Tumor resection in paramedian structures of the frontal lobe poses a risk for corpus callosum infarction

PURPOSE

Surgeons resecting intraparenchymal tumors should be aware of potential white matter ischemia resulting from damage to the medullary artery arising from the cerebral cortex. In the vicinity of the paramedian structure, crucial brain regions for higher brain function such as corpus callosum and cingulate cortex are located. However, the actual area of ischemia induced by damaging the medullary artery supplying the paramedian structures is not known. The present study investigated the ischemic field following tumor resection in paramedian structures of the frontal lobe.

METHODS

Patients having intraparenchymal tumors with lesions in the paramedian structures of the frontal lobe (superior frontal gyrus or cingulate gyrus) resected between April 2016 and June 2022 at Tohoku University Hospital were included in the study. Magnetic resonance images obtained within 72 h after surgery were used to retrospectively examine the extent of the resection and the distribution of ischemic complications. Related postoperative clinical symptoms were assessed using medical records.

RESULTS

Thirty-three cases matched the inclusion criteria. The median age was 48 years. Cases comprised patients with an astrocytoma IDH-mutant (n = 11), oligodendroglioma IDH-mutant, and 1p/19q-codeletion (n = 12), and glioblastoma IDH-wildtype (n = 10). The main locations were superior frontal gyrus only (n = 17), cingulate gyrus only (n = 8), and both the frontal lobe and cingulate gyrus (n = 8). The cingulate gyrus was removed in 19 cases. In 16 of the 19 cases, ischemic foci were observed in the adjacent corpus callosum. In the 14 cases in which the cingulate gyrus was not removed, no ischemic foci appeared in the corpus callosum. Three cases exhibited a prolonged disturbance of consciousness after the second postoperative day, all with corpus callosum infarction.

CONCLUSION

Surgeons resecting intraparenchymal tumors in the paramedian structures of the frontal lobe, especially the cingulate gyrus, should be aware of the potential for ischemia foci emerging in the corpus callosum.

Associations between cerebral blood flow and progression of white matter hyperintensities

Introduction

In an aging population, white matter hyperintensities (WMHs), observed on FLAIR MRI sequences, are indicators of cognitive decline, motor impairment, and increased vascular risk. However, the pathophysiological mechanisms underlying WMHs, including dynamic changes in cerebral blood flow (CBF) within and adjacent to lesions, remain poorly understood.

Methods

Our study examined a diverse cohort of 300 elderly participants through arterial spin labeling (ASL) on 3 Tesla MRI, analyzing both cross-sectional and longitudinal data. We characterized the relationship between CBF and WMH development in different lesion locations (based on distance from ventricles) and brain tissue types (WMH lesion, penumbra, and normal white matter).

Results

Our findings reveal that WMHs exhibit significantly lower relative CBF (rCBF) compared to penumbra, normal-appearing white matter, and gray matter, with juxtaventricular WMHs (JVWMH) displaying the most substantial reductions. Longitudinally, WMHs that increased in size over a two-year period had lower baseline rCBF than those that remained stagnant, particularly in juxtaventricular and periventricular regions.

Discussion

This study not only highlights the predictive value of rCBF in WMH progression but also provides location-specific hemodynamic information about WMHs that can guide clinical management of WMH-related brain changes and their clinical manifestations.

Delayed Deep White Matter Ischemia After Resection of Gliomas by Awake Surgery

BACKGROUND AND OBJECTIVES

Deep white matter (DWM) is perfused by the medullary arteries from the cortex, and ischemia sometimes occurs after glioma resection. However, the clinical significance of postoperative medullary artery-related ischemia has not been well studied. We retrospectively reviewed cases of delayed DWM ischemia after awake craniotomy to elucidate the clinical characteristics, mechanisms, and management of delayed ischemia.

METHODS

We identified 4 cases of intra-axial brain tumors, mainly gliomas, that underwent tumor resection by awake craniotomy at our hospital and developed DWM ischemic symptoms after surgery, despite no worsening of neurological symptoms at the end of surgery.

RESULTS

Four patients (3 men and 1 woman) presented with glioblastoma, oligodendroglioma, astrocytoma, and brain metastasis. The median age at surgery was 47.5 years (41-73 years). The tumors were located in the watershed area in the frontal lobe (n = 2) and the parietal lobe (n = 2), all of which were left-sided (n = 4). DWM ischemic symptoms, such as motor dysfunction, aphasia, dysarthria, and dysgraphia, developed at an average of 24 hours (14-48 hours) after resection by awake craniotomy. All 4 patients showed symptom improvement within a week after surgery and completely recovered within a month.

CONCLUSION

DWM ischemia is caused by sacrifice of the medullary artery, which feeds the tumor and adjacent brain tissue during tumor resection, and should be considered when delayed aphasia or paralysis occurs postoperatively. These symptoms are often transient and recovery usually occurs. Tumors located in the frontal or parietal lobes, particularly in the watershed area, should be carefully monitored for postoperative ischemia.

Dose-Dependent Effect of Current Smoking on Enlarged Perivascular Space Identified on Brain Magnetic Resonance Imaging

INTRODUCTION

Cerebral small-vessel disease (CSVD) is a common cause of cognitive decline and stroke. Several studies have shown that smoking is a risk factor for CSVD progression. However, the extent to which smoking exacerbates CSVD lesions remains unclear. In this study, we aimed to clarify the association between total smoking exposure and the severity of CSVD in healthy participants.

METHODS

We analyzed the data of participants aged ≥50 years who underwent brain screening. The participants' age, sex, body mass index, alcohol consumption history, and medical history (hypertension, diabetes mellitus, and dyslipidemia) were investigated. Smoking status was assessed in pack-years, and smokers were classified as current or past smokers. CSVD findings on magnetic resonance imaging were used to evaluate the severity of periventricular hyperintensity (PVH), deep subcortical white matter hyperintensity (DSWMH), and enlarged perivascular spaces (EPVSs). The EPVSs were measured in the basal ganglia and centrum semiovale regions. Multivariable ordinal logistic regression analyses were performed to evaluate the effect of smoking, adjusted for the participants' baseline characteristics.

RESULTS

A total of 2,137 participants were included in this study. The mean age of the participants was 58.7 years. The mean pack-years were 20.5 for past smokers and 26.8 for current smokers. Among current smokers, increased pack-years were significantly associated with a high EPVS burden in the basal ganglia (odds ratio: 1.14, 95% confidence interval: 1.00-1.28), whereas no such significant association was found for past smokers. No statistically significant association was found between pack-years and the risks of PVH, DSWMH, or EPVS in the centrum semiovale.

CONCLUSION

Current smoking was associated with a dose-dependent risk of EPVS in the basal ganglia in healthy participants.

Acute Magnetic Resonance Imaging Findings in Young Children With Moyamoya Disease

BACKGROUND

To describe the diffusion-weighted imaging (DWI) findings in young children with moyamoya disease (MMD) during the acute period of the condition.

METHODS

Clinical data were collected from 12 children with MMD aged less than six years, in whom abnormalities were observed on DWI scans obtained within one week after the appearance of symptoms related to MMD. The DWI abnormalities were classified into gyral, atypical territorial, honeycomb, classical territorial, multiple-dot, border zone, and deep lacunar patterns. The severity of arterial stenosis was graded by angiographic stages that have been previously described.

RESULTS

In all but one child, the DWI abnormalities were restricted to the cerebral cortex. The lesions were gyral in nature in seven children and atypical territorial in five; all differed from those of typical arterial strokes. Internal carotid artery stenosis was observed in all 12 children, although the stenosis was mild in 11. The severity of arterial stenosis did not match the regions of ischemic lesions in some children. There was no statistically significant difference in the severity of arterial stenosis according to the presence or absence of ischemic lesions or the pattern of the lesions.

CONCLUSIONS

Lesions located mainly in the cerebral cortex, i.e., not in arterial territories, are characteristic of young children with MMD.

Dilated perivascular spaces and steno-occlusive changes in children and adults with moyamoya disease

BACKGROUND

Dilated perivascular spaces (DPVS), known as one of imaging markers in cerebral small vessel disease, may be found in patients with moyamoya disease (MMD). However, little is known about DPVS in MMD. The purpose of this study was to investigate the distribution pattern of dPVS in children and adults with MMD and determine whether it is related to steno-occlusive changes of MMD.

METHODS

DPVS was scored in basal ganglia (BG) and white matter (WM) on T2-weighted imaging, using a validated 4-point semi-quantitative score. The degree of dPVS was classified as high (score > 2) or low (score ≤ 2) grade. The steno-occlusive changes on MR angiography (MRA) was scored using a validated MRA grading. Asymmetry of DPVS and MRA grading was defined as a difference of 1 grade or higher between hemispheres.

RESULTS

Fifty-one patients with MMD (mean age 24.9 ± 21.1 years) were included. Forty-five (88.2%) patients had high WM-DPVS grade (degree 3 or 4). BG-DPVS was found in 72.5% of all patients and all were low grade (degree 1 or 2). The distribution patterns of DPVS degree in BG (P = 1.000) and WM (P = 0.767) were not different between child and adult groups. The asymmetry of WM-DPVS (26%) and MRA grade (42%) were significantly correlated to each other (Kendall's tau-b = 0.604, P < 0.001).

CONCLUSIONS

DPVS of high grade in MMD is predominantly found in WM, which was not different between children and adults. The correlation between asymmetry of WM-DPVS degree and MRA grade suggests that weak cerebral artery pulsation due to steno-occlusive changes may affect WM-DPVS in MMD.

Arteries Around the Superior Limiting Sulcus: Motor Complication Avoidance in Insular and Insulo-Opercular Surgery

BACKGROUND AND OBJECTIVES

Insulo-opercular surgery can cause ischemic motor complications. A source of this is the arteries around the superior limiting sulcus (SLS), which reach the corona radiata, but the detailed anatomy remains unclear. To characterize arteries around the SLS including the long insular arteries (LIAs) and long medullary arteries, we classified them and examined their distribution in relation to the SLS, which helps reduce the risk of ischemia.

METHODS

Twenty adult cadaveric hemispheres were studied. Coronal brain slices were created perpendicular to the SLS representing insular gyri (anterior short, middle short, posterior short, anterior long, and posterior long). The arteries within 10-mm proximity of the SLS that reached the corona radiata were excavated and classified by the entry point.

RESULTS

A total of 122 arteries were identified. Sixty-three (52%), 20 (16%), and 39 (32%) arteries penetrated the insula (LIAs), peak of the SLS, and operculum (long medullary arteries), respectively. 100 and six (87%) arteries penetrated within 5 mm of the peak of the SLS. The arteries were distributed in the anterior short gyrus (19%), middle short gyrus (17%), posterior short gyrus (20%), anterior long gyrus (19%), and posterior long gyrus (25%). Seven arteries (5.7%) had anastomoses after they penetrated the parenchyma.

CONCLUSION

Approximately 90% of the arteries that entered the parenchyma and reached the corona radiata were within a 5-mm radius of the SLS in both the insula and operculum side. This suggests that using the SLS as a landmark during insulo-opercular surgery can decrease the chance of ischemia.

Visualization of the lenticulostriate arteries, long insular arteries, and long medullary arteries on intra-arterial computed tomography angiography with ultrahigh resolution in patients with glioma

PURPOSE

The anatomical association between the lesion and the perforating arteries supplying the pyramidal tract in insulo-opercular glioma resection should be evaluated. This study reported a novel method combining the intra-arterial administration of contrast medium and ultrahigh-resolution computed tomography angiography (UHR-IA-CTA) for visualizing the lenticulostriate arteries (LSAs), long insular arteries (LIAs), and long medullary arteries (LMAs) that supply the pyramidal tract in two patients with insulo-opercular glioma.

METHODS

This method was performed by introducing a catheter to the cervical segment of the internal carotid artery. The infusion rate was set at 3 mL/s for 3 s, and the delay time from injection to scanning was determined based on the time-to-peak on angiography. On 2- and 20-mm-thick UHR-IA-CTA slab images and fusion with magnetic resonance images, the anatomical associations between the perforating arteries and the tumor and pyramidal tract were evaluated.

RESULTS

This novel method clearly showed the relationship between the perforators that supply the pyramidal tract and tumor. It showed that LIAs and LMAs were far from the lesion but that the proximal LSAs were involved in both cases. Based on these results, subtotal resection was achieved without complications caused by injury of perforators.

CONCLUSION

UHR-IA-CTA can be used to visualize the LSAs, LIAs, and LMAs clearly and provide useful preoperative information for insulo-opercular glioma resection.

Cortical spreading depolarization-induced constriction of penetrating arteries can cause watershed ischemia: A potential mechanism for white matter lesions

Periventricular white matter lesions (WMLs) are common MRI findings in migraine with aura (MA). Although hemodynamic disadvantages of vascular supply to this region create vulnerability, the pathophysiological mechanisms causing WMLs are unclear. We hypothesize that prolonged oligemia, a consequence of cortical spreading depolarization (CSD) underlying migraine aura, may lead to ischemia/hypoxia at hemodynamically vulnerable watershed zones fed by long penetrating arteries (PAs). For this, we subjected mice to KCl-triggered single or multiple CSDs. We found that post-CSD oligemia was significantly deeper at medial compared to lateral cortical areas, which induced ischemic/hypoxic changes at watershed areas between the MCA/ACA, PCA/anterior choroidal and at the tip of superficial and deep PAs, as detected by histological and MRI examination of brains 2-4 weeks after CSD. BALB-C mice, in which MCA occlusion causes large infarcts due to deficient collaterals, exhibited more profound CSD-induced oligemia and were more vulnerable compared to Swiss mice such that a single CSD was sufficient to induce ischemic lesions at the tip of PAs. In conclusion, CSD-induced prolonged oligemia has potential to cause ischemic/hypoxic injury at hemodynamically vulnerable brain areas, which may be one of the mechanisms underlying WMLs located at the tip of medullary arteries seen in MA patients.

5-Year Associations among Cerebral Arterial Pulsatility, Perivascular Space Dilation, and White Matter Lesions

OBJECTIVE

High cerebral arterial pulsatility index (PI), white matter lesions (WMLs), enlarged perivascular spaces (PVSs), and lacunar infarcts are common findings in the elderly population, and considered indicators of small vessel disease (SVD). Here, we investigate the potential temporal ordering among these variables, with emphasis on determining whether high PI is an early or delayed manifestation of SVD.

METHODS

In a population-based cohort, 4D flow MRI data for cerebral arterial pulsatility was collected for 159 participants at baseline (age 64-68), and for 122 participants at follow-up 5 years later. Structural MRI was used for WML and PVS segmentation, and lacune identification. Linear mixed-effects (LME) models were used to model longitudinal changes testing for pairwise associations, and latent change score (LCS) models to model multiple relationships among variables simultaneously.

RESULTS

Longitudinal 5-year increases were found for WML, PVS, and PI. Cerebral arterial PI at baseline did not predict changes in WML or PVS volume. However, WML and PVS volume at baseline predicted 5-year increases in PI. This was shown for PI increases in relation to baseline WML and PVS volumes using LME models (R  ≥  0.24; p < 0.02 and R  ≥  0.23; p < 0.03, respectively) and LCS models ( β  = 0.28; p = 0.015 and β  = 0.28; p = 0.009, respectively). Lacunes at baseline were unrelated to PI.

INTERPRETATION

In healthy older adults, indicators of SVD are related in a lead-lag fashion, in which the expression of WML and PVS precedes increases in cerebral arterial PI. Hence, we propose that elevated PI is a relatively late manifestation, rather than a risk factor, for cerebral SVD. ANN NEUROL 2022;92:871-881.

Laterality of Posterior Cerebral Artery and White Matter Hyperintensities in Patients with Severe Internal Carotid Artery Stenosis

BACKGROUND

Collateral status of the circle of Willis was associated with white matter hyperintensities (WMHs) in patients with internal carotid artery (ICA) stenosis, but few have investigated the effect of leptomeningeal anastomoses.

OBJECTIVE

The aim of this study was to observe the association between WMHs and the laterality of the posterior cerebral artery (PCA) that presents leptomeningeal anastomoses in patients with severe ICA stenosis.

MATERIALS AND METHODS

WMHs and ipsilateral PCA laterality were evaluated in patients with unilateral ICA stenosis ≥70% (including occlusion) and contralateral ICA stenosis <50% or no stenosis. Ipsilateral PCA laterality was compared between two groups of no/mild and severe score of global, deep and periventricular WMHs, respectively.

RESULTS

We included 115 patients with unilateral ICA stenosis ≥70%. There were 60 patients with no/mild and 55 with severe global WMHs. The patients with severe global WMHs were older (OR = 1.849, 95% CI: 1.058-3.229, P = 0.031) and had higher incidence of negative PCA laterality (OR = 3.301, 95% CI: 1.140-9.558, P = 0.028). The patients with severe deep WMHs were also older (OR = 2.031, 95% CI: 1.130-3.651, P = 0.018) and had higher incidence of negative PCA laterality (OR = 4.250, 95% CI: 1.501-12.032, P = 0.006). There was no significant difference between the patients with no/mild and severe periventricular WMHs in the incidence of negative PCA laterality.

CONCLUSIONS

The incidence of negative PCA laterality was higher in patients with severe global and deep WMHs, but not higher in patients with severe periventricular WMHs. The leptomeningeal anastomoses may affect the deep WMHs in patients with severe ICA stenosis.

Imaging perivascular space structure and function using brain MRI

In this article, we provide an overview of current neuroimaging methods for studying perivascular spaces (PVS) in humans using brain MRI. In recent years, an increasing number of studies highlighted the role of PVS in cerebrospinal/interstial fluid circulation and clearance of cerebral waste products and their association with neurological diseases. Novel strategies and techniques have been introduced to improve the quantification of PVS and to investigate their function and morphological features in physiological and pathological conditions. After a brief introduction on the anatomy and physiology of PVS, we examine the latest technological developments to quantitatively analyze the structure and function of PVS in humans with MRI. We describe the applications, advantages, and limitations of these methods, providing guidance and suggestions on the acquisition protocols and analysis techniques that can be applied to study PVS in vivo. Finally, we review the human neuroimaging studies on PVS across the normative lifespan and in the context of neurological disorders.

Sex is a defining feature of neuroimaging phenotypes in major brain disorders

Sex is a biological variable that contributes to individual variability in brain structure and behavior. Neuroimaging studies of population-based samples have identified normative differences in brain structure between males and females, many of which are exacerbated in psychiatric and neurological conditions. Still, sex differences in MRI outcomes are understudied, particularly in clinical samples with known sex differences in disease risk, prevalence, and expression of clinical symptoms. Here we review the existing literature on sex differences in adult brain structure in normative samples and in 14 distinct psychiatric and neurological disorders. We discuss commonalities and sources of variance in study designs, analysis procedures, disease subtype effects, and the impact of these factors on MRI interpretation. Lastly, we identify key problems in the neuroimaging literature on sex differences and offer potential recommendations to address current barriers and optimize rigor and reproducibility. In particular, we emphasize the importance of large-scale neuroimaging initiatives such as the Enhancing NeuroImaging Genetics through Meta-Analyses consortium, the UK Biobank, Human Connectome Project, and others to provide unprecedented power to evaluate sex-specific phenotypes in major brain diseases.

Postcentral gyrus resection of opercular gliomas is a risk factor for motor deficits caused by damaging the radiologically invisible arteries supplying the descending motor pathway

BACKGROUND

Postoperative motor deficits are among the worst morbidities of glioma surgery. We aim to investigate factors associated with postoperative motor deficits in patients with frontoparietal opercular gliomas.

METHODS

Thirty-four patients with frontoparietal opercular gliomas were retrospectively investigated. We examined the postoperative ischemic changes and locations obtained from MRI.

RESULTS

Twenty-one patients (62%) presented postoperative ischemic changes. Postoperative MRI was featured with ischemic changes, all located at the subcortical area of the resection cavity. Six patients had postoperative motor deficits, whereas 28 patients did not. Compared to those without motor deficits, those with motor deficits were associated with old age, pre- and postcentral gyri resection, and postcentral gyrus resection (P = 0.023, 0,024, and 0.0060, respectively). A merged image of the resected cavity and T1-weighted brain atlas of the Montreal Neurological Institute showed that a critical area for postoperative motor deficits is the origin of the long insular arteries (LIAs) and the postcentral gyrus. Detail anatomical architecture created by the Human Connectome Project database and T2-weighted images showed that the subcortical area of the operculum of the postcentral gyrus is where the medullary arteries supply, and the motor pathways originated from the precentral gyrus run.

CONCLUSIONS

We verified that the origin of the LIAs could damage the descending motor pathways during the resection of frontoparietal opercular gliomas. Also, we identified that motor pathways run the subcortical area of the operculum of the postcentral gyrus, indicating that the postcentral gyrus is an unrecognized area of damaging the descending motor pathways.

Recurrent hemorrhage risk associated with medial target medullary artery anastomosis from the periventricular collateral vessel in adult patients with moyamoya disease

BACKGROUND

Although the association between periventricular target collateral anastomosis and recurrent ipsilateral hemorrhage has been evaluated in adult patients with moyamoya disease (MMD), no studies have investigated the relationship between target anastomotic territory and recurrent ipsilateral hemorrhage. The goal of this study was to assess this association.

METHODS

Consecutive adult MMD patients who had experienced initial intracranial hemorrhage and undergone conservative treatment were included. Two readers assessed angiographic results to identify the target anastomotic territory (medial medullary artery, lateral medullary artery, multiple medullary arteries, or nonmedullary artery) responsible for the hemorrhage. Cox proportional hazard regression models were used to estimate the risk of recurrent hemorrhage.

RESULTS

In the 36 hemispheres with initial hemorrhage, the target anastomotic territory was in the anastomotic territory of the medial medullary artery in 10 (27.8%), lateral medullary artery in 15 (41.7%), multiple medullary arteries in 2 (5.6%), and a nonmedullary artery in 9 (25.0%) hemispheres. During 45.1 ± 40.0 months of follow-up, recurrent ipsilateral hemorrhage occurred in 44.4% (16/36) of hemispheres. The target anastomotic territories responsible for the recurrent event were in the anastomotic territory of the medial medullary artery in 9 (56.3%) hemispheres, lateral medullary artery in 6 (37.5%) hemispheres, and multiple medullary arteries in 1 (6.3%) hemisphere. The anastomotic territory of the medial medullary artery was associated with recurrent hemorrhage before (HR = 2.94; 95% CI, 1.07-8.08; p = 0.037) and after (HR = 6.65; 95% CI, 1.32-33.60; p = 0.022) adjustments were made for confounding factors.

CONCLUSIONS

The incidence of recurrent ipsilateral hemorrhage varies with the target anastomotic territory in adult patients with MMD. Medial target medullary artery anastomosis is a significant risk factor for recurrent ipsilateral hemorrhage.

Heterogeneity of Cerebral White Matter Lesions and Clinical Correlates in Older Adults

BACKGROUND AND PURPOSE

Cerebral white matter signal abnormalities (WMSAs) are a significant radiological marker associated with brain and vascular aging. However, understanding their clinical impact is limited because of their pathobiological heterogeneity. We determined whether use of robust reliable automated procedures can distinguish WMSA classes with different clinical consequences.

METHODS

Data from generally healthy participants aged >50 years with moderate or greater WMSA were selected from the Human Connectome Project-Aging (n=130). WMSAs were segmented on T1 imaging. Features extracted from WMSA included total and regional volume, number of discontinuous clusters, size of noncontiguous lesion, contrast of lesion intensity relative to surrounding normal appearing tissue using a fully automated procedure. Hierarchical clustering was used to classify individuals into distinct classes of WMSA. Radiological and clinical variability was evaluated across the individual WMSA classes.

RESULTS

Class I was characterized by multiple, small, lower-contrast lesions predominantly in the deep WM; class II by large, confluent lesions in the periventricular WM; and class III by higher-contrast lesions restricted to the juxtaventricular WM. Class II was associated with lower myelin content than the other 2 classes. Class II was more prevalent in older subjects and was associated with a higher prevalence of hypertension and lower physical activity levels. Poor sleep quality was associated with a greater risk of class I.

CONCLUSIONS

We classified heterogeneous subsets of cerebral white matter lesions into distinct classes that have different clinical risk factors. This new method for identifying classes of WMSA will be important in understanding the underlying pathophysiology and in determining the impact on clinical outcomes.

Hemodynamic Response Function in Brain White Matter in a Resting State

The hemodynamic response function (HRF) characterizes temporal variations of blood oxygenation level-dependent (BOLD) signals. Although a variety of HRF models have been proposed for gray matter responses to functional demands, few studies have investigated HRF profiles in white matter particularly under resting conditions. In the present work we quantified the nature of the HRFs that are embedded in resting state BOLD signals in white matter, and which modulate the temporal fluctuations of baseline signals. We demonstrate that resting state HRFs in white matter could be derived by referencing to intrinsic avalanches in gray matter activities, and the derived white matter HRFs had reduced peak amplitudes and delayed peak times as compared with those in gray matter. Distributions of the time delays and correlation profiles in white matter depend on gray matter activities as well as white matter tract distributions, indicating that resting state BOLD signals in white matter encode neural activities associated with those of gray matter. This is the first investigation of derivations and characterizations of resting state HRFs in white matter and their relations to gray matter activities. Findings from this work have important implications for analysis of BOLD signals in the brain.

White Matter Hyperintensities Relate to Basal Ganglia Functional Connectivity and Memory Performance in aMCI and SVMCI

Cerebral small vessel diseases play a crucial role in both vascular and non-vascular dementias. The location of white matter hyperintensities (WMHs), a neuroimaging marker of cerebral small vessel disease, has been found to vary between different types of dementias, and those in the basal ganglia (BG) have been particularly associated with vascular cognitive impairment (VCI). However, anatomical variation of WMHs across BG nuclei and its effect on brain network dysconnectivity has not been clearly elucidated. The study sample consisted of 40 patients with amnestic mild cognitive impairment (aMCI), 40 with subcortical vascular MCI (SVMCI), and 40 healthy control subjects. We examined the volume of WMH using T2-weighted magnetic resonance imaging. We also assessed the disturbances in BG-cortical communication by measuring resting-state functional connectivity (rsFC) from the functional magnetic resonance imaging signal. WMHs were more pronounced in the SVMCI group particularly in the caudate regions. In SVMCI patients, while higher WMHs in the dorsal caudate correlated with weaker FC with executive control regions and worse immediate recall performance, WMHs in the ventral caudate were associated with weaker FC with anterior default mode regions and worse delayed recall performance. In contrast, in aMCI patients, BG WMHs were not correlated with their changes in functional connectivity changes, which showed weaker connectivity with almost all BG structures, rather than restricting to specific BG subdivisions as observed in the SVMCI group. Our findings demonstrate that heterogeneously distributed BG WMHs are associated with changes in functional network interactions and verbal episodic memory performance only in SVMCI patients, which establishes a link between cerebrovascular-related structural abnormality, functional integrity of BG circuits, and episodic memory impairments in SVMCI, and may reflect a differential role of the cerebrovascular pathology in disrupting network-level communications and cognition between Alzheimer's and subcortical vascular dementia.

White Matter fMRI Activation Cannot Be Treated as a Nuisance Regressor: Overcoming a Historical Blind Spot

Despite past controversies, increasing evidence has led to acceptance that white matter activity is detectable using functional magnetic resonance imaging (fMRI). In spite of this, advanced analytic methods continue to be published that reinforce a historic bias against white matter activation by using it as a nuisance regressor. It is important that contemporary analyses overcome this blind spot in whole brain functional imaging, both to ensure that newly developed noise regression techniques are accurate, and to ensure that white matter, a vital and understudied part of the brain, is not ignored in functional neuroimaging studies.

Restoration of periventricular vasculature after direct bypass for moyamoya disease: intra-individual comparison

BACKGROUND

While periventricular anastomosis, a unique abnormal vasculature in moyamoya disease, has been studied in relation to intracranial hemorrhage, no study has addressed its change after bypass surgery. The authors sought to test whether direct bypass surgery could restore normal periventricular vasculature.

METHODS

Patients who had undergone direct bypass surgery for moyamoya disease at a single institution were eligible for the study. Baseline, postoperative, and follow-up magnetic resonance angiography (MRA) scans were scheduled before surgery, after the first surgery, and 3 to 6 months after contralateral second surgery, respectively. Sliding-thin-slab maximum-intensity-projection coronal MRA images of periventricular anastomoses were scored according to the three subtypes (lenticulostriate, thalamic, and choroidal anastomosis). Baseline and postoperative MRA images were compared to obtain a matched comparison of score changes in the surgical and nonsurgical hemispheres within individuals (intra-individual comparison).

RESULTS

Of 110 patients, 42 were identified for intra-individual comparisons. The periventricular anastomosis score decreased significantly in the surgical hemispheres (median, 2 versus 1; p < 0.001), whereas the score remained unchanged in the nonsurgical hemispheres (median, 2 versus 2; p = 0.57); the score change varied significantly between the surgical and nonsurgical hemispheres (p < 0.001). Of the 104 periventricular-anastomosis-positive hemispheres undergoing surgery, 47 (45.2%) were assessed as negative in the follow-up MRA. Among the subtypes, choroidal anastomosis was most likely to be assessed as negative (79.7% of positive hemispheres).

CONCLUSIONS

Periventricular vasculature can be restored after direct bypass. The likelihood of correction of choroidal anastomosis is a subject requiring further studies.

Perivascular space fluid contributes to diffusion tensor imaging changes in white matter

Diffusion tensor imaging (DTI) has been extensively used to map changes in brain tissue related to neurological disorders. Among the most widespread DTI findings are increased mean diffusivity and decreased fractional anisotropy of white matter tissue in neurodegenerative diseases. Here we utilize multi-shell diffusion imaging to separate diffusion signal of the brain parenchyma from non-parenchymal fluid within the white matter. We show that unincorporated anisotropic water in perivascular space (PVS) significantly, and systematically, biases DTI measures, casting new light on the biological validity of many previously reported findings. Despite the challenge this poses for interpreting these past findings, our results suggest that multi-shell diffusion MRI provides a new opportunity for incorporating the PVS contribution, ultimately strengthening the clinical and scientific value of diffusion MRI.

Intractable Medial Anastomotic Branches from the Lenticulostriate Artery Causing Recurrent Hemorrhages in Moyamoya Disease

BACKGROUND

Although superficial temporal artery (STA) to middle cerebral artery (MCA) anastomosis is a beneficial treatment for hemorrhagic moyamoya disease, indeterminate mechanisms can cause rebleeding even after successful bypass surgery. We describe a case with a prominent collateral from the lenticulostriate artery (LSA) causing multiple recurrent hemorrhages after successful STA-MCA anastomosis.

CASE DESCRIPTION

A 49-year-old Japanese woman with moyamoya disease was referred to our institution after suffering intracranial hemorrhage on 2 occasions. Angiography revealed multiple anastomotic vessels branching from a prominent LSA to connect medullary arteries in the periventricular area corresponding to the location of the hemorrhage. She underwent STA-MCA anastomoses and the bypass widely perfused the MCA territory; however, intracranial hemorrhage recurred in the same hemisphere. Angiography revealed sustained dilatation of the medial anastomotic branches from the LSA with de novo pseudoaneurysm, whereas the lateral branches showed shrinkage. Subsequent surgical treatment included direct bypass targeting the medial hemispheric surface in which the medial branches were distributed; marked shrinkage of the branches and disappearance of the aneurysm were obtained without infarct.

CONCLUSIONS

Lenticulostriate anastomotic branches distributed medially to the anterior cerebral artery territory should be given more attention as an intractable cause of hemorrhage after successful STA-MCA anastomosis. Although challenging, direct bypass targeting the area reached by collateral vessels could be considered an alternative treatment strategy for this pathologic condition.

Characterization of the hemodynamic response function in white matter tracts for event-related fMRI

Accurate estimates of the BOLD hemodynamic response function (HRF) are crucial for the interpretation and analysis of event-related functional MRI data. To date, however, there have been no comprehensive measurements of the HRF in white matter (WM) despite increasing evidence that BOLD signals in WM change after a stimulus. We performed an event-related cognitive task (Stroop color-word interference) to measure the HRF in selected human WM pathways. The task was chosen in order to produce robust, distributed centers of activity throughout the cortex. To measure the HRF in WM, fiber tracts were reconstructed between each pair of activated cortical areas. We observed clear task-specific HRFs with reduced magnitudes, delayed onsets and prolonged initial dips in WM tracts compared with activated grey matter, thus calling for significant changes to current standard models for accurately characterizing the HRFs in WM and for modifications of standard methods of analysis of functional imaging data.

White matter hyperintensities and their subtypes in patients with carotid artery stenosis: a systematic review and meta-analysis

OBJECTIVE

We aimed to perform a systematic review and meta-analysis to clarify the association between white matter hyperintensities (WMHs) and carotid artery (CA) stenosis.

STUDY DESIGN

Systematic review and meta-analysis.

PARTICIPANTS

CA stenosis was set at ≥50%, and WMHs were assessed by MRI and evaluated quantitatively or semiquantitatively.

DATA SOURCES

A comprehensive literature search was performed in PubMed, EMBASE and Cochrane Library for studies evaluating the association between WMHs and CA stenosis ≥50% from inception to 13 September 2017.

MAIN OUTCOMES AND MEASURES

Standardised mean difference (SMD) with 95% CI was used to evaluate the association between WMHs and CA stenosis. Results were presented in a forest plot with a fixed-effects model or random-effects model. We assessed the quality of included studies using the Newcastle-Ottawa Scale. Funnel plots and Egger's and Begg's tests were conducted to assess publication bias. Sensitivity analysis was performed to evaluate the influence of each individual study.

RESULTS

Eight studies enrolling 677 patients were included. There was a positive relationship between the total WMHs and CA stenosis, with a pooled fixed-effects SMD of 0.326 (95% CI 0.194 to 0.459, p=0.000). Heterogeneity and publication bias were low among these studies. Subgroup analysis of three studies enrolling 225 patients showed an association between periventricular WMHs and CA stenosis, with a pooled fixed-effects SMD of 0.412 (95% CI 0.202 to 0.622, p=0.000).

CONCLUSION

This meta-analysis showed that the total WMHs and periventricular WMHs were associated with CA stenosis. WMHs may be considered as an individual risk stratification score when choosing a proper plan for therapy of CA stenosis.