Asymmetry of the cerebral blood flow: an ultrasound Doppler study in preterm newborns

The Utility of Cerebral Autoregulation Indices in Detecting Severe Brain Injury Varies by Cooling Treatment Phase in Neonates with Hypoxic-Ischemic Encephalopathy

Identifying the hemodynamic range that best supports cerebral perfusion using near infrared spectroscopy (NIRS) autoregulation monitoring is a potential physiologic marker for neonatal hypoxic-ischemic encephalopathy (HIE) during therapeutic hypothermia. However, an optimal autoregulation monitoring algorithm has not been identified for neonatal clinical medicine. We tested whether the hemoglobin volume phase (HVP), hemoglobin volume (HVx), and pressure passivity index (PPI) identify changes in autoregulation that are associated with brain injury on MRI or death. The HVP measures the phase difference between a NIRS metric of cerebral blood volume, the total hemoglobin (THb), and mean arterial blood pressure (MAP) at the frequency of maximum coherence. The HVx is the correlation coefficient between MAP and THb. The PPI is the percentage of coherent MAP-DHb (difference between oxygenated and deoxygenated hemoglobin, a marker of cerebral blood flow) epochs in a chosen time period. Neonates cooled for HIE were prospectively enrolled in an observational study in two neonatal intensive care units. In analyses adjusted for study site and encephalopathy level, all indices detected relationships between poor autoregulation in the first 6 h after rewarming with a higher injury score on MRI. Only HVx and PPI during hypothermia and the PPI during rewarming identified autoregulatory dysfunction associated with a poor outcome independent of study site and encephalopathy level. Our findings suggest that the accuracy of mathematical autoregulation algorithms in detecting the risk of brain injury or death may depend on temperature and postnatal age. Extending autoregulation monitoring beyond the standard 72 h of therapeutic hypothermia may serve as a method to provide personalized care by assessing the need for and efficacy of future therapies after the hypothermia treatment phase.

Single-subject gray matter networks in temporal lobe epilepsy patients with hippocampal sclerosis

OBJECTIVE

Previous studies have demonstrated structural brain network abnormalities in patients with temporal lobe epilepsy (TLE) using cortical thickness or gray matter (GM) volume. However, no studies have applied single-subject GM network analysis. Here, we first applied an analysis of similarity-based single-subject GM networks to individual patients with TLE.

MATERIALS AND METHODS

We recruited 51 patients with TLE and unilateral hippocampal sclerosis (22 left, 29 right TLE) and 51 age- and gender- matched healthy controls. Single-subject structural networks were extracted from three-dimensional T1-weighted magnetic resonance images for each subject. In this method, nodes were defined as small cortical regions and edges representing connecting regions that have high statistical similarity. The constructed graphs were analyzed using the graph theoretical approach. The following global and local network properties were calculated: betweenness centrality, clustering coefficient, and characteristic path length. In addition, small world properties (normalized path length λ, normalized clustering coefficient γ, and small-world network value σ) were obtained and compared with those for the controls.

RESULTS

Although the small-world configurations were retained, impaired global clustering coefficient was observed in left and right TLE. At a regional level, patients with left TLE showed a widespread decrease of the clustering coefficient beyond the ipsilateral temporal lobe and a decreased characteristic path length in the ipsilateral temporal pole. On the other hand, patients with right TLE showed a localized decrease of the clustering coefficient in the ipsilateral temporal lobe.

CONCLUSIONS

Our findings suggest that global and local network properties disrupted and moved toward randomized networks in TLE patients in comparison to controls. This network alteration was more extensive in left TLE than in right TLE patients. Single-subject GM networks may contribute to a better understanding of the pathophysiology of TLE.

Association of Asymmetrical White Matter Hyperintensities and Apolipoprotein E4 on Cognitive Impairment

BACKGROUND

Asymmetrical patterns of cerebral damage have been widely observed in a range of neurodegenerative diseases, including Alzheimer's disease (AD).

OBJECTIVE

To elucidate the clinical associations of asymmetrical white matter hyperintensities (WMH) in mild cognitive impairment (MCI) and AD.

METHODS

Regional WMH asymmetry of 340 participants (90 healthy controls, 132 MCI, 118 AD) was calculated as the difference in normalized hemispheric WMH volume (WMH/ICV) adjusted for structural brain asymmetry of respective lobar regions and total WMH. WMH asymmetry was analyzed in relation to disease classification, cognition, and APOE4 status using ANCOVA and multiple regression analysis, controlling for gender, age, ethnicity, and correcting for multiple comparisons using Bonferroni correction. Moderation analysis examined interaction effects of APOE4 on associations between cognition and WMH asymmetry.

RESULTS

Greater left-dominant occipital WMH asymmetry was observed in AD, compared to healthy controls and MCI, and was associated with poorer global cognition, memory, language, and executive functions among cognitively impaired participants (MCI and AD). Cognitively impaired APOE4 carriers displayed greater left-dominant WMH asymmetry in the whole brain and frontal lobe, compared to non-carriers. Importantly, effects were independent of structural brain asymmetry, global cerebral atrophy, and overall WMH burden. Moderation analysis demonstrated associations between left-dominant WMH asymmetry and cognition in cognitively impaired APOE4 non-carriers, but not APOE4 carriers.

CONCLUSION

Leftward asymmetry of WMH may be more pathological in nature, compared to symmetrical WMH. Furthermore, the detrimental effects of WMH asymmetry was more relevant in APOE4-negative cognitive impairment, compared to APOE4-positive which may be driven primarily by AD pathology.

Effect of Preterm Birth on Echogenicity in Basal Ganglia

In this study, the influence of prematurity on echogenicity of deep gray matter at 30-wk corrected age was assessed using ultrasound measurements. In an observational cohort study, ultrasound scans of 224 extremely preterm infants were prospectively collected. Gray values were assessed in putamen and globus pallidus. Intra- and inter-observer reliability was analyzed and showed excellent agreement. The globus pallidus to putamen ratio was significantly related to gestational age at birth, adjusted regression coefficient in points per wk: 1.28 (95% confidence interval [CI]: 0.38-2.19) for left and 2.12 (95% CI: 1.23-3.02) for right-side images. At 30-wk corrected age this was still the case, adjusted regression coefficient: 0.45 (95% CI: -0.57 to 1.47) for left and 1.29 (95% CI: 0.10-2.48) for right. The putamen is more hyperechoic with lower gestational age. Measuring ultrasound gray values in deep gray matter seems highly reproducible. Prematurity shows a negative correlation with echogenicity of the putamen, this persists at 30-wk corrected age, suggesting altered maturation.

Head Position Change Is Not Associated with Acute Changes in Bilateral Cerebral Oxygenation in Stable Preterm Infants during the First 3 Days of Life

OBJECTIVE

Several recent intraventricular hemorrhage prevention bundles include midline head positioning to prevent potential disturbances in cerebral hemodynamics. We aimed to study the impact of head position change on regional cerebral saturations (SctO2) in preterm infants (< 30 weeks gestational age) during the first 3 days of life.

STUDY DESIGN

Bilateral SctO2 was measured by near-infrared spectroscopy. The infant's head was turned sequentially to each side from midline (baseline) in 30-minute intervals while keeping the body supine. Bilateral SctO2 before and after each position change were compared using paired t-test.

RESULTS

In relatively stable preterm infants (gestational age 26.5 ± 1.7 weeks, birth weight 930 ± 220 g; n = 20), bilateral SctO2 remained within normal range (71.1-75.3%) when the head was turned from midline position to either side.

CONCLUSION

Stable preterm infants tolerated brief changes in head position from midline without significant alternation in bilateral SctO2; the impact on critically ill infants needs further evaluation.

Structural-functional coupling changes in temporal lobe epilepsy

Alterations in both structural connectivity (SC) and functional connectivity (FC) have been reported in temporal lobe epilepsy (TLE). However, the relationship between FC and SC remains less understood. This study used functional connectivity MRI and diffusion tensor imaging to examine coupling of FC and SC within the limbic network of TLE, as well as its relation to epilepsy duration, regional changes, and disease laterality in 14 patients with left TLE, 10 with right TLE, and 11 healthy controls. Structural and functional networks were separately constructed and the correlation estimated between structural and functional connectivity. This measure of SC-FC coupling was compared between left/right TLE and controls, and correlated with epilepsy duration. Elastic net regression was used to investigate regional structural and functional changes associated with SC-FC coupling. SC-FC coupling was decreased in left TLE compared to controls, and accompanied by reductions in FC for left and right TLE and in SC for left TLE. When examined in relation to disease duration, an increase in SC-FC coupling with longer epilepsy duration was observed, associated predominantly with structural loss of the fusiform and frontal inferior orbital gyrus in left TLE and functional hub redistribution in right TLE. These results suggest that decoupling between structural and functional networks in TLE is modulated by several factors, including epilepsy duration and regional changes in the fusiform, frontal inferior orbital gyrus, posterior cingulate, and hippocampus. SC-FC coupling may provide a more sensitive biomarker of disease burden in TLE than biomarkers based on single imaging modalities.

Respiratory support for premature neonates in the delivery room: effects on cardiovascular function and the development of brain injury

The transition to newborn life in preterm infants is complicated by immature cardiovascular and respiratory systems. Consequently, preterm infants often require respiratory support immediately after birth. Although aeration of the lung underpins the circulatory transition at birth, positive pressure ventilation can adversely affect cardiorespiratory function during this vulnerable period, reducing pulmonary blood flow and left ventricular output. Furthermore, pulmonary volutrauma is known to initiate pulmonary inflammatory responses, resulting in remote systemic involvement. This review focuses on the downstream consequences of positive pressure ventilation, in particular, interactions between cardiovascular output and the initiation of a systemic inflammatory cascade, on the immature brain. Recent studies have highlighted that positive pressure ventilation strategies are precursors of cerebral injury, probably mediated through cerebral blood flow instability. The presence of, or initiation of, an inflammatory cascade accentuates adverse cerebral blood flow, in addition to being a direct source of brain injury. Importantly, the degree of brain injury is dependent on the nature of the initial ventilation strategy used.

Structural connectivity differences in left and right temporal lobe epilepsy

Our knowledge on temporal lobe epilepsy (TLE) with hippocampal sclerosis has evolved towards the view that this syndrome affects widespread brain networks. Diffusion weighted imaging studies have shown alterations of large white matter tracts, most notably in left temporal lobe epilepsy, but the degree of altered connections between cortical and subcortical structures remains to be clarified. We performed a whole brain connectome analysis in 39 patients with refractory temporal lobe epilepsy and unilateral hippocampal sclerosis (20 right and 19 left) and 28 healthy subjects. We performed whole-brain probabilistic fiber tracking using MRtrix and segmented 164 cortical and subcortical structures with Freesurfer. Individual structural connectivity graphs based on these 164 nodes were computed by mapping the mean fractional anisotropy (FA) onto each tract. Connectomes were then compared using two complementary methods: permutation tests for pair-wise connections and Network Based Statistics to probe for differences in large network components. Comparison of pair-wise connections revealed a marked reduction of connectivity between left TLE patients and controls, which was strongly lateralized to the ipsilateral temporal lobe. Specifically, infero-lateral cortex and temporal pole were strongly affected, and so was the perisylvian cortex. In contrast, for right TLE, focal connectivity loss was much less pronounced and restricted to bilateral limbic structures and right temporal cortex. Analysis of large network components revealed furthermore that both left and right hippocampal sclerosis affected diffuse global and interhemispheric connectivity. Thus, left temporal lobe epilepsy was associated with a much more pronounced pattern of reduced FA, that included major landmarks of perisylvian language circuitry. These distinct patterns of connectivity associated with unilateral hippocampal sclerosis show how a focal pathology influences global network architecture, and how left or right-sided lesions may have differential and specific impacts on cerebral connectivity.

Hemispheric lateralization of microstructural white matter abnormalities in children with active benign childhood epilepsy with centrotemporal spikes (BECTS): a preliminary DTI study

PURPOSE

The deficit of white matter is reported to be involved during the disease progression in patients with benign childhood epilepsy with centrotemporal spikes (BECTS). The aim of this study is to investigate patterns of white matter damage in children with BECTS with left- or right-hemispheric focus by using diffusion tensor imaging (DTI), and its relationship with the cofactors such duration, seizure frequency and handedness.

METHODS

Diffusion tensor imaging (DTI) was performed in twenty-eight children with BECTS and eighteen healthy controls. The data were analyzed using both tract-based spatial statistics (TBSS) and region of interest (ROI) analyses. Correlations were investigated between the fractional anisotropy (FA) values of the identified altered regions and clinical features such as age, age of onset and seizure frequency.

RESULTS

The TBSS analysis revealed that white matter impairment in children with rolandic spikes on the ipsilateral hemisphere was much wider. The FA value was significantly lower in the body of the corpus callosum and forceps minor in BECTS patients with spikes on the ipsilateral hemisphere. The seizure frequency correlated positively with the FA values of body of corpus callosum (CC), bilateral cingulate gyrus and left uncinate fasciculi (UA).

CONCLUSION

The impaired WM integrity in patients with BECTS was greater in patients with spikes on the dominant hemisphere, possibly due to the greater vulnerability of the left hemisphere and excitotoxic effects of seizures.

Concomitant fractional anisotropy and volumetric abnormalities in temporal lobe epilepsy: cross-sectional evidence for progressive neurologic injury

Background

In patients with temporal lobe epilepsy and associated hippocampal sclerosis (TLEhs) there are brain abnormalities extending beyond the presumed epileptogenic zone as revealed separately in conventional magnetic resonance imaging (MRI) and MR diffusion tensor imaging (DTI) studies. However, little is known about the relation between macroscopic atrophy (revealed by volumetric MRI) and microstructural degeneration (inferred by DTI).

Methodology/Principal Findings

For 62 patients with unilateral TLEhs and 68 healthy controls, we determined volumes and mean fractional anisotropy (FA) of ipsilateral and contralateral brain structures from T1-weighted and DTI data, respectively. We report significant volume atrophy and FA alterations of temporal lobe, subcortical and callosal regions, which were more diffuse and bilateral in patients with left TLEhs relative to right TLEhs. We observed significant relationships between volume loss and mean FA, particularly of the thalamus and putamen bilaterally. When corrected for age, duration of epilepsy was significantly correlated with FA loss of an anatomically plausible route - including ipsilateral parahippocampal gyrus and temporal lobe white matter, the thalamus bilaterally, and posterior regions of the corpus callosum that contain temporal lobe fibres - that may be suggestive of progressive brain degeneration in response to recurrent seizures.

Conclusions/Significance

Chronic TLEhs is associated with interrelated DTI-derived and volume-derived brain degenerative abnormalities that are influenced by the duration of the disorder and the side of seizure onset. This work confirms previously contradictory findings by employing multi-modal imaging techniques in parallel in a large sample of patients.

MRI analysis in temporal lobe epilepsy: cortical thinning and white matter disruptions are related to side of seizure onset

PURPOSE

Past studies reported more widespread structural brain abnormalities in patients with left compared to right temporal lobe epilepsy (TLE), but the profile of these differences remains unknown. This study investigated the relationship between cortical thinning, white matter compromise, epilepsy variables, and the side of seizure onset, in patients with TLE.

METHODS

We performed diffusion tensor imaging tractography and cortical thickness analyses of 18 patients with left TLE (LTLE), 18 patients with right TLE (RTLE), and 36 controls. We investigated the relationship among brain structural abnormalities, side of seizure onset, age of seizure onset, and disease duration.

KEY FINDINGS

Patients with TLE displayed cortical thinning and white matter compromise, predominately on the side ipsilateral to the seizure onset. Relative to RTLE, patients with LTLE showed more widespread abnormalities, particularly in white matter fiber tracts. Greater compromise in white matter integrity was associated with earlier age of seizure onset, whereas cortical thinning was marginally associated with disease duration.

SIGNIFICANCE

These data support previous findings of LTLE showing greater structural compromise than RTLE, and suggest that mechanisms may not be uniform for gray and white matter compromise in patients with LTLE and RTLE. These results may indicate that LTLE is different from RTLE, possibly due to greater vulnerability of the left hemisphere to early injury and the progressive effects of seizures.

Side-to-side differences in transcranial Doppler parameters in normotensive and preeclamptic pregnant women

OBJECTIVE

This study was undertaken to investigate whether women with preeclampsia demonstrate larger side-to-side velocity differences in the middle cerebral artery (MCA) compared with normotensive pregnant women.

STUDY DESIGN

Forty-one preeclamptic women and 50 normotensive pregnant women were studied during the third trimester. Transcranial Doppler ultrasound was used to measure peak, end-diastolic, and mean velocities in both MCAs. An asymmetry index was calculated as 100 x Rt-Lt//(Rt+Lt)/2, for each of the following parameters: mean velocity (Vm), pulsatility index (PI), and cerebral perfusion pressure (CPP). Student t test, Pearson correlation, and regression analysis were used. Significance was taken as P<.05.

RESULTS

Both normotensive and preeclamptic pregnant women showed good correlation between Rt and Lt MCA Vm (R>0.8, P<.0001), PI (R>0.6, P.0001), and CPP (R>0.8, P<.0001). There were no differences in the asymmetry index for Vm, PI, or CPP between the two groups.

CONCLUSION

Preeclampsia does not appear to induce greater side-to-side velocity differences in the MCA distribution.