Changes in integrity of normal-appearing white matter in patients with moyamoya disease: a diffusion tensor imaging study

Resolution of white matter hyperintensity after surgical revascularization in moyamoya disease - A report of three cases

Background

Moyamoya disease often presents white matter hyperintensity (WMH) lesions on fluid-attenuated inversion recovery (FLAIR) images, which is generally accepted as irreversible. We, herein, describe three cases of moyamoya disease with WMH lesions that regressed or disappeared after surgical revascularization.

Case Description

This report included two pediatric and one young adult case that developed transient ischemic attacks or ischemic stroke due to bilateral Moyamoya disease. Before surgery, five of their six hemispheres had WMH lesions in the subcortical and/or periventricular white matter on FLAIR images. The lesions included morphologically two different patterns: "Striated" and "patchy" morphology. In all of them, combined bypass surgery was successfully performed on both sides, and no cerebrovascular events occurred during follow-up periods. On follow-up magnetic resonance examinations, the "striated" WMH lesions completely disappeared within six months, while the "patchy" WMH lesions slowly regressed over 12 months.

Conclusion

Based on radiological findings and the postoperative course of the WMH lesions, the "striated" WMH lesions may represent the inflammation or edema along the neuronal axons due to cerebral ischemia, while the "patchy" WMH lesions may represent vasogenic edema in the white matter through the blood-brain barrier breakdown. Earlier surgical revascularization may resolve these WMH lesions in Moyamoya disease.

White and Gray Matter Perfusion in Children with Moyamoya Angiopathy after Revascularization Surgery

INTRODUCTION

Surgical revascularization is very effective in patients with moyamoya angiopathy (MMA) and leads to improvements in cortical perfusion parameters. However, changes in white matter hemodynamics are still underestimated. To date, only a few studies have examined brain perfusion changes within deep white matter after bypass surgery in patients with MMA.

METHODS

Ten children with MMA were evaluated using the CT perfusion technique before and after revascularization surgery. Brain perfusion parameters within gray and white matter were compared before and after surgery. The correlations between the perfusion parameters before surgery and the Suzuki stage, as well as between the perfusion parameters and the cognitive scores, were also evaluated.

RESULTS

Brain perfusion parameters improved significantly in both gray matter (predominantly due to cerebral blood flow within the anterior circulation, p < 0.01) and white matter (predominantly due to cerebral blood volume within the semiovale centrum, p < 0.001). We revealed that the pattern of improvement in perfusion in white matter differed from the pattern of improvement in perfusion in gray matter. Significant correlations were revealed between the Suzuki stage before surgery and the perfusion parameters within the posterior cerebral artery circulation (adjusted p < 0.05). There were also significant correlations between cognitive scores and brain perfusion parameters in gray matter and white matter (adjusted p < 0.05).

CONCLUSIONS

The perfusion parameters of gray matter and white matter in the brain improve differently after bypass surgery in patients with MMA. Different hemodynamics within these compartments could explain this.

Diffusion-Weighted Magnetic Resonance Imaging Demonstrates White Matter Alterations in Watershed Regions in Children With Moyamoya Without Stroke or Silent Infarct

BACKGROUND

Moyamoya is a disease with progressive cerebral arterial stenosis leading to stroke and silent infarct. Diffusion-weighted magnetic resonance imaging (dMRI) studies show that adults with moyamoya have significantly lower fractional anisotropy (FA) and higher mean diffusivity (MD), axial diffusivity (AD), and radial diffusivity (RD) compared with controls, which raises concern for unrecognized white matter injury. Children with moyamoya have significantly lower FA and higher MD in their white matter compared with controls. However, it is unknown which white matter tracts are affected in children with moyamoya.

METHODS

We present a cohort of 15 children with moyamoya with 24 affected hemispheres without stroke or silent infarct compared with 25 controls. We analyzed dMRI data using unscented Kalman filter tractography and extracted major white matter pathways with a fiber clustering method. We compared the FA, MD, AD, and RD in each segmented white matter tract and combined white matter tracts found within the watershed region using analysis of variance.

RESULTS

Age and sex were not significantly different between children with moyamoya and controls. Specific white matter tracts affected included inferior fronto-occipital fasciculus, inferior longitudinal fasciculus, superior longitudinal fasciculus, thalamofrontal, uncinate fasciculus, and arcuate fasciculus. Combined watershed region white matter tracts in children with moyamoya had significantly lower FA (-7.7% ± 3.2%, P = 0.02) and higher MD (4.8% ± 1.9%, P = 0.01) and RD (8.7% ± 2.8%, P = 0.002).

CONCLUSIONS

Lower FA with higher MD and RD is concerning for unrecognized white matter injury. Affected tracts were located in watershed regions suggesting that the findings may be due to chronic hypoperfusion. These findings support the concern that children with moyamoya without overt stroke or silent infarction are sustaining ongoing injury to their white matter microstructure and provide practitioners with a noninvasive method of more accurately assessing disease burden in children with moyamoya.

White matter structural and network topological changes in moyamoya disease with limb paresthesia: A study based on diffusion kurtosis imaging

Purpose

To investigate the structural and network topological changes in the white matter (WM) in MMD patients with limb paresthesia by performing diffusion kurtosis imaging (DKI).

Materials and methods

A total of 151 MMD patients, including 46 with left-limb paresthesia (MLP), 52 with right-limb paresthesia (MRP), and 53 without paresthesia (MWP), and 28 healthy controls (HCs) underwent whole-brain DKI, while the surgical patients were reexamined 3-4 months after revascularization. The data were preprocessed to calculate the fractional anisotropy (FA) and mean kurtosis (MK) values. Voxel-wise statistics for FA and MK images were obtained by using tract-based spatial statistics (TBSS). Next, the whole-brain network was constructed, and global and local network parameters were analyzed using graph theory. All parameters were compared among the HC, MWP, MLP, and MRP groups, and changes in the MMD patients before and after revascularization were also compared.

Results

The TBSS analysis revealed significant reductions in FA and MK in extensive WM regions in the three patient groups. In comparison with the MWP group, the MLP group showed reductions in FA and MK in both right and left WM, mainly in the right WM, while the MRP group mainly showed a reduction in FA in the left WM region and demonstrated no significant change in MK. The graph theoretical analysis showed decreased global network efficiency, increased characteristic path length, and increased sigma in the MWP, MRP, and MLP groups in comparison with the HC group. Among local network parameters, the nodal efficiency decreased in the bilateral MFG and IFGtriang, while the degree decreased in the MFG.L and bilateral IFGtriang. Patients with right-limb paresthesia showed the lowest nodal efficiency and degree in MFG.L and IFGtriang.L, while those with left-limb paresthesia showed the lowest nodal efficiency in MFG.R and IFGtriang.R and the lowest degree in IFGtriang.R.

Conclusion

A DKI-based whole-brain structural and network analysis can be used to detect changes in WM damage and network topological changes in MMD patients with limb paresthesia. FA is more sensitive than MK in detecting WM injury, while MFG and IFGtriang are the key nodes related to the development of acroparesthesia.

Application of DTI and fMRI in moyamoya disease

Moyamoya disease (MMD) is a chronic and progressive cerebrovascular stenosis or occlusive disease that occurs near Willis blood vessels. Diffusion tensor imaging (DTI) and functional magnetic resonance imaging (fMRI) are used to detect the microstructure of white matter and the function of gray matter, respectively. The damage of these structures will lead to the change of cognitive level in patients with moyamoya disease. In this paper, the principles of DTI and fMRI, their applications and challenges in moyamoya disease are reviewed.

Early Diffusion Magnetic Resonance Imaging Changes in Normal-Appearing Brain in Pediatric Moyamoya Disease

BACKGROUND

Moyamoya disease often leads to ischemic strokes visible on diffusion-weighted imaging (DWI) and T2-weighted magnetic resonance imaging (MRI) with subsequent cognitive impairment. In adults with moyamoya, apparent diffusion coefficient (ADC) is correlated with regions of steal phenomenon and executive dysfunction prior to white matter changes.

OBJECTIVE

To investigate quantitative global diffusion changes in pediatric moyamoya patients prior to explicit structural ischemic damage.

METHODS

We retrospectively reviewed children (<20 yr old) with moyamoya disease and syndrome who underwent bypass surgery at our institution. We identified 29 children with normal structural preoperative MRI and without findings of cortical infarction or chronic white matter ischemic changes. DWI datasets were used to calculate ADC maps for each subject as well as for 60 age-matched healthy controls. Using an atlas-based approach, the cerebral white matter, cerebral cortex, thalamus, caudate, putamen, pallidum, hippocampus, amygdala, nucleus accumbens, and brainstem were segmented in each DWI dataset and used to calculate regional volumes and ADC values.

RESULTS

Multivariate analysis of covariance using the regional ADC and volume values as dependent variables and age and gender as covariates revealed a significant difference between the groups (P < .001). Post hoc analysis demonstrated significantly elevated ADC values for children with moyamoya in the cerebral cortex, white matter, caudate, putamen, and nucleus accumbens. No significant volume differences were found.

CONCLUSION

Prior to having bypass surgery, and in the absence of imaging evidence of ischemic stroke, children with moyamoya exhibit cerebral diffusion changes. These findings could reflect microstructural changes stemming from exhaustion of cerebrovascular reserve.

MR Diffusional Kurtosis Imaging-Based Assessment of Brain Microstructural Changes in Patients with Moyamoya Disease before and after Revascularization

BACKGROUND AND PURPOSE

Conventional imaging examinations are insufficient to accurately assess brain damage in patients with Moyamoya disease. Our aim was to observe brain microstructural changes in patients with Moyamoya disease by diffusional kurtosis imaging and provide support data for application of this technique in individualized assessment of disease severity and surgical outcome among patients with Moyamoya disease.

MATERIALS AND METHODS

A total of 64 patients with Moyamoya disease and 15 healthy volunteers underwent diffusional kurtosis imaging, and a second scanning was offered to surgical patients 3-4 months after revascularization. The diffusional kurtosis imaging parameter maps were obtained for mean kurtosis, axial kurtosis, radial kurtosis, fractional anisotropy, mean diffusivity, axial diffusivity, and radial diffusivity. The parameter values were measured in sensory pathway-related regions for all subjects. Differences in diffusional kurtosis imaging parameters of these brain regions were examined for healthy volunteers, patients without acroparesthesia, and asymptomatic and symptomatic sides of patients with acroparesthesia. Changes in diffusional kurtosis imaging parameters of patients with Moyamoya disease before and after revascularization were compared.

RESULTS

Compared with healthy volunteers, patients with Moyamoya disease showed decreased mean kurtosis, axial kurtosis, radial kurtosis, and fractional anisotropy in the corona radiata. Similarly, mean kurtosis, radial kurtosis, and fractional anisotropy decreased in the posterior limb of the internal capsule, whereas axial kurtosis decreased and radial kurtosis increased in the thalami of patients with Moyamoya disease compared with healthy volunteers. Compared with the asymptomatic contralateral hemisphere, the symptomatic group showed increased mean kurtosis in the contralateral primary somatosensory cortex, increased fractional anisotropy in the contralateral corona radiata and posterior limb of the internal capsule, and decreased axial kurtosis in the contralateral thalamus. Among patients with Moyamoya disease with acroparesthesia, mean kurtosis decreased in the primary somatosensory cortex on the operated side following revascularization.

CONCLUSIONS

The diffusional kurtosis imaging technique is applicable to patients with Moyamoya disease for detecting brain microstructural changes in white and gray matter before and after revascularization; this feature is useful in the assessment of disease severity and surgical outcome.

Cognitive reserve moderates the relationship between neuropsychological performance and white matter fiber bundle length in healthy older adults

Recent work using novel neuroimaging methods has revealed shorter white matter fiber bundle length (FBL) in older compared to younger adults. Shorter FBL also corresponds to poorer performance on cognitive measures sensitive to advanced age. However, it is unclear if individual factors such as cognitive reserve (CR) effectively moderate the relationship between FBL and cognitive performance. This study examined CR as a potential moderator of cognitive performance and brain integrity as defined by FBL. Sixty-three healthy adults underwent neuropsychological evaluation and 3T brain magnetic resonance imaging. Cognitive performance was measured using the Repeatable Battery of Assessment of Neuropsychological Status (RBANS). FBL was quantified from tractography tracings of white matter fiber bundles, derived from the diffusion tensor imaging. CR was determined by estimated premorbid IQ. Analyses revealed that lower scores on the RBANS were associated with shorter whole brain FBL (p = 0.04) and lower CR (p = 0.01) CR moderated the relationship between whole brain FBL and RBANS score (p < 0.01). Tract-specific analyses revealed that CR also moderated the association between FBL in the hippocampal segment of the cingulum and RBANS performance (p = 0.03). These results demonstrate that lower cognitive performance on the RBANS is more common with low CR and short FBL. On the contrary, when individuals have high CR, the relationship between FBL and cognitive performance is attenuated. Overall, CR protects older adults against lower cognitive performance despite age-associated reductions in FBL.

Pathophysiological consideration of medullary streaks on FLAIR imaging in pediatric moyamoya disease

OBJECTIVE Medullary streaks detected on fluid-attenuated inversion recovery (FLAIR) imaging have been considered to be reflected ischemic regions in pediatric moyamoya disease. The purpose of this study was to evaluate these medullary streaks both clinically and radiologically and to discuss associated pathophysiological concerns. METHODS The authors retrospectively reviewed data from 14 consecutive pediatric patients with moyamoya disease treated between April 2009 and June 2016. Clinical and radiological features and postoperative imaging changes were analyzed. In 4 patients, hyperintense medullary streaks on FLAIR imaging (HMSF) at the level of the centrum semiovale were detected. RESULTS The HMSF were coincident with hyperintense medullary streaks on a T2-weighted image, though they were not completely coincident with the vasculature on either a T2*-weighted image or contrast-enhanced CT. Analysis revealed significantly higher values in terms of MR angiography scores, number of flow voids of the basal ganglia, and the presence of the medullary artery in the group with HMSF than in those without. In contrast, the presence of white matter damage was significantly less frequent in the HMSF group. All HMSF disappeared after surgery, and the mean apparent diffusion coefficient at the same level was significantly reduced postoperatively. CONCLUSIONS Although HMSF should be associated with collateral circulation in moyamoya disease, other factors may be involved, including stagnated cerebrospinal fluid or vasogenic edema that is relevant to the impaired state of the white matter. Findings in this study provide insight into the pathophysiological basis of the perivascular space in moyamoya disease.

Reversibility of White Matter Hyperintensity by Revascularization Surgery in Moyamoya Disease

BACKGROUND

White matter lesions (WMLs) indicate progressive cerebral small vessel disease and are frequently observed in aging people and stroke patients. The purpose of this study was to evaluate WMLs and the influence of revascularization surgery for WMLs in patients with moyamoya disease.

METHODS

A total of 42 hemispheres in 21 patients with moyamoya disease were included in this analysis. WMLs were detected on fluid-attenuated inversion recovery (FLAIR) imaging in 24 hemispheres. The distribution pattern of WMLs was categorized. WMLs were measured by manually creating a region of interest, and the total WML volume in the hemisphere was estimated and compared with the control group. Clinical features of patients with WMLs and postoperative changes were analyzed.

RESULTS

The total WML volume in moyamoya disease was significantly higher than that of controls (P = .014). WMLs were observed in the internal watershed zone, especially in the watershed zone between the anterior cerebral artery and the middle cerebral artery. Patients with WMLs had significantly higher magnetic resonance angiography scores compared with controls (P = .015). A given patient's total WML volume per hemisphere was significantly decreased after surgery (P = .001).

CONCLUSIONS

WMLs on FLAIR imaging increase in patients with moyamoya disease and are reversible by revascularization surgery. Improvement of cerebral blood flow is partly related to the decrease in WMLs. The present results provide insight into the potential role of revascularization surgery.

Chronic ischemia alters brain microstructural integrity and cognitive performance in adult moyamoya disease

BACKGROUND AND PURPOSE

The mechanisms underlying frontal lobe dysfunction in moyamoya disease (MMD) are unknown. We aimed to determine whether chronic ischemia induces subtle microstructural brain changes in adult MMD and evaluated the association of changes with neuropsychological performance.

METHODS

MRI, including 3-dimensional T1-weighted imaging and diffusion tensor imaging, was performed in 23 adult patients with MMD and 23 age-matched controls and gray matter density and major diffusion tensor imaging indices were compared between them; any alterations in the patients were tested for associations with age, ischemic symptoms, hemodynamic compromise, and neuropsychological performance.

RESULTS

Decrease in gray matter density, associated with hemodynamic compromise (P<0.05), was observed in the posterior cingulate cortex of patients with MMD. Widespread reduction in fractional anisotropy and increases in radial diffusivity and mean diffusivity in some areas were also observed in bilateral cerebral white matter. The fractional anisotropy (r=0.54; P<0.0001) and radial diffusivity (r=-0.41; P<0.01) of white matter significantly associated with gray matter density of the cingulate cortex. The mean fractional anisotropy of the white matter tracts of the lateral prefrontal, cingulate, and inferior parietal regions were significantly associated with processing speed, executive function/attention, and working memory.

CONCLUSIONS

In adult MMD, there were more white matter abnormalities than gray matter changes. Disruption of white matter may play a pivotal role in the development of cognitive dysfunction.

Executive function and diffusion in frontal white matter of adults with moyamoya disease

BACKGROUND

Cognitive impairment is a frequent complication of moyamoya disease (MMD) in adults. Chronic hypoperfusion in frontal lobes can lead to subtle brain injury, resulting in cognitive dysfunctions. Apparent diffusion coefficient (ADC) in normal-appearing white matter on conventional magnetic resonance imaging correlates with cerebral hemodynamics in the frontal lobe.

OBJECTIVE

The purpose of this study was to examine the relationship of ADC with executive function in patients with MMD.

METHODS

Thirty-one patients (25 women and 6 men; mean age, 32.6 ± 10.4 years) were included in this study. Executive function was evaluated by the Frontal Assessment Battery (FAB) at 21.5 ± 7.5 years after disease onset. ADC was measured in the normal-appearing frontal white matter.

RESULTS

ADC was statistically related to the occurrence of executive dysfunction in multivariate analysis (P = .0179). Total FAB score and ADC were negatively correlated (r(2) = .22; P = .0072; Spearman correlation coefficient, -.41; P = .024). Elevated ADC predicted executive dysfunction (area under the receiver operating characteristic curve, .73; 95% confidence interval, .55-.91; P = .029).

CONCLUSIONS

The association of ADC with executive function might suggest that ADC is useful in screening for executive dysfunction during follow-up in the outpatient setting.