular amyloid and cortical thickness. The radiological variables of interest were quantified using previously validated computer-assisted tools, and all results were visually reviewed to ensure their accuracy.

RESULTS

Between March 15, 2006, and Dec 1, 2014, we recruited 369 individuals (26 patients with HCHWA-D and 28 age-matched, healthy controls; 63 patients with sporadic CAA without dementia; two healthy control cohorts with 63 and 126 individuals; and 63 patients with Alzheimer's disease). The 26 patients with HCHWA-D had thinner cortices (2·31 mm [SD 0·18]) than the 28 healthy controls (mean difference -0·112 mm, 95% CI -0·190 to -0·034, p=0·006). The 63 patients with sporadic CAA without dementia had thinner cortices (2·17 mm [SD 0·11]) than the two healthy control cohorts (n=63, mean difference -0·14 mm, 95% CI -0·17 to -0·10, p<0·0001; and n=126, -0·10, -0·13 to -0·06, p<0·0001). All differences remained independent in multivariable analyses. The 63 patients with Alzheimer's disease displayed more severe atrophy than the patients with sporadic CAA (2·1 mm [SD 0·14], difference 0·07 mm, 95% CI 0·11 to 0·02, p=0·005). We found strong associations between cortical thickness and vascular dysfunction in the patients with HCHWA-D (ρ=-0·58, p=0·003) or sporadic CAA (r=-0·4, p=0·015), but not in controls. Vascular dysfunction was identified as a mediator of the effect of hereditary CAA on cortical atrophy, accounting for 63% of the total effect.

INTERPRETATION

The appearance of cortical thinning in patients with HCHWA-D indicates that vascular amyloid is an independent contributor to cortical atrophy. These results were reproduced in patients with the more common sporadic CAA. Our findings also suggest that CAA-related cortical atrophy is at least partly mediated by vascular dysfunction. Our results also support the view that small vessel diseases such as CAA can cause cortical atrophy even in the absence of Alzheimer's disease, a conclusion that can help radiologists, neurologists, and other clinicians who diagnose these common geriatric conditions.

FUNDING

National Institutes of Health.

Cerebral hypoperfusion and glucose hypometabolism: Key pathophysiological modulators promote neurodegeneration, cognitive impairment, and Alzheimer's disease

Aging, hypertension, diabetes, hypoxia/obstructive sleep apnea (OSA), obesity, vitamin B12/folate deficiency, depression, and traumatic brain injury synergistically promote diverse pathological mechanisms including cerebral hypoperfusion and glucose hypometabolism. These risk factors trigger neuroinflammation and oxidative-nitrosative stress that in turn decrease nitric oxide and enhance endothelin, Amyloid-β deposition, cerebral amyloid angiopathy, and blood-brain barrier disruption. Proinflammatory cytokines, endothelin-1, and oxidative-nitrosative stress trigger several pathological feedforward and feedback loops. These upstream factors persist in the brain for decades, upregulating amyloid and tau, before the cognitive decline. These cascades lead to neuronal Ca²⁺ increase, neurodegeneration, cognitive/memory decline, and Alzheimer's disease (AD). However, strategies are available to attenuate cerebral hypoperfusion and glucose hypometabolism and ameliorate cognitive decline. AD is the leading cause of dementia among the elderly. There is significant evidence that pathways involving inflammation and oxidative-nitrosative stress (ONS) play a key pathophysiological role in promoting cognitive dysfunction. Aging and several comorbid conditions mentioned above promote diverse pathologies. These include inflammation, ONS, hypoperfusion, and hypometabolism in the brain. In AD, chronic cerebral hypoperfusion and glucose hypometabolism precede decades before the cognitive decline. These comorbid disease conditions may share and synergistically activate these pathophysiological pathways. Inflammation upregulates cerebrovascular pathology through proinflammatory cytokines, endothelin-1, and nitric oxide (NO). Inflammation-triggered ONS promotes long-term damage involving fatty acids, proteins, DNA, and mitochondria; these amplify and perpetuate several feedforward and feedback pathological loops. The latter includes dysfunctional energy metabolism (compromised mitochondrial ATP production), amyloid-β generation, endothelial dysfunction, and blood-brain-barrier disruption. These lead to decreased cerebral blood flow and chronic cerebral hypoperfusion- that would modulate metabolic dysfunction and neurodegeneration. In essence, hypoperfusion deprives the brain from its two paramount trophic substances, viz., oxygen and nutrients. Consequently, the brain suffers from synaptic dysfunction and neuronal degeneration/loss, leading to both gray and white matter atrophy, cognitive dysfunction, and AD. This Review underscores the importance of treating the above-mentioned comorbid disease conditions to attenuate inflammation and ONS and ameliorate decreased cerebral blood flow and hypometabolism. Additionally, several strategies are described here to control chronic hypoperfusion of the brain and enhance cognition. © 2016 Wiley Periodicals, Inc.

Cerebral blood flow and metabolism associated with cerebral microbleeds in small vessel disease

OBJECTIVE

Cerebral microbleeds (CMBs), probably reflecting microangiopathy, have not yet sufficiently been examined in association with cerebral blood flow (CBF) and metabolism. We investigated the relationships between CMBs, and CBF and metabolism in symptomatic small vessel disease.

METHODS

We enrolled 22 patients with symptomatic small vessel disease without severe stenosis (>50 %) in major cerebral arteries. Volumes of white matter lesions (WMLs) and number of CMBs were assessed on images of fluid-attenuated inversion recovery and gradient-echo T2*-weighted magnetic resonance imaging, respectively. Patients were divided into two groups according to the median number of CMBs (group I <5, n = 10; group II ≥5, n = 12). Parametric images of CBF, cerebral metabolic rate of oxygen (CMRO2), oxygen extraction fraction and cerebral blood volume were estimated using positron emission tomography and (15)O-labeled gases. The functional values in the cortex-subcortex, basal ganglia, and centrum semiovale were compared between the two groups.

RESULTS

Volumes of WMLs of group II were larger than those of group I (median: 38.4; range: 25.1-91.5 mL vs. median: 11.3; range: 4.2-73.4 mL, p = 0.01). In the centrum semiovale, the mean CBF of group II was significantly lower than that of group I (12.6 ± 2.6 vs. 15.6 ± 3.3 mL/100 g/min, p = 0.04). In the other regions, there were no significant differences in either CBF or CMRO2 between the two groups.

CONCLUSIONS

Our study indicated that increases in the number of CMBs with larger volumes of WMLs were associated with cerebral ischemia in the deep white matter in patients with symptomatic small vessel disease.

Microbleeds may expand acutely after traumatic brain injury

BACKGROUND AND PURPOSE

Susceptibility weighted imaging (SWI) is a very sensitive tool for the detection of microbleeds in traumatic brain injury (TBI). The number and extent of such traumatic microbleeds (TMBs) have been shown to correlate with the severity of the injury and the clinical outcome. However, the acute dynamics of TMBs have not been revealed so far. Since TBI is known to constitute dynamic pathological processes, we hypothesized that TMBs are not constant in their appearance, but may progress acutely after injury.

MATERIALS AND METHODS

We present here five closed moderate/severe (Glasgow coma scale≤13) TBI patients who underwent SWI very early (average=23.4 h), and once again a week (average=185.8 h) after the injury. The TMBs were mapped at both time points by a conventional radiological approach and their numbers and volumes were measured with manual tracing tools by two observers. TMB counts and extents were compared between time points.

RESULTS

TMBs were detected in four patients, three of them displaying an apparent TMB change. In these patients, TMB confluence and apparent growth were detected in the corpus callosum, coronal radiation or subcortical white matter, while unchanged TMBs were also present. These changes caused a decrease in the TMB count associated with an increase in the overall TMB volume over time.

CONCLUSION

We have found a compelling evidence that diffuse axonal injury-related microbleed development is not limited strictly to the moment of injury: the TMBs might expand in the acute phase of TBI. The timing of SWI acquisition may be relevant for optimizing the prognostic utility of this imaging biomarker.

The APOE4 allele shows opposite sex bias in microbleeds and Alzheimer's disease of humans and mice

The apolipoprotein APOE4 allele confers greater risk of Alzheimer's disease (AD) for women than men, in conjunction with greater clinical deficits per unit of AD neuropathology (plaques, tangles). Cerebral microbleeds, which contribute to cognitive dysfunctions during AD, also show APOE4 excess, but sex-APOE allele interactions are not described. We report that elderly men diagnosed for mild cognitive impairment and AD showed a higher risk of cerebral cortex microbleeds with APOE4 allele dose effect in 2 clinical cohorts (ADNI and KIDS). Sex-APOE interactions were further analyzed in EFAD mice carrying human APOE alleles and familial AD genes (5XFAD (+/-) /human APOE(+/+)). At 7 months, E4FAD mice had cerebral cortex microbleeds with female excess, in contrast to humans. Cerebral amyloid angiopathy, plaques, and soluble Aβ also showed female excess. Both the cerebral microbleeds and cerebral amyloid angiopathy increased in proportion to individual Aβ load. In humans, the opposite sex bias of APOE4 allele for microbleeds versus the plaques and tangles is the first example of organ-specific, sex-linked APOE allele effects, and further shows AD as a uniquely human condition.