Decreased cerebrovascular dilatory capacity in subjects with asymptomatic periventricular hyperintensities

Diffuse microvascular dysfunction and loss of white matter integrity predict poor outcomes in patients with acute ischemic stroke

We sought to investigate the relationship between blood-brain barrier (BBB) permeability and microstructural white matter integrity, and their potential impact on long-term functional outcomes in patients with acute ischemic stroke (AIS). We studied 184 AIS subjects with perfusion-weighted MRI (PWI) performed <9 h from last known well time. White matter hyperintensity (WMH), acute infarct, and PWI-derived mean transit time lesion volumes were calculated. Mean BBB leakage rates (K2 coefficient) and mean diffusivity values were measured in contralesional normal-appearing white matter (NAWM). Plasma matrix metalloproteinase-2 (MMP-2) levels were studied at baseline and 48 h. Admission stroke severity was evaluated using the NIH Stroke Scale (NIHSS). Modified Rankin Scale (mRS) was obtained at 90-days post-stroke. We found that higher mean K2 and diffusivity values correlated with age, elevated baseline MMP-2 levels, greater NIHSS and worse 90-day mRS (all p < 0.05). In multivariable analysis, WMH volume was associated with mean K2 ( p = 0.0007) and diffusivity ( p = 0.006) values in contralesional NAWM. In summary, WMH severity measured on brain MRI of AIS patients is associated with metrics of increased BBB permeability and abnormal white matter microstructural integrity. In future studies, these MRI markers of diffuse cerebral microvascular dysfunction may improve prediction of cerebral tissue infarction and functional post-stroke outcomes.

Understanding a role for hypoxia in lesion formation and location in the deep and periventricular white matter in small vessel disease and multiple sclerosis

The deep and periventricular white matter is preferentially affected in several neurological disorders, including cerebral small vessel disease (SVD) and multiple sclerosis (MS), suggesting that common pathogenic mechanisms may be involved in this injury. Here we consider the potential pathogenic role of tissue hypoxia in lesion development, arising partly from the vascular anatomy of the affected white matter. Specifically, these regions are supplied by a sparse vasculature fed by long, narrow end arteries/arterioles that are vulnerable to oxygen desaturation if perfusion is reduced (as in SVD, MS and diabetes) or if the surrounding tissue is hypoxic (as in MS, at least). The oxygen crisis is exacerbated by a local preponderance of veins, as these can become highly desaturated 'sinks' for oxygen that deplete it from surrounding tissues. Additional haemodynamic deficiencies, including sluggish flow and impaired vasomotor reactivity and vessel compliance, further exacerbate oxygen insufficiency. The cells most vulnerable to hypoxic damage, including oligodendrocytes, die first, resulting in demyelination. Indeed, in preclinical models, demyelination is prevented if adequate oxygenation is maintained by raising inspired oxygen concentrations. In agreement with this interpretation, there is a predilection of lesions for the anterior and occipital horns of the lateral ventricles, namely regions located at arterial watersheds, or border zones, known to be especially susceptible to hypoperfusion and hypoxia. Finally, mitochondrial dysfunction due to genetic causes, as occurs in leucodystrophies or due to free radical damage, as occurs in MS, will compound any energy insufficiency resulting from hypoxia. Viewing lesion formation from the standpoint of tissue oxygenation not only reveals that lesion distribution is partly predictable, but may also inform new therapeutic strategies.

The Role of White Matter Damage in the Risk of Periprocedural Diffusion-Weighted Lesions after Carotid Artery Stenting

Background

White matter hyperintensities (WMH) are a common finding in aged individuals affected by carotid artery disease and are a risk factor for first-ever and recurrent stroke. We investigated if white matter damage increases the risk of brain microembolism during carotid artery stenting (CAS), as evaluated by the appearance of new areas of restricted diffusion on diffusion-weighted images (DWI).

Methods

We evaluated 47 patients with severe internal carotid artery (ICA) stenosis undergoing CAS, comparing preprocedural clinical, ultrasound and radiological characteristics. WMH volume was computed on FLAIR images before CAS. After CAS, the DWI scan was looked over for areas of restricted diffusion (DWI lesions). A first univariate analysis was adopted to compare groups according to the occurrence of DWI lesions. Then, the variable DWI lesion was modelled by means of a logistic regression model.

Results

Seventeen patients developed at least 1 DWI lesion after CAS. Compared with non-DWI, DWI patients were more commonly treated in the left ICA (p = 0.007) and had a more severe WMH damage (p = 0.027). Indeed, the risk of a DWI lesion was higher in left versus right stenosis (OR = 9.0, 95% CI 1.9-42.7, p = 0.005) and increased for each log-unit of WMH lesion load (OR = 7.05, 95% CI 1.07-46.49, p = 0.042). A WMH lesion load of at least 5.25 cm³ had a 50% probability of occurrence of a new DWI lesion.

Conclusions

Treated side and preexisting white matter damage are risk conditions for brain microembolism during CAS. This should be taken into account to optimize severe carotid artery disease management.

Cerebral blood flow in small vessel disease: A systematic review and meta-analysis

White matter hyperintensities are frequent on neuroimaging of older people and are a key feature of cerebral small vessel disease. They are commonly attributed to chronic hypoperfusion, although whether low cerebral blood flow is cause or effect is unclear. We systematically reviewed studies that assessed cerebral blood flow in small vessel disease patients, performed meta-analysis and sensitivity analysis of potential confounders. Thirty-eight studies (n = 4006) met the inclusion criteria, including four longitudinal and 34 cross-sectional studies. Most cerebral blood flow data were from grey matter. Twenty-four cross-sectional studies (n = 1161) were meta-analysed, showing that cerebral blood flow was lower in subjects with more white matter hyperintensity, globally and in most grey and white matter regions (e.g. mean global cerebral blood flow: standardised mean difference-0.71, 95% CI -1.12, -0.30). These cerebral blood flow differences were attenuated by excluding studies in dementia or that lacked age-matching. Four longitudinal studies (n = 1079) gave differing results, e.g., more baseline white matter hyperintensity predated falling cerebral blood flow (3.9 years, n = 575); cerebral blood flow was low in regions that developed white matter hyperintensity (1.5 years, n = 40). Cerebral blood flow is lower in subjects with more white matter hyperintensity cross-sectionally, but evidence for falling cerebral blood flow predating increasing white matter hyperintensity is conflicting. Future studies should be longitudinal, obtain more white matter data, use better age-correction and stratify by clinical diagnosis.

Vascular risk factor burden correlates with cerebrovascular reactivity but not resting state coactivation in the default mode network

PURPOSE

White matter hyperintensities (WMH) are prevalent among older adults and are often associated with cognitive decline and increased risk of stroke and dementia. Vascular risk factors (VRFs) are linked to WMH, yet the impact of multiple VRFs on gray matter function is still unclear. The goal of this study was to test for associations between the number of VRFs and cerebrovascular reactivity (CVR) and resting state (RS) coactivation among individuals with WMH.

MATERIALS AND METHODS

Twenty-nine participants with suspected WMH were grouped based on the number of VRFs (subgroups: 0, 1, or ≥2). CVR and RS coactivation were measured with blood oxygenation level-dependent (BOLD) imaging on a 3T magnetic resonance imaging (MRI) system during hypercapnia and rest, respectively. Default-mode (DMN), sensory-motor, and medial-visual networks, generated using independent component analysis of RS-BOLD, were selected as networks of interest (NOIs). CVR-BOLD was analyzed using two methods: 1) a model-based approach using CO2 traces, and 2) a dual-regression (DR) approach using NOIs as spatial inputs. Average CVR and RS coactivations within NOIs were compared between VRF subgroups. A secondary analysis investigated the correlation between CVR and RS coactivation.

RESULTS

VRF subgroup differences were detected using DR-based CVR in the DMN (F20,2  = 5.17, P = 0.015) but not the model-based CVR nor RS coactivation. DR-based CVR was correlated with RS coactivation in the DMN (r(2)  = 0.28, P = 0.006) but not the sensory-motor nor medial-visual NOIs.

CONCLUSION

In individuals with WMH, CVR in the DMN was inversely associated with the number of VRFs and correlated with RS coactivation.

The vascular depression hypothesis: mechanisms linking vascular disease with depression

The 'Vascular Depression' hypothesis posits that cerebrovascular disease may predispose, precipitate or perpetuate some geriatric depressive syndromes. This hypothesis stimulated much research that has improved our understanding of the complex relationships between late-life depression (LLD), vascular risk factors, and cognition. Succinctly, there are well-established relationships between LLD, vascular risk factors and cerebral hyperintensities, the radiological hallmark of vascular depression. Cognitive dysfunction is common in LLD, particularly executive dysfunction, a finding predictive of poor antidepressant response. Over time, progression of hyperintensities and cognitive deficits predicts a poor course of depression and may reflect underlying worsening of vascular disease. This work laid the foundation for examining the mechanisms by which vascular disease influences brain circuits and influences the development and course of depression. We review data testing the vascular depression hypothesis with a focus on identifying potential underlying vascular mechanisms. We propose a disconnection hypothesis, wherein focal vascular damage and white matter lesion location is a crucial factor, influencing neural connectivity that contributes to clinical symptomatology. We also propose inflammatory and hypoperfusion hypotheses, concepts that link underlying vascular processes with adverse effects on brain function that influence the development of depression. Testing such hypotheses will not only inform the relationship between vascular disease and depression, but also provide guidance on the potential repurposing of pharmacological agents that may improve LLD outcomes.

Preserved acetazolamide reactivity in lacunar patients with severe white-matter lesions: 15O-labeled gas and H2O positron emission tomography studies

Limited evidence exists on the relationships between severity of white-matter lesions (WMLs) and cerebral hemodynamics in patients without major cerebral artery disease. To examine changes of cerebral blood flow (CBF), oxygen metabolism, and vascular reserve capacity associated with severity of WML in patients with lacunar stroke, we used a positron emission tomography (PET). Eighteen lacunar patients were divided into two groups according to the severity of WMLs, assessed by Fazekas classification; grades 0 to 1 as mild WML group and grades 2 to 3 as severe WML group. Rapid dual autoradiography was performed with (15)O-labeled gas-PET followed by (15)O-labeled water-PET with acetazolamide (ACZ) challenge. Compared with the mild WML group, the severe WML group showed lower CBF (20.6±4.4 versus 29.9±8.2 mL/100 g per minute, P=0.008), higher oxygen extraction fraction (OEF) (55.2±7.4 versus 46.7±5.3%, P=0.013), and lower cerebral metabolic rate of oxygen (CMRO(2)) (1.95±0.41 versus 2.44±0.42 mL/100 g per minute, P=0.025) in the centrum semiovale. There were no significant differences in the ACZ reactivity between the two groups (48.6±22.6% versus 42.5±17.2%, P=0.524). Lacunar patients with severe WMLs exhibited reduced CBF and CMRO(2), and increased OEF in the centrum semiovale. The ACZ reactivity was preserved in both patients with severe and mild WMLs in each site of the brain.

Age-related white matter changes

Age-related white matter changes (WMC) are considered manifestation of arteriolosclerotic small vessel disease and are related to age and vascular risk factors. Most recent studies have shown that WMC are associated with a host of poor outcomes, including cognitive impairment, dementia, urinary incontinence, gait disturbances, depression, and increased risk of stroke and death. Although the clinical relevance of WMC has been extensively studied, to date, only very few clinical trials have evaluated potential symptomatic or preventive treatments for WMC. In this paper, we reviewed the current understanding in the pathophysiology, epidemiology, clinical importance, chemical biomarkers, and treatments of age-related WMC.

Framingham cardiovascular risk profile correlates with impaired hippocampal and cortical vasoreactivity to hypercapnia

Vascular risk factors affect cerebral blood flow (CBF) and cerebral vascular reactivity, contributing to cognitive decline. Hippocampus is vulnerable to both Alzheimer's disease (AD) pathology and ischemia; nonetheless, the information about the impact of vascular risk on hippocampal perfusion is minimal. Cognitively, healthy elderly (NL=18, 69.9±6.7 years) and subjects with mild cognitive impairment (MCI=15, 74.9±8.1 years) were evaluated for the Framingham cardiovascular risk profile (FCRP). All underwent structural imaging and resting CBF assessment with arterial spin labeling (ASL) at 3T magnetic resonance imaging (MRI). In 24 subjects (NL=17, MCI=7), CBF was measured after a carbon dioxide rebreathing challenge. Across all subjects, FCRP negatively correlated with hippocampal (ρ=-0.41, P=0.049) and global cortical (ρ=-0.46, P=0.02) vasoreactivity to hypercapnia (VR(h)). The FCRP-VR(h) relationships were most pronounced in the MCI group: hippocampus (ρ=-0.77, P=0.04); global cortex (ρ=-0.83, P=0.02). The FCRP did not correlate with either volume or resting CBF. The hippocampal VR(h) was lower in MCI than in NL subjects (Z=-2.0, P=0.047). This difference persisted after age and FCRP correction (F([3,20])=4.6, P=0.05). An elevated risk for vascular pathology is associated with a reduced response to hypercapnia in both hippocampal and cortical tissue. The VR(h) is more sensitive to vascular burden than either resting CBF or brain volume.

Associations between total cerebral blood flow and age related changes of the brain

Background and Purpose

Although total cerebral blood flow (tCBF) is known to be related to age, less is known regarding the associations between tCBF and the morphologic changes of the brain accompanying cerebral aging. The purpose of this study was to investigate whether total cerebral blood flow (tCBF) is related to white matter hyperintensity (WMH) volume and/or cerebral atrophy. Furthermore, we investigate whether tCBF should be expressed in mL/min, as was done in all previous MR studies, or in mL/100 mL/min, which yielded good results in precious SPECT, PET and perfusion MRI studies investigating regional cerebral blood flow.

Materials and Methods

Patients were included from the nested MRI sub-study of the PROSPER study. Dual fast spin echo and FLAIR images were obtained in all patients. In addition, single slice phase contrast MR angiography was used for flow measurements in the internal carotids and vertebral arteries. tCBF was expressed in both mL/min and mL/100 mL/min.

Results

We found a significant correlation between tCBF in mL/min and both age (r = −.124; p = p≤.001) and parenchymal volume (r = 0.430; p≤.001). We found no association between tCBF in mL/min and %-atrophy (r = −.077; p = .103) or total WMH volume (r = −.069; p = .148). When tCBF was expressed in mL/100 mL/min the correlation between tCBF and age was no longer found (r = −.001; p = .985). Multivariate regression analyses corrected for age showed a significant correlation between tCBF in mL/100 mL/min and WMH volume (r = −.106; p = .044). No significant association between tCBF in mL/100 mL/min and %-atrophy was found.

Conclusion

From this study we conclude that, when evaluating tCBF alterations due to various pathologies, tCBF should in mL/100 mL/min instead of mL/min. Furthermore, changes or differences in WMH volume should be accounted for.

Effect of cerebrovascular risk factors on regional cerebral blood flow

PURPOSE

To prospectively investigate which cerebrovascular risk factors are related to regional cerebral blood flow (rCBF), as measured noninvasively with arterial spin-labeling (ASL) magnetic resonance (MR) imaging, in a large group of patients with symptomatic atherosclerotic disease.

MATERIALS AND METHODS

Ethics committee approval and informed consent were obtained. One hundred thirty consecutive patients (107 men, 23 women; mean age, 58 years +/- 10 [standard deviation]) with symptomatic atherosclerotic disease were included in the study. Cerebrovascular risk factors (body mass index, carotid artery stenosis, diabetes mellitus, hyperhomocysteinemia, hyperlipidemia, hypertension, and smoking) were assessed by means of a questionnaire and physical, ultrasonographic, and laboratory examinations. The control group consisted of 10 subjects (eight men, two women; mean age, 58 years +/- 15) without symptomatic atherosclerotic disease. rCBF measurements were performed with ASL MR imaging. The effects of the individual cerebrovascular risk factors on the rCBF were assessed by using linear regression analysis.

RESULTS

Hypertension was significantly associated with higher rCBF (adjusted beta = 6.5 mL/min/100 g; 95% confidence interval: 1.4 mL/min/100 g, 11.7 mL/min/100 g). Hyperhomocysteinemia was significantly related to lower rCBF (adjusted beta = -7.4 mL/min/100 g; 95% confidence interval: -12.7 mL/min/100 g, -2.1 mL/min/100 g). No significant associations between rCBF and the other cerebrovascular risk factors were found.

CONCLUSION

In patients with symptomatic atherosclerotic disease, hypertension is related to higher rCBF and hyperhomocysteinemia is related to lower rCBF.

The enigma of vascular cognitive disorder and vascular dementia

The prevalence, morphology and pathogenesis of vascular dementia (VaD), recently termed vascular cognitive impairment, are a matter of discussion, and currently used clinical diagnostic criteria show moderate sensitivity (average 50%) and variable specificity (range 64-98%). In Western clinic-based series, VaD is suggested in 8-10% of cognitively impaired aged subjects. Its prevalence in autopsy series varies from 0.03 to 58%, with reasonable values of 8-15%, while in Japan it is seen in 22-35%. Neuropathologic changes associated with cognitive impairment include multifocal and/or diffuse disease and focal lesions: multi-infarct encephalopathy, white matter lesions or arteriosclerotic subcortical (leuko)encephalopathy, multilacunar state, mixed cortico-subcortical type, borderline/watershed lesions, rare granular cortical atrophy, post-ischemic encephalopathy and hippocampal sclerosis. They result from systemic, cardiac and local large or small vessel disease. Recent data indicate that cognitive decline is commonly associated with widespread small ischemic/vascular lesions (microinfarcts, lacunes) throughout the brain with predominant involvement of subcortical and functionally important brain areas. Their pathogenesis is multifactorial, and their pathophysiology affects neuronal networks involved in cognition, memory, behavior and executive functioning. Vascular lesions often coexist with Alzheimer disease (AD) and other pathologies. Minor cerebrovascular lesions, except for severe amyloid angiopathy, appear not essential for cognitive decline in full-blown AD, while both mild Alzheimer pathology and small vessel disease may interact synergistically. The lesion pattern of "pure" VaD, related to arteriosclerosis and microangiopathies, differs from that in mixed-type dementia (AD with vascular encephalopathy), more often showing large infarcts, which suggests different pathogenesis of both types of lesions. Due to the high variability of cerebrovascular pathology and its causative factors, no validated neuropathologic criteria for VaD are available, and a large variability across laboratories still exists in the procedures for morphologic examination and histology techniques.

Endothelial function and white matter hyperintensities in older adults with cardiovascular disease

BACKGROUND AND PURPOSE

The presence of white matter hyperintensities on brain MRI is common among elderly individuals. Previous research suggests that cardiovascular risk factors are associated with increased white matter hyperintensities. Examining the role of direct physiological measures of vascular function will help to clarify the vascular mechanisms related to white matter hyperintensities. The aim of the present study was to examine the association between endothelial-dependent and endothelial-independent vasodilatation and white matter hyperintensity volume.

METHODS

Twenty-five older adults with a range of cardiovascular diseases underwent brain MRI and completed assessments of blood vessel integrity using endothelial-dependent and independent flow-mediated dilation of the brachial artery. A semi-automated pixel-based method was used to quantify total brain volume and white matter hyperintensity volume, with white matter hyperintensity volume corrected for total brain volume. The association between measures of flow-mediated dilation and log-transformed white matter hyperintensities was examined.

RESULTS

Correlation analysis revealed that endothelial-dependent vasodilatation was significantly and inversely associated with white matter hyperintensity volume. In contrast, endothelial-independent vasodilatation was not associated with white matter hyperintensities. Neither endothelial-dependent nor endothelial-independent vasodilatation was associated with total brain volume.

CONCLUSIONS

These data provide preliminary evidence that the integrity of the vascular endothelium is associated with white matter hyperintensities in older adults with cardiovascular disease. Impaired vascular function may be one mechanism that contributes to the development of white matter hyperintensities in the brain. Additional longitudinal research combining measures of vessel function, neuroimaging and cognition will be helpful in clarifying this potential mechanism.

Relationship between cerebral vasomotor reactivity and white matter lesions in elderly subjects without large artery occlusive disease

BACKGROUND AND PURPOSE

The relationships between cerebral vasomotor reactivity (CVR) and white matter lesions (WMLs) were investigated mainly in patients with carotid stenosis. We aimed to study the relationship in asymptomatic elderly subjects without large artery occlusive disease.

METHODS

A total of 33 elderly individuals (mean age was 76.2 years) who were free from neurological deficit or cognitive impairment were studied. Bilateral mean blood flow velocity was measured in the middle cerebral artery using a 2-MHz pulsed transcranial Doppler (TCD) system together with intravenous administration of acetazolamide as vasodilatory stimuli. WMLs on a fluid-attenuated inversion recovery (FLAIR) sequence of MRI were classified into two categories: subcortical deep white matter hyperintensity (SDWMH) and periventricular hyperintensity (PVH). The lesions in each category were then divided into three grades (grade 0-I, grade II, grade III) according to the Fazekas scale.

RESULTS

CVR was inversely associated with the extent of SDWMH and PVH. The differences in CVR were statistically significant among different severity of WMLs: for SDWMH (70%+/- 10% in grade 0-I, 60%+/- 10% in grade II, and 40%+/- 10% in grade III, P < .001); for PVH (80%+/- 10% in grade 0-I, 60%+/- 10% in grade II, and 40%+/- 10% in grade III, P < .001).

CONCLUSIONS

Impaired CVR is related to the extent of WMLs in asymptomatic elderly individuals without large artery stenosis. The findings in our study suggest that dysfunction of cerebral vascular autoregulation might be an important factor in the development of WMLs in the asymptomatic elderly without large artery occlusive disease.

Identifying regions of compromised hemodynamics in symptomatic carotid occlusion by cerebrovascular reactivity and oxygen extraction fraction

OBJECTIVES

Oxygen extraction fraction (OEF) and cerebrovascular reserve (CVR) are both proven predictors of stroke risk in symptomatic patients with carotid occlusion. Accordingly, hemispheric comparisons of CVR and OEF are significantly correlated. However, there was also substantial disagreement: hemispheres identified as compromised by CVR were normal by OEF. Our aim was to determine whether regional comparisons could resolve the CVR-OEF discordance. We also studied the relationship between white matter (WM) infarction and hemodynamic compromise.

METHODS

Quantitative CVR and OEF were measured in 12 symptomatic patients with internal carotid artery occlusion. CVR and OEF comparisons were made in the anterior watershed (AWS), middle cerebral artery (MCA) and WM territories using various thresholds for hemodynamic compromise. Associations with WM infarction were also recorded.

RESULTS

Comparison of CVR and OEF for the AWS and MCA showed high sensitivity (100%) with specificities of 83 and 40%, respectively. There was also agreement (k=Cohen's Kappa) for the AWS (k=0.83) and MCA (k=0.39) territories. CVR-OEF discordance was reduced with regional analysis. Hemodynamic compromise was more often found in patients with WM infarction.

DISCUSSION

Regional comparison of CVR and OEF reduced the discordance compared with hemispheric analysis, especially for the AWS territory. Despite the persistence of some regions with compromised CVR and normal OEF, CVR is able to identify all regions with elevated OEF making it a useful screening technology. Future studies are needed to understand whether those remaining regions with compromised CVR are also at increased stroke risk despite normal OEF.

Advances in magnetic resonance imaging methods for the evaluation of bipolar disorder

This article reviews the current state of magnetic resonance imaging techniques as applied to bipolar disorder. Addressed are conventional methods of structural neuroimaging and recently developed techniques. This latter group comprises volumetric analysis, voxel-based morphometry, the assessment of T2 white matter hyperintensities, shape analysis, cortical surface-based analysis, and diffusion tensor imaging. Structural analysis methods used in magnetic resonance imaging develop exponentially, and now present opportunities to identify disease-specific neuroanatomic alterations. Greater acuity and complementarity in measuring these alterations has led to the generation of further hypotheses regarding the pathophysiology of bipolar disorder. Included in the summary of findings is consideration of a resulting neuroanatomic model. Integrative issues and future directions in this relatively young field, including multi-modal approaches enabling us to produce more comprehensive results, are discussed.

Relationship of deep white matter hyperintensities and cerebral blood flow in severe carotid artery stenosis

Leukoaraiosis (LA) has been associated with abnormalities of both large and small blood vessels. This study attempts to clarify the pathogenesis of LA by testing the hypothesis that increased frequency of LA with occlusive extra-cranial arterial disease results directly from global reduction in cerebral blood flow (CBF). Thirty-five normal subjects and 55 patients with carotid stenosis (>70%) were studied using MR. CBF was measured using phase contrast MR angiography and LA was scored using previously validated scoring system. Patients were divided into those with evidence of previous infarction on MRI and those without. LA was more severe in patients than in normal subjects (P<0.01) and correlated with age in normal subjects but not in patients. CBF in patients with (809+/-214 ml/min) and without infarction (mean 792+/-181 ml/min) was significantly lower than in normal subjects (mean 1073+/-194 ml/min). There was no correlation between the severity of LA and measured CBF in any group. The severity of LA is greater in patients with severe carotid stenosis but is not correlated to reductions in CBF. This suggests that microvascular abnormality is the dominant pathogenetic factor in LA even in the presence of severe stenotic/occlusive large vessel disease.

Cerebral hemodynamics and silent cerebral white matter lesions in middle-aged essential hypertensive patients

Cerebral white matter lesions (WML) represent a subclinical form of ischemic brain damage that have been associated with risk of future stroke. Studies have shown an association between WML and impaired cerebral autoregulation in hypertensives who had previously suffered a stroke. The aim of the study was to evaluate cerebral hemodynamics in asymptomatic hypertensives according to the presence or absence of WML. Fifty never-treated essential hypertensives (32 men, 18 women), aged 50-60 years, without clinical evidence of target organ damage were studied. All patients underwent 24-h ambulatory blood pressure monitoring, and brain-magnetic resonance imaging to establish the presence or absence of WML. Baseline cerebral blood flow velocity (CBF), pulsatility index (PI; differences between systolic and diastolic velocities), and CBF after acetazolamide infusion (vasomotor reactivity of cerebral vessels), were measured by transcranial Doppler ultrasonography in both left and right middle cerebral arteries, and averaged. Twenty hypertensive patients (40%) were found to have WML on brain resonance. No differences were observed on resting and stimulating CBF between hypertensives with and without WML. In contrast, patients with WML exhibited significantly higher PI compared with hypertensives without WML (0.79 +/- 0.13 vs 0.66 +/- 0.12; p = 0.003). Moreover, PI correlated with 24-h pulse pressure (r = 0.361; p = 0.015). We conclude that the presence of silent WML in middle-aged hypertensives is associated with increased cerebrovascular pulsatility. This increased pulsatility is also associated with higher pulse pressure values, suggesting a pathogenetic link between pulse pressure, pulsatility and the development of WML.

High total cerebral blood flow is associated with a decrease of white matter lesions

BACKGROUND

Low cerebral blood flow (CBF) has been associated with the presence of white matter lesions (WMLs). However, the power of these studies was insufficient (n=20-35) to determine whether flow is associated with WMLs.

PURPOSE

The aim of this study was to investigate whether total cerebral blood flow (tCBF) is associated with the severity of white matter lesions (WMLs) in a large patient sample.

SUBJECTS AND METHODS

228 patients with clinical symptoms of cardiovascular disease had MRI of the brain, consisting of a T2-w FLAIR and a 2D phase-contrast flow measurement of the internal carotid arteries and the basilar artery. WMLs were graded according to prevalence and size of deep and periventricular WMLs. To determine the relation between tCBF and WMLs we used linear and logistic regression analysis adjusted for age, gender, intima media thickness and hypertension.

RESULTS

We observed an inverse association between the tCBF and the total number of WMLs adjusted for age, gender, intima media thickness and hypertension [B=-1, 0 WML 95% CI (-2.0 to 0.0, p=0.045) per 100 mL increase in tCBF]. The adjusted odds ratio for the presence of severe WMLs in patients with high tCBF (> 675 mL/min) was 0.5 (95% CI 0.2-1.0) compared with patients with normal tCBF.

CONCLUSION

In this study we found that high tCBF is associated with a decrease in presence and severity of WMLs.

Cerebral white matter changes and geriatric syndromes: is there a link?

Cerebral white matter lesions (WMLs), also called "leukoaraiosis," are common neuroradiological findings in elderly people. WMLs are often located at periventricular and subcortical areas and manifest as hyperintensities in magnetic resonance imaging. Recent studies suggest that cardiovascular risk factors are associated with the development of WMLs. These lesions are associated with different geriatric syndromes such as falls, executive cognitive impairment, depressive symptoms, and urinary incontinence. Damage to associative pathways in frontal and subcortical regions due to hypoperfusion may disrupt frontal executive, motor control, and other systems, resulting in these manifestations. WMLs are associated with substantial disability and should not be considered a benign and silent condition as once believed. Interventions addressing cardiovascular risk factors should be undertaken in early or mid-life in order to prevent late-life functional impairment associated with WMLs. After these lesions develop and impair executive cognitive functions, the patient's ability to comply with a complex risk reduction program may be significantly compromised.

Vasoreactivity in patients with periventricular white matter lucency

OBJECTIVES

Cerebral hypoperfusion has been evidenced in patients with periventricular white matter lucency (PWML), however, our knowledge is limited regarding vasoreactivity (VR) changes in these patients. Therefore, we compared the cerebral blood flow velocity (CBFV) responses during different vasoregulatory challenges in healthy volunteers, to those in patients with PWML.

MATERIAL AND METHODS

In 20 patients with PWML and in 20 healthy volunteers the VR of the middle cerebral artery (MCA) system was measured by analyzing the changes of CBFV during different stimulation paradigms (ventilation, tilting and acetazolamide tests). During transcranial Doppler (TCD) registration the systemic blood pressure, the expiratory partial CO(2) pressure (pCO(2)) and the electroencephalograph (EEG) were monitored.

RESULTS

The relative velocity change was significantly smaller in the PWML group than in the normal control group during hypercapnia (16 +/- 12% vs 32 +/- 17%; P < 0.001) and this finding was confirmed by assessment of pCO(2)-corrected velocity change (4.7 +/- 3.7 cm/s/kPa vs 18.4 +/- 6.8 cm/s/KPa; P < 0.001). Although CBFV measurements during acetazolamide test tended to support these findings, the changes of other parameters measured did not reach the level of significance. One patient showed considerable orthostatic reaction (mean arterial blood pressure decrease by 70 mmHg) but it was not associated with significant changes in CBFV.

CONCLUSION

Patients with PWML showed an impaired VR in the MCA flow territory supporting the concept of the microangiopathic origin of leukoaraiotic changes.

White matter hyperintensities in subjects with cocaine and opiate dependence and healthy comparison subjects

The prevalence, severity, and location of white matter signal hyperintensities (WMH) on brain magnetic resonance images were compared in patients with cocaine or opiate dependence and healthy subjects. Patients with cocaine (n=32) and opiate dependence (n=32), whose diagnoses were confirmed with the Structured Clinical Interview for DSM-IV, and age- and sex-matched healthy subjects (n=32) were scanned using a 1.5 T whole body GE magnetic resonance scanner. Axial proton-density and T2-weighted images were obtained as well as fluid-attenuated inversion recovery axial images. The severity of WMH was assessed separately for deep (and insular) and periventricular WMH, using a modified composite version of the rating scales of Fazekas and Coffey. The cocaine-dependent group had greater severity of WMH than the opiate-dependent group, which in turn had greater severity of WMH than the healthy comparison group (odds ratios=2.54 and 2.90, respectively). The cocaine-dependent group had greater lesion severity of deep and insular WMH than the opiate-dependent group and the healthy comparison group (odds ratio>3.25 for deep WMH; odds ratio>4.38 for insular WMH). For periventricular WMH, there were no significant differences between the three groups. The frontal lobes were the predominant locations of WMH in both substance-dependent groups. The greater prevalence and severity of WMH in cocaine-dependent subjects than in opiate-dependent subjects may reflect the fact that cocaine induces more ischemia via vasoconstriction than opiates. Also, there was a trend for lower WMH severity in substance-dependent women relative to the healthy comparison group, possibly due to estrogen's protective effect against cerebrovascular accidents.

Acetazolamide as a vasodilatory stimulus in cerebrovascular diseases and in conditions affecting the cerebral vasculature

Pathologic processes affecting the brain vessels may damage cerebral vasodilatory capacity. Early detection of cerebral dysfunction plays an important role in the prevention of cerebrovascular diseases. In recent decades acetazolamide (AZ) has frequently been used for this purpose. In the present work the mechanism of action and the previous studies are reviewed. The authors conclude that AZ tests are useful in cerebrovascular research. Further investigations are recommended to prove how impaired reserve capacity and reactivity influence the stroke risk in patients and whether these tests may indicate therapeutic interventions.

MR assessment of cerebral vascular response: a comparison of two methods

PURPOSE

To compare the results and reproducibility of two MR-based methods of measuring the cerebrovascular response (CVR).

MATERIALS AND METHODS

In eight volunteers, CVR was assessed with two MR-based methods upon a challenge with acetazolamide. CVR was assessed by measuring changes in total cerebral blood flow (TCBF) using phase contrast (PC) MRI, and by measuring perfusion MRI. To assess reproducibility the measurements were repeated after 1 week.

RESULTS

The average CVR with the PC-MRI method was 46% (SD = 16%), and for perfusion MR the measured CVR was 44% (SD = 16%). The coefficient of variation (COV) for PC-MRI was 28%, while perfusion MR had a COV of 26%. The limits of agreement between the two methods were -49% and 45%, demonstrating a lack of agreement between the two methods in terms of CVR estimation.

CONCLUSION

CVR estimates based on PC-MRI and perfusion MRI showed reproducibility but a lack of agreement in healthy volunteers. This lack of agreement can be attributed to the different aspects of the CVR reflected by these methods: TCBF reflects changes in CBF, whereas our perfusion MRI method reflects cerebral blood volume (CBV).

Cerebral white matter lesions in essential hypertension

The pathogenesis and clinical significance of cerebral white matter lesions (WML) remain controversial. Most studies have shown that age, hypertension, diabetes mellitus, and a history of stroke or heart disease are the most important factors related to the presence of cerebral WML. Moreover, some studies suggest that the presence of WML are closely related to cerebrovascular disease and cognitive impairment in elderly patients with vascular risk factors, particularly hypertension. In this review, different points of view about cerebral WML are discussed, with special focus on the presence of WML in essential hypertension. Some authors suggest that the presence of WML in hypertensive patients could be considered an early marker of brain damage.

Noninvasive magnetic resonance imaging evaluation of cerebral blood flow with acetazolamide challenge in patients with cerebrovascular stenosis

To evaluate the utility of using magnetic resonance imaging (MRI) of cerebral blood flow (CBF) in conjunction with pharmacologic flow augmentation, the authors imaged 14 patients with ischemic symptoms referable to large artery cerebrovascular stenosis of the anterior circulation. CBF was measured by using continuous arterial spin labeling (CASL) both at rest and 10 minutes after 1 g intravenous acetazolamide on a commercial 1.5 Tesla scanner. Quantitative CBF images were calculated along with augmentation images showing the effects of acetazolamide. Interpretable studies were obtained from all patients. Based on the image data as well as a region of interest analysis of CBF changes in middle cerebral artery distributions, varying patterns of augmentation were observed that suggested differing mechanisms of ischemic symptomatology. The ability to obtain this information in conjunction with a structural MRI examination extends the diagnostic potential for MRI in cerebrovascular disease and allows the value of augmentation testing in clinical management to be assessed more widely. J. Magn. Reson. Imaging 1999;10:870-875.

Cerebral effects of a single dose of intravenous vinpocetine in chronic stroke patients: a PET study

The effects of vinpocetine (Cavinton) on the cerebral glucose metabolism of chronic stroke patients are studied with positron emission tomography. The regional and global cerebral metabolic rates of glucose (CMRglu) and the kinetic constants related to them are quantified before and after single-dose intravenous vinpocetine treatment. These measurements are completed with transcranial Doppler sonography and single photon emission computed tomography to explore the possible mechanisms underlying the resulting changes in glucose uptake and metabolism in the brain. The authors' findings indicate that a single-dose vinpocetine treatment, although it does not affect significantly the regional or global metabolic rates of glucose, improves significantly the transport of glucose (both uptake and release) through the blood-brain barrier in the whole brain, the entire contralateral hemisphere, and in the brain tissue around the infarct area of the symptomatic hemisphere. These changes are in accord with increased blood flow in the entire contralateral hemisphere as well as decreased blood flow velocity and increased peripheral vessel resistance in the entire symptomatic hemisphere.

Cerebral blood flow correlated with carotid blood flow in neurologically normal elderly with severe white matter lesions

Previous studies of white matter signal hyperintensity (WMSH) on T2-weighted MRI (magnetic resonance imaging) have shown it to be related to decreased cerebral blood flow (CBF). However, there have been few studies on the relationship of WMSH and the internal carotid blood flow (CaBF). Doppler ultrasound sonography is widely used for evaluation of CaBF. We analyzed the relationship between CBF, CaBF, and WMSH. The subjects had not suffered cerebral ischemic episodes although they had some risk factors for stroke. They received MRI and were classified into three groups, i.e. mild, moderate, and severe WMSH. The % stenosis of the internal carotid artery (ICA) was measured with angiography. Doppler sonography was used to measure the mean bilateral CaBF. The oxygen-15 steady-state technique and PET (positron emission tomography) were used to measure CBF. There were significant correlations between the % stenosis of ICA and the ipsilateral CaBF and between the % stenosis of ICA and hemispheric CBF. There was a significant relationship between CBF and CaBF in the severe WMSH group, remaining significant after partialling out of the effects of the % stenosis. This indicated that an atherosclerotic change of the cerebral artery occurred in a way that carotid vascular resistence and cerebrovascular resistence were 'proportional'. Copyright Rapid Science Ltd

Regional cerebral blood flow and cerebrovascular risk factors in the elderly population

Regional cerebral blood flow (rCBF) was studied in 60 elderly persons (aged 65 to 84 years) recruited from a population-based study, with single photon emission computed tomography using technetium 99m-labeled hexamethylpropylene amine oxime. We investigated whether it is only age that affects rCBF or whether other factors can be indentified that explain this relationship. Using multiple linear regression analysis, increasing age was significantly associated with rCBF decrease in parietal, temporo-parietal, and temporal cortex, but not in frontal cortex. Adjustment with several risk factors for cerebrovascular disease, including hypertension, history of myocardial infarction, factor VIIc, factor VIIIc, cholesterol and HDL cholesterol, smoking, and diabetes mellitus had no influence on these relations. Conversely, the association between age and rCBF was no longer statistically significant after adjustment with fibrinogen and indicators of carotid atherosclerosis, including intima-media wall thickness of the carotid artery and plaques in the carotid artery. Correction with local ratings of cortical atrophy did not affect the relations between age and rCBF. The results suggest that in the elderly population rCBF declines with age in posterior cortical areas and that these changes may well be explained by the presence of atherosclerosis. Reduced contractility of the vascular muscle wall with increasing age resulting from atherosclerosis may be the underlying mechanism.

Cerebrovascular reactivity in hypertensive patients: a transcranial Doppler study

PURPOSE

We studied the usefulness of transcranial Doppler sonography for assessing changes in vasoreactivity in patients with hypertension and the hemodynamic consequences of hypertension.

METHODS

The study group comprised 25 patients with chronic severe hypertension and 25 age- and sex-matched healthy subjects. Cerebrovascular reserve capacity was assessed by transcranial Doppler recording of the blood flow velocity in both middle cerebral arteries before and 5, 10, 15, and 20 minutes after intravenous injection of 1 g of acetazolamide (Diamox). Blood pressure, blood gases, and other blood parameters were also measured before and after acetazolamide injection. The sizes of the left atrium, left ventricle, and aortic root were measured by echocardiography and correlated with the vasoreactivity after acetazolamide injection.

RESULTS

After acetazolamide injection, no significant changes in blood pressure were observed in either group. The mean blood flow velocity in the middle cerebral arteries of hypertensive patients (60.8 +/- 2.6 cm/sec) was not significantly different from that of controls (58.8 +/- 1.9 cm/sec) before acetazolamide injection. Ten minutes after acetazolamide injection, the percentage change in blood flow velocity was significantly lower in the hypertensive group (36.2 +/- 4.5%) than in the controls (52.6 +/- 3.7%). A significant negative correlation (p < 0.05) between decreased vasoreactivity and increased size of the left atrium and aortic root was observed.

CONCLUSIONS

Vasoreactivity decreases in hypertensive patients without neurologic deficits or computed tomography abnormalities. Enlargement of the left atrium correlates well with the severity of the impairment in vasoreactivity. Transcranial Doppler sonography can be a sensitive tool in the investigation of vascular impairment caused by hypertension and in the follow-up of hypertensive patients.

T2*-weighted magnetic resonance imaging of cerebrovascular reactivity in rat reversible focal cerebral ischemia

Cerebrovascular carbon dioxide (CO2) reactivity is an important hemodynamic index in cerebrovascular disease. In the present study T2*-weighted magnetic resonance image (T2* WI) was evaluated as a non-invasive method to investigate changes in CO2 reactivity. Fourteen rats were subjected to permanent or, 30 and 90 min of temporary middle cerebral artery occlusion. A series of T2* WIs and diffusion-weighted magnetic resonance images (DWI) was performed hourly under normo- and hypercapnic conditions. Triphenyltetrazolium chloride (TTC) staining of brain sections was obtained at the end of experiment to evaluate ischemic damage. During ischemia, a 4-6% signal increase upon hypercapnia was observed on T2* WI in the non-ischemic hemisphere, while no such reactivity was seen in the putamen and cortex ipsilateral to the MCA occlusion. After reperfusion, CO2 reactivity recovered in the putamen and cortex in the 30 min ischemia group and in the cortex alone of the 90 min ischemia groups. The areas with irreversible CO2 reactivity dysfunction coincidentally revealed no recovery on DWI and lack of TTC staining. The results indicate that T2* WI can be used to monitor changes in CO2 reactivity after various ischemic insults that may indicate tissue viability.

Vascular risk factors, atherosclerosis, cerebral white matter lesions and cerebral perfusion in a population-based study

We studied risk factors for cerebral vascular disease (blood pressure and hypertension, factor VIIc, factor VIIIc, fibrinogen), indicators of atherosclerosis (intima-media thickness and plaques in the carotid artery) and cerebral white matter lesions in relation to regional cerebral blood flow (rCBF) in 60 persons (aged 65-85 years) recruited from a population-based study. rCBF was assessed with single-photon emission tomography using technetium-99m d, l-hexamethylpropylene amine oxime (99mTc-HMPAO). Statistical analysis was performed with multiple linear regression with adjustment for age, sex and ventricle-to-brain ratio. A significant positive association was found between systolic and diastolic blood pressure and temporo-parietal rCBF. In analysis with quartiles of the distribution, we found a threshold effect for the relation of low diastolic blood pressure (</=60 mmHg) and low temporo-parietal rCBF. Levels of plasma fibrinogen were inversely related to parietal rCBF, with a threshold effect of high fibrinogen levels (>3.2 g/l) and low rCBF. Increased atherosclerosis was related to low rCBF in all cortical regions, but these associations were not significant. No consistent relation was observed between severity of cerebral white matter lesions and rCBF. Our results may have implications for blood pressure control in the elderly population.

Proton magnetic resonance spectroscopy and gadolinium-DTPA perfusion imaging of asymptomatic MRI white matter lesions

In the elderly, asymptomatic white matter hyperintensities are common on T2-weighted magnetic resonance imaging (MRI). In symptomatic patients, such MRI appearances correlate with varied postmortem findings including demyelination or stroke. What structural correlates underlie the T2 hyperintensities in patients whose lesions are asymptomatic is controversial. Therefore, in order to investigate the underlying metabolism and perfusion in white matter lesions (exhibiting T2 hyperintensity), 13 patients underwent proton magnetic resonance spectroscopy and dynamic gadolinium-DTPA perfusion-weighted MR imaging. N-acetyl aspartate (NA) levels were reduced in the lesions compared with age-matched controls (P = 0.031), implying neuronal/axonal loss. Creatine levels were also reduced (P = 0.001). Choline levels were unchanged in the lesions. Lactate was identified in the lesions of 5 of the 13 patients. Although not statistically significant, perfusion studies exhibited a trend toward lower cerebral blood volumes in patients with high grade extracranial carotid stenosis and lactate-containing lesions. These findings suggest that neuronal/axonal loss underlies the majority of T2-weighted asymptomatic lesions in the older population, and in many cases these changes may be due to chronic ischemia.