Quantitative magnetic resonance analysis in vascular dementia

Contribution of white matter hyperintensities to ventricular enlargement in older adults

Lateral ventricles might increase due to generalized tissue loss related to brain atrophy. Alternatively, they may expand into areas of tissue loss related to white matter hyperintensities (WMH). We assessed longitudinal associations between lateral ventricle and WMH volumes, accounting for total brain volume, blood pressure, history of stroke, cardiovascular disease, diabetes and smoking at ages 73, 76 and 79, in participants from the Lothian Birth Cohort 1936, including MRI data from all available time points. Lateral ventricle volume increased steadily with age, WMH volume change was more variable. WMH volume decreased in 20% and increased in remaining subjects. Over 6 years, lateral ventricle volume increased by 3% per year of age, 0.1% per mm Hg increase in blood pressure, 3.2% per 1% decrease of total brain volume, and 4.5% per 1% increase of WMH volume. Over time, lateral ventricle volumes were 19% smaller in women than men. Ventricular and WMH volume changes are modestly associated and independent of general brain atrophy, suggesting that their underlying processes do not fully overlap.

Callosal tissue loss parallels subtle decline in psychomotor speed. a longitudinal quantitative MRI study. The LADIS Study

Cross-sectional studies have suggested that corpus callosum (CC) atrophy is related to impairment in global cognitive function, mental speed, and executive functions in the elderly. Longitudinal studies confirming these findings have been lacking. We investigated whether CC tissue loss is associated with change in cognitive performance over time in subjects with age-related white matter lesions (WML). Two-hundred-fifty-three subjects, aged 65-84 years, were evaluated by using repeated MRI and neuropsychological evaluation at baseline and after 3 years. The effect of overall and regional CC tissue loss on cognitive decline was analyzed with hierarchical linear regression models. After controlling for age, sex, education, and baseline cognitive performance, the rates of tissue loss in the total CC area, and in rostrum/genu and midbody subregions were significantly associated with decline in a compound measure of cognitive speed and motor control, but not in those of executive functions, memory, or global cognitive function. Total CC area and midbody remained significant predictors of speed also after adjusting for baseline WML volume, WML progression, and global brain atrophy. However, the relationship between anterior CC and speed performance was mediated by WML volume. In conclusion, the overall and regional rate of CC tissue loss parallels longitudinal slowing of psychomotor performance. The adverse effect of CC tissue loss on psychomotor function may be driven by altered interhemispheric information transfer between homologous cortical areas.

Corpus callosum atrophy in patients with mild Alzheimer's disease

BACKGROUND/OBJECTIVES

Several studies have found atrophy of the corpus callosum (CC) in patients with Alzheimer's disease (AD). However, it remains unclear whether callosal atrophy is already present in the early stages of AD, and to what extent it may be associated with other structural changes in the brain, such as age-related white matter changes (ARWMC) and progression of the disease.

METHODS

Twenty-eight patients in the early stages of AD and 50 non-demented elderly subjects with varying degrees of ARWMC were investigated using MRI. The CC was assessed semi-automatically, and ARWMC were rated according to the Fazekas scale.

RESULTS

A significant difference in posterior CC size could be detected between non-demented elderly subjects and early stage AD patients. The sizes of the total CC, rostral body and splenium at baseline were correlated with change from baseline MMSE score after a 1-year follow-up in AD patients. There was no association between CC size and ARWMC.

CONCLUSIONS

The present findings indicate that posterior CC atrophy is present in mild AD independently of ARWMC. Furthermore, CC atrophy may be associated with cognitive deterioration.

Regional white matter integrity differentiates between vascular dementia and Alzheimer disease

BACKGROUND AND PURPOSE

Considerable clinical and radiological overlap between vascular dementia (VaD) and Alzheimer disease (AD) often makes the diagnosis difficult. Diffusion-tensor imaging studies showed that fractional anisotropy (FA) could be a useful marker for white matter changes. This study aimed to identify regional FA changes to identify a biomarker that could be used to differentiate VaD from AD.

METHODS

T1-weighted and diffusion-tensor imaging scans were obtained in 13 VaD patients, 16 AD patients, and 22 healthy elderly controls. We used tract-based spatial statistics to study regional changes in fractional anisotropy in AD, VaD, and elderly controls. We then used probabilistic tractography to parcel the corpus callosum in 7 regions according to its connectivity with major cerebral cortices using diffusion-tensor imaging data set. We compared the volume and mean FA in each set of transcallosal fibers between groups using ANOVA and then applied a discriminant analysis based on FA and T2-weighted imaging measures.

RESULTS

FA reduction in forceps minor was the most significant area of difference between AD and VaD. Segmentation of the corpus callosum using tractography and comparison of FA changes of each segment confirmed the FA changes in transcallosal prefrontal tracts of patients with VaD when compared to AD. The best discriminant model was the combination of transcallosal prefrontal FA and Fazekas score with 87.5% accuracy, 100% specificity, and 93% sensitivity (P<0.0001).

CONCLUSIONS

Integrating mean FA in the forceps minor to the Fazekas score provides a useful quantitative marker for differentiating AD from VaD.

Regional white matter pathology in mild cognitive impairment: differential influence of lesion type on neuropsychological functioning

BACKGROUND AND PURPOSE

Associations between regional white matter lesion pathology and neuropsychological performance across the aging spectrum are not well understood and, to date, research has been largely contradictory and inconclusive. The current study set out to clarify some of the inconsistencies in the literature by relating volumetric analyses of white matter lesions (deep white matter lesions and periventricular lesions) to neuropsychological performance in a large clinical sample of older adults diagnosed with mild cognitive impairment.

METHODS

Seventy older adults with mild cognitive impairment were administered a comprehensive neuropsychological battery. White matter lesions identified on T2-weighted FLAIR images were quantified using a semi-automated volumetric approach (pixel thresholding).

RESULTS

Results showed that, in contrast to performance on memory and naming tasks, total white matter lesions strongly predicted executive impairments, slowed processing speed, and visuospatial/construction difficulties. In addition, separate regression analyses demonstrated that results were primarily accounted for by deep white matter lesions (but not periventricular lesions), most likely due to frontal-subcortical circuitry disruption. Moreover, deep white matter lesions, but not periventricular lesions, significantly predicted overall poorer neuropsychological functioning after controlling for age, education, and level of depression.

CONCLUSIONS

Taken together, findings demonstrate a differential influence of lesion type on cognitive impairment in mild cognitive impairment and implicate deep white matter lesions as being most detrimental in terms of neuropsychological functioning. Clinical, theoretical, and methodological implications of these results are discussed.

Corpus callosum atrophy is associated with mental slowing and executive deficits in subjects with age-related white matter hyperintensities: the LADIS Study

BACKGROUND

Previous research has indicated that corpus callosum atrophy is associated with global cognitive decline in neurodegenerative diseases, but few studies have investigated specific cognitive functions.

OBJECTIVE

To investigate the role of regional corpus callosum atrophy in mental speed, attention and executive functions in subjects with age-related white matter hyperintensities (WMH).

METHODS

In the Leukoaraiosis and Disability Study, 567 subjects with age-related WMH were examined with a detailed neuropsychological assessment and quantitative magnetic resonance imaging. The relationships of the total corpus callosum area and its subregions with cognitive performance were analysed using multiple linear regression, controlling for volume of WMH and other confounding factors.

RESULTS

Atrophy of the total corpus callosum area was associated with poor performance in tests assessing speed of mental processing--namely, trail making A and Stroop test parts I and II. Anterior, but not posterior, corpus callosum atrophy was associated with deficits of attention and executive functions as reflected by the symbol digit modalities and digit cancellation tests, as well as by the subtraction scores in the trail making and Stroop tests. Furthermore, semantic verbal fluency was related to the total corpus callosum area and the isthmus subregion.

CONCLUSIONS

Corpus callosum atrophy seems to contribute to cognitive decline independently of age, education, coexisting WMH and stroke. Anterior corpus callosum atrophy is related to the frontal-lobe-mediated executive functions and attention, whereas overall corpus callosum atrophy is associated with the slowing of processing speed.

Neuroradiological findings in vascular dementia

INTRODUCTION

There are multiple diagnostic criteria for vascular dementia (VaD) that may define different populations. Utilizing the criteria of the National Institute of Neurological Disorders and Stroke and Association Internationale pour la Recherche et l'Enseignement en Neurosciences (NINDS-AIREN) has provided improved consistency in the diagnosis of VaD. The criteria include a table listing brain imaging lesions associated with VaD.

METHODS

The different neuroradiological aspects of the criteria are reviewed based on the imaging data from an ongoing large-scale clinical trial testing a new treatment for VaD. The NINDS-AIREN criteria were applied by a centralized imaging rater to determine eligibility for enrollment in 1,202 patients using brain CT or MRI.

RESULTS

Based on the above data set, the neuroradiological features that are associated with VaD and that can result from cerebral small-vessel disease with extensive leukoencephalopathy or lacunae (basal ganglia or frontal white matter), or may be the consequence of single strategically located infarcts or multiple infarcts in large-vessel territories, are illustrated. These features may also be the consequence of global cerebral hypoperfusion, intracerebral hemorrhage, or other mechanisms such as genetically determined arteriopathies.

CONCLUSION

Neuroimaging confirmation of cerebrovascular disease in VaD provides information about the topography and severity of vascular lesions. Neuroimaging may also assist with the differential diagnosis of dementia associated with normal pressure hydrocephalus, chronic subdural hematoma, arteriovenous malformation or tumoral diseases.

White matter hyperintensities are significantly associated with cortical atrophy in Alzheimer's disease

BACKGROUND AND OBJECTIVE

Methodological variability in the assessment of white matter hyperintensities (WMH) in dementia may explain inconsistent reports of its prevalence and impact on cognition. We used a method of brain MRI segmentation for quantifying both tissue and WMH volumes in Alzheimer's disease (AD) and examined the association between WMH and structural and cognitive variables.

METHODS

A consecutive series of 81 patients meeting NINCDS-ADRDA criteria for probable AD was studied. Nineteen healthy volunteers of comparable age served as the control group. Patients had a complete neurological and neuropsychological evaluation, and a three dimensional MRI was obtained. Images were segmented into grey matter, white matter, and cerebrospinal fluid. WMH were edited on segmented images, and lobar assignments were based on Talairach coordinates.

RESULTS

Mild and moderate to severe AD patients had significantly more WMH than controls (p<0.05). WMH preferentially involved the frontal lobes (70%), were inversely correlated with grey matter cortical volume (R(2) = 0.23, p<0.001), and were significantly associated with vascular risk factors and with a worse performance on memory tasks.

CONCLUSION

Objective measurements of tissue volumes in AD demonstrated that WMH are significantly related to cortical atrophy and neuropsychological impairment.

Hypertension and neuronal degeneration in excised rat spinal cord studied by high-b value q-space diffusion magnetic resonance imaging

Hypertension is one of the major risk factors of stroke and vascular dementia (VaD). We used stroke prone spontaneous hypertensive rats (SPSHRs) as a model for neuronal degeneration frequently occurring in humans with vascular disease. Recently, high b value q-space diffusion-weighted imaging (DWI) was shown to be very sensitive to the pathophysiological state of the white matter. We studied the spinal cords of SPSHR rats ex vivo after the appearance of motor impairments using diffusion anisotropy and q-space diffusion imaging (measured at a high b value of up to 1 x 10(5) s/mm(2)). The diffusion anisotropy images computed from low b value data set (b(max) approximately 2500 s/mm(2)) showed a small but statistically significant decrease (approximately 12%, P < 0.05) in the diffusion anisotropy in the spinal cords of the SPSHR group as compared to control rats. However, more significant changes were found in the high b value q-space diffusion images. The q-space displacement values in the white matter of the SPSHR group were found to be higher by more than 70% (P < 0.002) than that of the control group. These observations concurred with electron microscopy (EM) that showed significant demyelination in the spinal cords of the SPSHR group. These results seem to indicate that high b value q-space DWI might be a sensitive method for following demyelination and axonal loss associated with vascular insults.

Temporal changes in brain volume and cognition in a randomized treatment trial of vascular dementia

OBJECTIVE

To measure changes in brain and ischemic volume over time by magnetic resonance imaging (MRI) as part of a randomized treatment trial of vascular dementia.

METHODS

Participants who met criteria for vascular dementia underwent comprehensive neurological and neuropsychological testing on entrance, during, and at completion of the 1-year study. For those centers who had easily available MRI, MRI of the brain was to be performed on entry and completion of the study. Image analysis was performed on all balanced and T2-weighted MR films to determine ventricular, sulcal, ischemic, and hemispheric brain volumes.

RESULTS

Of the 105 patients who met the criteria for vascular dementia, 40 had a baseline MRI study that met protocol requirements and was of excellent image quality. The baseline ventricular volume in these 40 patients with high-quality MR correlated with most measures of cognitive and behavioral function, including the total Alzheimer's Disease Assessment Score (ADAS) (r = 0.51, P = .0024), as well as activities of daily living (r = 0.61, P = .0002). The baseline ischemic brain volume correlated well only with the gait and postural stability scale (r = 0.74, P = .009). Of the 40 participants, 25 had MRI studies at baseline and at completion of the study that were comparable and of excellent image quality. For these 25 patients, the mean ventricular volumes increased by 9% over the study year (P = .001) and the mean ischemic brain volume increased by 18% (P = .01). Temporal changes in the sulcal and nonischemic brain volume did not reach significance. None of the 14 clinical score measures changed significantly between baseline and completion of the study in these 25 patients.

CONCLUSION

In summary, ventricular volume correlated well with cognitive measures in patients with vascular dementia and was a more sensitive marker for change during the study year than the clinical scales used in this study. This study also points out the practical limitations of brain imaging as a surrogate measure of clinical outcome in multicenter randomized treatment trials of brain disease.

Magnetic resonance imaging and magnetic resonance spectroscopy in dementias

This article reviews recent studies of magnetic resonance imaging and magnetic resonance spectroscopy in dementia, including Alzheimer's disease, frontotemporal dementia, dementia with Lewy bodies, idiopathic Parkinson's disease, Huntington's disease, and vascular dementia. Magnetic resonance imaging and magnetic resonance spectroscopy can detect structural alteration and biochemical abnormalities in the brain of demented subjects and may help in the differential diagnosis and early detection of affected individuals, monitoring disease progression, and evaluation of therapeutic effect.

Corpus callosum atrophy in patients with leukoaraiosis may indicate global cognitive impairment

BACKGROUND AND PURPOSE

The extent of white matter high-intensity lesions (WMLs) on T2-weighted MR images may be an indicator of cognitive impairment, especially impairment related to frontal lobe dysfunction. However, it is unclear whether the extent of WMLs is an independent predictor of cognitive impairment. In patients with extensive WMLs, atrophy of the corpus callosum may be an important predictor of global cognitive impairment. The purpose of this study was to investigate the relation of the extent of WMLs and callosal size with cognitive functions in a patient population with a wide range of extent of WMLs.

METHODS

We studied 62 patients, aged 49 to 86 years, who underwent MRI because of neurological symptoms and were diagnosed as having lacunar stroke or no specific neurological disease: 28 with lacunar infarcts and 34 without. Multivariate analysis was used to test the independent predictive value of patient age, sex, educational level, other medical illness, lacunar infarct, corpus callosum area, and extent of WMLs with respect to scores of Mini-Mental State Examination or verbal fluency task.

RESULTS

Only callosal size and age were significant independent predictors of the scores of the Mini-Mental State Examination, while only the extent of WMLs was an independent predictor of the score of the verbal fluency task.

CONCLUSIONS

Callosal atrophy may be an important predictor of global cognitive impairment in patients with WMLs, whereas the extent of WMLs per se may be related to impairment of frontal lobe function independent of callosal atrophy.