Magnetic resonance imaging evidence of progression of subacute brain atrophy in moderate to severe traumatic brain injury

Moderate-Severe TBI as a Progressive Disorder: Patterns and Predictors of Cognitive Declines in the Chronic Stages of Injury

BACKGROUND

Moderate-severe traumatic brain injury (TBI) has been associated with progressive cognitive decline in the chronic injury stages in a small number of studies.

OBJECTIVE

This study aimed to (i) replicate our previous findings of decline from 1 to 3+ years post-injury in a larger, non-overlapping sample and (ii) extend these findings by examining the proportion of decliners in 2 earlier time windows, and by investigating novel predictors of decline.

METHODS

N = 48 patients with moderate-severe TBI underwent neuropsychological assessment at 2, 5, 12 months, and 30+ months post-injury. We employed the Reliable Change Index (RCI) to evaluate decline, stability and improvement across time and logistic regression to identify predictors of decline (demographic/cognitive reserve; injury-related).

RESULTS

The proportions of patients showing decline were: 12.5% (2-5 months post-injury), 17% (5-12 months post-injury), and 27% (12-30+ months post-injury). Measures of verbal retrieval were most sensitive to decline. Of the predictors, only left progressive hippocampal volume loss from 5 to 12 months post-injury significantly predicted cognitive decline from 12 to 30+ months post-injury.

CONCLUSIONS

Identical to our previous study, 27% of patients declined from 12 to 30+ months post-injury. Additionally, we found that the further from injury, the greater the proportion of patients declining. Importantly, earlier progressive hippocampal volume loss predicted later cognitive decline. Taken together, the findings highlight the need for ongoing research and treatment that target these deleterious mechanisms affecting patients in the chronic stages of moderate-severe TBI.

Neuroimaging Correlates of Post-Traumatic Stress Disorder in Traumatic Brain Injury: A Systematic Review of the Literature

Neuroimaging is widely utilized in studying traumatic brain injury (TBI) and post-traumatic stress disorder (PTSD). The risk for PTSD is greater after TBI than after non-TBI trauma, and PTSD is associated with worse outcomes after TBI. Studying the neuroimaging correlates of TBI-related PTSD may provide insights into the etiology of both conditions and help identify those TBI patients most at risk of developing persistent symptoms. The objectives of this systematic review were to examine the current literature on neuroimaging in TBI-related PTSD, summarize key findings, and highlight strengths and limitations to guide future research. A Preferred Reporting Items for Systematic Review and Meta-Analysis Protocols (PRISMA) compliant literature search was conducted in PubMed (MEDLINE®), PsycINFO, Embase, and Scopus databases prior to January 2022. The database query yielded 4486 articles, which were narrowed based on specified inclusion criteria to a final cohort of 16 studies, composed of 854 participants with TBI. There was no consensus regarding neuroimaging correlates of TBI-related PTSD among the included articles. A small number of studies suggest that TBI-related PTSD is associated with white matter tract changes, particularly in frontotemporal regions, as well as changes in whole-brain networks of resting-state connectivity. Future studies hoping to identify reliable neuroimaging correlates of TBI-related PTSD would benefit from ensuring consistent case definition, preferably with clinician-diagnosed TBI and PTSD, selection of comparable control groups, and attention to imaging timing post-injury. Prospective studies are needed and should aim to further differentiate predisposing factors from sequelae of TBI-related PTSD.

Longitudinal Patterns of Functional Connectivity in Moderate-to-Severe Traumatic Brain Injury

Longitudinal neuroimaging studies aid our understanding of recovery mechanisms in moderate-to-severe traumatic brain injury (TBI); however, there is a dearth of longitudinal functional connectivity research. Our aim was to characterize longitudinal functional connectivity patterns in two clinically important brain networks, the frontoparietal network (FPN) and the default mode network (DMN), in moderate-to-severe TBI. This inception cohort study of prospectively collected longitudinal data used resting-state functional magnetic resonance imaging (fMRI) to characterize functional connectivity patterns in the FPN and DMN. Forty adults with moderate-to-severe TBI (mean ± standard deviation [SD]; age = 39.53 ± 16.49 years, education = 13.92 ± 3.20 years, lowest Glasgow Coma Scale score = 6.63 ± 3.24, sex = 70% male) were scanned at approximately 0.5, 1-1.5, and 3+ years post-injury. Seventeen healthy, uninjured participants (mean ± SD; age = 38.91 ± 15.57 years, education = 15.11 ± 2.71 years, sex = 29% male) were scanned at baseline and approximately 11 months afterwards. Group independent component analyses and linear mixed-effects modeling with linear splines that contained a knot at 1.5 years post-injury were employed to investigate longitudinal network changes, and associations with covariates, including age, sex, and injury severity. In patients with TBI, functional connectivity in the right FPN increased from approximately 0.5 to 1.5 years post-injury (unstandardized estimate = 0.19, standard error [SE] = 0.07, p = 0.009), contained a slope change in the opposite direction, from positive to negative at 1.5 years post-injury (estimate = -0.21, SE = 0.11, p = 0.009), and marginally declined afterwards (estimate = -0.10, SE = 0.06, p = 0.079). Functional connectivity in the DMN increased from approximately 0.5 to 1.5 years (estimate = 0.15, SE = 0.05, p = 0.006), contained a slope change in the opposite direction, from positive to negative at 1.5 years post-injury (estimate = -0.19, SE = 0.08, p = 0.021), and was estimated to decline from 1.5 to 3+ years (estimate = -0.04, SE = 0.04, p = 0.303). Similarly, the left FPN increased in functional connectivity from approximately 0.5 to 1.5 years post-injury (estimate = 0.15, SE = 0.05, p = 0.002), contained a slope change in the opposite direction, from positive to negative at 1.5 years post-injury (estimate = -0.18, SE = 0.07, p = 0.008), and was estimated to decline thereafter (estimate = -0.04, SE = 0.03, p = 0.254). At approximately 0.5 years post-injury, patients showed hypoconnectivity compared with healthy, uninjured participants at baseline. Covariates were not significantly associated in any of the models. Findings of early improvement but a tapering and possible decline in connectivity thereafter suggest that compensatory effects are time-limited. These later reductions in connectivity mirror growing evidence of behavioral and structural decline in chronic moderate-to-severe TBI. Targeting such declines represents a novel avenue of research and offers potential for improving clinical outcomes.

The focused quantitative EEG bio-marker in studying childhood atrophic encephalopathy

Although it is a normal involution process in advanced age, brain atrophy—also termed atrophic encephalopathy—can also occur prematurely in childhood as a consequential effect of brain tissues injury through trauma or central nervous system infection, though in both normal and premature occurrences this condition always presents with loss of volume relative to the skull. A common tool for the functional study of brain activities is an electroencephalogram, but analyses of this have reportedly identified mismatches between qualitative and quantitative forms, particularly in the use of Delta-alpha ratio (DAR) indices, meaning that the values may be case dependent. The current study thus examines the value of Focused Occipital Beta-Alpha Ratio (FOBAR) as a modified biomarker for evaluating brain functional changes resulting from brain atrophy. This cross-sectional design study involves 260 patients under 18 years of age. Specifically, 207 patients with brain atrophy are compared with 53 control subjects with CT scan-proven normal brain volume. All the children underwent digital electroencephalography with brain mapping. Results show that alpha posterior dominant rhythm was present in 88 atrophic children and 44 controls. Beta as posterior dominant rhythm was present in an overwhelming 91.5% of atrophic subjects, with 0.009 p-values. The focused occipital Beta-alpha ratio correlated significantly with brain volume loss presented in diagonal brain fraction. The FOBAR and DAR values of the QEEG showed no significant correlation. This work concludes that QEEG cerebral dysfunctional studies may be etiologically and case dependent from the nature of the brain injury. Also, the focused Beta-alpha ratio of the QEEG is a prospective and potential biomarker of consideration in studying childhood atrophic encephalopathy.

GABAergic circuits of the basolateral amygdala and generation of anxiety after traumatic brain injury

Traumatic brain injury (TBI) has reached epidemic proportions around the world and is a major public health concern in the United States. Approximately 2.8 million individuals sustain a traumatic brain injury and are treated in an Emergency Department yearly in the U.S., and about 50,000 of them die. Persistent symptoms develop in 10-15% of the cases including neuropsychiatric disorders. Anxiety is the second most common neuropsychiatric disorder that develops in those with persistent neuropsychiatric symptoms after TBI. Abnormalities or atrophy in the temporal lobe has been shown in the overwhelming number of TBI cases. The basolateral amygdala (BLA), a temporal lobe structure that consolidates, stores and generates fear and anxiety-based behavioral outputs, is a critical brain region in the anxiety circuitry. In this review, we sought to capture studies that characterized the relationship between human post-traumatic anxiety and structural/functional alterations in the amygdala. We compared the human findings with results obtained with a reproducible mild TBI animal model that demonstrated a direct relationship between the alterations in the BLA and an anxiety-like phenotype. From this analysis, both preliminary insights, and gaps in knowledge, have emerged which may open new directions for the development of rational and more efficacious treatments.

Patterns of change in cortical morphometry following traumatic brain injury in adults

Progressive cortical volumetric loss following moderate–severe traumatic brain injury (TBI) has been observed; however, regionally specific changes in the structural determinants of cortical volume, namely, cortical thickness (CT) and cortical surface area (CSA), are unknown and may inform the patterns and neural substrates of neurodegeneration and plasticity following injury. We aimed to (a) assess differences in CT and CSA between TBI participants and controls in the early chronic stage post‐injury, (b) describe longitudinal changes in cortical morphometry following TBI, and (c) examine how regional changes in CT and CSA are associated. We acquired magnetic resonance images for 67 participants with TBI at up to 4 time‐points spanning 5 months to 7 years post‐injury, and 18 controls at 2 time‐points. In the early chronic stage, TBI participants displayed thinner cortices than controls, predominantly in frontal regions, but no CSA differences. Throughout the chronic period, TBI participants showed widespread CT reductions in posterior cingulate/precuneus regions and moderate CT increase in frontal regions. Additionally, CSA showed a significant decrease in the orbitofrontal cortex and circumscribed increase in posterior regions. No changes were identified in controls. Relationships between regional cortical changes in the same morphological measure revealed coordinated patterns within participants, whereas correlations between regions with CT and CSA change yielded bi‐directional relationships. This suggests that these measures may be differentially affected by neurodegenerative mechanisms such as transneuronal degeneration following TBI and that degeneration may be localized to the depths of cortical sulci. These findings emphasize the importance of dissecting morphometric contributions to cortical volume change.

Electrocorticography reveals thalamic control of cortical dynamics following traumatic brain injury

The return of consciousness after traumatic brain injury (TBI) is associated with restoring complex cortical dynamics; however, it is unclear what interactions govern these complex dynamics. Here, we set out to uncover the mechanism underlying the return of consciousness by measuring local field potentials (LFP) using invasive electrophysiological recordings in patients recovering from TBI. We found that injury to the thalamus, and its efferent projections, on MRI were associated with repetitive and low complexity LFP signals from a highly structured phase space, resembling a low-dimensional ring attractor. But why do thalamic injuries in TBI patients result in a cortical attractor? We built a simplified thalamocortical model, which connotes that thalamic input facilitates the formation of cortical ensembles required for the return of cognitive function and the content of consciousness. These observations collectively support the view that thalamic input to the cortex enables rich cortical dynamics associated with consciousness.

Global hippocampal and selective thalamic nuclei atrophy differentiate chronic TBI from Non-TBI

Traumatic brain injury (TBI) may increase susceptibility to neurodegenerative diseases later in life. One neurobiological parallel between chronic TBI and neurodegeneration may be accelerated aging and the nature of atrophy across subcortical gray matter structures. The main aim of the present investigation is to evaluate and rank the degree that subcortical gray matter atrophy differentiates chronic moderate-severe TBI from non-TBI participants by evaluating morphometric differences between groups. Forty individuals with moderate-severe chronic TBI (9.23 yrs from injury) and 33 healthy controls (HC) underwent high resolution 3D T1-weighted structural magnetic resonance imaging. Whole brain volume was classified into white matter, cortical and subcortical gray matter structures with hippocampi and thalami further segmented into subfields and nuclei, respectively. Extensive atrophy was observed across nearly all brain regions for chronic TBI participants. A series of multivariate logistic regression models identified subcortical gray matter structures of the hippocampus and thalamus as the most sensitive to differentiating chronic TBI from non-TBI participants (McFadden R² = .36, p < .001). Further analyses revealed the pattern of hippocampal atrophy to be global, occurring across nearly all subfields. The pattern of thalamic atrophy appeared to be much more selective and non-uniform, with largest between-group differences evident for nuclei bordering the ventricles. Subcortical gray matter was negatively correlated with time since injury (r = -.31, p = .054), while white matter and cortical gray matter were not. Cognitive ability was lower in the chronic TBI group (Cohen's d = .97, p = .003) and correlated with subcortical structures including the pallidum (r² = .23, p = .038), thalamus (r² = .36, p = .007) and ventral diencephalon (r² = .23, p = .036). These data may support an accelerated aging hypothesis in chronic moderate-severe TBI that coincides with a similar neuropathological profile found in neurodegenerative diseases.

Neuroimaging Correlates of Syndromal Anxiety Following Traumatic Brain Injury: A Systematic Review of the Literature

BACKGROUND

Traumatic brain injury (TBI) can precipitate new-onset psychiatric symptoms or worsen existing psychiatric conditions. To elucidate specific mechanisms for this interaction, neuroimaging is often used to study both psychiatric conditions and TBI. This systematic review aims to synthesize the existing literature of neuroimaging findings among patients with anxiety after TBI.

METHODS

We conducted a Preferred Reporting Items for Systematic Review and Meta-Analyses-compliant literature search via PubMed (MEDLINE), PsychINFO, EMBASE, and Scopus databases before May, 2019. We included studies that clearly defined TBI, measured syndromic anxiety as a primary outcome, and statistically analyzed the relationship between neuroimaging findings and anxiety symptoms.

RESULTS

A total of 5982 articles were retrieved from the systematic search, of which 65 studied anxiety and 13 met eligibility criteria. These studies were published between 2004 and 2017, collectively analyzing 764 participants comprised of 470 patients with TBI and 294 non-TBI controls. Imaging modalities used included magnetic resonance imaging, functional magnetic resonance imaging, diffusion tensor imaging, electroencephalogram, magnetic resonance spectrometry, and magnetoencephalography. Eight of 13 studies presented at least one significant finding and together reflect a complex set of changes that lead to anxiety in the setting of TBI. The left cingulate gyrus in particular was found to be significant in 2 studies using different imaging modalities. Two studies also revealed perturbances in functional connectivity within the default mode network.

CONCLUSIONS

This is the first systemic review of neuroimaging changes associated with anxiety after TBI, which implicated multiple brain structures and circuits, such as the default mode network. Future research with consistent, rigorous measurements of TBI and syndromic anxiety, as well as attention to control groups, previous TBIs, and time interval between TBI and neuroimaging, are warranted. By understanding neuroimaging correlates of psychiatric symptoms, this work could inform future post-TBI screening and surveillance, preventative efforts, and early interventions to improve neuropsychiatric outcomes.

Progressive Neurodegeneration Across Chronic Stages of Severe Traumatic Brain Injury

OBJECTIVE

To examine the trajectory of structural gray matter changes across 2 chronic periods of recovery in individuals who have sustained severe traumatic brain injury (TBI), adding to the growing literature indicating that neurodegenerative processes occur in the months to years postinjury.

PARTICIPANTS

Patients who experienced posttraumatic amnesia of 1 hour or more, and/or scored 12 or less on the Glasgow Coma Scale at the emergency department or the scene of the accident, and/or had positive brain imaging findings were recruited while receiving inpatient care, resulting in 51 patients with severe TBI.

METHODS

Secondary analyses of gray matter changes across approximately 5 months, 1 year, and 2.5 years postinjury were undertaken, using an automated segmentation protocol with improved accuracy in populations with morphological anomalies. We compared patients and matched controls on regions implicated in poorer long-term clinical outcome (accumbens, amygdala, brainstem, hippocampus, thalamus). To model brain-wide patterns of change, we then conducted an exploratory principal component analysis (PCA) on the linear slopes of all regional volumes across the 3 time points. Finally, we assessed nonlinear trends across earlier (5 months-1 year) versus later (1-2.5 years) time-windows with PCA to compare degeneration rates across time. Chronic degeneration was predicted cortically and subcortically brain-wide, and within specific regions of interest.

RESULTS

(1) From 5 months to 1 year, patients showed significant degeneration in the accumbens, and marginal degeneration in the amygdala, brainstem, thalamus, and the left hippocampus when examined unilaterally, compared with controls. (2) PCA components representing subcortical and temporal regions, and regions from the basal ganglia, significantly differed from controls in the first time-window. (3) Progression occurred at the same rate across both time-windows, suggesting neither escalation nor attenuation of degeneration across time.

CONCLUSION

Localized yet progressive decline emphasizes the necessity of developing interventions to offset degeneration and improve long-term functioning.

Platelet-like particles reduce coagulopathy-related and neuroinflammatory pathologies post-experimental traumatic brain injury

Coagulopathy may occur following traumatic brain injury (TBI), thereby negatively affecting patient outcomes. Here, we investigate the use of platelet-like particles (PLPs), poly(N-isopropylacrylamide-co-acrylic-acid) microgels conjugated with a fibrin-specific antibody, to improve hemostasis post-TBI. The objective of this study was to diminish coagulopathy in a mouse TBI model (controlled cortical impact) via PLP treatment, and subsequently decrease blood-brain barrier (BBB) permeability and neuroinflammation. Following an acute intravenous injection of PLPs post-TBI, we analyzed BBB permeability, ex vivo coagulation parameters, and neuroinflammation at 24 hr and 7 days post-TBI. Both PLP-treatment and control particle-treatment had significantly decreased BBB permeability and improved clot structure 24 hr post-injury. Additionally, no significant change in tissue sparing was observed between 24 hr and 7 days for PLP-treated cohorts compared to that observed in untreated cohorts. Only PLP-treatment resulted in significant reduction of astrocyte expression at 7 days and percent difference from 24 hr to 7 days. Finally, PLP-treatment significantly reduced the percent difference from 24 hr to 7 days in microglia/macrophage density compared to the untreated control. These results suggest that PLP-treatment addressed acute hypocoagulation and decreased BBB permeability followed by decreased neuroinflammation and fold-change tissue loss by 7 days post-injury. These promising results indicate that PLPs could be a potential therapeutic modality for TBI.

Hippocampal atrophy is associated with psychotic symptom severity following traumatic brain injury

Psychosis is a rare, but particularly serious sequela of traumatic brain injury. However, little is known as to the neurobiological processes that may contribute to its onset. Early evidence suggests that psychotic symptom development after traumatic brain injury may co-occur with hippocampal degeneration, invoking the possibility of a relationship. Particularly regarding the hippocampal head, these degenerative changes may lead to dysregulation in dopaminergic circuits, as is reported in psychoses due to schizophrenia, resulting in the positive symptom profile typically seen in post-injury psychosis. The objective of this study was to examine change in hippocampal volume and psychotic symptoms across time in a sample of moderate-to-severe traumatic brain injury patients. We hypothesized that hippocampal volume loss would be associated with increased psychotic symptom severity. From a database of n = 137 adult patients with prospectively collected, longitudinal imaging and neuropsychiatric outcomes, n = 24 had complete data at time points of interest (5 and 12 months post-traumatic brain injury) and showed increasing psychotic symptom severity on the Personality Assessment Inventory psychotic experiences subscale of the schizophrenia clinical scale across time. Secondary analysis employing stepwise regression with hippocampal volume change (independent variable) and Personality Assessment Inventory psychotic symptom change (dependent variable) from 5 to 12 months post-injury was conducted including age, sex, marijuana use, family history of schizophrenia, years of education and injury severity as control variables. Total right hippocampal volume loss predicted an increase in the Personality Assessment Inventory psychotic experiences subscale (F_{(1, 22)} = 5.396, adjusted R² = 0.161, P = 0.030; β = −0.017, 95% confidence interval = −0.018, −0.016) as did volume of the right hippocampal head (F_{(1, 22)} = 5.764, adjusted R² = 0.172, P = 0.025; β = −0.019, 95% confidence interval = −0.021, −0.017). Final model goodness-of-fit was confirmed using k-fold (k = 5) cross-validation. Consistent with our hypotheses, the current findings suggest that hippocampal degeneration in the chronic stages of moderate-to-severe traumatic brain injury may play a role in the delayed onset of psychotic symptoms after traumatic brain injury. These findings localized to the right hippocampal head are supportive of a proposed aetiological mechanism whereby atrophy of the hippocampal head may lead to the dysregulation of dopaminergic networks following traumatic brain injury; possibly accounting for observed clinical features of psychotic disorder after traumatic brain injury (including prolonged latency period to symptom onset and predominance of positive symptoms). If further validated, these findings may bear important clinical implications for neurorehabilitative therapies following traumatic brain injury.

Residual and compensatory changes of resting‐state EEG in successful recovery after moderate TBI

Purpose:

Even in years after recovery from moderate traumatic brain injury (moderate TBI), patients complain about residual cognitive impairment and fatigue. We hypothesized that non‐linear and linear resting‐state electroencephalography (rsEEG) features might also reflect neural underpinnings of these deficits.

Methods:

We analyzed a 10‐minute rsEEG in 77 moderate TBI‐survivors and 151 healthy volunteers after cognitive and psychological assessment. The rsEEG analysis included linear measures, such as power spectral density and peak alpha frequency, and non‐linear parameters such as Higuchi fractal dimension, envelope frequency, and Hjorth complexity.

Results:

The patients with moderate TBI had higher scores for fatigue and sleepiness and lower scores for mood and life satisfaction than controls. The behavioral test for directed attention showed a smaller and non‐significant between‐group difference. In rsEEG patterns, moderate TBI‐group had significantly higher deltaand theta‐rhythm power, which correlated with higher sleepiness and fatigue scores. The higher beta and lower alpha power were associated with a higher attention level in moderate TBI patients. Non‐linear rsEEG features were significantly higher in moderate TBI patients than in healthy controls but correlated with sleepiness and fatigue scores in both controls and patients.

Conclusion:

The rsEEG patterns may reflect compensatory processes supporting directed attention and residual effect of moderate TBI causing subjective fatigue in patients even after full physiological recovery.

Remotely delivered environmental enrichment intervention for traumatic brain injury: Study protocol for a randomised controlled trial

INTRODUCTION

Individuals with moderate-severe traumatic brain injury (m-sTBI) experience progressive brain and behavioural declines in the chronic stages of injury. Longitudinal studies found that a majority of patients with m-sTBI exhibit significant hippocampal atrophy from 5 to 12 months post-injury, associated with decreased cognitive environmental enrichment (EE). Encouragingly, engaging in EE has been shown to lead to neural improvements, suggesting it is a promising avenue for offsetting hippocampal neurodegeneration in m-sTBI. Allocentric spatial navigation (ie, flexible, bird's eye view approach), is a good candidate for EE in m-sTBI because it is associated with hippocampal activation and reduced ageing-related volume loss. Efficacy of EE requires intensive daily training, prohibitive within most current health delivery systems. The present protocol is a novel, remotely delivered and self-administered intervention designed to harness principles from EE and allocentric spatial navigation to offset hippocampal atrophy and potentially improve hippocampal functions such as navigation and memory for patients with m-sTBI.

METHODS AND ANALYSIS

Eighty-four participants with chronic m-sTBI are being recruited from an urban rehabilitation hospital and randomised into a 16-week intervention (5 hours/week; total: 80 hours) of either targeted spatial navigation or an active control group. The spatial navigation group engages in structured exploration of different cities using Google Street View that includes daily navigation challenges. The active control group watches and answers subjective questions about educational videos. Following a brief orientation, participants remotely self-administer the intervention on their home computer. In addition to feasibility and compliance measures, clinical and experimental cognitive measures as well as MRI scan data are collected pre-intervention and post-intervention to determine behavioural and neural efficacy.

ETHICS AND DISSEMINATION

Ethics approval has been obtained from ethics boards at the University Health Network and University of Toronto. Findings will be presented at academic conferences and submitted to peer-reviewed journals.

TRIAL REGISTRATION NUMBER

Version 3, ClinicalTrials.gov Registry (NCT04331392).

Propylparaben Reduces the Long-Term Consequences in Hippocampus Induced by Traumatic Brain Injury in Rats: Its Implications as Therapeutic Strategy to Prevent Neurodegenerative Diseases

BACKGROUND

Severe traumatic brain injury (TBI), an important risk factor for Alzheimer's disease, induces long-term hippocampal damage and hyperexcitability. On the other hand, studies support that propylparaben (PPB) induces hippocampal neuroprotection in neurodegenerative diseases.

OBJECTIVE

Experiments were designed to evaluate the effects of subchronic treatment with PPB on TBI-induced changes in the hippocampus of rats.

METHODS

Severe TBI was induced using the lateral fluid percussion model. Subsequently, rats received subchronic administration with PPB (178 mg/kg, TBI+PPB) or vehicle (TBI+PEG) daily for 5 days. The following changes were examined during the experimental procedure: sensorimotor dysfunction, changes in hippocampal excitability, as well as neuronal damage and volume.

RESULTS

TBI+PEG group showed sensorimotor dysfunction (p < 0.001), hyperexcitability (64.2%, p < 0.001), and low neuronal preservation ipsi- and contralateral to the trauma. Magnetic resonance imaging (MRI) analysis revealed lower volume (17.2%; p < 0.01) and great damage to the ipsilateral hippocampus. TBI+PPB group showed sensorimotor dysfunction that was partially reversed 30 days after trauma. This group showed hippocampal excitability and neuronal preservation similar to the control group. However, MRI analysis revealed lower hippocampal volume (p < 0.05) when compared with the control group.

CONCLUSION

The present study confirms that post-TBI subchronic administration with PPB reduces the long-term consequences of trauma in the hippocampus. Implications of PPB as a neuroprotective strategy to prevent the development of Alzheimer's disease as consequence of TBI are discussed.

Traumatic Brain Injury and Risk of Long-Term Brain Changes, Accumulation of Pathological Markers, and Developing Dementia: A Review

Traumatic brain injuries (TBI) have received widespread media attention in recent years as being a risk factor for the development of dementia and chronic traumatic encephalopathy (CTE). This has sparked fears about the potential long-term effects of TBI of any severity on cognitive aging, leading to a public health concern. This article reviews the evidence surrounding TBI as a risk factor for the later development of changes in brain structure and function, and an increased risk of neurodegenerative disorders. A number of studies have shown evidence of long-term brain changes and accumulation of pathological biomarkers (e.g., amyloid and tau proteins) related to a history of moderate-to-severe TBI, and research has also demonstrated that individuals with moderate-to-severe injuries have an increased risk of dementia. While milder injuries have been found to be associated with an increased risk for dementia in some recent studies, reports on long-term brain changes have been mixed and often are complicated by factors related to injury exposure (i.e., number of injuries) and severity/complications, psychiatric conditions, and opioid use disorder. CTE, although often described as a neurodegenerative disorder, remains a neuropathological condition that is poorly understood. Future research is needed to clarify the significance of CTE pathology and determine whether that can explain any clinical symptoms. Overall, it is clear that most individuals who sustain a TBI (particularly milder injuries) do not experience worse outcomes with aging, as the incidence for dementia is found to be less than 7% across the literature.

Prognostic-factors for neurodegeneration in chronic moderate-to-severe traumatic brain injury: a systematic review protocol

BACKGROUND

Traumatic brain injury (TBI) is a leading cause of death and disability. Recently, a paradigm shift in our understanding of moderate-to-severe TBI has led to its reconceptualization as a progressive neurodegenerative disorder. Widespread progressive atrophy is observed in the months and years post-injury, long after the acute effects of the injury have resolved. Some studies have begun to examine prognostic demographic, injury-related, and post-injury risk factors that contribute to these declines. A synthesis of this information, and in particular, an increased understanding of post-injury factors that may be modifiable, would improve our ability to design interventions to reduce neurodegeneration in moderate-to-severe TBI. This systematic review aims to identify prognostic factors for neural deterioration in moderate-to-severe TBI, and thereby inform future intervention research in this population.

METHODS

This review protocol was informed by and conducted in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analysis Protocols (PRISMA-P) guidelines. Search strategies (designed to identify literature on prognostic factors of neurodegeneration in adults with moderate-to-severe TBI) optimized for MEDLINE, EMBASE PsychINFO, CINAHL, SportDiscus, and Cochrane Central Register of Controlled Trials will be developed with the assistance of a health sciences librarian. Retrieved studies will be screened by two team members. Studies must report on longitudinal neuroimaging (i.e., two or more scans in the same cohort) or neuroimaging in a cross-sectional study and potential prognostic factors for neurodegeneration, such as demographics (e.g., gender, age, education), injury (e.g., severity, etiology), or post-injury characteristics (e.g., type and length of therapy, activity level, mood).

DISCUSSION

By identifying prognostic factors for neurodegeneration, this systematic review can help inform injury management, as well as intervention research designed to offset the effects of modifiable prognostic factors, such as low levels of cognitive or physical activity. In turn, this systematic review can increase our understanding of how to improve outcome following moderate-to-severe TBI.

SYSTEMATIC REVIEW REGISTRATION

PROSPERO CRD42019122389.

The scale of neurodegeneration in moderate-to-severe traumatic brain injury: a systematic review protocol

BACKGROUND

Our understanding of recovery after moderate-to-severe traumatic brain injury (TBI) has shifted. Until recently, it was presumed that following a period of acute neurological vulnerability, the brain remained stable in the chronic stages of injury. However, recent research has shown neurodegeneration in the chronic stages of moderate-to-severe TBI, challenging the assumption of neurological stability. While there is extensive evidence that neurodegeneration occurs, debate remains regarding the scale and timing. This systematic review will evaluate the scale and timelines of neurodegeneration in adult patients with moderate-to-severe TBI.

METHODS

Literature searches will be conducted in six electronic databases (from inception onwards), including MEDLINE, EMBASE, PsycINFO, CINAHL, SportDiscus, and Cochrane Central Register of Controlled Trials. We will include observational studies that examine neurodegenerative changes within a single sample of TBI patients or studies that compare neuroimaging outcomes between TBI patients and healthy controls. Our primary outcome is structural neuroimaging, and our secondary outcome is diffusion tensor imaging for detection of post-injury white matter changes. All screening, data extraction, and study quality appraisal will be performed independently by the same two study members. It is expected that a narrative summary of the literature will be produced. If feasible, we will conduct a random-effects meta-analysis. However, given the expected heterogeneity between studies (with respect to, for example, timing of imaging, regions imaged) we do not expect to perform a meta-analysis; rather, a narrative synthesis of our findings is expected to be performed.

DISCUSSION

Understanding the scale and timelines of neurodegeneration in moderate-to-severe TBI (as well as which brain areas are most vulnerable to chronic declines) can inform intervention research designed to offset such changes. This may help improve patient outcome following moderate-to-severe TBI and, in turn, reduce the burden of the injury.

SYSTEMATIC REVIEW REGISTRATION

PROSPERO CRD42019117548.

Exposure to surgery under general anaesthesia and brain magnetic resonance imaging changes in older adults

BACKGROUND

Preclinical studies suggest that exposure to general anaesthesia (GA) could cause neurodegeneration consistent with Alzheimer's disease (AD) pathology. Brain magnetic resonance imaging (MRI) is useful to study structural brain changes. We tested the hypothesis that exposure to surgery with GA (surgery/GA) is associated with greater cortical thinning and increased frequency of white matter lesions.

METHODS

This is a cross-sectional analysis of 70-91-yr-old participants enrolled in the Mayo Clinic Study of Aging who had baseline MRI. The thickness of selected cortical regions, the volume of white matter hyperintensities, and the frequency of cortical infarctions were compared in participants who were and were not exposed to surgery/GA within 20 yr before the first MRI obtained after enrolment.

RESULTS

Of 1410 participants with MRI scans, 932 were exposed to surgery/GA before scanning. In adjusted analyses, cortical thickness in regions vulnerable to AD was significantly less in those exposed to surgery/GA in the prior 20 yr (difference -0.023 mm, [95% confidence interval (CI) -0.041 to -0.005], P=0.014). Those with surgery in the prior 20 yr were more likely to have 'abnormal thickness' compared with those without surgery (odds ratio=1.45, [95% CI 1.10-1.90], P=0.009). Exposure was not associated with white matter hyperintensities or the presence of brain infarcts.

CONCLUSIONS

This study suggests that exposure of older adults to surgical anaesthesia is associated with thinning in cortical regions implicated in AD. The pathogenesis and mechanisms driving these neurodegenerative changes, and the potential clinical significance of these findings, require further study.

Spatial patterns of progressive brain volume loss after moderate-severe traumatic brain injury

Traumatic brain injury leads to significant loss of brain volume, which continues into the chronic stage. This can be sensitively measured using volumetric analysis of MRI. Here we: (i) investigated longitudinal patterns of brain atrophy; (ii) tested whether atrophy is greatest in sulcal cortical regions; and (iii) showed how atrophy could be used to power intervention trials aimed at slowing neurodegeneration. In 61 patients with moderate-severe traumatic brain injury (mean age = 41.55 years ± 12.77) and 32 healthy controls (mean age = 34.22 years ± 10.29), cross-sectional and longitudinal (1-year follow-up) brain structure was assessed using voxel-based morphometry on T₁-weighted scans. Longitudinal brain volume changes were characterized using a novel neuroimaging analysis pipeline that generates a Jacobian determinant metric, reflecting spatial warping between baseline and follow-up scans. Jacobian determinant values were summarized regionally and compared with clinical and neuropsychological measures. Patients with traumatic brain injury showed lower grey and white matter volume in multiple brain regions compared to controls at baseline. Atrophy over 1 year was pronounced following traumatic brain injury. Patients with traumatic brain injury lost a mean (± standard deviation) of 1.55% ± 2.19 of grey matter volume per year, 1.49% ± 2.20 of white matter volume or 1.51% ± 1.60 of whole brain volume. Healthy controls lost 0.55% ± 1.13 of grey matter volume and gained 0.26% ± 1.11 of white matter volume; equating to a 0.22% ± 0.83 reduction in whole brain volume. Atrophy was greatest in white matter, where the majority (84%) of regions were affected. This effect was independent of and substantially greater than that of ageing. Increased atrophy was also seen in cortical sulci compared to gyri. There was no relationship between atrophy and time since injury or age at baseline. Atrophy rates were related to memory performance at the end of the follow-up period, as well as to changes in memory performance, prior to multiple comparison correction. In conclusion, traumatic brain injury results in progressive loss of brain tissue volume, which continues for many years post-injury. Atrophy is most prominent in the white matter, but is also more pronounced in cortical sulci compared to gyri. These findings suggest the Jacobian determinant provides a method of quantifying brain atrophy following a traumatic brain injury and is informative in determining the long-term neurodegenerative effects after injury. Power calculations indicate that Jacobian determinant images are an efficient surrogate marker in clinical trials of neuroprotective therapeutics.

NeuroQuant® and NeuroGage® reveal effects of traumatic brain injury on brain volume

This report describes the case of a 58-year-old man with moderate traumatic brain injury (TBI) and pre-accident brain disorders who had multiple persistent neuropsychiatric symptoms. NeuroQuant® 2.0 and NeuroGage® 2.0 MRI brain volume analyses were used during the chronic stage of injury (> 1 year after injury) to help understand the effects of the TBI on his brain volume. NeuroQuant® showed widespread cross-sectional atrophy, especially in the frontal and temporal lobes, consistent with encephalomalacia seen on the MRIs. Several of his clinical symptoms were consistent with the volume abnormalities. NeuroGage® longitudinal analyses of volume change from the time 1 to time 2 magnetic resonance imaging showed abnormally rapid atrophy and ventricular enlargement. The high rates of volume change were much more consistent with the relatively recent effects of TBI than with effects of the much more chronic pre-accident brain disorders.

The Biological Basis of Chronic Traumatic Encephalopathy following Blast Injury: A Literature Review

The United States Department of Defense Blast Injury Research Program Coordinating Office organized the 2015 International State-of-the-Science meeting to explore links between blast-related head injury and the development of chronic traumatic encephalopathy (CTE). Before the meeting, the planning committee examined articles published between 2005 and October 2015 and prepared this literature review, which summarized broadly CTE research and addressed questions about the pathophysiological basis of CTE and its relationship to blast- and nonblast-related head injury. It served to inform participants objectively and help focus meeting discussion on identifying knowledge gaps and priority research areas. CTE is described generally as a progressive neurodegenerative disorder affecting persons exposed to head injury. Affected individuals have been participants primarily in contact sports and military personnel, some of whom were exposed to blast. The symptomatology of CTE overlaps with Alzheimer's disease and includes neurological and cognitive deficits, psychiatric and behavioral problems, and dementia. There are no validated diagnostic criteria, and neuropathological evidence of CTE has come exclusively from autopsy examination of subjects with histories of exposure to head injury. The perivascular accumulation of hyperphosphorylated tau (p-tau) at the depths of cortical sulci is thought to be unique to CTE and has been proposed as a diagnostic requirement, although the contribution of p-tau and other reported pathologies to the development of clinical symptoms of CTE are unknown. The literature on CTE is limited and is focused predominantly on head injuries unrelated to blast exposure (e.g., football players and boxers). In addition, comparative analyses of clinical case reports has been challenging because of small case numbers, selection biases, methodological differences, and lack of matched controls, particularly for blast-exposed individuals. Consequently, the existing literature is not sufficient to determine whether the development of CTE is associated with head injury frequency (e.g., single vs. multiple exposures) or head injury type (e.g., impact, nonimpact, blast-related). Moreover, the incidence and prevalence of CTE in at-risk populations is unknown. Future research priorities should include identifying additional risk factors, pursuing population-based longitudinal studies, and developing the ability to detect and diagnose CTE in living persons using validated criteria.

Neurodegenerative Dementias After Traumatic Brain Injury

Traumatic brain injury (TBI) is often considered to be a risk factor for the later development of neurodegenerative conditions, but some findings do not support a link. Differences in research methods, clinical samples, and limitations encountered when assessing and documenting TBI details likely contribute to the mixed reports in the literature. Despite some variability in findings, a review of the literature does provide support for the notion that TBI appears to be associated with earlier onset of some neurodegenerative disorders, although clearly not everyone with a TBI appears to be at an increased risk. Whereas a mechanistic link remains unknown, TBI has been found to initiate an accumulation of pathological processes related to several neurodegenerative disorders. The authors propose a hypothetical model that relates TBI to the development of pathological burden overlapping with some neurodegenerative conditions, in which onset of cognitive/behavioral impairments is hastened in some individuals, but pathological processes stabilize afterward, resulting in a similar course of decline to individuals with dementia who do not have a history of TBI.

Longitudinal evaluation of ventricular volume changes associated with mild traumatic brain injury in military service members

PRIMARY OBJECTIVE

To investigate differences in longitudinal trajectories of ventricle-brain ratio (VBR), a general measure of brain atrophy, between Veterans with and without history of mild traumatic brain injury (mTBI).

RESEARCH DESIGN

Structural magnetic resonance imaging (MRI) was used to calculate VBR in 70 Veterans with a history of mTBI and 34 Veterans without such history at two time points approximately 3 and 8 years after a combat deployment.

MAIN OUTCOMES AND RESULTS

Both groups demonstrated a quadratic relationship between VBR and age that is consistent with normal developmental trajectories. Veterans with history of mTBI had larger total brain volume, but no interaction between mTBI and age was observed for brain volume, ventricular volume, or VBR.

CONCLUSIONS

In our longitudinal sample of deployed Veterans, mTBI was not associated with gross brain atrophy as reflected by abnormally high VBR or abnormal increases in VBR over time.

Imaging of Chronic Concussion

Conventional imaging findings in patients with cerebral concussion and chronic traumatic encephalopathy are absent or subtle in the majority of cases. The most common abnormalities include cerebral volume loss, enlargement of the cavum of the septum pellucidum, cerebral microhemorrhages, and white matter signal abnormalities, all of which have poor sensitivity and specificity. Advanced imaging modalities, such as diffusion tensor imaging (DTI), blood oxygen level dependent functional MR Imaging (BOLD fMRI), MR spectroscopy, perfusion imaging, positron emission tomography (PET), single photon emission computed tomography (SPECT), and magnetoencephalography detect physiologic abnormalities in symptomatic patients and, although currently in the investigation phase, may become useful in the clinical arena.

Visual Dysfunctions at Different Stages after Blast and Non-blast Mild Traumatic Brain Injury

PURPOSE

To assess the prevalence of visual dysfunctions and associated symptoms in war fighters at different stages after non-blast- or blast-induced mild traumatic brain injury (mTBI).

METHODS

A comprehensive retrospective review of the electronic health records of 500 U.S. military personnel with a diagnosis of deployment-related mTBI who received eye care at the Landstuhl Regional Medical Center. For analysis, the data were grouped by mechanism of injury, and each group was further divided in three subgroups based on the number of days between injury and initial eye examination.

RESULTS

The data showed a high frequency of visual symptoms and visual dysfunctions. However, the prevalence of visual symptoms and visual dysfunctions did not differ significantly between mechanism of injury and postinjury stage, except for eye pain and diplopia. Among visual symptoms, binocular dysfunctions were more common, including higher near vertical phoria, reduced negative fusional vergence break at near, receded near point of convergence, decreased stereoacuity, and reduced positive relative accommodation.

CONCLUSIONS

The lack of difference in terms of visual sequelae between subgroups (blast vs. nonblast) suggests that research addressing the assessment and management of mTBI visual sequelae resulting from civilian nonblast events is relevant to military personnel where combat injury results primarily from a blast event.

The far-reaching scope of neuroinflammation after traumatic brain injury

The 'silent epidemic' of traumatic brain injury (TBI) has been placed in the spotlight as a result of clinical investigations and popular press coverage of athletes and veterans with single or repetitive head injuries. Neuroinflammation can cause acute secondary injury after TBI, and has been linked to chronic neurodegenerative diseases; however, anti-inflammatory agents have failed to improve TBI outcomes in clinical trials. In this Review, we therefore propose a new framework of targeted immunomodulation after TBI for future exploration. Our framework incorporates factors such as the time from injury, mechanism of injury, and secondary insults in considering potential treatment options. Structuring our discussion around the dynamics of the immune response to TBI - from initial triggers to chronic neuroinflammation - we consider the ability of soluble and cellular inflammatory mediators to promote repair and regeneration versus secondary injury and neurodegeneration. We summarize both animal model and human studies, with clinical data explicitly defined throughout this Review. Recent advances in neuroimmunology and TBI-responsive neuroinflammation are incorporated, including concepts of inflammasomes, mechanisms of microglial polarization, and glymphatic clearance. Moreover, we highlight findings that could offer novel therapeutic targets for translational and clinical research, assimilate evidence from other brain injury models, and identify outstanding questions in the field.

The Effect of Traumatic Brain Injury History with Loss of Consciousness on Rate of Cognitive Decline Among Older Adults with Normal Cognition and Alzheimer's Disease Dementia

Traumatic brain injury (TBI) is thought to be a risk factor for dementia, including dementia due to Alzheimer's disease (AD). However, the influence of TBI history on the neuropsychological course of AD is unknown and, more broadly, the effect of TBI history on age-related cognitive change is poorly understood. We examined the relationship between history of TBI with loss of consciousness (LOC) history and cognitive change in participants with normal cognition and probable AD, stratified by APOEɛ4 allele status. The sample included 706 participants (432 with normal cognition; 274 probable AD) from the National Alzheimer's Coordinating Center (NACC) dataset that completed the Uniform Data Set evaluation between 2005 and 2014. Normal and probable AD participants with a history of TBI were matched to an equal number of demographically and clinically similar participants without a TBI history. In this dataset, TBI with LOC was defined as brain trauma with brief or extended unconsciousness. For the normal and probable AD cohorts, there was an average of 3.2±1.9 and 1.8±1.1 years of follow-up, respectively. 30.8% of the normal cohort were APOEɛ4 carriers, whereas 70.8% of probable AD participants were carriers. Mixed effects regressions showed TBI with LOC history did not affect rates of cognitive change in APOEɛ4 carriers and non-carriers. Findings from this study suggest that TBI with LOC may not alter the course of cognitive function in older adults with and without probable AD. Future studies that better characterize TBI (e.g., severity, number of TBIs, history of subconconcussive exposure) are needed to clarify the association between TBI and long-term neurocognitive outcomes.

Altered Effective Connectivity of Hippocampus-Dependent Episodic Memory Network in mTBI Survivors

Traumatic brain injuries (TBIs) are generally recognized to affect episodic memory. However, less is known regarding how external force altered the way functionally connected brain structures of the episodic memory system interact. To address this issue, we adopted an effective connectivity based analysis, namely, multivariate Granger causality approach, to explore causal interactions within the brain network of interest. Results presented that TBI induced increased bilateral and decreased ipsilateral effective connectivity in the episodic memory network in comparison with that of normal controls. Moreover, the left anterior superior temporal gyrus (aSTG, the concept forming hub), left hippocampus (the personal experience binding hub), and left parahippocampal gyrus (the contextual association hub) were no longer network hubs in TBI survivors, who compensated for hippocampal deficits by relying more on the right hippocampus (underlying perceptual memory) and the right medial frontal gyrus (MeFG) in the anterior prefrontal cortex (PFC). We postulated that the overrecruitment of the right anterior PFC caused dysfunction of the strategic component of episodic memory, which caused deteriorating episodic memory in mTBI survivors. Our findings also suggested that the pattern of brain network changes in TBI survivors presented similar functional consequences to normal aging.

Peripheral Inflammatory Markers and Antioxidant Response during the Post-Acute and Chronic Phase after Severe Traumatic Brain Injury

Traumatic brain injury (TBI) is a mechanical insult to the brain caused by external forces and associated with inflammation and oxidative stress. The patients may show different profiles of neurological recovery and a combination of oxidative damage and inflammatory processes can affect their courses. It is known that an overexpression of cytokines can be seen in peripheral blood in the early hours/days after the injury, but little is known about the weeks and months encompassing the post-acute and chronic phases. In addition, no information is available about the antioxidant responses mediated by the major enzymes that regulate reactive oxygen species levels: superoxide dismutase, catalase, peroxidases, and GSH-related enzymes. This study investigates the 6-month trends of inflammatory markers and antioxidant responses in 22 severe TBI patients with prolonged disorders of consciousness, consecutively recruited in a dedicated neurorehabilitation facility. Patients with a high degree of neurological impairment often show an uncertain outcome. In addition, the profiles of plasma activities were related to the neurological recovery after 12 months. Venous peripheral blood samples were taken blindly as soon as clinical signs and laboratory markers confirmed the absence of infections, 3 and 6 months later. The clinical and neuropsychological assessment continued up to 12 months. Nineteen patients completed the follow-up. In the chronic phase, persistent high plasma levels of cytokines can interfere with cognitive functioning and higher post-acute levels of cytokines [interferon (IFN)-γ, tumor necrosis factor (TNF)-α, IL1b, IL6] are associated with poorer cognitive recoveries 12 months later. Moreover, higher IFN-γ, higher TNF-α, and lower glutathione peroxidase activity are associated with greater disability. The results add evidence of persistent inflammatory response, provide information about long-term imbalance of antioxidant activity, and suggest that the over-production of cytokines and the alteration of the redox homeostasis in the post-acute phase might adversely affect the neurological and functional recovery. Inflammatory and antioxidant activity markers might offer a feasible way to highlight some of the processes opposing recovery after a severe TBI.

Feasibility of online self-administered cognitive training in moderate-severe brain injury

PURPOSE

Cognitive environmental enrichment (C-EE) offers promise for offsetting neural decline that is observed in chronic moderate-severe traumatic brain injury (TBI). Brain games are a delivery modality for C-EE that can be self-administered over the Internet without therapist oversight. To date, only one study has examined the feasibility of self-administered brain games in TBI, and the study focused predominantly on mild TBI. Therefore, the primary purpose of the current study was to examine the feasibility of self-administered brain games in moderate-severe TBI. A secondary and related purpose was to examine the feasibility of remote monitoring of any C-EE-induced adverse symptoms with a self-administered evaluation tool.

METHOD

Ten patients with moderate-severe TBI were asked to complete 12 weeks (60 min/day, five days/week) of online brain games with bi-weekly self-evaluation, intended to measure any adverse consequences of cognitive training (e.g., fatigue, eye strain).

RESULTS

There was modest weekly adherence (42.6% ± 4.4%, averaged across patients and weeks) and 70% patient retention; of the seven retained patients, six completed the self-evaluation questionnaire at least once/week for each week of the study.

CONCLUSIONS

Even patients with moderate-severe TBI can complete a demanding, online C-EE intervention and a self-administered symptom evaluation tool with limited therapist oversight, though at daily rate closer to 30 than 60 min per day. Further self-administered C-EE research is underway in our lab, with more extensive environmental support. Implications for Rehabilitation Online brain games (which may serve as a rehabilitation paradigm that can help offset the neurodegeneration observed in chronic TBI) can be feasibly self-administered by moderate-to-severe TBI patients. Brain games are a promising therapy modality, as they can be accessed by all moderate-to-severe TBI patients irrespective of geographic location, clinic and/or therapist availability, or impairments that limit mobility and access to rehabilitation services. Future efficacy trials that examine the effect of brain games for offsetting neurodegeneration in moderate-to-severe TBI patients are warranted.

Assessing the Relationship between Neurocognitive Performance and Brain Volume in Chronic Moderate-Severe Traumatic Brain Injury

Objectives

Characterize the scale and pattern of long-term atrophy in gray matter (GM), white matter (WM), and cerebrospinal fluid (CSF) in chronic moderate–severe traumatic brain injury (TBI) and its relationship to neurocognitive outcomes.

Participants

The TBI group consisted of 17 males with primary diagnosis of moderate–severe closed head injury. Participants had not received any systematic, post-acute rehabilitation and were recruited on average 8.36 years post-injury. The control group consisted of 15 males matched on age and education.

Main measures

Neurocognitive battery included widely used tests of verbal memory, visual memory, executive functioning, and attention/organization. GM, WM, and CSF volumes were calculated from segmented T1-weighted anatomical MR images. Voxel-based morphometry was employed to identify brain regions with differences in GM and WM between TBI and control groups.

Results

Chronic TBI results in significant neurocognitive impairments, and significant loss of GM and WM volume, and significant increase in CSF volume. Brain atrophy is not widespread, but it is rather distributed in a fronto-thalamic network. The extent of volume loss is predictive of performance on the neurocognitive tests.

Conclusion

Significant brain atrophy and associated neurocognitive impairments during the chronic stages of TBI support the notion that TBI results in a chronic condition with lifelong implications.

Progressive inflammation-mediated neurodegeneration after traumatic brain or spinal cord injury

Traumatic brain injury (TBI) has been linked to dementia and chronic neurodegeneration. Described initially in boxers and currently recognized across high contact sports, the association between repeated concussion (mild TBI) and progressive neuropsychiatric abnormalities has recently received widespread attention, and has been termed chronic traumatic encephalopathy. Less well appreciated are cognitive changes associated with neurodegeneration in the brain after isolated spinal cord injury. Also under-recognized is the role of sustained neuroinflammation after brain or spinal cord trauma, even though this relationship has been known since the 1950s and is supported by more recent preclinical and clinical studies. These pathological mechanisms, manifested by extensive microglial and astroglial activation and appropriately termed chronic traumatic brain inflammation or chronic traumatic inflammatory encephalopathy, may be among the most important causes of post-traumatic neurodegeneration in terms of prevalence. Importantly, emerging experimental work demonstrates that persistent neuroinflammation can cause progressive neurodegeneration that may be treatable even weeks after traumatic injury.

A Review of the Effectiveness of Neuroimaging Modalities for the Detection of Traumatic Brain Injury

The incidence of traumatic brain injury (TBI) in the United States was 3.5 million cases in 2009, according to the Centers for Disease Control and Prevention. It is a contributing factor in 30.5% of injury-related deaths among civilians. Additionally, since 2000, more than 260,000 service members were diagnosed with TBI, with the vast majority classified as mild or concussive (76%). The objective assessment of TBI via imaging is a critical research gap, both in the military and civilian communities. In 2011, the Department of Defense (DoD) prepared a congressional report summarizing the effectiveness of seven neuroimaging modalities (computed tomography [CT], magnetic resonance imaging [MRI], transcranial Doppler [TCD], positron emission tomography, single photon emission computed tomography, electrophysiologic techniques [magnetoencephalography and electroencephalography], and functional near-infrared spectroscopy) to assess the spectrum of TBI from concussion to coma. For this report, neuroimaging experts identified the most relevant peer-reviewed publications and assessed the quality of the literature for each of these imaging technique in the clinical and research settings. Although CT, MRI, and TCD were determined to be the most useful modalities in the clinical setting, no single imaging modality proved sufficient for all patients due to the heterogeneity of TBI. All imaging modalities reviewed demonstrated the potential to emerge as part of future clinical care. This paper describes and updates the results of the DoD report and also expands on the use of angiography in patients with TBI.

Structural Image Analysis of the Brain in Neuropsychology Using Magnetic Resonance Imaging (MRI) Techniques

Magnetic resonance imaging (MRI) of the brain provides exceptional image quality for visualization and neuroanatomical classification of brain structure. A variety of image analysis techniques provide both qualitative as well as quantitative methods to relate brain structure with neuropsychological outcome and are reviewed herein. Of particular importance are more automated methods that permit analysis of a broad spectrum of anatomical measures including volume, thickness and shape. The challenge for neuropsychology is which metric to use, for which disorder and the timing of when image analysis methods are applied to assess brain structure and pathology. A basic overview is provided as to the anatomical and pathoanatomical relations of different MRI sequences in assessing normal and abnormal findings. Some interpretive guidelines are offered including factors related to similarity and symmetry of typical brain development along with size-normalcy features of brain anatomy related to function. The review concludes with a detailed example of various quantitative techniques applied to analyzing brain structure for neuropsychological outcome studies in traumatic brain injury.

Aging, neurodegenerative disease, and traumatic brain injury: the role of neuroimaging

Traumatic brain injury (TBI) is a highly prevalent condition with significant effects on cognition and behavior. While the acute and sub-acute effects of TBI recover over time, relatively little is known about the long-term effects of TBI in relation to neurodegenerative disease. This issue has recently garnered a great deal of attention due to publicity surrounding chronic traumatic encephalopathy (CTE) in professional athletes, although CTE is but one of several neurodegenerative disorders associated with a history of TBI. Here, we review the literative on neurodegenerative disorders linked to remote TBI. We also review the evidence for neuroimaging changes associated with unhealthy brain aging in the context of remote TBI. We conclude that neuroimaging biomarkers have significant potential to increase understanding of the mechanisms of unhealthy brain aging and neurodegeneration following TBI, with potential for identifying those at risk for unhealthy brain aging prior to the clinical manifestation of neurodegenerative disease.

Chronic neurodegeneration after traumatic brain injury: Alzheimer disease, chronic traumatic encephalopathy, or persistent neuroinflammation?

It has long been suggested that prior traumatic brain injury (TBI) increases the subsequent incidence of chronic neurodegenerative disorders, including Alzheimer disease, Parkinson disease, and amyotrophic lateral sclerosis. Among these, the association with Alzheimer disease has the strongest support. There is also a long-recognized association between repeated concussive insults and progressive cognitive decline or other neuropsychiatric abnormalities. The latter was first described in boxers as dementia pugilistica, and has received widespread recent attention in contact sports such as professional American football. The term chronic traumatic encephalopathy was coined to attempt to define a "specific" entity marked by neurobehavioral changes and the extensive deposition of phosphorylated tau protein. Nearly lost in the discussions of post-traumatic neurodegeneration after traumatic brain injury has been the role of sustained neuroinflammation, even though this association has been well established pathologically since the 1950s, and is strongly supported by subsequent preclinical and clinical studies. Manifested by extensive microglial and astroglial activation, such chronic traumatic brain inflammation may be the most important cause of post-traumatic neurodegeneration in terms of prevalence. Critically, emerging preclinical studies indicate that persistent neuroinflammation and associated neurodegeneration may be treatable long after the initiating insult(s).

Negative neuroplasticity in chronic traumatic brain injury and implications for neurorehabilitation

Based on growing findings of brain volume loss and deleterious white matter alterations during the chronic stages of injury, researchers posit that moderate-severe traumatic brain injury (TBI) may act to “age” the brain by reducing reserve capacity and inducing neurodegeneration. Evidence that these changes correlate with poorer cognitive and functional outcomes corroborates this progressive characterization of chronic TBI. Borrowing from a framework developed to explain cognitive aging (Mahncke et al., Progress in Brain Research, 157, 81–109, 2006a; Mahncke et al., Proceedings of the National Academy of Sciences of the United States of America, 103(33), 12523–12528, 2006b), we suggest here that environmental factors (specifically environmental impoverishment and cognitive disuse) contribute to a downward spiral of negative neuroplastic change that may modulate the brain changes described above. In this context, we review new literature supporting the original aging framework, and its extrapolation to chronic TBI. We conclude that negative neuroplasticity may be one of the mechanisms underlying cognitive and neural decline in chronic TBI, but that there are a number of points of intervention that would permit mitigation of this decline and better long-term clinical outcomes.

Interpretation of magnetic resonance imaging in the chronic phase of traumatic brain injury: what is missed in the original reports?

PRIMARY OBJECTIVE

To find eventual differences in detecting the late stage TBI findings in MRI between two neuroradiologists and to compare the results with the original reports.

METHODS AND PROCEDURE

Two neuroradiologists with different levels of experience (R1 and R2) reviewed 89 cranial 1.5 T MRI examinations of patients with clinically evident TBI. They recorded the nature, location and side of the finding and stated their view of traumatic axonal injury (TAI). The original reports were reviewed accordingly.

MAIN OUTCOMES AND RESULTS

TAI was reported as being evident or possible in 51 patients with TBI. However, only 30 (76%) of these concerned the same patients. R1 reported more contusion findings, but both found the same number of spot-like haemorrhages. The most striking difference was in the reporting of localized atrophy. R1 reported atrophy in 51/178 (29%) frontal lobes, whereas R2 in 14/178 (8%). Many of the findings were missed in the original reports.

CONCLUSIONS

The interpretation of TBI findings in late stage MRI yields significant variability between neuroradiologists. This may endanger diagnostics and lead to false treatment decisions and medico-legal problems. Standardized quantitative imaging analysis programs and advances in MRI technology should be utilized to improve radiological TBI diagnosis.

Scale and pattern of atrophy in the chronic stages of moderate-severe TBI

BACKGROUND

Moderate-severe traumatic brain injury (TBI) is increasingly being understood as a progressive disorder, with growing evidence of reduced brain volume and white matter (WM) integrity as well as lesion expansion in the chronic phases of injury. The scale of these losses has yet to be investigated, and pattern of change across structures has received limited attention.

OBJECTIVES

(1) To measure the percentage of patients in our TBI sample showing atrophy from 5 to 20 months post-injury in the whole brain and in structures with known vulnerability to acute TBI, and (2) To examine relative vulnerability and patterns of volume loss across structures.

METHODS

Fifty-six TBI patients [complicated mild to severe, with mean Glasgow Coma Scale (GCS) in severe range] underwent MRI at, on average, 5 and 20 months post-injury; 12 healthy controls underwent MRI twice, with a mean gap between scans of 25.4 months. Mean monthly percent volume change was computed for whole brain (ventricle-to-brain ratio; VBR), corpus callosum (CC), and right and left hippocampi (HPC).

RESULTS

(1) Using a threshold of 2 z-scores below controls, 96% of patients showed atrophy across time points in at least one region; 75% showed atrophy in at least 3 of the 4 regions measured. (2) There were no significant differences in the proportion of patients who showed atrophy across structures. For those showing decline in VBR, there was a significant association with both the CC and the right HPC (P < 0.05 for both comparisons). There were also significant associations between those showing decline in (i) right and left HPC (P < 0.05); (ii) all combinations of genu, body and splenium of the CC (P < 0.05), and (iii) head and tail of the right HPC (P < 0.05 all sub-structure comparisons).

CONCLUSIONS

Atrophy in chronic TBI is robust, and the CC, right HPC and left HPC appear equally vulnerable. Significant associations between the right and left HPC, and within substructures of the CC and right HPC, raise the possibility of common mechanisms for these regions, including transneuronal degeneration. Given the 96% incidence rate of atrophy, a genetic explanation is unlikely to explain all findings. Multiple and possibly synergistic mechanisms may explain findings. Atrophy has been associated with poorer functional outcomes, but recent findings suggest there is potential to offset this. A better, understanding of the underlying mechanisms could permit targeted therapy enabling better long-term outcomes.

Prospective longitudinal MRI study of brain volumes and diffusion changes during the first year after moderate to severe traumatic brain injury

The objectives of this prospective study in 62 moderate–severe TBI patients were to investigate volume change in cortical gray matter (GM), hippocampus, lenticular nucleus, lobar white matter (WM), brainstem and ventricles using a within subject design and repeated MRI in the early phase (1–26 days) and 3 and 12 months postinjury and to assess changes in GM apparent diffusion coefficient (ADC) in normal appearing tissue in the cortex, hippocampus and brainstem. The impact of Glasgow Coma Scale (GCS) score at admission, duration of post-traumatic amnesia (PTA), and diffusion axonal injury (DAI) grade on brain volumes and ADC values over time was assessed. Lastly, we determined if MRI-derived brain volumes from the 3-month scans provided additional, significant predictive value to 12-month outcome classified with the Glasgow Outcome Scale—Extended after adjusting for GCS, PTA and age.

Cortical GM loss was rapid, largely finished by 3 months, but the volume reduction was unrelated to GCS score, PTA, or presence of DAI. However, cortical GM volume at 3 months was a significant independent predictor of 12-month outcome. Volume loss in the hippocampus and lenticular nucleus was protracted and statistically significant first at 12 months. Slopes of volume reduction over time for the cortical and subcortical GGM were significantly different. Hippocampal volume loss was most pronounced and rapid in individuals with PTA > 2 weeks. The 3-month volumes of the hippocampus and lentiform nucleus were the best independent predictors of 12-month outcome after adjusting for GCS, PTA and age. In the brainstem, volume loss was significant at both 3 and 12 months. Brainstem volume reduction was associated with lower GCS score and the presence of DAI. Lobar WM volume was significantly decreased first after 12 months. Surprisingly DAI grade had no impact on lobar WM volume. Ventricular dilation developed predominantly during the first 3 months, and was strongly associated with volume changes in the brainstem and cortical GM, but not lobar WM volume.

Higher ADC values were detected in the cortex in individuals with severe TBI, DAI and PTA > 2 weeks, from 3 months. There were no associations between ADC values and brain volumes, and ADC values did not predict outcome.

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Longitudinal study of brain volume changes following TBI

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3 month MRI derived volumes are independent predictors of outcome at 12 months.

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PTA, GCS and DAI have different impacts on different brain volumes.

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Subcortical and cortical GM volume losses follow significantly different trajectories.

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Significant changes in cortical ADC values develop slowly while volume changes are rapid.

Is there evidence for neurodegenerative change following traumatic brain injury in children and youth? A scoping review

While generalized cerebral atrophy and neurodegenerative change following traumatic brain injury (TBI) is well recognized in adults, it remains comparatively understudied in the pediatric population, suggesting that research should address the potential for neurodegenerative change in children and youth following TBI. This focused review examines original research findings documenting evidence for neurodegenerative change following TBI of all severities in children and youth. Our relevant inclusion and exclusion criteria identified a total of 16 articles for review. Taken together, the studies reviewed suggest there is evidence for long-term neurodegenerative change following TBI in children and youth. In particular both cross-sectional and longitudinal studies revealed volume loss in selected brain regions including the hippocampus, amygdala, globus pallidus, thalamus, periventricular white matter, cerebellum, and brain stem as well as overall decreased whole brain volume and increased CSF and ventricular space. Diffusion Tensor Imaging (DTI) studies also report evidence for decreased cellular integrity, particularly in the corpus callosum. Sensitivity of the hippocampus and deep limbic structures in pediatric populations are similar to findings in the adult literature and we consider the data supporting these changes as well as the need to investigate the possibility of neurodegenerative onset in childhood associated with mild traumatic brain injury (mTBI).

Combination therapy of human umbilical cord blood cells and granulocyte colony stimulating factor reduces histopathological and motor impairments in an experimental model of chronic traumatic brain injury

Traumatic brain injury (TBI) is associated with neuro-inflammation, debilitating sensory-motor deficits, and learning and memory impairments. Cell-based therapies are currently being investigated in treating neurotrauma due to their ability to secrete neurotrophic factors and anti-inflammatory cytokines that can regulate the hostile milieu associated with chronic neuroinflammation found in TBI. In tandem, the stimulation and mobilization of endogenous stem/progenitor cells from the bone marrow through granulocyte colony stimulating factor (G-CSF) poses as an attractive therapeutic intervention for chronic TBI. Here, we tested the potential of a combined therapy of human umbilical cord blood cells (hUCB) and G-CSF at the acute stage of TBI to counteract the progressive secondary effects of chronic TBI using the controlled cortical impact model. Four different groups of adult Sprague Dawley rats were treated with saline alone, G-CSF+saline, hUCB+saline or hUCB+G-CSF, 7-days post CCI moderate TBI. Eight weeks after TBI, brains were harvested to analyze hippocampal cell loss, neuroinflammatory response, and neurogenesis by using immunohistochemical techniques. Results revealed that the rats exposed to TBI treated with saline exhibited widespread neuroinflammation, impaired endogenous neurogenesis in DG and SVZ, and severe hippocampal cell loss. hUCB monotherapy suppressed neuroinflammation, nearly normalized the neurogenesis, and reduced hippocampal cell loss compared to saline alone. G-CSF monotherapy produced partial and short-lived benefits characterized by low levels of neuroinflammation in striatum, DG, SVZ, and corpus callosum and fornix, a modest neurogenesis, and a moderate reduction of hippocampal cells loss. On the other hand, combined therapy of hUCB+G-CSF displayed synergistic effects that robustly dampened neuroinflammation, while enhancing endogenous neurogenesis and reducing hippocampal cell loss. Vigorous and long-lasting recovery of motor function accompanied the combined therapy, which was either moderately or short-lived in the monotherapy conditions. These results suggest that combined treatment rather than monotherapy appears optimal for abrogating histophalogical and motor impairments in chronic TBI.

Progressive neurodegeneration after experimental brain trauma: association with chronic microglial activation

Recent clinical studies indicate that traumatic brain injury (TBI) produces chronic and progressive neurodegenerative changes leading to late neurologic dysfunction, but little is known about the mechanisms underlying such changes. Microglial-mediated neuroinflammationis an important secondary injury mechanism after TBI. In human studies, microglial activation has been found to persist for many years after the initial brain trauma, particularly after moderate to severe TBI. In the present study, adult C57Bl/6 mice were subjected to single moderate-level controlled cortical impact and were followed up by longitudinal T2-weighted magnetic resonance imaging in combination with stereologic histologic assessment of lesion volume expansion, neuronal loss, and microglial activation for up to 1 year after TBI. Persistent microglial activation was observed in the injured cortex through 1 year after injury and was associated with progressive lesion expansion, hippocampal neurodegeneration, and loss of myelin. Notably, highly activated microglia that expressed major histocompatibility complex class II (CR3/43), CD68, and NADPH oxidase (NOX2) were detected at the margins of the expanding lesion at 1 year after injury; biochemical markers of neuroinflammation and oxidative stress were significantly elevated at this time point. These data support emerging clinical TBI findings and provide a mechanistic link between TBI-induced chronic microglial activation and progressive neurodegeneration.