Diffusion tensor imaging analysis of frontal lobes in pediatric traumatic brain injury

Investigating brain-gut microbiota dynamics and inflammatory processes in an autistic-like rat model using MRI biomarkers during childhood and adolescence

Autism spectrum disorder (ASD) is characterized by social interaction deficits and repetitive behaviors. Recent research has linked that gut dysbiosis may contribute to ASD-like behaviors. However, the exact developmental time point at which gut microbiota alterations affect brain function and behavior in patients with ASD remains unclear. We hypothesized that ASD-related brain microstructural changes and gut dysbiosis induce metabolic dysregulation and proinflammatory responses, which collectively contribute to the social behavioral deficits observed in early childhood. We used an autistic-like rat model that was generated via prenatal valproic acid exposure. We analyzed brain microstructural changes using diffusion tensor imaging (DTI) and examined microbiota, blood, and fecal samples for inflammation biomarkers. The ASD model rats exhibited significant brain microstructural changes in the anterior cingulate cortex, hippocampus, striatum, and thalamus; reduced microbiota diversity (Prevotellaceae and Peptostreptococcaceae); and altered metabolic signatures. The shift in microbiota diversity and density observed at postnatal day (PND) 35, which is a critical developmental period, underscored the importance of early ASD interventions. We identified a unique metabolic signature in the ASD model, with elevated formate and reduced acetate and butyrate levels, indicating a dysregulation in short-chain fatty acid (SCFA) metabolism. Furthermore, increased astrocytic and microglial activation and elevated proinflammatory cytokines-interleukin-1 beta (IL-1β), interleukin-6 (IL-6), interferon-gamma (IFN-γ), and tumor necrosis factor-alpha (TNF-α)-were observed, indicating immune dysregulation. This study provided insights into the complex interplay between the brain and the gut, and indicated DTI metrics as potential imaging-based biomarkers in ASD, thus emphasizing the need for early childhood interventions.

Traumatic brain injury biomarkers in pediatric patients: a systematic review

Traumatic brain injury (TBI) is the main cause of pediatric trauma death and disability worldwide. Recent studies have sought to identify biomarkers of TBI for the purpose of assessing functional outcomes. The aim of this systematic review was to evaluate the utility of TBI biomarkers in the pediatric population by summarizing recent findings in the medical literature. A total of 303 articles were retrieved from our search. An initial screening to remove duplicate studies yielded 162 articles. After excluding all articles that did not meet the inclusion criteria, 56 studies were gathered. Among the 56 studies, 36 analyzed serum biomarkers; 11, neuroimaging biomarkers; and 9, cerebrospinal fluid (CSF) biomarkers. Most studies assessed biomarkers in the serum, reflecting the feasibility of obtaining blood samples compared to obtaining CSF or performing neuroimaging. S100B was the most studied serum biomarker in TBI, followed by SNE and UCH-L1, whereas in CSF analysis, there was no unanimity. Among the different neuroimaging techniques employed, diffusion tensor imaging (DTI) was the most common, seemingly holding diagnostic power in the pediatric TBI clinical setting. The number of cross-sectional studies was similar to the number of longitudinal studies. Our data suggest that S100B measurement has high sensitivity and great promise in diagnosing pediatric TBI, ideally when associated with head CT examination and clinical decision protocols. Further large-scale longitudinal studies addressing TBI biomarkers in children are required to establish more accurate diagnostic protocols and prognostic tools.

Acute treatment with TrkB agonist LM22A-4 confers neuroprotection and preserves myelin integrity in a mouse model of pediatric traumatic brain injury

Young children have a high risk of sustaining a traumatic brain injury (TBI), which can have debilitating life-long consequences. Importantly, the young brain shows particular vulnerability to injury, likely attributed to ongoing maturation of the myelinating nervous system at the time of insult. Here, we examined the effect of acute treatment with the partial tropomyosin receptor kinase B (TrkB) agonist, LM22A-4, on pathological and neurobehavioral outcomes after pediatric TBI, with the hypothesis that targeting TrkB would minimize tissue damage and support functional recovery. We focused on myelinated tracts-the corpus callosum and external capsules-based on recent evidence that TrkB activation potentiates oligodendrocyte remyelination. Male mice at postnatal day 21 received an experimental TBI or sham surgery. Acutely post-injury, extensive cell death, a robust glial response and disruption of compact myelin were evident in the injured brain. TBI or sham mice then received intranasal saline vehicle or LM22A-4 for 14 days. Behavior testing was performed from 4 weeks post-injury, and brains were collected at 5 weeks for histology. TBI mice showed hyperactivity, reduced anxiety-like behavior, and social memory impairments. LM22A-4 ameliorated the abnormal anxiolytic phenotype but had no effect on social memory deficits. Use of spectral confocal reflectance microscopy detected persistent myelin fragmentation in the external capsule of TBI mice at 5 weeks post-injury, which was accompanied by regionally distinct deficits in oligodendrocyte progenitor cells and post-mitotic oligodendrocytes, as well as chronic reactive gliosis and atrophy of the corpus callosum and injured external capsule. LM22A-4 treatment ameliorated myelin deficits in the perilesional external capsule, as well as tissue volume loss and the extent of reactive gliosis. However, there was no effect of this TrkB agonist on oligodendroglial populations detected at 5 weeks post-injury. Collectively, our results demonstrate that targeting TrkB immediately after TBI during early life confers neuroprotection and preserves myelin integrity, and this was associated with some improved neurobehavioral outcomes as the pediatric injured brain matures.

Emerging Utility of Applied Magnetic Resonance Imaging in the Management of Traumatic Brain Injury

Traumatic brain injury (TBI) is a widespread and expensive problem globally. The standard diagnostic workup for new TBI includes obtaining a noncontrast computed tomography image of the head, which provides quick information on operative pathologies. However, given the limited sensitivity of computed tomography for identifying subtle but meaningful changes in the brain, magnetic resonance imaging (MRI) has shown better utility for ongoing management and prognostication after TBI. In recent years, advanced applications of MRI have been further studied and are being implemented as clinical tools to help guide care. These include functional MRI, diffusion tensor imaging, MR perfusion, and MR spectroscopy. In this review, we discuss the scientific basis of each of the above techniques, the literature supporting their use in TBI, and how they may be clinically implemented to improve the care of TBI patients.

Connectome mapping with edge density imaging differentiates pediatric mild traumatic brain injury from typically developing controls: proof of concept

BACKGROUND

Although acute neurologic impairment might be transient, other long-term effects can be observed with mild traumatic brain injury. However, when pediatric patients with mild traumatic brain injury present for medical care, conventional imaging with CT and MR imaging often does not reveal abnormalities.

OBJECTIVE

To determine whether edge density imaging can separate pediatric mild traumatic brain injury from typically developing controls.

MATERIALS AND METHODS

Subjects were recruited as part of the "Therapeutic Resources for Attention Improvement using Neuroimaging in Traumatic Brain Injury" (TRAIN-TBI) study. We included 24 adolescents (χ=14.1 years of age, σ=1.6 years, range 10-16 years), 14 with mild traumatic brain injury (TBI) and 10 typically developing controls. Neurocognitive assessments included the pediatric version of the California Verbal Learning Test (CVLT) and the Attention Network Task (ANT). Diffusion MR imaging was acquired on a 3-tesla (T) scanner. Edge density images were computed utilizing fiber tractography. Principal component analysis (PCA) and support vector machines (SVM) were used in an exploratory analysis to separate mild TBI and control groups. The diagnostic accuracy of edge density imaging, neurocognitive tests, and fractional anisotropy (FA) from diffusion tensor imaging (DTI) was computed with two-sample t-tests and receiver operating characteristic (ROC) metrics.

RESULTS

Support vector machine-principal component analysis of edge density imaging maps identified three white matter regions distinguishing pediatric mild TBI from controls. The bilateral tapetum, sagittal stratum, and callosal splenium identified mild TBI subjects with sensitivity of 79% and specificity of 100%. Accuracy from the area under the ROC curve (AUC) was 94%. Neurocognitive testing provided an AUC of 61% (CVLT) and 71% (ANT). Fractional anisotropy yielded an AUC of 48%.

CONCLUSION

In this proof-of-concept study, we show that edge density imaging is a new form of connectome mapping that provides better diagnostic delineation between pediatric mild TBI and healthy controls than DTI or neurocognitive assessments of memory or attention.

The Impact of Traumatic Injury to the Immature Human Brain: A Scoping Review with Insights from Advanced Structural Neuroimaging

Traumatic brain injury (TBI) during critical periods of early-life brain development can affect the normal formation of brain networks responsible for a range of complex social behaviors. Because of the protracted nature of brain and behavioral development, deficits in cognitive and socioaffective behaviors may not become evident until late adolescence and early adulthood, when such skills are expected to reach maturity. In addition, multiple pre- and post-injury factors can interact with the effects of early brain insult to influence long-term outcomes. In recent years, with advancements in magnetic-resonance-based neuroimaging techniques and analysis, studies of the pediatric population have revealed a link between neurobehavioral deficits, such as social dysfunction, with white matter damage. In this review, in which we focus on contributions from Australian researchers to the field, we have highlighted pioneering longitudinal studies in pediatric TBI, in relation to social deficits specifically. We also discuss the use of advanced neuroimaging and novel behavioral assays in animal models of TBI in the immature brain. Together, this research aims to understand the relationship between injury consequences and ongoing brain development after pediatric TBI, which promises to improve prediction of the behavioral deficits that emerge in the years subsequent to early-life injury.

Longitudinal Neuroimaging in Pediatric Traumatic Brain Injury: Current State and Consideration of Factors That Influence Recovery

Traumatic brain injury (TBI) is a leading cause of death and disability for children and adolescents in the U.S. and other developed and developing countries. Injury to the immature brain varies greatly from that of the mature, adult brain due to numerous developmental, pre-injury, and injury-related factors that work together to influence the trajectory of recovery during the course of typical brain development. Substantial damage to brain structure often underlies subsequent functional limitations that persist for years following pediatric TBI. Advances in neuroimaging have established an important role in the acute management of pediatric TBI, and magnetic resonance imaging (MRI) techniques have a particular relevance for the sequential assessment of long-term consequences from injuries sustained to the developing brain. The present paper will discuss the various factors that influence recovery and review the findings from the present neuroimaging literature to assess altered development and long-term outcome following pediatric TBI. Four MR-based neuroimaging modalities have been used to examine recovery from pediatric TBI longitudinally: (1) T1-weighted structural MRI is sensitive to morphological changes in gray matter volume and cortical thickness, (2) diffusion-weighted MRI is sensitive to changes in the microstructural integrity of white matter, (3) MR spectroscopy provides a sensitive assessment of metabolic and neurochemical alterations in the brain, and (4) functional MRI provides insight into the functional changes that occur as a result of structural damage and typical developmental processes. As reviewed in this paper, 13 cohorts have contributed to only 20 studies published to date using neuroimaging to examine longitudinal changes after TBI in pediatric patients. The results of these studies demonstrate considerable heterogeneity in post-injury outcome; however, the existing literature consistently shows that alterations in brain structure, function, and metabolism can persist for an extended period of time post-injury. With larger sample sizes and multi-site cooperation, future studies will be able to further examine potential moderators of outcome, such as the developmental, pre-injury, and injury-related factors discussed in the present review.

Every hit matters: White matter diffusivity changes in high school football athletes are correlated with repetitive head acceleration event exposure

Recent evidence of short-term alterations in brain physiology associated with repeated exposure to moderate intensity subconcussive head acceleration events (HAEs), prompts the question whether these alterations represent an underlying neural injury. A retrospective analysis combining counts of experienced HAEs and longitudinal diffusion-weighted imaging explored whether greater exposure to incident mechanical forces was associated with traditional diffusion-based measures of neural injury—reduced fractional anisotropy (FA) and increased mean diffusivity (MD). Brains of high school athletes (N = 61) participating in American football exhibited greater spatial extents (or volumes) experiencing substantial changes (increases and decreases) in both FA and MD than brains of peers who do not participate in collision-based sports (N = 15). Further, the spatial extents of the football athlete brain exhibiting traditional diffusion-based markers of neural injury were found to be significantly correlated with the cumulative exposure to HAEs having peak translational acceleration exceeding 20 g. This finding demonstrates that subconcussive HAEs induce low-level neurotrauma, with prolonged exposure producing greater accumulation of neural damage. The duration and extent of recovery associated with periods in which athletes do not experience subconcussive HAEs now represents a priority for future study, such that appropriate participation and training schedules may be developed to minimize the risk of long-term neurological dysfunction.

•

Brain volumes evidencing injury are larger in football athletes than controls.

•

Spatial extent of decreased FA correlates with head acceleration event exposure.

•

Spatial extent of increased MD correlates with head acceleration event exposure.

Bridging the gap: Mechanisms of plasticity and repair after pediatric TBI

Traumatic brain injury is the leading cause of death and disability in the United States, and may be associated with long lasting impairments into adulthood. The multitude of ongoing neurobiological processes that occur during brain maturation confer both considerable vulnerability to TBI but may also provide adaptability and potential for recovery. This review will examine and synthesize our current understanding of developmental neurobiology in the context of pediatric TBI. Delineating this biology will facilitate more targeted initial care, mechanism-based therapeutic interventions and better long-term prognostication and follow-up.

Relevance of neuroimaging for neurocognitive and behavioral outcome after pediatric traumatic brain injury

This study aims to (1) investigate the neuropathology of mild to severe pediatric TBI and (2) elucidate the predictive value of conventional and innovative neuroimaging for functional outcome. Children aged 8–14 years with trauma control (TC) injury (n = 27) were compared to children with mild TBI and risk factors for complicated TBI (mild^RF+, n = 20) or moderate/severe TBI (n = 17) at 2.8 years post-injury. Neuroimaging measures included: acute computed tomography (CT), volumetric analysis on post-acute conventional T1-weighted magnetic resonance imaging (MRI) and post-acute diffusion tensor imaging (DTI, analyzed using tract-based spatial statistics and voxel-wise regression). Functional outcome was measured using Common Data Elements for neurocognitive and behavioral functioning. The results show that intracranial pathology on acute CT-scans was more prevalent after moderate/severe TBI (65%) than after mild^RF+ TBI (35%; p = .035), while both groups had decreased white matter volume on conventional MRI (ps ≤ .029, ds ≥ −0.74). The moderate/severe TBI group further showed decreased fractional anisotropy (FA) in a widespread cluster affecting all white matter tracts, in which regional associations with neurocognitive functioning were observed (FSIQ, Digit Span and RAVLT Encoding) that consistently involved the corpus callosum. FA had superior predictive value for functional outcome (i.e. intelligence, attention and working memory, encoding in verbal memory and internalizing problems) relative to acute CT-scanning (i.e. internalizing problems) and conventional MRI (no predictive value). We conclude that children with mild^RF+ TBI and moderate/severe TBI are at risk of persistent white matter abnormality. Furthermore, DTI has superior predictive value for neurocognitive out-come relative to conventional neuroimaging.

A jugular vein compression collar prevents alterations of endogenous electrocortical dynamics following blast exposure during special weapons and tactical (SWAT) breacher training

Exposure to explosive blasts places one at risk for traumatic brain injury, especially for special weapons and tactics (SWAT) and military personnel, who may be repeatedly exposed to blasts. In the current study, the effectiveness of a jugular vein compression collar to prevent alterations in resting-state electrocortical activity following a single-SWAT breacher training session was investigated. SWAT team personnel were randomly assigned to wear a compression collar during breacher training and resting state electroencephalography (EEG) was measured within 2 days prior to and two after breacher training. It was hypothesized that significant changes in brain dynamics-indicative of possible underlying neurodegenerative processes-would follow blast exposure for those who did not wear the collar, with ameliorated changes for the collar-wearing group. Using recurrence quantification analysis (RQA) it was found that participants who did not wear the collar displayed longer periods of laminar electrocortical behavior (as indexed by RQA's vertical max line measure) after breacher training. It is proposed that the blast wave exposure for the no-collar group may have reduced the number of pathways, via axonal disruption-for electrical transmission-resulting in the EEG signals becoming trapped in laminar states for longer periods of time. Longer laminar states have been associated with other electrocortical pathologies, such as seizure, and may be important for understanding head trauma and recovery.

Paediatric traumatic brain injury: prognostic insights and outlooks

PURPOSE OF REVIEW

Traumatic brain injury (TBI) is a leading cause of death and disability in children. Prognostication of outcome following TBI is challenging in this population and likely requires complex, multimodal models to achieve clinically relevant accuracy. This review highlights injury characteristics, physiological indicators, biomarkers and neuromonitoring modalities predictive of outcome that may be integrated for future development of sensitive and specific prognostic models.

RECENT FINDINGS

Paediatric TBI is responsible for physical, psychosocial and neurocognitive deficits that may significantly impact quality of life. Outcome prognostication can be difficult in the immature brain, but is aided by the identification of novel biomarkers (neuronal, astroglial, myelin, inflammatory, apoptotic and autophagic) and neuromonitoring techniques (electroencephalogram and MRI). Investigation in the future may focus on assessing the prognostic ability of combinations of biochemical, protein, neuroimaging and functional biomarkers and the use of mathematical models to develop multivariable predication tools to improve the prognostic ability following childhood TBI.

SUMMARY

Prognostication of outcome following paediatric TBI is multidimensional, influenced by injury severity, age, physiological factors, biomarkers, electroencephalogram and neuroimaging. Further development, integration and validation of combinatorial prognostic algorithms are necessary to improve the accuracy and timeliness of prognosis in a meaningful fashion.

White matter microstructure predicts longitudinal social cognitive outcomes after paediatric traumatic brain injury: a diffusion tensor imaging study

BACKGROUND

Deficits in social cognition may be among the most profound and disabling sequelae of paediatric traumatic brain injury (TBI); however, the neuroanatomical correlates of longitudinal outcomes in this domain remain unexplored. This study aimed to characterize social cognitive outcomes longitudinally after paediatric TBI, and to evaluate the use of sub-acute diffusion tensor imaging (DTI) to predict these outcomes.

METHODS

The sample included 52 children with mild complex-severe TBI who were assessed on cognitive theory of mind (ToM), pragmatic language and affective ToM at 6- and 24-months post-injury. For comparison, 43 typically developing controls (TDCs) of similar age and sex were recruited. DTI data were acquired sub-acutely (mean = 5.5 weeks post-injury) in a subset of 65 children (TBI = 35; TDC = 30) to evaluate longitudinal prospective relationships between white matter microstructure assessed using Tract-Based Spatial Statistics and social cognitive outcomes.

RESULTS

Whole brain voxel-wise analysis revealed significantly higher mean diffusivity (MD), axial diffusivity (AD) and radial diffusivity (RD) in the sub-acute TBI group compared with TDC, with differences observed predominantly in the splenium of the corpus callosum (sCC), sagittal stratum (SS), dorsal cingulum (DC), uncinate fasciculus (UF) and middle and superior cerebellar peduncles (MCP & SCP, respectively). Relative to TDCs, children with TBI showed poorer cognitive ToM, affective ToM and pragmatic language at 6-months post-insult, and those deficits were related to abnormal diffusivity of the sCC, SS, DC, UF, MCP and SCP. Moreover, children with TBI showed poorer affective ToM and pragmatic language at 24-months post-injury, and those outcomes were predicted by sub-acute alterations in diffusivity of the DC and MCP.

CONCLUSIONS

Abnormal microstructure within frontal-temporal, limbic and cerebro-cerebellar white matter may be a risk factor for long-term social difficulties observed in children with TBI. DTI may have potential to unlock early prognostic markers of long-term social outcomes.

Neuroimaging of the Injured Pediatric Brain: Methods and New Lessons

Traumatic brain injury (TBI) is a significant public health problem in the United States, especially for children and adolescents. Current epidemiological data estimate over 600,000 patients younger than 20 years are treated for TBI in emergency rooms annually. While many patients experience a full recovery, for others there can be long-lasting cognitive, neurological, psychological, and behavioral disruptions. TBI in youth can disrupt ongoing brain development and create added family stress during a formative period. The neuroimaging methods used to assess brain injury improve each year, providing researchers a more detailed characterization of the injury and recovery process. In this review, we cover current imaging methods used to quantify brain disruption post-injury, including structural magnetic resonance imaging (MRI), diffusion MRI, functional MRI, resting state fMRI, and magnetic resonance spectroscopy (MRS), with brief coverage of other methods, including electroencephalography (EEG), single-photon emission computed tomography (SPECT), and positron emission tomography (PET). We include studies focusing on pediatric moderate-severe TBI from 2 months post-injury and beyond. While the morbidity of pediatric TBI is considerable, continuing advances in imaging methods have the potential to identify new treatment targets that can lead to significant improvements in outcome.

Diffusion MRI in pediatric brain injury

Traumatic brain injury (TBI) is a major public health issue around the world and can be especially devastating in children as TBI can derail cognitive and social development. White matter (WM) is particularly vulnerable to disruption post-TBI, as myelination is ongoing during this period. Diffusion magnetic resonance imaging (dMRI) is a versatile modality for identifying and quantifying WM disruption and can detect diffuse axonal injury (DAI or TAI (traumatic axonal injury)). This review covers dMRI studies of pediatric TBI, including mild to severe injuries, and covering all periods post-injury. While there have been considerable advances in our understanding of pediatric TBI through the use of dMRI, there are still large gaps in our knowledge, which will be filled in by larger studies and more longitudinal studies. Heterogeneity post-injury is an obstacle in all TBI studies, but we expect that larger better-characterized samples will aid in identifying clinically meaningful subgroups within the pediatric TBI patient population.

Brain volumetric correlates of inhibition and cognitive flexibility 16 years following childhood traumatic brain injury

Executive functions (EFs), such as inhibition and cognitive flexibility, are essential for everyday functioning, including regulation of socially appropriate emotional responses. These skills develop during childhood and continue maturing into early adulthood. The current study aimed to investigate the very long-term impact of childhood traumatic brain injury (TBI) on inhibition and cognitive flexibility, and to examine whether global white matter is associated with these abilities. Twenty-eight young adult survivors of childhood TBI (mean age at 16-year follow-up = 21.67 years, SD = 2.70) and 16 typically developing controls (TDCs), group-matched for age, sex, and socioeconomic status, completed tests of inhibition and cognitive flexibility and underwent structural MRI. Survivors of childhood TBI did not significantly differ from TDCs on EF or white matter volume. However, the relationship between EF and white matter volume differed between survivors of TBI and TDCs. Survivors of TBI did not mimic the brain behavior relationship that characterized EF in TDCs. The inverse brain behavior relationship, exhibited by childhood TBI survivors, suggests disruptions in the whole brain underpinning EF following childhood TBI.

Investigating Microstructural Abnormalities and Neurocognition in Sub-Acute and Chronic Traumatic Brain Injury Patients with Normal-Appearing White Matter: A Preliminary Diffusion Tensor Imaging Study

For a significant percentage of subjects, with chronic traumatic brain injury (TBI), who report persisting cognitive impairment and functional loss, the diagnosis is often impeded by the fact that routine neuroimaging often does not reveal any abnormalities. In this paper, we used diffusion tensor imaging (DTI) to investigate the apparently normal white matter (as assessed by routine magnetic resonance imaging) in the brains of 19 subjects with sub-acute (9) and chronic (10) TBI. We also assessed memory, executive function, and visual-motor coordination in these subjects. Using a voxel-wise approach, we investigated if parameters of diffusion were significantly different between TBI subjects and 17 healthy controls (HC), who were demographically matched to the TBI group. We also investigated if changes in DTI parameters were associated with neuropsychological performance in either group. Our results indicate significantly increased mean and axial diffusivity (MD and AD, respectively) values in widespread brain locations in TBI subjects, while controlling for age, sex, and time since injury. HC performed significantly better than the TBI subjects on tests of memory and executive function, indicating the persisting functional loss in chronic TBI. We found no correlation between diffusion parameters and performance on test of executive function in either group. We found negative correlation between FA and composite memory scores, and positive correlation between RD and visuomotor coordination test scores, in various tracts in both groups. Our study suggests that changes in MD and AD can indicate persisting micro-structure abnormalities in normal-appearing white matter in the brains of subjects with chronic TBI. Our results also suggest that FA in major white matter tracts is correlated with memory in health and in disease, alike; larger and longitudinal studies are needed to discern potential differences in these correlations in the two groups.

Both hemorrhagic and non-hemorrhagic traumatic MRI lesions are associated with the microstructural damage of the normal appearing white matter

Traumatic microbleeds (TMBs) and non-hemorrhagic lesions (NHLs) on MRI are regarded as surrogate markers of diffuse axonal injury. However, the actual relation between lesional and diffuse pathology remained unclear, since lesions were related to clinical parameters, largely influenced by extracranial factors. The aim of this study is to directly compare TMBs, NHLs and their regional features with the co-existing diffuse injury of the normal appearing white matter (NAWM) as measured by diffusion tensor imaging (DTI). Thirty-eight adults with a closed traumatic brain injury (12 mild, 4 moderate and 22 severe) who underwent susceptibility weighted imaging (SWI), T1-, T2 weighted and FLAIR MRI and routine CT were included in the study. TMB (on SWI) and NHL (on T1-, T2 weighted and FLAIR images) features and Rotterdam scores were evaluated. DTI metrics such as fractional anisotropy (FA) and mean diffusivity (MD) were measured over different NAWM regions. Clinical parameters including age; Glasgow Coma Scale; Rotterdam score; TMB and NHL features were correlated to regional NAWM diffusivity using multiple regression. Overall NHL presence and basal ganglia area TMB load were significantly, negatively correlated with the subcortical NAWM FA values (partial r=-0.37 and -0.36; p=0.006 and 0.025, respectively). The presence of any NHL, or TMBs located in the basal ganglia area indicates diffuse NAWM damage even after adjusting for clinical and CT parameters. To estimate DAI, a conventional lesional MRI pathology evaluation might at least in part substitute the use of quantitative DTI, which is yet not widely feasible in a clinical setting.

The new neurometabolic cascade of concussion

Since the original descriptions of postconcussive pathophysiology, there has been a significant increase in interest and ongoing research to study the biological underpinnings of concussion. The initial ionic flux and glutamate release result in significant energy demands and a period of metabolic crisis for the injured brain. These physiological perturbations can now be linked to clinical characteristics of concussion, including migrainous symptoms, vulnerability to repeat injury, and cognitive impairment. Furthermore, advanced neuroimaging now allows a research window to monitor postconcussion pathophysiology in humans noninvasively. There is also increasing concern about the risk for chronic or even progressive neurobehavioral impairment after concussion/mild traumatic brain injury. Critical studies are underway to better link the acute pathobiology of concussion with potential mechanisms of chronic cell death, dysfunction, and neurodegeneration. This "new and improved" article summarizes in a translational fashion and updates what is known about the acute neurometabolic changes after concussive brain injury. Furthermore, new connections are proposed between this neurobiology and early clinical symptoms as well as to cellular processes that may underlie long-term impairment.

Gray matter abnormalities in pediatric mild traumatic brain injury

Pediatric mild traumatic brain injury (pmTBI) is the most prevalent neurological insult in children and is associated with both acute and chronic neuropsychiatric sequelae. However, little is known about underlying pathophysiology changes in gray matter diffusion and atrophy from a prospective stand-point. Fifteen semi-acute pmTBI patients and 15 well-matched healthy controls were evaluated with a clinical and neuroimaging battery, with a subset of participants returning for a second visit. Clinical measures included tests of attention, processing speed, executive function, working memory, memory, and self-reported post-concussive symptoms. Measures of diffusion (fractional anisotropy [FA]) and atrophy were also obtained for cortical and subcortical gray matter structures to characterize effects of injury as a function of time. Patients exhibited decreased scores in the domains of attention and processing speed relative to controls during the semi-acute injury stage, in conjunction with increased anisotropic diffusion in the left superior temporal gyrus and right thalamus. Evidence of increased diffusion in these regions was also present at four months post-injury, with performance on cognitive tests partially normalizing. In contrast, signs of cortical atrophy in bilateral frontal areas and other left-hemisphere cortical areas only emerged at four months post-injury for patients. Current results suggest potentially differential time-courses of recovery for neurobehavioral markers, anisotropic diffusion and atrophy following pmTBI. Importantly, these data suggest that relying on patient self-report or standard clinical assessments may underestimate the time for true injury recovery.

White matter disruption in moderate/severe pediatric traumatic brain injury: advanced tract-based analyses

Traumatic brain injury (TBI) is the leading cause of death and disability in children and can lead to a wide range of impairments. Brain imaging methods such as DTI (diffusion tensor imaging) are uniquely sensitive to the white matter (WM) damage that is common in TBI. However, higher-level analyses using tractography are complicated by the damage and decreased FA (fractional anisotropy) characteristic of TBI, which can result in premature tract endings. We used the newly developed autoMATE (automated multi-atlas tract extraction) method to identify differences in WM integrity. 63 pediatric patients aged 8–19 years with moderate/severe TBI were examined with cross sectional scanning at one or two time points after injury: a post-acute assessment 1–5 months post-injury and a chronic assessment 13–19 months post-injury. A battery of cognitive function tests was performed in the same time periods. 56 children were examined in the first phase, 28 TBI patients and 28 healthy controls. In the second phase 34 children were studied, 17 TBI patients and 17 controls (27 participants completed both post-acute and chronic phases). We did not find any significant group differences in the post-acute phase. Chronically, we found extensive group differences, mainly for mean and radial diffusivity (MD and RD). In the chronic phase, we found higher MD and RD across a wide range of WM. Additionally, we found correlations between these WM integrity measures and cognitive deficits. This suggests a distributed pattern of WM disruption that continues over the first year following a TBI in children.

•

We examined pediatric traumatic brain injury patients at 2 time points post injury.

•

Cross sectional analyses were completed at the post-acute and chronic stages.

•

We used novel tract-based methods to reveal widespread white matter disruption.

•

White matter disruption chronically was related to cognitive deficits.

Diffusion Tensor Imaging (DTI) findings following pediatric non-penetrating TBI: a meta-analysis

This study meta-analyzed research examining Diffusion Tensor Imaging following pediatric non-penetrating traumatic brain injury to identify the location and extent of white matter changes. Fractional anisotropy (FA) and apparent diffusion coefficient (ADC) data from 20 studies were analyzed. FA increased and ADC decreased in most white matter tracts in the short-term (moderate-to-large effects), and FA decreased and ADC increased in the medium- to long-term (moderate-to-very-large effects). Whole brain (short-term), cerebellum and corpus callosum (medium- to long-term) FA values have diagnostic potential, but the impact of age/developmental stage and injury severity on FA/ADC, and the predictive value, is unclear.

Traumatic brain injury and cognition

Traumatic brain injury (TBI) is a major cause of death and disability, and therefore an important health and socioeconomic problem for our society. Individuals surviving from a moderate to severe TBI frequently suffer from long-lasting cognitive deficits. Such deficits include different aspects of cognition such as memory, attention, executive functions, and awareness of their deficits. This chapter presents a review of the main neuropsychological and neuroimaging studies of patients with TBI. These studies found that patients evolve differently according to the severity of the injury, the mechanism causing the injury, and the lesion location. Further research is necessary to develop rehabilitation methods that enhance brain plasticity and recovery after TBI. In this chapter, we summarize current knowledge and controversies, focusing on cognitive sequelae after TBI. Recommendations from the Common Data Elements are provided, with an emphasis on diagnosis, outcome measures, and studies organization to make data more comparable across studies. Final considerations on neuroimaging advances, rehabilitation approaches, and genetics are described in the final section of the chapter.

The neuropathology of traumatic brain injury

Traumatic brain injury, a leading cause of mortality and morbidity, is divided into three grades of severity: mild, moderate, and severe, based on the Glasgow Coma Scale, the loss of consciousness, and the development of post-traumatic amnesia. Although mild traumatic brain injury, including concussion and subconcussion, is by far the most common, it is also the most difficult to diagnose and the least well understood. Proper recognition, management, and treatment of acute concussion and mild traumatic brain injury are the fundamentals of an emerging clinical discipline. It is also becoming increasingly clear that some mild traumatic brain injuries have persistent, and sometimes progressive, long-term debilitating effects. Evidence indicates that a single traumatic brain injury can precipitate or accelerate multiple age-related neurodegenerations, increase the risk of developing Alzheimer's disease, Parkinson's disease, and motor neuron disease, and that repetitive mild traumatic brain injuries can provoke the development of a tauopathy, chronic traumatic encephalopathy. Clinically, chronic traumatic encephalopathy is associated with behavioral changes, executive dysfunction, memory loss, and cognitive impairments that begin insidiously and progress slowly over decades. Pathologically, chronic traumatic encephalopathy produces atrophy of the frontal and temporal lobes, thalamus, and hypothalamus, septal abnormalities, and abnormal deposits of hyperphosphorylated tau (τ) as neurofibrillary tangles and disordered neurites throughout the brain. The incidence and prevalence of chronic traumatic encephalopathy and the genetic risk factors critical to its development are currently unknown. Chronic traumatic encephalopathy frequently occurs as a sole diagnosis, but may be associated with other neurodegenerative disorders, including Alzheimer's disease, Lewy body disease, and motor neuron disease. Currently, chronic traumatic encephalopathy can be diagnosed only at autopsy; however, promising efforts to develop imaging, spinal fluid, and peripheral blood biomarkers are underway to diagnose and monitor the course of disease in living subjects.

Application of advanced neuroimaging modalities in pediatric traumatic brain injury

Neuroimaging is commonly used for the assessment of children with traumatic brain injury and has greatly advanced how children are acutely evaluated. More recently, emphasis has focused on how advanced magnetic resonance imaging methods can detect subtler injuries that could relate to the structural underpinnings of the neuropsychological and behavioral alterations that frequently occur. We examine several methods used for the assessment of pediatric brain injury. Susceptibility-weighted imaging is a sensitive 3-dimensional high-resolution technique in detecting hemorrhagic lesions associated with diffuse axonal injury. Magnetic resonance spectroscopy acquires metabolite information, which serves as a proxy for neuronal (and glial, lipid, etc) structural integrity and provides sensitive assessment of neurochemical alterations. Diffusion-weighted imaging is useful for the early detection of ischemic and shearing injury. Diffusion tensor imaging allows better structural evaluation of white matter tracts. These methods are more sensitive than conventional imaging in demonstrating subtle injury that underlies a child's clinical symptoms. There also is an increasing desire to develop computational methods to fuse imaging data to provide a more integrated analysis of the extent to which components of the neurovascular unit are affected. The future of traumatic brain injury neuroimaging research is promising and will lead to novel approaches to predict and improve outcomes.

The neuropathology of sport

The benefits of regular exercise, physical fitness and sports participation on cardiovascular and brain health are undeniable. Physical activity reduces the risk for cardiovascular disease, type 2 diabetes, hypertension, obesity, and stroke, and produces beneficial effects on cholesterol levels, antioxidant systems, inflammation, and vascular function. Exercise also enhances psychological health, reduces age-related loss of brain volume, improves cognition, reduces the risk of developing dementia, and impedes neurodegeneration. Nonetheless, the play of sports is associated with risks, including a risk for mild TBI (mTBI) and, rarely, catastrophic traumatic injury and death. There is also growing awareness that repetitive mTBIs, such as concussion and subconcussion, can occasionally produce persistent cognitive, behavioral, and psychiatric problems as well as lead to the development of a neurodegeneration, chronic traumatic encephalopathy (CTE). In this review, we summarize the beneficial aspects of sports participation on psychological, emotional, physical and cognitive health, and specifically analyze some of the less common adverse neuropathological outcomes, including concussion, second-impact syndrome, juvenile head trauma syndrome, catastrophic sudden death, and CTE. CTE is a latent neurodegeneration clinically associated with behavioral changes, executive dysfunction and cognitive impairments, and pathologically characterized by frontal and temporal lobe atrophy, neuronal and axonal loss, and abnormal deposits of paired helical filament (PHF)-tau and 43 kDa TAR deoxyribonucleic acid (DNA)-binding protein (TDP-43). CTE often occurs as a sole diagnosis, but may be associated with other neurodegenerative disorders, including motor neuron disease (CTE-MND). Although the incidence and prevalence of CTE are not known, CTE has been reported most frequently in American football players and boxers. Other sports associated with CTE include ice hockey, professional wrestling, soccer, rugby, and baseball.

Pediatric traumatic brain injury: language outcomes and their relationship to the arcuate fasciculus

Pediatric traumatic brain injury (TBI) may result in long-lasting language impairments alongside dysarthria, a motor-speech disorder. Whether this co-morbidity is due to the functional links between speech and language networks, or to widespread damage affecting both motor and language tracts, remains unknown. Here we investigated language function and diffusion metrics (using diffusion-weighted tractography) within the arcuate fasciculus, the uncinate fasciculus, and the corpus callosum in 32 young people after TBI (approximately half with dysarthria) and age-matched healthy controls (n=17). Only participants with dysarthria showed impairments in language, affecting sentence formulation and semantic association. In the whole TBI group, sentence formulation was best predicted by combined corpus callosum and left arcuate volumes, suggesting this "dual blow" seriously reduces the potential for functional reorganisation. Word comprehension was predicted by fractional anisotropy in the right arcuate. The co-morbidity between dysarthria and language deficits therefore seems to be the consequence of multiple tract damage.

Traumatic injury to the immature frontal lobe: a new murine model of long-term motor impairment in the absence of psychosocial or cognitive deficits

Traumatic brain injury in children commonly involves the frontal lobes and is associated with distinct structural and behavioral changes. Despite the clinical significance of injuries localized to this region during brain development, the mechanisms underlying secondary damage and long-term recovery are poorly understood. Here, we have characterized the first model of unilateral focal traumatic injury to the developing frontal lobe. Male C57Bl/6J mice at postnatal day (p)21, an age approximating a toddler-aged child, received a controlled cortical impact or sham surgery to the left frontal lobe and were euthanized 1 or 7 days later. A necrotic cavity and local inflammatory response were largely confined to the unilateral frontal lobe, dorsal corpus callosum and striatum anterior to the bregma. While cell death and accumulated β-amyloid precursor protein were characteristic features of the pericontusional motor cortex, corpus callosum, cingulum and dorsal striatum, underlying structures including the hippocampus showed no overt pathology. To determine the long-term functional consequences of injury at p21, two additional cohorts were subjected to a battery of behavioral tests in adolescence (p35-45) or adulthood (p70-80). In both cohorts, brain-injured mice showed normal levels of anxiety, sociability, spatial learning and memory. The signature phenotypic features were deficits in motor function and motor learning, coincident with a reduction in ipsilateral cortical brain volumes. Together, these findings demonstrate classic morphological features of a focal traumatic injury, including early cell death and axonal injury, and long-term volumetric loss of cortical volumes. The presence of deficits in sensorimotor function and coordination in the absence of abnormal findings related to anxiety, sociability and memory likely reflects several variables, including the unique location of the injury and the emergence of favorable compensatory mechanisms during subsequent brain development.

Consonant accuracy after severe pediatric traumatic brain injury: a prospective cohort study

PURPOSE

The authors sought to describe longitudinal changes in Percentage of Consonants Correct-Revised (PCC-R) after severe pediatric traumatic brain injury (TBI), to compare the odds of normal-range PCC-R in children injured at older and younger ages, and to correlate predictor variables and PCC-R outcomes.

METHOD

In 56 children injured between age 1 month and 11 years, PCC-R was calculated over 12 monthly sessions beginning when the child produced ≥ 10 words. At each session, the authors compared odds of normal-range PCC-R in children injured at younger (≤ 60 months) and older (> 60 months) ages. Correlations were calculated between final PCC-R and age at injury, injury mechanism, gender, maternal education, residence, treatment, Glasgow Coma Score, and intact brain volume.

RESULTS

PCC-Rs varied within and between children. Odds of normal-range PCC-R were significantly higher for the older than for the younger group at all sessions but the first; odds of normal-range PCC-R were 9 to 33 times higher in the older group in sessions 3 to 12. Age at injury was significantly correlated with final PCC-R.

CONCLUSION

Over a 12-month period, severe TBI had more adverse effects for children whose ages placed them in the most intensive phase of PCC-R development than for children injured later.

Whole brain approaches for identification of microstructural abnormalities in individual patients: comparison of techniques applied to mild traumatic brain injury

PURPOSE

Group-wise analyses of DTI in mTBI have demonstrated evidence of traumatic axonal injury (TAI), associated with adverse clinical outcomes. Although mTBI is likely to have a unique spatial pattern in each patient, group analyses implicitly assume that location of injury will be the same across patients. The purpose of this study was to optimize and validate a procedure for analysis of DTI images acquired in individual patients, which could detect inter-individual differences and be applied in the clinical setting, where patients must be assessed as individuals.

MATERIALS AND METHODS

After informed consent and in compliance with HIPAA, 34 mTBI patients and 42 normal subjects underwent 3.0 Tesla DTI. Four voxelwise assessment methods (standard Z-score, "one vs. many" t-test, Family-Wise Error Rate control using pseudo t-distribution, EZ-MAP) for use in individual patients, were applied to each patient's fractional anisotropy (FA) maps and tested for its ability to discriminate patients from controls. Receiver Operating Characteristic (ROC) analyses were used to define optimal thresholds (voxel-level significance and spatial extent) for reliable and robust detection of mTBI pathology.

RESULTS

ROC analyses showed EZ-MAP (specificity 71%, sensitivity 71%), "one vs. many" t-test and standard Z-score (sensitivity 65%, specificity 76% for both methods) resulted in a significant area under the curve (AUC) score for discriminating mTBI patients from controls in terms of the total number of abnormal white matter voxels detected while the FWER test was not significant. EZ-MAP is demonstrated to be robust to assumptions of Gaussian behavior and may serve as an alternative to methods that require strict Gaussian assumptions.

CONCLUSION

EZ-MAP provides a robust approach for delineation of regional abnormal anisotropy in individual mTBI patients.

Diffusion abnormalities in pediatric mild traumatic brain injury

Pediatric mild traumatic brain injury (pmTBI) is the most prevalent neurological insult in children and is associated with both acute and chronic neurobehavioral sequelae. However, little is known about underlying pathophysiology and how injuries change as a function of recovery. Fractional anisotropy, axial diffusivity, and radial diffusivity were examined in 15 semi-acute pmTBI patients and 15 well-matched controls, with a subset of participants returning for a second visit. A novel analytic strategy was applied to capture spatially heterogeneous white matter injuries (lesions) in addition to standard analyses. Evidence of cognitive dysfunction after pmTBI was observed in the domains of attention (p = 0.02, d = -0.92) and processing speed (p = 0.05, d = -0.73) semi-acutely. Region of interest (ROI) and voxelwise analyses indicated increased anisotropic diffusion for pmTBI patients, with an elevated number of clusters with high anisotropy. Metrics of increased anisotropy were able to objectively classify pmTBI from healthy controls at 90% accuracy but were not associated with neuropsychological deficits. Little evidence of recovery in white matter abnormalities was observed over a 4-month interval in returning patients, indicating that physiological recovery may lag behind subjective reports of normality. Increased anisotropic diffusion has been previously linked with cytotoxic edema after TBI, and the magnitude and duration of these abnormalities appear to be greater in pediatric patients. Current findings suggest that developing white matter may be more susceptible to initial mechanical injury forces and that anisotropic diffusion provides an objective biomarker of pmTBI.

Diffusion tensor imaging in moderate-to-severe pediatric traumatic brain injury: changes within an 18 month post-injury interval

Traumatic brain injury (TBI) is a leading cause of death and disability in children, yet little is known regarding the pattern of TBI-related microstructural change and its impact on subsequent development. Diffusion tensor imaging (DTI) was used to examine between-group differences at two time points (planned intervals of 3 months and 18 months post-injury) and within-group longitudinal change in a group of children and adolescents aged 7-17 years with moderate-to-severe TBI (n = 20) and a comparison group of children with orthopedic injury (OI) (n = 21). In the 3- and 18-month cross-sectional analyses, tract-based spatial statistics (TBSS) generally revealed decreased fractional anisotropy (FA) and increased apparent diffusion coefficient (ADC) in the TBI group in regions of frontal, temporal, parietal, and occipital white matter as well as several deep subcortical structures, though areas of FA decrease were more prominent at the 3-month assessment, and areas of ADC increase were more prominent at the 18 month assessment, particularly in the frontal regions. In terms of the within-group changes over time, the OI group demonstrated primarily diffuse increases in FA over time, consistent with previous findings of DTI-measured white matter developmental change. The TBI group demonstrated primarily regions of FA decrease and ADC increase over time, consistent with presumed continued degenerative change, though regions of ADC decrease were also appreciated. These results suggest that TBI-related microstructural changes are dynamic in children and continue until at least 18 months post-injury. Understanding the course of these changes in DTI metrics may be important in TBI for facilitating advances in management and intervention.

A decade of DTI in traumatic brain injury: 10 years and 100 articles later

SUMMARY

The past decade has seen an increase in the number of articles reporting the use of DTI to detect brain abnormalities in patients with traumatic brain injury. DTI is well-suited to the interrogation of white matter microstructure, the most important location of pathology in TBI. Additionally, studies in animal models have demonstrated the correlation of DTI findings and TBI pathology. One hundred articles met the inclusion criteria for this quantitative literature review. Despite significant variability in sample characteristics, technical aspects of imaging, and analysis approaches, the consensus is that DTI effectively differentiates patients with TBI and controls, regardless of the severity and timeframe following injury. Furthermore, many have established a relationship between DTI measures and TBI outcomes. However, the heterogeneity of specific outcome measures used limits interpretation of the literature. Similarly, few longitudinal studies have been performed, limiting inferences regarding the long-term predictive utility of DTI. Larger longitudinal studies, using standardized imaging, analysis approaches, and outcome measures will help realize the promise of DTI as a prognostic tool in the care of patients with TBI.

Pediatric brain injury: can DTI scalars predict functional outcome?

Diffusion imaging has made significant inroads into the clinical diagnosis of a variety of diseases by inferring changes in microstructure, namely cell membranes, myelin sheath and other structures that inhibit water diffusion. This review discusses recent progress in the use of diffusion parameters in predicting functional outcome. Studies in the literature using only scalar parameters from diffusion measurements, such as apparent diffusion coefficient (ADC) and fractional anisotropy (FA), are summarized. Other more complex mathematical models and post-processing uses are also discussed briefly.

The effect of pediatric traumatic brain injury on behavioral outcomes: a systematic review

AIM

To review systematically the empirical evidence on traumatic brain injury (TBI) during childhood and subsequent behavioral problems.

METHOD

An initial literature search with keywords 'brain injury,''children,' and 'behavior' was conducted using Web of Knowledge and PubMed databases. Ancestry was also used. Original research studies published between 1990 and February 2012 focusing on behavioral outcomes of children sustaining TBI from ages 0 to 18 years were included.

RESULTS

Fifty studies, varying considerably in methodologies, were included in the review. Findings showed that up to 50% of brain-injured children are at risk for presenting with specific behavioral problems and disorders. These problems may emerge shortly or several years after injury and often persist and even worsen with time. These behavioral impairments appear to be moderated by the family environment.

INTERPRETATION

Survivors of childhood TBI are at risk for developing and sustaining behavioral impairments. Stronger research is needed to identify cognitive and environmental factors that contribute to the onset and maintenance of these problems. Healthcare providers should ensure adequate follow-up and assessment of a child's behavioral, social, and neurocognitive domains. Caregivers should be encouraged to provide positive environments and parenting styles, which may help reduce chronic behavioral problems after brain injury.

Neuroimaging correlates of novel psychiatric disorders after pediatric traumatic brain injury

OBJECTIVE

To study magnetic resonance imaging (MRI) correlates of novel (new-onset) psychiatric disorders (NPD) after traumatic brain injury (TBI) and orthopedic injury (OI).

METHOD

Participants were 7 to 17 years of age at the time of hospitalization for either TBI or OI. The study used a prospective, longitudinal, controlled design with standardized psychiatric assessments conducted at baseline (reflecting pre-injury function) and 3 months post-injury. MRI assessments including diffusion tensor imaging (DTI)-derived fractional anisotropy (FA), volumetric measures of gray and white matter regions, volumetric measures of lesions, and cortical thickness were conducted. Injury severity was assessed by standard clinical scales. The outcome measure was the presence of an NPD identified during the first 3 months after injury.

RESULTS

There were 88 participants (TBI, 44; OI, 44). NPD occurred more frequently in the TBI (21/44; 48%) versus the OI (6/44; 14%) group (Fisher's exact test, p = .001). NPD in TBI participants was not related to injury severity. Multivariate analysis of covariance of the relationship between FA in hypothesized regions of interest (bilateral frontal and temporal lobes, bilateral centrum semiovale, bilateral uncinate fasciculi) and NPD and group (TBI versus OI) was significant, and both variables (NPD, p < .05; group, p < .001) were jointly significantly related to FA. NPD was not significantly related to volumetric measures of white or gray matter structures, volumetric measures of lesions, or cortical thickness measures.

CONCLUSIONS

Lowered white matter integrity may be more important in the pathophysiology of NPD than indices of gray matter or white matter atrophic changes, macroscopic lesions, and injury severity.

Diffuse and spatially variable white matter disruptions are associated with blast-related mild traumatic brain injury

Mild traumatic brain injury (mTBI) due to explosive blast is common among military service members and often associated with long term psychological and cognitive disruptions. Little is known about the neurological effects of blast-related mTBI and whether they differ from those of civilian, non-blast mTBI. Given that brain damage from blasts may be diffuse and heterogeneous, we tested the hypothesis that blast mTBI is associated with subtle white matter disruptions in the brain that are spatially inconsistent across individuals. We used diffusion tensor imaging to examine white matter integrity, as quantified by fractional anisotropy (FA), in a group of American military service members with (n=25) or without (n=33) blast-related mTBI who had been deployed as part of Operation Iraqi Freedom or Operation Enduring Freedom. History of civilian non-blast mTBI was equally common across groups, which enabled testing of both blast and non-blast mTBI effects on measures sensitive to (1) concentrated, spatially consistent (average FA within a region of interest [ROI]), (2) concentrated, spatially variable (number of ROIs with low average FA), and (3) diffuse (number of voxels with low FA) disruptions of white matter integrity. Blast mTBI was associated with a diffuse, global pattern of lower white matter integrity, and this pattern was not affected by previous civilian mTBI. Neither type of mTBI had an effect on the measures sensitive to more concentrated and spatially consistent white matter disruptions. Additionally, individuals with more than one blast mTBI tended to have a larger number of low FA voxels than individuals with a single blast injury. These results indicate that blast mTBI is associated with disrupted integrity of several white matter tracts, and that these disruptions are diluted by averaging across the large number of voxels within an ROI. The reported pattern of effects supports the conclusion that the neurological effects of blast mTBI are diffuse, widespread, and spatially variable.

Diffusion tensor imaging findings in young children with benign external hydrocephalus differ from the normal population

PURPOSE

To compare a pediatric population diagnosed with benign external hydrocephalus (BEH) to normal age-matched controls using diffusion tensor imaging (DTI) techniques.

METHODS

We retrospectively identified 17 BEH patients by specific clinical and neuroimaging criteria. Fractional anisotropy (FA) and mean diffusivity (MD) values obtained from DTI scans were compared to a population of age-matched controls and group differences were examined by mixed model analysis. A longitudinal comparison was completed on a subset that underwent multiple scans (n = 8).

RESULTS

In the genu of the corpus callosum (gCC), six of 15 BEH children had an FA value above the upper limit of 95% prediction interval, nine of 15 BEH children had MD values below the lower limit of 95% prediction interval. A similar trend applied to the other regions of interest (ROIs): splenium of the corpus callosum (sCC), ALIC, and PLIC. Statistical analysis demonstrated significant differences in FA within the gCC, sCC, and PLIC and in MD within the sCC between BEH patients and controls given (P = 0.05). No statistical differences were identified at any ROIs at the later scans.

CONCLUSIONS

We found a significant increase in FA and decrease in MD in children with BEH compared with normal children in specific white matter (WM) ROIs, notably in the gCC and sCC; furthermore, in longitudinal comparison, DTI parameters normalized over time. The current study further demonstrates the ability of DTI to distinguish between subtle diffusion changes in periventricular white matter and establishes preliminary objective radiographic parameters for watchful observation of patients with BEH.

To exclude or not to exclude: white matter hyperintensities in diffusion tensor imaging research

OBJECTIVE

A practical methodological issue for diffusion tensor imaging (DTI) researchers is determining what to do about incidental findings, such as white matter hyperintensities (WMHI). The purpose of this study was to compare healthy control subjects with or without WMHIs on whole brain DTI.

METHOD

Participants were 30 subjects (age = 37.7, SD = 11.3, Range = 18-60; 70% female) who had no known developmental, general medical, neurological or psychiatric condition that could have had an adverse affect on brain morphology.

RESULTS

MRI (3 Tesla) revealed, at minimum, a WMHI in eight subjects (26.7%). Fractional anisotropy (FA) was calculated for 19 regions of interest (ROI). Frequency distributions of FA scores for the 19 ROIs were calculated. The 10th percentile for each ROI was selected as a cut-off score. Having four or more low FA scores occurred in 16.7%. More subjects with incidental findings met criterion for low FA scores (37.5%), compared to 9.1% of subjects with no findings. When subjects with minor WMHIs were retained and only those with multiple incidental findings were excluded, 8.3% of the retained subjects met criterion for low FA scores compared to 50.0% of the excluded subjects.

CONCLUSIONS

The decision to include or exclude subjects who have incidental findings can influence the results of a study.

Longitudinal changes in cortical thickness in children after traumatic brain injury and their relation to behavioral regulation and emotional control

The purpose of this study was to assess patterns of cortical development over time in children who had sustained traumatic brain injury (TBI) as compared to children with orthopedic injury (OI), and to examine how these patterns related to emotional control and behavioral dysregulation, two common post-TBI symptoms. Cortical thickness was measured at approximately 3 and 18 months post-injury in 20 children aged 8.2-17.5 years who had sustained moderate-to-severe closed head injury and 21 children aged 7.4-16.7 years who had sustained OI. At approximately 3 months post-injury, the TBI group evidenced decreased cortical thickness bilaterally in aspects of the superior frontal, dorsolateral frontal, orbital frontal, and anterior cingulate regions compared to the control cohort, areas of anticipated vulnerability to TBI-induced change. At 18 months post-injury, some of the regions previously evident at 3 months post-injury remained significantly decreased in the TBI group, including bilateral frontal, fusiform, and lingual regions. Additional regions of significant cortical thinning emerged at this time interval (bilateral frontal regions and fusiform gyrus and left parietal regions). However, differences in other regions appeared attenuated (no longer areas of significant cortical thinning) by 18 months post-injury including large bilateral regions of the medial aspects of the frontal lobes and anterior cingulate. Cortical thinning within the OI group was evident over time in dorsolateral frontal and temporal regions bilaterally and aspects of the left medial frontal and precuneus, and right inferior parietal regions. Longitudinal analyses within the TBI group revealed decreases in cortical thickness over time in numerous aspects throughout the right and left cortical surface, but with notable "sparing" of the right and left frontal and temporal poles, the medial aspects of both the frontal lobes, the left fusiform gyrus, and the cingulate bilaterally. An analysis of longitudinal changes in cortical thickness over time (18 months-3 months) in the TBI versus OI group demonstrated regions of relative cortical thinning in the TBI group in bilateral superior parietal and right paracentral regions, but relative cortical thickness increases in aspects of the medial orbital frontal lobes and bilateral cingulate and in the right lateral orbital frontal lobe. Finally, findings from analyses correlating the longitudinal cortical thickness changes in TBI with symptom report on the Emotional Control subscale of the Behavior Rating Inventory of Executive Function (BRIEF) demonstrated a region of significant correlation in the right medial frontal and right anterior cingulate gyrus. A region of significant correlation between the longitudinal cortical thickness changes in the TBI group and symptom report on the Behavioral Regulation Index was also seen in the medial aspect of the left frontal lobe. Longitudinal analyses of cortical thickness highlight an important deviation from the expected pattern of developmental change in children and adolescents with TBI, particularly in the medial frontal lobes, where typical patterns of thinning fail to occur over time. Regions which fail to undergo expected cortical thinning in the medial aspects of the frontal lobes correlate with difficulties in emotional control and behavioral regulation, common problems for youth with TBI. Examination of post-TBI brain development in children may be critical to identification of children that may be at risk for persistent problems with executive functioning deficits and the development of interventions to address these issues.

The effects of pediatric traumatic brain injury on verbal and visual-spatial working memory

The purpose of this study was to investigate the effects of pediatric traumatic brain injury (TBI) on verbal and visual-spatial working memory (WM). WM tasks examined memory span through recall of the last item of a series of stimuli. Additionally, both verbal and visual-spatial tests had a dual-task condition assessing the effect of increasing demands on the central executive (CE). Inhibitory control processes in verbal WM were examined through intrusion errors. The TBI group (n = 73) performed more poorly on verbal and visual-spatial WM tasks than orthopedic-injured children (n = 30) and non-injured children (n = 40). All groups performed more poorly on the dual-task conditions, reflecting an effect of increasing CE load. This effect was not greater for the TBI group. There were no group differences in intrusion errors on the verbal WM task, suggesting that problems in WM experienced by children with TBI were not primarily due to difficulties in inhibitory control. Finally, injury-related characteristics, namely days to follow commands, accounted for significant variance in WM performance, after controlling for relevant demographic variables. Findings suggest that WM impairments in TBI are general rather than modality-specific and that severity indices measured over time are better predictors of WM performance than those taken at a single time point.

Diffusion tensor tractography indices in patients with frontal lobe injury and its correlation with neuropsychological tests

OBJECTIVES

Diffusion tensor tractography (DTT) was performed to quantify diffuse axonal injury (DAI) in major white matter (WM) fiber bundles (FBs) of patients with frontal lobe injury and to correlate these changes with neuropsychological tests (NPT) at 6 month follow-up.

PATIENTS AND METHODS

DTT was performed in 21 patients with moderate traumatic brain injury (TBI) within week and after 6 month follow-up, and in controls. DTI indices were calculated from the entire FBs in patients as well as controls. Bonferroni multiple comparisons Post hoc test was performed for determining the changes in DTI indices. Paired t-test was performed between DTI indices at baseline and follow-up. Pearson's correlation was performed between NPT scores and DTI indices.

RESULTS

Significant changes in DTI indices were observed in some of the FBs as compared to controls which incompletely recovered at 6 month follow-up. DTI indices of different WM FBs correlated significantly with some of the NPT.

CONCLUSION

We conclude that DTT based quantification helps in assessment of DAI in patients with moderate frontal lobe injury. Some of the FBs recover partially at 6 month follow-up and correlate with NPT scores.

Comparing quantitative tractography metrics of motor and sensory pathways in children with periventricular leukomalacia and different levels of gross motor function

INTRODUCTION

The neural tracts responsible for gross motor dysfunction in children with spastic cerebral palsy (CP) caused by periventricular leukomalacia remain unknown. This study investigated both sensory and motor tracts using diffusion tensor tractography (DTT).

METHODS

Brain MRIs with diffusion tensor imaging (DTI) performed on 19 children (ten boys and nine girls) with bilateral spastic CP were analyzed. DTT was reconstructed from DTI. Participants were classified according to gross motor function measured with Gross Motor Function Classification System (GMFCS). Those with GMFCS levels I-III comprised the high-functioning group (n = 11), and those with GMFCS levels IV-V comprised the low-functioning group (n = 8). We compared DTT-based metrics, such as fractional anisotropy, apparent diffusion coefficient, and fiber number and volume, between the groups.

RESULTS

In the corticospinal tract, the volume and number of fibers were significantly higher in the high-functioning group (p < 0.001), whereas the fractional anisotropy and apparent diffusion coefficient of the corticospinal tract did not differ significantly between the groups. In the somotosensory tract and posterior thalamic radiation, none of the DTT parameters differed significantly between the groups.

CONCLUSIONS

Children with bilateral spastic CP with differing levels of gross motor function have corresponding differences detectable on DTT in their corticospinal tracts but not in their somatosensory tracts and posterior thalamic radiations. In addition, the number and volume of fibers, but not fractional anisotropy values or apparent diffusion coefficients, are lower in the corticospinal tracts in children with low gross motor function than in those with high gross motor function.

Morphometry and diffusion MR imaging years after childhood traumatic brain injury

OBJECTIVE

Our goal was to detect possible unrecognized injury in cerebral white matter (WM) in adult survivors of traumatic brain injury (TBI) during childhood, who showed no detectable axonal injury or chronic contusion on late conventional MRI.

MATERIAL AND METHODS

We used voxel-based morphometry (VBM) to detect subtle structural changes in brain morphology and diffusion-tensor imaging (DTI) to non-invasively probe WM integrity. By means of VBM and DTI we examined a group of 12 adult patients who suffered from childhood closed head injury without axonal injury on late conventional MRI.

RESULTS

Patients sustained complicated mild or moderate-to-severe TBI with a mean of 7 points based on the Glasgow Coma Scale. The mean time after trauma was 19 years (range 7-31 years). For VBM, group comparisons of segmented T1-weighted grey matter and WM images were performed, while for DTI we compared the fractional anisotropy and mean diffusivity (MD) between the groups. Patients presented with higher MD in the right cerebral white matter, bilaterally in the forceps major and in the body and splenium of the corpus callosum. These findings were supported by VBM, which showed reduced WM volume bilaterally, mainly along the callosal splenium.

CONCLUSION

Our results indicate that persistent focal long-term volume reduction and underlying WM structural changes may occur after TBI during childhood and that their effects extend into adulthood. Normal late conventional MR findings after childhood TBI do not rule out non-apparent axonal injury.

The pathophysiology of concussions in youth

Mild traumatic brain injury, especially sport-related concussion, is common among young persons. Consequences of transient pathophysiologic dysfunction must be considered in the context of a developing or immature brain, as must the potential for an accumulation of damage with repeated exposure. This review summarizes the underlying neurometabolic cascade of concussion, with emphasis on the young brain in terms of acute pathophysiology, vulnerability, alterations in plasticity and activation, axonal injury, and cumulative risk from chronic, repetitive damage, and discusses their implications in the context of clinical care for the concussed youth, highlighting areas for future investigation.

Brain activation during a social attribution task in adolescents with moderate to severe traumatic brain injury

The ability to make accurate judgments about the mental states of others, sometimes referred to as theory of mind (ToM), is often impaired following traumatic brain injury (TBI), and this deficit may contribute to problems with interpersonal relationships. The present study used an animated social attribution task (SAT) with functional magnetic resonance imaging (fMRI) to examine structures mediating ToM in adolescents with moderate to severe TBI. The study design also included a comparison group of matched, typically developing (TD) adolescents. The TD group exhibited activation within a number of areas that are thought to be relevant to ToM, including the medial prefrontal and anterior cingulate cortex, fusiform gyrus, and posterior temporal and parietal areas. The TBI subjects had significant activation within many of these same areas, but their activation was generally more intense and excluded the medial prefrontal cortex. Exploratory regression analyses indicated a negative relation between ToM-related activation and measures of white matter integrity derived from diffusion tensor imaging, while there was also a positive relation between activation and lesion volume. These findings are consistent with alterations in the level and pattern of brain activation that may be due to the combined influence of diffuse axonal injury and focal lesions.