Cerebral blood flow and oxygen metabolism in patients with vascular dementia of the Binswanger type

Willis Lecture: Biomarkers for Inflammatory White Matter Injury in Binswanger Disease Provide Pathways to Precision Medicine

Binswanger disease is the small vessel form of vascular cognitive impairment and dementia. Deposition of Alzheimer disease proteins can begin in midlife and progress slowly, whereas aging of the vasculature also can begin in midlife, continuing to progress into old age, making mixed dementia the most common type of dementia. Biomarkers facilitate the early diagnosis of dementias. It is possible to diagnose mixed dementia before autopsy with biomarkers for vascular disease derived from diffusor tensor images on magnetic resonance imaging and Alzheimer disease proteins, Aβ (amyloid β), and phosphorylated tau, in cerebrospinal fluid or in brain with positron emission tomography. The presence of vascular disease accelerates cognitive decline. Both misfolded proteins and vascular disease promote inflammation, which can be detected in cerebrospinal fluid by the presence of MMPs (matrix metalloproteinases), angiogenic growth factors, and cytokines. MMPs disrupt the blood-brain barrier and break down myelin, producing Binswanger disease's 2 main pathological features. Advances in detecting biomarkers in plasma will provide early detection of dementia and aided by machine learning and artificial intelligence, will enhance diagnosis and form the basis for early treatments.

Pathogenesis and research progress in leukoaraiosis

Leukoaraiosis is a common imaging marker of cerebral small vessel disease. In recent years, with the continuous advances in brain imaging technology, the detection rate of leukoaraiosis is higher and its clinical subtypes are gradually gaining attention. Although leukoaraiosis has long been considered an incidental finding with no therapeutic necessity, there is now growing evidence linking it to, among other things, cognitive impairment and a high risk of death after stroke. Due to different research methods, some of the findings are inconsistent and even contradictory. Therefore, a comprehensive and in-depth study of risk factors for leukoaraiosis is of great clinical significance. In this review, we summarize the literature on leukoaraiosis in recent years with the aim of elucidating the disease in terms of various aspects (including pathogenesis, imaging features, and clinical features, etc.).

Increased capillary stalling is associated with endothelial glycocalyx loss in subcortical vascular dementia

Proper regulation and patency of cerebral microcirculation are crucial for maintaining a healthy brain. Capillary stalling, i.e., the brief interruption of microcirculation has been observed in the normal brain and several diseases related to microcirculation. We hypothesized that endothelial glycocalyx, which is located on the luminal side of the vascular endothelium and involved in cell-to-cell interaction regulation in peripheral organs, is also related to cerebral capillary stalling. We measured capillary stalling and the cerebral endothelial glycocalyx (cEG) in male mice using in vivo optical coherence tomography angiography (OCT-A) and two-photon microscopy. Our findings revealed that some capillary segments were prone to capillary stalling and had less cEG. In addition, we demonstrated that the enzymatic degradation of the cEG increased the capillary stalling, mainly by leukocyte plugging. Further, we noted decreased cEG along with increased capillary stalling in a mouse model of subcortical vascular dementia (SVaD) with impaired cortical microcirculation. Moreover, gene expression related to cEG production or degradation changed in the SVaD model. These results indicate that cEG mediates capillary stalling and impacts cerebral blood flow and is involved in the pathogenesis of SVaD.

Brain Oxygen Extraction Is Differentially Altered by Alzheimer's and Vascular Diseases

BACKGROUND

Alzheimer's disease and vascular cognitive impairment (VCI), as well as their concurrence, represent the most common types of cognitive dysfunction. Treatment strategies for these two conditions are quite different; however, there exists a considerable overlap in their clinical manifestations, and most biomarkers reveal similar abnormalities between these two conditions.

PURPOSE

To evaluate the potential of cerebral oxygen extraction fraction (OEF) as a biomarker for differential diagnosis of Alzheimer's disease and VCI. We hypothesized that in Alzheimer's disease OEF will be reduced (decreased oxygen consumption due to decreased neural activity), while in vascular diseases OEF will be elevated (increased oxygen extraction due to abnormally decreased blood flow).

STUDY TYPE

Prospective cross-sectional.

POPULATION

Sixty-five subjects aged 52-89 years, including 33 mild cognitive impairment (MCI), 7 dementia, and 25 cognitively normal subjects.

FIELD STRENGTH/SEQUENCE

3T T₂ -relaxation-under-spin-tagging (TRUST) and fluid-attenuated inversion recovery imaging (FLAIR).

ASSESSMENT

OEF, consensus diagnoses of cognitive impairment, vascular risk factors (such as hypertension, hypercholesterolemia, diabetes, smoking, and obesity), cognitive assessments, and cerebrospinal fluid concentration of amyloid and tau were assessed.

STATISTICAL TESTS

Multiple linear regression analyses of OEF with diagnostic category (normal, MCI, or dementia), vascular risks, cognitive performance, amyloid and tau pathology.

RESULTS

When evaluating the entire group, OEF was found to be lower with more severe cognitive impairment (β = -2.70 ± 1.15, T = -2.34, P = 0.02), but was higher with greater vascular risk factors (β = 1.36 ± 0.55, T = 2.48, P = 0.02). Further investigation of the subgroup of participants with low vascular risks (N = 44) revealed that lower OEF was associated with worse cognitive performance (β = 0.04 ± 0.01, T = 3.27, P = 0.002) and greater amyloid burden (β = 92.12 ± 41.23, T = 2.23, P = 0.03). Among cognitively impaired individuals (N = 40), higher OEF was associated with greater vascular risk factors (β = 2.19 ± 0.71, T = 3.08, P = 0.004).

DATA CONCLUSION

These findings suggest that OEF is differentially affected by Alzheimer's disease and VCI pathology and may be useful in etiology-based diagnosis of cognitive impairment.

LEVEL OF EVIDENCE

1 TECHNICAL EFFICACY: Stage 3 J. MAGN. RESON. IMAGING 2020;52:1829-1837.

Small Vessel Disease-Related Dementia: An Invalid Neurovascular Coupling?

The arteriosclerosis-dependent alteration of brain perfusion is one of the major determinants in small vessel disease, since small vessels have a pivotal role in the brain's autoregulation. Nevertheless, as far as we know, endothelium distress can potentiate the flow dysregulation and lead to subcortical vascular dementia that is related to small vessel disease (SVD), also being defined as subcortical vascular dementia (sVAD), as well as microglia activation, chronic hypoxia and hypoperfusion, vessel-tone dysregulation, altered astrocytes, and pericytes functioning blood-brain barrier disruption. The molecular basis of this pathology remains controversial. The apparent consequence (or a first event, too) is the macroscopic alteration of the neurovascular coupling. Here, we examined the possible mechanisms that lead a healthy aging process towards subcortical dementia. We remarked that SVD and white matter abnormalities related to age could be accelerated and potentiated by different vascular risk factors. Vascular function changes can be heavily influenced by genetic and epigenetic factors, which are, to the best of our knowledge, mostly unknown. Metabolic demands, active neurovascular coupling, correct glymphatic process, and adequate oxidative and inflammatory responses could be bulwarks in defense of the correct aging process; their impairments lead to a potentially catastrophic and non-reversible condition.

B Vitamins and Fatty Acids: What Do They Share with Small Vessel Disease-Related Dementia?

Many studies have been written on vitamin supplementation, fatty acid, and dementia, but results are still under debate, and no definite conclusion has yet been drawn. Nevertheless, a significant amount of lab evidence confirms that vitamins of the B group are tightly related to gene control for endothelium protection, act as antioxidants, play a co-enzymatic role in the most critical biochemical reactions inside the brain, and cooperate with many other elements, such as choline, for the synthesis of polyunsaturated phosphatidylcholine, through S-adenosyl-methionine (SAM) methyl donation. B-vitamins have anti-inflammatory properties and act in protective roles against neurodegenerative mechanisms, for example, through modulation of the glutamate currents and a reduction of the calcium currents. In addition, they also have extraordinary antioxidant properties. However, laboratory data are far from clinical practice. Many studies have tried to apply these results in everyday clinical activity, but results have been discouraging and far from a possible resolution of the associated mysteries, like those represented by Alzheimer's disease (AD) or small vessel disease dementia. Above all, two significant problems emerge from the research: No consensus exists on general diagnostic criteria-MCI or AD? Which diagnostic criteria should be applied for small vessel disease-related dementia? In addition, no general schema exists for determining a possible correct time of implementation to have effective results. Here we present an up-to-date review of the literature on such topics, shedding some light on the possible interaction of vitamins and phosphatidylcholine, and their role in brain metabolism and catabolism. Further studies should take into account all of these questions, with well-designed and world-homogeneous trials.

Small vessel disease to subcortical dementia: a dynamic model, which interfaces aging, cholinergic dysregulation and the neurovascular unit

Background

Small vessels have the pivotal role for the brain’s autoregulation. The arteriosclerosis-dependent alteration of the brain perfusion is one of the major determinants in small vessel disease. Endothelium distress can potentiate the flow dysregulation and lead to subcortical vascular dementia (sVAD). sVAD increases morbidity and disability. Epidemiological studies have shown that sVAD shares with cerebrovascular disease most of the common risk factors. The molecular basis of this pathology remains controversial.

Purpose

To detect the possible mechanisms between small vessel disease and sVAD, giving a broad vision on the topic, including pathological aspects, clinical and laboratory findings, metabolic process and cholinergic dysfunction.

Methods

We searched MEDLINE using different search terms (“vascular dementia”, “subcortical vascular dementia”, “small vessel disease”, “cholinergic afferents”, etc). Publications were selected from the past 20 years. Searches were extended to Embase, Cochrane Library, and LILIACS databases. All searches were done from January 1, 1998 up to January 31, 2018.

Results

A total of 560 studies showed up, and appropriate studies were included. Associations between traditional vascular risk factors have been isolated. We remarked that SVD and white matter abnormalities are seen frequently with aging and also that vascular and endothelium changes are related with age; the changes can be accelerated by different vascular risk factors. Vascular function changes can be heavily influenced by genetic and epigenetic factors.

Conclusion

Small vessel disease and the related dementia are two pathologies that deserve attention for their relevance and impact in clinical practice. Hypertension might be a historical problem for SVD and SVAD, but low pressure might be even more dangerous; CBF regional selective decrease seems to be a critical factor for small vessel disease-related dementia. In those patients, endothelium damage is a super-imposed condition. Several issues are still debatable, and more research is needed.

Low-Grade Inflammation Is Associated with Apathy Indirectly via Deep White Matter Lesions in Community-Dwelling Older Adults: The Sefuri Study

Low-grade inflammation is implicated in the pathogenesis of atherosclerosis, metabolic syndrome, and apathy as a form of vascular depression. We analyzed the brain magnetic resonance imaging findings in 259 community-dwelling older adults (122 men and 137 women, with a mean age of 68.4 years). The serum concentrations of high-sensitivity C-reactive protein (hsCRP) were measured by a quantitative enzyme-linked immunosorbent assay. Logistic regression analysis revealed that the log₁₀ hsCRP value and the presence of a metabolic syndrome were independently associated with confluent but not punctate deep white matter lesions (DWMLs). Path analysis based on structural equation modeling (SEM) indicated that the direct path from the log₁₀ hsCRP to the DWMLs was significant (β = 0.119, p = 0.039). The direct paths from the metabolic syndrome to the log₁₀ hsCRP and to the DWMLs were also significant. The direct path from the DWMLs to apathy (β = −0.165, p = 0.007) was significant, but the direct path from the log₁₀ hsCRP to apathy was not significant. Inflammation (i.e., elevated serum hsCRP levels) was associated with DWMLs independent of common vascular risk factors, while DWMLs were associated with apathy. The present analysis with SEM revealed the more realistic scheme that low-grade inflammation was associated with apathy indirectly via DWMLs in community-dwelling older adults.

Linking Atrial Fibrillation with Alzheimer's Disease: Epidemiological, Pathological, and Mechanistic Evidence

Many studies have shown a relationship between atrial fibrillation (AF) and vascular dementia. AF is a major risk factor for stroke, and stroke is the greatest risk factor for vascular dementia. However, the relationship between Alzheimer's disease (AD), the leading cause of dementia, and AF remains unclear. At least four epidemiological studies have reported AF significantly raises the risk of AD 1.5- to 2.5-fold. Chronic cerebral hypoperfusion, resulting from persistent AF, could explain the link as hypoperfusion may mechanistically exacerbate amyloid-β (Aβ) neuropathology, such as senile plaques and amyloid angiopathy, by upregulating Aβ-producing enzymes and lowering Aβ clearance efficiency. In addition, hypoperfusion may exacerbate tau pathology directly through upregulation of tau-phosphorylating enzymes and indirectly via the amyloid cascade. However, most neuropathological studies do not support the direct link between AD pathology and AF but rather suggests vascular neuropathology is related to, or coexistent with, AF and lowers the threshold for clinically-evident AD. Vascular neuropathology may thus mediate the link between AD and AF. From a treatment perspective, an observational study has shown that catheter ablation is associated with less incidence of AD in AF patients, suggesting rhythm-control suppresses hypoperfusion-induced AD neuropathology. In addition, rate-control may lower the rate of cognitive decline in cognitively impaired elderly subjects with AF. Further studies are warranted to clarify the mechanisms underlying the linkage between AF and AD. However, anticoagulation and rhythm-/rate-control against AF may hold promise even for AD patients.

Protective effects of a radical scavenger edaravone on oligodendrocyte precursor cells against oxidative stress

Oligodendrocyte precursor cells (OPCs) play critical roles in maintaining the number of oligodendrocytes in white matter. Previously, we have shown that oxidative stress dampens oligodendrocyte regeneration after white matter damage, while a clinically proven radical scavenger, edaravone, supports oligodendrocyte repopulation. However, it is not known how edaravone exerts this beneficial effect against oxidative stress. Using in vivo and in vitro experiments, we have examined whether edaravone exhibits direct OPC-protective effects. For in vivo experiments, prolonged cerebral hypoperfusion was induced by bilateral common carotid artery stenosis in mice. OPC damage was observed on day 14 after the onset of cerebral hypoperfusion, and edaravone was demonstrated to decrease OPC death in cerebral white matter. In vitro experiments also confirmed that edaravone reduced oxidative-stress-induced OPC death. Because white matter damage is a major hallmark of many neurological diseases, and OPCs are instrumental in white matter repair after injury, our current study supports the idea that radical scavengers may provide a potential therapeutic approach for white matter related diseases.

Comparison of cerebral blood flow and structural penumbras in relation to white matter hyperintensities: A multi-modal magnetic resonance imaging study

Normal-appearing white matter (NAWM) surrounding WMHs is associated with decreased structural integrity and perfusion, increased risk of WMH growth, and is referred to as the WMH penumbra. Studies comparing structural and cerebral blood flow (CBF) penumbras within the same individuals are lacking, however, and would facilitate our understanding of mechanisms resulting in WM damage. This study aimed to compare both CBF and structural WMH penumbras in non-demented aging. Eighty-two elderly volunteers underwent 3T-MRI including fluid attenuated inversion recovery (FLAIR), pulsed arterial spin labeling and diffusion tensor imaging (DTI). A NAWM layer mask was generated for periventricular and deep WMHs. Mean CBF, DTI-fractional anisotropy (DTI-FA), DTI-mean diffusivity (DTI-MD) and FLAIR intensity for WMHs and its corresponding NAWM layer masks were computed and compared against its mean within total brain NAWM using mixed effects models. For both periventricular and deep WMHs, DTI-FA, DTI-MD and FLAIR intensity changes extended 2-9 mm surrounding WMHs (p ≤ 0.05), while CBF changes extended 13-14 mm (p ≤ 0.05). The CBF penumbra is more extensive than structural penumbras in relation to WMHs and includes WM tissue both with and without microstructural changes. Findings implicate CBF as a potential target for the prevention of both micro and macro structural WM damage.

Reduced blood flow in normal white matter predicts development of leukoaraiosis

The purpose of this study was to investigate whether low cerebral blood flow (CBF) is associated with subsequent development of white matter hyperintensities (WMH). Patients were included from a longitudinal magnetic resonance (MR) imaging study of minor stroke/transient ischemic attack patients. Images were co-registered and new WMH at 18 months were identified by comparing follow-up imaging with baseline fluid-attenuated inversion recovery (FLAIR). Regions-of-interest (ROIs) were placed on FLAIR images in one of three categories: (1) WMH seen at both baseline and follow-up imaging, (2) new WMH seen only on follow-up imaging, and (3) regions of normal-appearing white matter at both time points. Registered CBF maps at baseline were used to measure CBF in the ROIs. A multivariable model was developed using mixed-effects logistic regression to determine the effect of baseline CBF on the development on new WMH. Forty patients were included. Mean age was 61±11 years, 30% were female. Low baseline CBF, female sex, and presence of diabetes were independently associated with the presence of new WMH on follow-up imaging. The odds of having new WMH on follow-up imaging reduces by 0.61 (95% confidence interval=0.57 to 0.65) for each 1 mL/100 g per minute increase in baseline CBF. We conclude that regions of white matter with low CBF develop new WMH on follow-up imaging.

Quantitative T2, T2*, and T2' MR imaging in patients with ischemic leukoaraiosis might detect microstructural changes and cortical hypoxia

INTRODUCTION

Quantitative MRI with T2, T2*, and T2' mapping has been shown to non-invasively depict microstructural changes (T2) and oxygenation status (T2* and T2') that are invisible on conventional MRI. Therefore, we aimed to assess whether T2 and T2' quantification detects cerebral (micro-)structural damage and chronic hypoxia in lesions and in normal appearing white matter (WM) and gray matter (GM) of patients with ischemic leukoaraiosis (IL). Measurements were complemented by the assessment of the cerebral blood flow (CBF) and the degree of GM and WM atrophy.

METHODS

Eighteen patients with IL and 18 age-matched healthy controls were included. High-resolution, motion-corrected T2, T2*, and T2' mapping, CBF mapping (pulsed arterial spin labeling, PASL), and segmentation of GM and WM were used to depict specific changes in both groups. All parameters were compared between patients and healthy controls, using t testing. Values of p < 0.05 were accepted as statistically significant.

RESULTS

Patients showed significantly increased T2 in lesions (p < 0.01) and in unaffected WM (p = 0.045) as well as significantly increased T2* in lesions (p = 0.003). A significant decrease of T2' was detected in patients in unaffected WM (p = 0.027), while no T2' changes were observed in GM (p = 0.13). Both unaffected WM and GM were significantly decreased in volume in the patient-group (p < 0.01). No differences of PASL-based CBF could be shown.

CONCLUSION

Non-invasive quantitative MRI with T2, T2*, and T2' mapping might be used to detect subtle structural and metabolic changes in IL. Assessing the grade of microstructural damage and hypoxia might be helpful to monitor disease progression and to perform risk assessment.

Endothelial dysfunction is associated with the severity of cerebral small vessel disease

The pathogenesis of cerebral small vessel disease, a disease that involves white matter lesions (WMLs) and cerebral microbleeds (CMBs), is thought to be associated with endothelial dysfunction. Flow-mediated dilation (FMD) has been used to measure endothelium-dependent vasodilation. The aim of this study was to investigate the association between endothelial function (as measured by FMD) and cerebral small vessel disease. Patients with a history of cerebrovascular disease and comorbidities were enrolled in this study (n=102; 69 males, 70.1±9.2 years). The patients were divided into two groups according to the severity of WMLs, which were assessed by Fazekas classification; grades 0 to 1 as mild WMLs group and grades 2 to 3 as severe WMLs group. A gradient-echo MRI was performed in 96 patients (94.1%) to evaluate whether CMBs were present. The patients in the severe WMLs group (n=40) were older (P=0.001), more frequently exhibited hypertension (P=0.045) and diabetes mellitus (P=0.026) and possessed lower FMD values (P<0.001) than the patients in the mild WMLs group (n=62). CMBs were observed in 30 patients (31.3%). Using receiver operating characteristic curves, the optimal FMD cutoff values for predicting the presence of severe WMLs and CMBs were 3.9% and 3.7%, respectively. On multivariate logistic analysis, FMD <4.0% (odds ratio 9.50; 95% confidence interval 3.55-28.83) was independently associated with severe WMLs. Additionally, FMD <3.8% (5.82; 2.23-16.50) was also associated with the presence of CMBs. Endothelial dysfunction as evaluated by FMD may be predictive of the severity of cerebral small vessel disease.

Analysis of Cerebral Blood Flow with Single Photon Emission Computed Tomography in Mild Subcortical Ischemic Vascular Dementia

PURPOSE

The mechanism of cognitive dysfunction of subcortical ischemic vascular dementia (SIVaD) is not yet fully understood. The objective of this study was to investigate and compare the distribution of regional cerebral perfusion (CP) change in the mild forms of SIVaD, a relatively homogeneous subtype of vascular dementia, using statistical parametric mapping (SPM) analysis of the technetium-99m hexamethylproplyeneamineoxime (Tc-99m HMPAO) single photon emission computed tomography (SPECT).

MATERIALS AND METHODS

A total of 28 patients with mild SIVaD and 33 healthy controls were prospectively recruited and underwent SPECT imaging studies between January 2012 and May 2013. SPECT was performed to measure the regional CP, and SPM was applied to the analysis of the SPECT data.

RESULTS

The regional CP was significantly decreased in the bilateral insula, anterior and posterior cingulated gyrus, precentral gyrus, and subcallosal gyrus as well as the right inferior parietal lobule in the SIVaD patients compared to the controls (corrected p = 0.01). The pattern of CP abnormality correlated well with those previously reported in later forms of SIVaD.

CONCLUSIONS

Reduction of CP in the brain areas mentioned was present earlier on in the natural course of SIVaD pathophysiology. Our study suggests that cognitive dysfunction of SIVaD may be related to these regional CP deficits.

A radical scavenger edaravone inhibits matrix metalloproteinase-9 upregulation and blood-brain barrier breakdown in a mouse model of prolonged cerebral hypoperfusion

Matrix metalloproteinase-9 (MMP-9) plays key roles in the brain pathophysiology, especially in blood-brain barrier (BBB) breakdown. Therefore, inhibiting MMP-9 activity may be a promising therapy for protecting brains in cerebrovascular diseases. Here we show that in a mouse prolonged cerebral hypoperfusion model, a clinically proven radical scavenger edaravone suppressed MMP-9 and reduced BBB damage in cerebral white matter. Prolonged cerebral hypoperfusion was induced by bilateral common carotid artery stenosis in male adult C57BL/6J mice (10 weeks old). After 7 days of cerebral hypoperfusion, white matter region (e.g. corpus callosum) exhibited significant BBB leakage, assessed by IgG staining. Correspondingly, immunostaining and western blotting showed that MMP-9 was upregulated in the white matter. Edaravone treatment (3mg/kg, i.p. at days 0 and 3) inhibited both BBB leakage and MMP-9 increase. Under the early phase of cerebral hypoperfusion conditions, oligodendrocyte precursor cells (OPCs) mainly contribute to the MMP-9 increase, but our immunostaining data showed that very little OPCs expressed MMP-9 in the edaravone-treated animals at day 7. Therefore, in vitro studies with primary rat OPCs were conducted to examine whether edaravone would directly suppressed MMP-9 expressions in OPCs. OPC cultures were exposed to sub-lethal CoCl2 for 7 days to induce prolonged chemical hypoxic stress. Prolonged chemical hypoxic stress increased MMP-9 expression in OPCs, and radical scavenging with edaravone (10μM for 7 days) ameliorated the increase. Taken together, our proof-of-concept study demonstrates that radical scavengers may provide a potential therapeutic approach for white matter injury by suppressing BBB damage.

A mouse model of chronic cerebral hypoperfusion characterizing features of vascular cognitive impairment

Vascular dementia or vascular cognitive impairment occurs as a result of persistently compromised blood flow to the brain and represents the second most common type of dementia after Alzheimer's disease. In order to investigate its underlying mechanisms, a mouse model of chronic cerebral hypoperfusion has been developed, which involves the narrowing of the bilateral common carotid arteries with newly designed microcoils. This mouse model provides a unique platform to investigate the mechanisms of angiogenesis following chronic cerebral hypoperfusion and to explore potential drugs or cell therapies designed to enhance angiogenesis as a preclinical step toward developing novel treatments for dementia of vascular origin.

Early monitoring of cerebral hypoperfusion in rats by laser speckle imaging and functional photoacoustic microscopy

Because cerebral hypoperfusion brings damage to the brain, prevention of cerebrovascular diseases correlative to hypoperfusion by studying animal models makes great sense. Since complicated cerebrovascular adaptive changes in hypoperfusion could not be revealed only by cerebral blood flow (CBF) velocity imaging, we performed multi-parameter imaging by combining laser speckle imaging and functional photoacoustic microscopy. The changes in CBF, hemoglobin oxygen saturation (SO(2)), and total hemoglobin concentration (HbT) in single blood vessels of ipsilateral cortex were observed during transient cerebral hypoperfusion by ligating the unilateral common carotid artery in rats. CBF, SO(2), and HbT, respectively, decreased to 37 ± 3%, 71 ± 7.5%, and 92 ± 1.3% of baseline in 6 s immediately after occlusion, and then recovered to 77 ± 4.8%, 84 ± 8%, and 96 ± 2% of baseline in 60 s. These parameters presented the decrease with different degree and the following recovery over time after ligation, the recovery of SO(2) lagged behind those of CBF and HbT, which had the similar response. The results demonstrated that complete monitoring of both cerebral hemodynamic response and oxygen metabolic changes occurred at the earliest period of cerebral hypoperfusion was possible by using the two image modalities with high temporal and spatial resolution.

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.

Lessons from a mouse model characterizing features of vascular cognitive impairment with white matter changes

With the demographic shift in age in advanced countries inexorably set to progress in the 21st century, dementia will become one of the most important health problems worldwide. Vascular cognitive impairment is the second most common type of dementia after Alzheimer's disease and is frequently responsible for the cognitive decline of the elderly. It is characterized by cerebrovascular white matter changes; thus, in order to investigate the underlying mechanisms involved in white matter changes, a mouse model of chronic cerebral hypoperfusion has been developed, which involves the narrowing of the bilateral common carotid arteries with newly designed microcoils. The purpose of this paper is to provide a comprehensive summary of the achievements made with the model that shows good reproducibility of the white matter changes characterized by blood-brain barrier disruption, glial activation, oxidative stress, and oligodendrocyte loss following chronic cerebral hypoperfusion. Detailed characterization of this model may help to decipher the substrates associated with impaired memory and move toward a more integrated therapy of vascular cognitive impairment.

Vascular aspects of multiple sclerosis

Three types of vascular dysfunction have been described in multiple sclerosis (MS). First, findings from epidemiological studies suggest that patients with MS have a higher risk for ischaemic stroke than people who do not have MS. The underlying mechanism is unknown, but might involve endothelial dysfunction secondary to inflammatory disease activity and increased plasma homocysteine concentrations. Second, patients with MS have global cerebral hypoperfusion, which might predispose them to the development of ischaemic stroke. The widespread decrease in perfusion in normal-appearing white matter and grey matter in MS seems not to be secondary to axonal degeneration, but might be a result of reduced axonal activity, reduced astrocyte energy metabolism, and perhaps increased blood concentrations of endothelin-1. Data suggest that a subtype of focal MS lesions might have an ischaemic origin, and there seems to be a link between reduced white matter perfusion and cognitive dysfunction in MS. Third, the pathology of MS might be the consequence of a chronic state of impaired venous drainage from the CNS, for which the term chronic cerebrospinal venous insufficiency (CCSVI) has been coined. A number of recent vascular studies do not support the CCSVI theory, but some elements of CCSVI might be explained by slower cerebral venous blood flow secondary to the reduced cerebral perfusion in patients with MS compared with healthy individuals.

Abnormal functional connectivity in patients with vascular cognitive impairment, no dementia: a resting-state functional magnetic resonance imaging study

The functional connectivity (FC) method was used to investigate the changes in the resting state of patients with vascular cognitive impairment, no dementia (VCIND). Resting-state functional magnetic resonance images (fMRIs) were acquired from 16 patients with subcortical ischemic vascular disease (SIVD) who fulfilled the criteria for VCIND, as well as 18 age- and sex-matched subjects with SIVD with no cognitive impairment (control group). Posterior cingulate cortex connectivity was gathered by investigating synchronic low-frequency fMRI signal fluctuations with a temporal correlation method. Compared with the control group, the patients showed FC decrease in the left middle temporal gyrus, the left anterior cingulate/left middle frontal gyrus, the right caudate, the right middle frontal gyrus, and the left medial frontal gyrus/paracentral lobule. There were also some regions that showed increased connectivity. These regions included the right inferior temporal gyrus, the left middle temporal gyrus, the left precentral gyrus, and the left superior parietal lobule. Our findings revealed the change in resting-state patterns of neuronal activity in patients with VCIND. This change may be caused by subcortical white matter lesions that destroyed direct and indirect fiber tract connectivity across the cerebral white matter and influenced the cortical FC and hypoperfusion resulted from small vascular disease. The results of the increased connectivity may be evoked by the compensatory recruitment and plasticity mechanism. Our findings suggest that the simplicity and noninvasiveness of this method makes it a potential tool to help thoroughly understand the pathogenesis of VCIND.

Magnetic resonance imaging in cerebral small vessel disease and its use as a surrogate disease marker

Cerebral small vessel disease is an important cause of vascular cognitive impairment and dementia. On brain imaging, discrete lacunar infarcts and/or more diffuse regions of white matter hyperintensities or leucoaraiosis are seen. Magnetic resonance imaging plays a crucial role in diagnosis, and advanced magnetic resonance imaging techniques are providing new information on disease mechanisms and offering potential as surrogate disease markers. Longitudinal studies have demonstrated detectable progression of lesion load over short time periods, and weak correlations with cognition. Stronger correlations with cognition have been found with diffusion tensor imaging, which is more sensitive to white matter tract structure, supporting a role for disconnection in the pathogenesis of cognitive impairment. Brain volume also consistently correlates with cognition in asymptomatic small vessel disease, sporadic small vessel disease, and Cerebral Autosomal Dominant Arteriopathy with Subcortical Infarcts and Leukoencephalopathy. Gradient echo magnetic resonance imaging identifies microbleeds in a significant proportion of patients with small vessel disease, although their role in clinical management remains to be determined. Surrogate markers to monitor disease progression and evaluate new therapies would have major clinical use. The greater sensitivity of diffusion tensor imaging parameters and brain volume to change, and the stronger correlation of these parameters with cognition, suggest that they may be more powerful surrogates. However, data from longitudinal and intervention studies are required to determine if this is indeed the case. In this systematic review, we describe the use of both conventional and advanced magnetic resonance imaging techniques in patient groups with the full spectrum of clinical small vessel disease, from normal populations with WMH to patients groups with lacunar stroke and dementia.

Quantitative analysis of hemodynamic and metabolic changes in subcortical vascular dementia using simultaneous near-infrared spectroscopy and fMRI measurements

Subcortical vascular dementia (SVD) is a form of vascular dementia from small vessel disease with white matter lesions and lacunes. We hypothesized that hemodynamic and metabolic changes in the cortex during a simple motor task may reflect the impaired neurovascular coupling in SVD. We used fMRI and near-infrared spectroscopy (NIRS) simultaneously, which together provided multiple hemodynamic responses as well as a robust estimation of the cerebral metabolic rate of oxygen (CMRO(2)). During the task periods, the oxy-hemoglobin, total-hemoglobin, blood oxygenation level-dependent (BOLD) response, cerebral blood flow (CBF), and CMRO(2) decreased statistically significantly in the primary motor and somatosensory cortices of SVD patients, whereas the oxygen extraction fraction increased when compared with controls. Notably, the flow-metabolism coupling ratio, n representing the ratio of oxygen supply to its utilization, showed a robust reduction in the SVD patient group (n(Control)=1.99 ± 0.23; n(SVD)=1.08 ± 0.24), which implies a loss of metabolic reserve. These results support the pathological small vessel compromise, including an increased vessel stiffness, impaired vascular reactivity, and impaired neurovascular coupling in SVD. In conclusion, simultaneous measurement by NIRS and fMRI can reveal various hemodynamic and metabolic changes and may be used for as an early detection or monitoring of SVD.

Lacune-associated cerebral hypoperfusion correlates with cognitive testing

The hypothesis was tested among 83 patients with multiple lacunar infarctions that cerebral hypoperfusion will correlate with cognitive impairments. Patients were subdivided according to Cognitive Capacity Screening Examination (CCSE) scores into a cognitively impaired group (Group D, n = 40; mean age, 68.2 years) with CCSE scores between 6 and 25 (mean, 19.9) and a cognitively intact group (Group I, n = 43; mean age, 66.0) with normal scores (mean, 29.4). Gray and white matter tissue densities were measured by plain computed tomography (CT), and their compartmental perfusions were estimated during stable xenon inhalation. Eighty infarcts in basal ganglia and white matter were detected in Group D and 62 in Group I. Cognitive impairments correlated with (a) multiplicity and bilaterality of lacunes; (b) hypertension, diabetes mellitus, and multiplicity of risk factors for stroke; (c) hypoperfusion of white and gray matter, but particularly of frontal white matter; (d) leuko-araiosis; (e) aging; and (f) lower education. The conclusion was that hypertension and diabetes mellitus are potent risk factors for cerebral small vessel disease or arteriolosclerosis ultimately resulting in lacunar infarcts, leuko-araiosis, white matter hypoperfusion, and impaired cognitive test performance.

Blood pressure lowering with valsartan is associated with maintenance of cerebral blood flow and cerebral perfusion reserve in hypertensive patients with cerebral small vessel disease

BACKGROUND

The purpose of this study was to determine the effect of systemic blood pressure-lowering treatment with an angiotensin II receptor blocker, valsartan, on cerebral hemodynamics in patients with hypertension and evidence of cerebral small vessel disease.

METHODS

We used positron emission tomography and acetazolamide challenge tests to measure cerebral blood flow (CBF) and cerebrovascular reserve (CVR) in 8 patients with hypertension (mean age 70.8 years) with lacunar infarcts and white matter lesions before and after valsartan therapy.

RESULTS

Systemic blood pressure was significantly decreased from baseline after treatment with valsartan. The baseline global CBFs before and after treatment were 38.2 +/- 5.6 mL/min/100 g and 39.9 +/- 9.0 mL/min/100 g, respectively. The CVRs before and after treatment were 52.2 +/- 18.4% and 39.7 +/- 18.9%, respectively. Differences in these parameters were not significant. Both regional CBF and CVR in the corona radiata with moderate or severe white matter lesions were also preserved after valsartan therapy compared with those before treatment.

CONCLUSIONS

Cerebral hemodynamics were preserved after blood pressure lowering with valsartan therapy. Valsartan could be a feasible antihypertensive regimen in terms of cerebral circulation in patients with cerebral small vessel disease.

Cerebral white matter: neuroanatomy, clinical neurology, and neurobehavioral correlates

Lesions of the cerebral white matter (WM) result in focal neurobehavioral syndromes, neuropsychiatric phenomena, and dementia. The cerebral WM contains fiber pathways that convey axons linking cerebral cortical areas with each other and with subcortical structures, facilitating the distributed neural circuits that subserve sensorimotor function, intellect, and emotion. Recent neuroanatomical investigations reveal that these neural circuits are topographically linked by five groupings of fiber tracts emanating from every neocortical area: (1) cortico-cortical association fibers; (2) corticostriatal fibers; (3) commissural fibers; and cortico-subcortical pathways to (4) thalamus and (5) pontocerebellar system, brain stem, and/or spinal cord. Lesions of association fibers prevent communication between cortical areas engaged in different domains of behavior. Lesions of subcortical structures or projection/striatal fibers disrupt the contribution of subcortical nodes to behavior. Disconnection syndromes thus result from lesions of the cerebral cortex, subcortical structures, and WM tracts that link the nodes that make up the distributed circuits. The nature and the severity of the clinical manifestations of WM lesions are determined, in large part, by the location of the pathology: discrete neurological and neuropsychiatric symptoms result from focal WM lesions, whereas cognitive impairment across multiple domains--WM dementia--occurs in the setting of diffuse WM disease. We present a detailed review of the conditions affecting WM that produce these neurobehavioral syndromes, and consider the pathophysiology, clinical effects, and broad significance of the effects of aging and vascular compromise on cerebral WM, in an attempt to help further the understanding, diagnosis, and treatment of these disorders.

Hypoperfusion of the cerebral white matter in multiple sclerosis: possible mechanisms and pathophysiological significance

Multiple sclerosis (MS) is a disease of the central nervous system characterized by patchy areas of demyelination, inflammation, axonal loss and gliosis, and a diffuse axonal degeneration throughout the so-called normal-appearing white matter (NAWM). A number of recent studies using perfusion magnetic resonance imaging in both relapsing and progressive forms of MS have shown a decreased perfusion of the NAWM, which does not appear to be secondary to axonal loss. The reduced perfusion of the NAWM in MS might be caused by a widespread astrocyte dysfunction, possibly related to a deficiency in astrocytic beta(2)-adrenergic receptors and a reduced formation of cAMP, resulting in a reduced uptake of K(+) at the nodes of Ranvier and a reduced release of K(+) in the perivascular spaces. Pathologic and imaging studies suggest that ischemic changes might be involved in the development of a subtype of focal demyelinating lesions (type III lesions), and there appears to exist a relationship between decreased white matter perfusion and cognitive dysfunction in patients with MS.

Association between arterial stiffness and cerebral white matter lesions in community-dwelling elderly subjects

The presence of cerebral white matter lesions (WMLs) on MRI is suggested to be a predictive factor for vascular dementia and stroke. To investigate the relationship between arterial stiffness and WMLs, we performed brain MRI to evaluate the presence of two subtypes of WML-periventricular hyperintensities (PVH) and deep white matter lesions (DWML)-and furthermore, determined the brachial-ankle pulse wave velocity (ba-PWV) as a marker of arterial stiffness in 132 elderly asymptomatic subjects (49 men and 83 women, 70.3+/-9.0 years). PVH and DWML were observed in 41 (31.0%) and 53 (40.2%) subjects, respectively. The ba-PWV values were significantly greater in subjects with PVH than in those without. DWML also tended to be associated with ba-PWV, but the correlation was not statistically significant. In multiple logistic regression analysis, age and decreased DBP were independently associated with PVH. ba-PWV was also detected as an independent factor for the appearance of PVH (adjusted odds ratio: 2.84, p=0.015) but not DWML. These results indicate that the increase in arterial stiffness contributes to the pathogenesis of PVH rather than DWML. Although further study is needed to clarify the difference between WML subtypes, our study suggests that the measurement of ba-PWV is a simple and useful tool for detecting cerebral arterial dysfunction.

Hyperglycaemia as a determinant of cognitive decline in patients with type 1 diabetes

Individuals with type 1 diabetes show mild performance deficits in a range of neuropsychological tests compared to healthy controls, but the mechanisms underlying this cognitive deterioration are still poorly understood. Basically, two diabetes-related mechanisms can be postulated: recurrent severe hypoglycaemia and/or chronic hyperglycaemia. Intensive insulin therapy in type 1 diabetes, resulting in a durable improvement of glycaemic control, has been shown to lower the risk of long-term microvascular and macrovascular complications. The down side of striving for strict glycaemic control is the considerably elevated risk of severe hypoglycaemia, sometimes leading to seizure or coma. While retrospective studies in adult patients with type 1 diabetes have suggested an association between a history of recurrent severe hypoglycaemia and a modest or even severe degree of cognitive impairment, large prospective studies have failed to confirm this association. Only fairly recently, better appreciation of the possible deleterious effects of chronic hyperglycaemia on brain function and structure is emerging. In addition, it can be hypothesized that hyperglycaemia associated microvascular changes in the brain are responsible for the cognitive decline in patients with type 1 diabetes. This review presents various pathophysiological considerations concerning the cognitive decline in patients with type 1 diabetes.

Clinical diagnosis of vascular dementia

Vascular dementia (VaD) is a heterogeneous clinical entity based on various vascular pathophysiological processes underlying the subtypes of cerebrovascular disease (CVD). Several diagnostic criteria are currently being used for the clinical diagnosis of VaD, but they are mostly more than 10 years old and need to be renovated including the use of functional brain imaging methods such as single photon emission computerized tomography (SPECT). There is a limitation in the diagnosis based on the strict dichotomy between AD and VaD, and the concept of "AD with CVD" or "mixed dementia" should be included in the clinical diagnosis of VaD.

Regional cerebral blood flow and blood volume in patients with subcortical arteriosclerotic encephalopathy (SAE)

The aim of the present study was a detailed analysis of the regional cerebral blood flow and blood volume in patients with subcortical arteriosclerotic encephalopathy (SAE) by means of functional magnetic resonance imaging (MRI). A group of 26 patients with SAE and a group of 16 age-matched healthy volunteers were examined. Using a well-established dynamic susceptibility contrast-enhanced MRI method, the regional cerebral blood flow (rCBF) and blood volume (rCBV) were quantified for each subject in 12 different regions in the brain parenchyma. As compared to healthy volunteers, patients with SAE showed significantly reduced rCBF and rCBV values in white matter regions and in the occipital cortex. Regions containing predominantly grey matter show almost normal rCBF and rCBV values. In conclusion, quantitative analysis of rCBF and rCBV values demonstrates clearly that SAE is a disease that is associated with a reduced microcirculation predominantly in white matter.

18FDG PET in vascular dementia: differentiation from Alzheimer's disease using voxel-based multivariate analysis

The brain metabolic pattern of vascular dementia (VaD) remains poorly characterized. Univariate voxel-based analysis ignores the functional correlations among structures and may lack sensitivity and specificity. Here, we applied a novel voxel-based multivariate technique to a large ((18)F)2-fluoro-2-deoxy-D-glucose positron emission tomography data set. The sample consisted of 153 subjects, one-third each being probable subcortical VaD, probable Alzheimer disease (AD) (matched for Mini-Mental-State examination (MMSE) and age), and normal controls (NCs). We first applied principal component (PC) analysis and removed PCs significantly correlated to age. The remainders were used as feature vectors in a canonical variate analysis to generate canonical variates (CVs), that is, linear combinations of PC-scores. The first two CVs efficiently separated the groups. CV(1) separated VaD from AD with 100% accuracy, whereas CV(2) separated NC from demented subjects with 72% sensitivity and 96% specificity. Images depicting CV(1) and CV(2) showed that lower metabolism differentiating VaD from AD mainly concerned the deep gray nuclei, cerebellum, primary cortices, middle temporal gyrus, and anterior cingulate gyrus, whereas lower metabolism in AD versus VaD concerned mainly the hippocampal region and orbitofrontal, posterior cingulate, and posterior parietal cortices. The hypometabolic pattern common to VaD and AD mainly concerned the posterior parietal, precuneus, posterior cingulate, prefrontal, and anterior hippocampal regions, and linearly correlated with the MMSE. This study shows the potential of voxel-based multivariate methods to highlight independent functional networks in dementing diseases. By maximizing the separation between groups, this method extracted a metabolic pattern that efficiently differentiated VaD and AD.

Gray matter reduction is correlated with white matter hyperintensity volume: A voxel-based morphometric study in a large epidemiological sample

Both brain atrophy and T2-weighted white matter hyperintensities (WMH) are common findings in the brains of asymptomatic elderly individuals as well as in disease-specific brains. The study of the relationship between these two salient features is therefore important. To investigate such a relationship, we performed a brain magnetic resonance imaging (MRI) study on 397 asymptomatic individuals aged between 60 and 64 years, who were recruited randomly from a large community sample. WMH were delineated on T2-weighted fluid attenuation inversion recovery (FLAIR) whole brain scans using an automated procedure. The results showed that gray matter reduction, subarachnoid CSF (SA-CSF) increase and lateral ventricular dilation were significantly correlated with WMH load. Deep white matter hyperintensity (DWMH) had significant correlation with all three global atrophy indices, but periventricular white matter hyperintensity (PVWMH) was correlated only with gray matter volume. Voxel-based morphometric (VBM) analysis showed that regional gray matter reduction correlated more closely with WMH load of the proximate region than with WMH elsewhere. The results suggest that WMH have a relationship with brain atrophy in middle age, although the study cannot determine which process, i.e. the development of WMH or atrophy, is primary. The study also demonstrates that DWMH has a more significant relationship with structural brain changes, and may therefore be more functionally relevant than PVWMH. Further delineation of this relationship needs a longitudinal study of the changes in both WMH and indices of brain atrophy.

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 blood flow patterns in Binswanger's disease: a SPECT study using three-dimensional stereotactic surface projections

We investigated regional cerebral blood flow (rCBF) patterns in Binswanger's disease (BD) patients using single photon emission computed tomography (SPECT). SPECT data on 22 patients with BD were analyzed using three-dimensional stereotactic surface projections (3D-SSP) and were compared with those of 22 patients with Alzheimer's disease (AD). rCBF patterns in patients with BD were different from those with AD. The BD group had greater CBF reduction in the frontal and anterior cingulate cortices, while the AD group had greater CBF reduction in the temporoparietal and posterior cingulate cortices. However, the rCBF pattern of each patient was more variable, and could be divided into three patterns: anterior cerebral hypoperfusion, posterior cerebral hypoperfusion, and diffuse cerebral hypoperfusion patterns. A distinct CBF reduction in the temporoparietal and/or posterior cingulate cortices, indistinguishable from the CBF pattern observed in AD, was demonstrated in 8 of 22 (36%) patients with BD, in particular there was bilateral hemispheric involvement with a diffuse hypoperfusion pattern. Although no pathological confirmation could be performed, some of the BD patients with CBF reduction in the posterior cerebral cortices may represent additional changes in the brain due to AD. In the future, a longitudinal study including pathology will be needed to determine whether these patients have coexisting AD pathology.

Long-term measurement of cerebral blood flow and metabolism in a rat chronic hypoperfusion model

1. Rat bilateral common carotid artery occlusion (BCAO) was used as a chronic cerebral hypoperfusion model. We observed autoradiographically the long-term changes in regional cerebral blood flow (rCBF) and regional cerebral glucose utilization (rCGU) after 2 days and 1, 4 and 8 weeks of BCAO and in controls. Regions evaluated included the cerebral cortex, white matter and basal ganglia. Pathological changes were also observed with Klüver-Barrera and haematoxylin-eosin staining. 2. After 2 days, rCBF was significantly reduced to 33-58% in the cortex, white matter and amygdala and similar reductions were observed after 1 week. 3. After 4 weeks, rCBF recovered; however, rCBF remained significantly reduced in the occipital cortex, white matter, globus pallidus and substantia nigra. 4. After 2 days, rCGU was mostly maintained but, after 1 week, rCGU was reduced significantly to 40-70% in the cortex, white matter, basal ganglia and thalamus. Four weeks later, these reductions were no longer seen. 5. Rarefaction of the white matter was observed from 1 week. 6. These results showed that the BCAO in rats is an appropriate model for chronic cerebral hypoperfusion and that uncoupling of rCBF and rCGU was observed from 2 days until 4 weeks in the white matter.

Analysis of cerebral blood flow of subcortical vascular dementia with single photon emission computed tomography: adaptation of statistical parametric mapping

BACKGROUND AND OBJECTIVES

Subcortical vascular dementia (VaD) is a relatively homogeneous subtype of VaD, but the mechanisms of cognitive dysfunction of subcortical VaD are not fully understood. This study investigates the changes of cerebral blood flow (CBF) in patients with subcortical VaD and the contribution of the white matter hyperintensity (WMHI) and clinical severity to CBF changes.

METHODS

99mTc-ethyl cysteinate dimer single photon emission computed tomography (SPECT) was performed to measure the regional CBF and statistical parametric mapping SPM99 software was applied to automated and objective analysis of the SPECT image data. Twenty-three patients (12 male, 11 female) with mild to moderate dementia who met both the criteria of the DSM-IV and probable and possible NINDS-AIREN for VaD and had subcortical white matter changes and lacunar infarctions in brain MRI were evaluated against 17 normal control subjects (7 male, 10 female). The severity of the WMHI was measured by the semi-quantitative scale method proposed by Mäntyla. The Clinical Dementia Rating scale measured the severity of dementia.

RESULTS

SPM analysis of the SPECT image reveals significantly reduced regional CBF in the right thalamus, left caudate nucleus, cingulate, bilateral superior temporal, and left ventral subcallosal gyri in subcortical VaD patients compared to the normal controls (corrected P<0.001). Of four WMHIs, only the deep WMHI was associated with the small CBF reduction in the left superior temporal gyrus (uncorrected P<0.01). The reduction of the CBF according to the severity of dementia was noted in the anterior and posterior association areas (uncorrected P<0.01).

CONCLUSIONS

Our study suggests that cognitive dysfunction of subcortical VaD may be related to the reduction of the CBF in the brain areas mentioned, which are probably not associated with the severity of periventricular WMHI and dementia.

Impact of subcortical ischemic lesions on behavior and cognition

Both cerebrovascular disease and AD are common in the elderly. There are various types of underlying damage to tissue and vessels in vascular cognitive impairment, and the neural mechanisms producing cognitive impairment and the clinical picture are different among the subtypes. Among them, small subcortical infarcts disrupting cortico-subcortical circuits and white matter lesions are the commonest types, and the combination of these two types of lesions might be more realistic than each pure form. Moreover, cognitive impairment of vascular origin may be superimposed on AD. Both vascular and degenerative mechanisms contribute to the development of cognitive impairment, especially in old age, whether they are two independent parallel processes or interacting pathologies. Subcortical small lesions involving the thalamus, caudate, and globus pallidus disrupt cortico-subcortical circuits, resulting in cognitive dysfunction. Disruption of the frontal-subcortical circuits leads to cognitive impairment with striking frontal lobe features, and disruption of the memory-related circuits leads to amnesia. White matter changes, which are certainly related to chronic cerebral ischemia in some patients, are another issue. Patients with dementia and white matter changes may have either AD with cerebrovascular changes or a form of VaD, or a combination of these two etiologies. However, our series of studies have suggested that white matter changes in AD patients are superimposed phenomena of vascular origin and that white matter changes contribute to specific neurological and neuropsychiatric manifestations, but not to global cognitive impairment, which is more closely associated with the degenerative process.

Subcortical ischaemic vascular dementia

Vascular dementia is the second most common type of dementia. The subcortical ischaemic form (SIVD) frequently causes cognitive impairment and dementia in elderly people. SIVD results from small-vessel disease, which produces either arteriolar occlusion and lacunes or widespread incomplete infarction of white matter due to critical stenosis of medullary arterioles and hypoperfusion (Binswanger's disease). Symptoms include motor and cognitive dysexecutive slowing, forgetfulness, dysarthria, mood changes, urinary symptoms, and short-stepped gait. These manifestations probably result from ischaemic interruption of parallel circuits from the prefrontal cortex to the basal ganglia and corresponding thalamocortical connections. Brain imaging (computed tomography and magnetic resonance imaging) is essential for correct diagnosis. The main risk factors are advanced age, hypertension, diabetes, smoking, hyperhomocysteinaemia, hyperfibrinogenaemia, and other conditions that can cause brain hypoperfusion such as obstructive sleep apnoea, congestive heart failure, cardiac arrhythmias, and orthostatic hypotension. Cerebral autosomal dominant arteriopathy with subcortical infarcts and leucoencephalopathy (CADASIL)and some forms of cerebral amyloid angiopathy have a genetic basis. Treatment is symptomatic and prevention requires control of treatable risk factors.

Persistent hypertension does not alter the cerebral blood flow and glucose utilization in young-adult Dahl salt-sensitive rats

The Dahl- Iwai salt-sensitive (DS) rat develops hypertension due to a high-salt diet without any structural alterations of the brain arteries and arterioles. We investigated the effect of persistent hypertension on the regional cerebral blood flow (rCBF) and regional cerebral glucose utilization (rCGU) in the DS rats. The rats were fed either a high-salt diet (HSD; 8% NaCl, n = 5) or a low-salt diet (LSD; 0.3% NaCl, n = 6) from 8 to 16 weeks of age, and the HSD group developed hypertension lasting for 1 month. At 16 weeks of age, the rCBF was measured in the sensorimotor and visual cortices using the hydrogen clearance method, and the rCGU was measured in 26 different brain structures using the [(14)C]deoxyglucose method. The mean arterial pressure was significantly higher in the HSD group (168+/-7 mm Hg) than in the LSD group (139+/-3 mm Hg) (P < 0.01). The mean rCBF and the rCGU values tended to be lower in the HSD group than in the LSD group; however, there were no statistically significant differences except for the reduced rCGU value in the nucleus accumbens. These results suggest that hypertension itself does not alter either the rCBF or the rCGU in young-adult DS rats. This indicates that the functional / structural changes of the cerebral arteries and arterioles that are associated with hypertension appear to be responsible for altered rCBF and rCGU in other animal models of hypertension.