Acute White-Matter Abnormalities in Sports-Related Concussion: A Diffusion Tensor Imaging Study from the NCAA-DoD CARE Consortium

Soma and neurite density imaging detects brain microstructural impairments in amyotrophic lateral sclerosis

OBJECTIVE

To investigate whole-brain microstructural changes in amyotrophic lateral sclerosis (ALS) using soma and neurite density imaging (SANDI), a novel multicompartment model of diffusion-weighted imaging that estimates apparent soma and neurite density.

METHODS

This study consists of 41 healthy controls and 43 patients with ALS, whose diffusion-weighted data were acquired. The SANDI-derived (including signal fractions of soma (fsoma), neurite (fneurite), and extra-cellular space (fextra)) and diffusion tensor imaging (DTI)-derived metrics were obtained. Voxel-based analyses were performed to evaluate intergroup differences and the correlation of SANDI and DTI metrics with clinical parameters.

RESULTS

In ALS patients, fneurite reduction involved both gray matter (primarily the bilateral precentral gyri, supplementary motor area, medial frontal gyrus, anterior cingulate cortex, inferior frontal gyrus, orbital gyrus, paracentral lobule, postcentral gyrus, middle cingulate cortex, hippocampus and parahippocampal gyrus, and insula, and left anterior parts of the temporal lobe) and white matter (primarily the bilateral corticospinal tract, body of corpus callosum, and brainstem) (P <0.05 after false discovery rate correction). The fextra increment showed a similar spatial distribution in ALS patients. Interestingly, the decreased fsoma in ALS primarily located in gray matter; while, the increased fsoma primarily involved white matter. The spatial distribution of fneurite/fextra/fsoma changes was larger than that detected by conventional DTI metrics, and the fneurite/fextra/fsoma were correlated with disease severity.

CONCLUSIONS

SANDI may serve as a clinically relevant model, superior to conventional DTI, for characterizing microstructural impairments such as neurite degeneration and soma alteration in ALS.

Association of Alzheimer's Disease Polygenic Risk Score with Concussion Severity and Recovery Metrics

BACKGROUND

Identification of genetic alleles associated with both Alzheimer's disease (AD) and concussion severity/recovery could help explain the association between concussion and elevated dementia risk. However, there has been little investigation into whether AD risk genes associate with concussion severity/recovery, and the limited findings are mixed.

OBJECTIVE

We used AD polygenic risk scores (PRS) and APOE genotypes to investigate any such associations in the NCAA-DoD Grand Alliance CARE Consortium (CARE) dataset.

METHODS

We assessed six concussion outcomes in 931 participants, including two recovery measures (number of days to asymptomatic and to return to play (RTP)) and four severity measures (scores on SAC and BESS, SCAT symptom severity and total number of symptoms). We calculated the PRS using a published score and performed multiple linear regression to assess the relationship of the PRS with outcomes. We also used ANOVAs, t-tests, and chi-square tests to examine outcomes by APOE genotype.

RESULTS

Higher PRS was associated with longer injury to RTP time in the normal RTP (< 24 days) subgroup (p = 0.024). A one standard deviation increase in the PRS resulted in a 9.89 hour increase to RTP time. This result was no longer significant after inclusion of covariates. There were no other consistently significant effects.

CONCLUSIONS

Our findings suggest high AD genetic risk is not associated with more severe concussions or poor recovery in young adults. Future studies should attempt to replicate these findings in larger samples with longer follow-up using PRS calculated from diverse populations.

Characterizing the Effect of Repetitive Head Impact Exposure and mTBI on Adolescent Collision Sports Players' Brain with Diffusion Magnetic Resonance Imaging

Athletes in collision sports frequently sustain repetitive head impacts (RHI), which, while not individually severe enough for a clinical mild traumatic brain injury (mTBI) diagnosis, can compromise neuronal organization by transferring mechanical energy to the brain. Although numerous studies target athletes with mTBI, there is a lack of longitudinal research on young collision sport participants, highlighting an unaddressed concern regarding cumulative RHI effects on brain microstructures. Therefore, this study aimed to investigate the microstructural changes in the brains' of high school rugby players due to repeated head impacts and to establish a correlation between clinical symptoms, cumulative effects of RHI exposure, and changes in the brain's microstructure. We conducted a longitudinal magnetic resonance imaging (MRI) study on 36 male high school rugby players across a season using 3D T1-weighted and multi-shell diffusion MRI sequences, comparing them with 20 matched controls. Players with concussions were separately tracked up to 6 weeks post-injury with three-times scans within this period. The Sport Concussion Assessment Tool (SCAT5) symptom scale assessed mTBI symptoms, and mouthguard-embedded kinematic sensors recorded head impacts. No significant volumetric changes in subcortical structures were found post-rugby season. However, there were substantial differences in mean diffusivity (MD) and axial diffusivity (AD) between the rugby players and controls across widespread brain regions. Diffusion metrics, especially AD, MD, and radial diffusivity of certain brain tracts, displayed strong correlations with SCAT5 symptom severity. Repeated head impacts during a rugby season may adversely affect the structural organization of the brain's white matter. The observed diffusion changes, closely tied to SCAT5 symptom burden, stress the profound effects of seasonal head impacts and highlight individual variability in response to repetitive head impact exposure. To better manage sports-related mTBI and guide return-to-play decisions, comprehensive studies on brain injury mechanisms and recovery post-mTBI/RHI exposure are required.

Reduced Cortical Excitability is Associated with Cognitive Symptoms in Concussed Adolescent Football Players

Background

American tackle football is associated with high rates of concussion, leading to neurophysiological disturbances and debilitating clinical symptoms. Previous investigations of the neurophysiological effects of concussion have largely ignored aperiodic neurophysiological activity, which is a marker of cortical excitability.

Purpose

We examined whether concussion during a season of high school football is related to changes in aperiodic and periodic neurophysiological activity and whether any such changes are associated with clinical outcomes.

Materials and Methods

Pre- and post-season resting-state magnetoencephalography (MEG) data were collected from 91 high school football players over as many as four seasons of play, for a total of 278 data collections. During these seasons of football play, a cohort of 10 individuals were diagnosed with concussion. MEG data were source-imaged, frequency-transformed and parameterized, and linear mixed models were used to examine effects of concussion on pre-to-post-season changes in neurophysiological activity. Scores on the Post-Concussive Symptom Inventory were correlated with pre-to-post-season neurophysiological changes to determine their clinical relevance.

Results

Concussion was associated with increased aperiodic exponents in superior frontal cortices, indicating a relative reduction in cortical excitability. This slowing of aperiodic neurophysiology mediated concussion effects on raw delta and gamma power and was associated with worse cognitive concerns across participants. Pre-to-post-season changes in aperiodic-corrected alpha and theta rhythmic activity were also decreased in posterior cortices in concussed players.

Conclusion

These findings indicate that concussion alters both the excitability and rhythmic signaling of the cortex, with differing spatial topographies and implications for clinical symptoms.

Characterizing the Effects of Concussion and Head Impact Exposure: Design, Methods, and Participant Traits of the CARE 2.0 Study

OBJECTIVE

This article describes the design, methods, and participant characteristics of the second phase of the Concussion Assessment, Research, and Education (CARE) Consortium study ("CARE 2.0") of the effects of concussion and repetitive head impact exposure on neuropsychiatric health.

METHODS

The authors conducted a prospective multisite observational study of male and female collegiate athletes and military service academy cadets and midshipmen participating in the CARE study. Participants were assessed at three time points: undergraduate baseline (UB), before departure from university or service academy (exit), and up to 6 years following graduation (postgrad) via an online battery of brain health assessments. Participant characteristics were compared across the three time points and four levels of head impact exposure.

RESULTS

A total of 4,643 participants completed the exit assessment, and 3,981 completed the postgrad assessment. Relative to the UB assessment cohort, the exit and postgrad assessment cohorts differed with respect to the percentage of women, baseline Wechsler Test of Adult Reading scores, National Collegiate Athletic Association division category, sport contact level, and number of previous concussions. The median standardized difference across balancing variables, assessment time points, and degree of head impact exposure was 0.12 (with 90% of effect sizes ≤0.29).

CONCLUSIONS

Although there were some statistically significant differences between participants across assessments, the effect sizes were modest, and overall the data suggest that the exit and postgrad cohorts reflect the characteristics of the baseline cohort. The CARE study design and its large, richly characterized sample provide an opportunity to answer important questions about cumulative and persistent effects of concussion and repetitive head impact exposure on neuropsychiatric health.

Evidence for Altered White Matter Organization After Mild Traumatic Brain Injury: A Scoping Review on the Use of Diffusion Magnetic Resonance Imaging and Blood-Based Biomarkers to Investigate Acute Pathology and Relationship to Persistent Post-Concussion Symptoms

Mild traumatic brain injury (mTBI) is the most common form of traumatic brain injury. Post-concussive symptoms typically resolve after a few weeks although up to 20% of people experience these symptoms for >3 months, termed persistent post-concussive symptoms (PPCS). Subtle white matter (WM) microstructural damage is thought to underlie neurological and cognitive deficits experienced post-mTBI. Evidence suggests that diffusion magnetic resonance imaging (dMRI) and blood-based biomarkers could be used as surrogate markers of WM organization. We conducted a scoping review according to PRISMA-ScR guidelines, aiming to collate evidence for the use of dMRI and/or blood-based biomarkers of WM organization, in mTBI and PPCS, and document relationships between WM biomarkers and symptoms. We focused specifically on biomarkers of axonal or myelin integrity post-mTBI. Biomarkers excluded from this review therefore included the following: astroglial, perivascular, endothelial, and inflammatory markers. A literature search performed across four databases, EMBASE, Scopus, Google Scholar, and ProQuest, identified 100 records: 68 analyzed dMRI, 28 assessed blood-based biomarkers, and 4 used both. Blood biomarker studies commonly assessed axonal cytoskeleton proteins (i.e., tau); dMRI studies assessed measures of WM organization (i.e., fractional anisotropy). Significant biomarker alterations were frequently associated with heightened symptom burden and prolonged recovery time post-injury. These data suggest that dMRI and blood-based biomarkers may be useful proxies of WM organization, although few studies assessed these complementary measures in parallel, and the relationship between modalities remains unclear. Further studies are warranted to assess the benefit of a combined biomarker approach in evaluating alterations to WM organization after mTBI.

Diffusion tensor analysis of white matter tracts is prognostic of persisting post-concussion symptoms in collegiate athletes

BACKGROUND AND OBJECTIVES

After a concussion diagnosis, the most important issue for patients and loved ones is how long it will take them to recover. The main objective of this study is to develop a prognostic model of concussion recovery. This model would benefit many patients worldwide, allowing for early treatment intervention.

METHODS

The Concussion Assessment, Research and Education (CARE) consortium study enrolled collegiate athletes from 30 sites (NCAA athletic departments and US Department of Defense service academies), 4 of which participated in the Advanced Research Core, which included diffusion-weighted MRI (dMRI) data collection. We analyzed the dMRI data of 51 injuries of concussed athletes scanned within 48 h of injury. All athletes were cleared to return-to-play by the local medical staff following a standardized, graduated protocol. The primary outcome measure is days to clearance of unrestricted return-to-play. Injuries were divided into early (return-to-play < 28 days) and late (return-to-play >= 28 days) recovery based on the return-to-play clinical records. The late recovery group meets the standard definition of Persisting Post-Concussion Symptoms (PPCS). Data were processed using automated, state-of-the-art, rigorous methods for reproducible data processing using brainlife.io. All processed data derivatives are made available at https://brainlife.io/project/63b2ecb0daffe2c2407ee3c5/dataset. The microstructural properties of 47 major white matter tracts, 5 callosal, 15 subcortical, and 148 cortical structures were mapped. Fractional Anisotropy (FA) and Mean Diffusivity (MD) were estimated for each tract and structure. Correlation analysis and Receiver Operator Characteristic (ROC) analysis were then performed to assess the association between the microstructural properties and return-to-play. Finally, a Logistic Regression binary classifier (LR-BC) was used to classify the injuries between the two recovery groups.

RESULTS

The mean FA across all white matter volume was negatively correlated with return-to-play (r = -0.38, p = 0.00001). No significant association between mean MD and return-to-play was found, neither for FA nor MD for any other structure. The mean FA of 47 white matter tracts was negatively correlated with return-to-play (rμ = -0.27; rσ = 0.08; rmin = -0.1; rmax = -0.43). Across all tracts, a large mean ROC Area Under the Curve (AUCFA) of 0.71 ± 0.09 SD was found. The top classification performance of the LR-BC was AUC = 0.90 obtained using the 16 statistically significant white matter tracts.

DISCUSSION

Utilizing a free, open-source, and automated cloud-based neuroimaging pipeline and app (https://brainlife.io/docs/tutorial/using-clairvoy/), a prognostic model has been developed, which predicts athletes at risk for slow recovery (PPCS) with an AUC=0.90, balanced accuracy = 0.89, sensitivity = 1.0, and specificity = 0.79. The small number of participants in this study (51 injuries) is a significant limitation and supports the need for future large concussion dMRI studies and focused on recovery.

Biofluid, Imaging, Physiological, and Functional Biomarkers of Mild Traumatic Brain Injury and Subconcussive Head Impacts

Post-concussive symptoms are frequently reported by individuals who sustain mild traumatic brain injuries (mTBIs) and subconcussive head impacts, even when evidence of intracranial pathology is lacking. Current strategies used to evaluate head injuries, which primarily rely on self-report, have a limited ability to predict the incidence, severity, and duration of post-concussive symptoms that will develop in an individual patient. In addition, these self-report measures have little association with the underlying mechanisms of pathology that may contribute to persisting symptoms, impeding advancement in precision treatment for TBI. Emerging evidence suggests that biofluid, imaging, physiological, and functional biomarkers associated with mTBI and subconcussive head impacts may address these shortcomings by providing more objective measures of injury severity and underlying pathology. Interest in the use of biomarker data has rapidly accelerated, which is reflected by the recent efforts of organizations such as the National Institute of Neurological Disorders and Stroke and the National Academies of Sciences, Engineering, and Medicine to prioritize the collection of biomarker data during TBI characterization in acute-care settings. Thus, this review aims to describe recent progress in the identification and development of biomarkers of mTBI and subconcussive head impacts and to discuss important considerations for the implementation of these biomarkers in clinical practice.

Biclustering Multivariate Longitudinal Data with Application to Recovery Trajectories of White Matter After Sport-Related Concussion

Biclustering is the task of simultaneously clustering the samples and features of a data set. In doing so, subsets of samples that exhibit similar behaviors across subsets of features can be identified. Motivated by a longitudinal diffusion tensor imaging study of sport-related concussion (SRC), we present the problem of biclustering multivariate longitudinal data in which subjects and features are grouped simultaneously based on longitudinal patterns rather than magnitude. We propose a penalized regression based method for solving this problem by exploiting the heterogeneity in the longitudinal patterns within subjects and features. We evaluate the performance of the proposed methods via a simulation study and apply them to the motivating dataset, revealing distinctive patterns of white-matter abnormalities within subgroups of SRC cases.

Association of Alzheimer's disease polygenic risk score with concussion severity and recovery metrics

Identification of genetic alleles associated with both Alzheimer's disease (AD) and concussion severity/recovery could help explain the association between concussion and elevated dementia risk. However, there has been little investigation into whether AD risk genes associate with concussion severity/recovery, and the limited findings are mixed. We used AD polygenic risk scores (PRS) and APOE genotypes to investigate any such associations in the NCAA-DoD Grand Alliance CARE Consortium (CARE) dataset. We assessed six outcomes in 931 total participants. The outcomes were two concussion recovery measures (number of days to asymptomatic status, number of days to return to play (RTP)) and four concussion severity measures (scores on SAC and BESS, SCAT symptom severity, and total number of symptoms). We calculated PRS using a published score [1] and performed multiple linear regression (MLR) to assess the relationship of PRS with the outcomes. We also used t-tests and chi-square tests to examine outcomes by APOE genotype, and MLR to analyze outcomes in European and African genetic ancestry subgroups. Higher PRS was associated with longer injury to RTP in the normal RTP (<24 days) subgroup ( p = 0.024), and one standard deviation increase in PRS resulted in a 9.89 hour increase to the RTP interval. There were no other consistently significant effects, suggesting that high AD genetic risk is not strongly associated with more severe concussions or poor recovery in young adults. Future studies should attempt to replicate these findings in larger samples with longer follow-up using PRS calculated from diverse populations.

Widespread White Matter Abnormalities in Concussed Athletes Detected by 7T Diffusion Magnetic Resonance Imaging

Sports-related concussions may cause white matter injuries and persistent post-concussive symptoms (PPCS). We hypothesized that athletes with PPCS would have neurocognitive impairments and white matter abnormalities that could be revealed by advanced neuroimaging using ultra-high field strength diffusion tensor (DTI) and diffusion kurtosis (DKI) imaging metrics and cerebrospinal fluid (CSF) biomarkers. A cohort of athletes with PPCS severity limiting the ability to work/study and participate in sport school and/or social activities for ≥6 months completed 7T magnetic resonance imaging (MRI) (morphological T1-weighed volumetry, DTI and DKI), extensive neuropsychological testing, symptom rating, and CSF biomarker sampling. Twenty-two athletes with PPCS and 22 controls were included. Concussed athletes performed below norms and significantly lower than controls on all but one of the psychometric neuropsychology tests. Supratentorial white and gray matter, as well as hippocampal volumes did not differ between concussed athletes and controls. However, of the 72 examined white matter tracts, 16% of DTI and 35% of DKI metrics (in total 28%) were significantly different between concussed athletes and controls. DKI fractional anisotropy and axial kurtosis were increased, and DKI radial diffusivity and radial kurtosis decreased in concussed athletes when compared with controls. CSF neurofilament light (NfL; an axonal injury marker), although not glial fibrillary acidic protein, correlated with several diffusion metrics. In this first 7T DTI and DKI study investigating PPCS, widespread microstructural alterations were observed in the white matter, correlating with CSF markers of axonal injury. More white matter changes were observed using DKI than using DTI. These white matter alterations may indicate persistent pathophysiological processes following concussion in sport.

Neural Mechanisms Associated With Postural Control in Collegiate Soccer and Non-Soccer Athletes

BACKGROUND AND PURPOSE

Sport-specific training may improve postural control, while repetitive head acceleration events (RHAEs) may compromise it. Understanding the neural mechanisms underlying postural control may contextualize changes due to training and RHAE. The goal of this study was to determine whether postural sway during the Balance Error Scoring System (BESS) is related to white matter organization (WMO) in collegiate athletes.

METHODS

Collegiate soccer ( N = 33) and non-soccer athletes ( N = 44) completed BESS and diffusion tensor imaging. Postural sway during each BESS stance, fractional anisotropy (FA), and mean diffusivity (MD) were extracted for each participant. Partial least squares analyses determined group differences in postural sway and WMO and the relationship between postural sway and WMO in soccer and non-soccer athletes separately.

RESULTS

Soccer athletes displayed better performance during BESS 6, with lower FA and higher MD in the medial lemniscus (ML) and inferior cerebellar peduncle (ICP), compared to non-soccer athletes. In soccer athletes, lower sway during BESS 2, 5, and 6 was associated with higher FA and lower MD in the corticospinal tract, ML, and ICP. In non-soccer athletes, lower sway during BESS 2 and 4 was associated with higher FA and lower MD in the ML and ICP. BESS 1 was associated with higher FA, and BESS 3 was associated with lower MD in the same tracts in non-soccer athletes.

DISCUSSION AND CONCLUSIONS

Soccer and non-soccer athletes showed unique relationships between sway and WMO, suggesting that sport-specific exposures are partly responsible for changes in neurological structure and accompanying postural control performance and should be considered when evaluating postural control after injury.Video Abstract available for more insights from the authors (see the Video, Supplemental Digital Content, available at: http://links.lww.com/JNPT/A472 ).

Association of Vascular Risk Factors and CSF and Imaging Biomarkers With White Matter Hyperintensities in Former American Football Players

BACKGROUND AND OBJECTIVES

Recent data link exposure to repetitive head impacts (RHIs) from American football with increased white matter hyperintensity (WMH) burden. WMH might have unique characteristics in the context of RHI beyond vascular risk and normal aging processes. We evaluated biological correlates of WMH in former American football players, including markers of amyloid, tau, inflammation, axonal injury, neurodegeneration, and vascular health.

METHODS

Participants underwent clinical interviews, MRI, and lumbar puncture as part of the Diagnostics, Imaging, and Genetics Network for the Objective Study and Evaluation of Chronic Traumatic Encephalopathy Research Project. Structural equation modeling tested direct and indirect effects between log-transformed total fluid-attenuated inversion recovery (FLAIR) lesion volumes (TLV) and the revised Framingham stroke risk profile (rFSRP), MRI-derived global metrics of cortical thickness and fractional anisotropy (FA), and CSF levels of amyloid β1-42, p-tau181, soluble triggering receptor expressed on myeloid cells 2 (sTREM2), and neurofilament light. Covariates included age, race, education, body mass index, APOE ε4 carrier status, and evaluation site. Models were performed separately for former football players and a control group of asymptomatic men unexposed to RHI.

RESULTS

In 180 former football players (mean age = 57.2, 36% Black), higher log(TLV) had direct associations with the following: higher rFSRP score (B = 0.26, 95% CI 0.07-0.40), higher p-tau181 (B = 0.17, 95% CI 0.01-0.43), lower FA (B = -0.28, 95% CI -0.42 to -0.13), and reduced cortical thickness (B = -0.25, 95% CI -0.45 to -0.08). In 60 asymptomatic unexposed men (mean age = 59.3, 40% Black), there were no direct effects on log(TLV) (rFSRP: B = -0.03, 95% CI -0.48 to 0.57; p-tau181: B = -0.30, 95% CI -1.14 to 0.37; FA: B = -0.07, 95% CI -0.48 to 0.42; or cortical thickness: B = -0.28, 95% CI -0.64 to 0.10). The former football players showed stronger associations between log(TLV) and rFSRP (1,069% difference in estimates), p-tau181 (158%), and FA (287%) than the unexposed men.

DISCUSSION

Risk factors and biological correlates of WMH differed between former American football players and asymptomatic unexposed men. In addition to vascular health, p-tau181 and diffusion tensor imaging indices of white matter integrity showed stronger associations with WMH in the former football players. FLAIR WMH may have specific risk factors and pathologic underpinnings in RHI-exposed individuals.

Longitudinal Associations Between Blood Biomarkers and White Matter MRI in Sport-Related Concussion: A Study of the NCAA-DoD CARE Consortium

BACKGROUND AND OBJECTIVES

To study longitudinal associations between blood-based neural biomarkers (including total tau, neurofilament light [NfL], glial fibrillary acidic protein [GFAP], and ubiquitin C-terminal hydrolase-L1) and white matter neuroimaging biomarkers in collegiate athletes with sport-related concussion (SRC) from 24 hours postinjury to 1 week after return to play.

METHODS

We analyzed clinical and imaging data of concussed collegiate athletes in the Concussion Assessment, Research, and Education (CARE) Consortium. The CARE participants completed same-day clinical assessments, blood draws, and diffusion tensor imaging (DTI) at 3 time points: 24-48 hours postinjury, point of becoming asymptomatic, and 7 days after return to play. DTI probabilistic tractography was performed for each participant at each time point to render 27 participant-specific major white matter tracts. The microstructural organization of these tracts was characterized by 4 DTI metrics. Mixed-effects models with random intercepts were applied to test whether white matter microstructural abnormalities are associated with the blood-based biomarkers at the same time point. An interaction model was used to test whether the association varies across time points. A lagged model was used to test whether early blood-based biomarkers predict later microstructural changes.

RESULTS

Data from 77 collegiate athletes were included in the following analyses. Among the 4 blood-based biomarkers, total tau had significant associations with the DTI metrics across the 3 time points. In particular, high tau level was associated with high radial diffusivity (RD) in the right corticospinal tract (β = 0.25, SE = 0.07, p FDR-adjusted = 0.016) and superior thalamic radiation (β = 0.21, SE = 0.07, p FDR-adjusted = 0.042). NfL and GFAP had time-dependent associations with the DTI metrics. NfL showed significant associations only at the asymptomatic time point (|β|s > 0.12, SEs <0.09, psFDR-adjusted < 0.05) and GFAP showed a significant association only at 7 days after return to play (βs > 0.14, SEs <0.06, psFDR-adjusted < 0.05). The p values for the associations of early tau and later RD were not significant after multiple comparison adjustment, but were less than 0.1 in 7 white matter tracts.

DISCUSSION

This prospective study using data from the CARE Consortium demonstrated that in the early phase of SRC, white matter microstructural integrity detected by DTI neuroimaging was associated with elevated levels of blood-based biomarkers of traumatic brain injury. Total tau in the blood showed the strongest association with white matter microstructural changes.

Current and Emerging Techniques in Neuroimaging of Sport-Related Concussion

SUMMARY

Sport-related concussion (SRC) affects an estimated 1.6 to 3.8 million Americans each year. Sport-related concussion results from biomechanical forces to the head or neck that lead to a broad range of neurologic symptoms and impaired cognitive function. Although most individuals recover within weeks, some develop chronic symptoms. The heterogeneity of both the clinical presentation and the underlying brain injury profile make SRC a challenging condition. Adding to this challenge, there is also a lack of objective and reliable biomarkers to support diagnosis, to inform clinical decision making, and to monitor recovery after SRC. In this review, the authors provide an overview of advanced neuroimaging techniques that provide the sensitivity needed to capture subtle changes in brain structure, metabolism, function, and perfusion after SRC. This is followed by a discussion of emerging neuroimaging techniques, as well as current efforts of international research consortia committed to the study of SRC. Finally, the authors emphasize the need for advanced multimodal neuroimaging to develop objective biomarkers that will inform targeted treatment strategies after SRC.

The consideration of post-exercise impact on SCAT3 scores in athletes immediately following a head injury

METHODS

Symptoms were assessed immediately following completion of a rugby match (median 60 minutes). Players removed from the match for assessment due to a head hit were classified as head injured. Controls completed match without head hit.

RESULTS

209 players (67 female; 33 ± 13 years) participated with 80 experiencing a head injury. Symptom severity was significantly greater in head injured (26.2 ± 17.6) compared with controls (8.9 ± 11.5, P < 0.001). 21% of control players reporting >16 symptom severity, misclassifying them as suspected concussion. There were no significant sex differences. Factor analysis produced four symptom clusters of which Headache was most discriminatory between the head injured (median = 1.7) and controls (median = 0.0).

CONCLUSION

These findings demonstrate that exercise and contact during a game affect symptom assessment, increasing the likelihood of misclassifying players with suspected concussion. Factor characterization of symptoms associated with head injury using an exercised comparison group provides more useful discrimination. These results highlight the necessity for objective measures to diagnose concussions outside of symptom self-report.

Concussions in young adult athletes: No effect on cerebral white matter

Introduction

The media's recent focus on possible negative health outcomes following sports- related concussion has increased awareness as well as anxiety among parents and athletes. However, the literature on concussion outcomes is equivocal and limited by a variety of diagnostic approaches.

Methods

The current study used a rigorous, open- access concussion identification method-the Ohio State University Traumatic Brain Injury Identification method (OSU TBI-ID) to identify concussion and periods of repeated, subclinical head trauma in 108 young adult athletes who also underwent a comprehensive protocol of cognitive tests, mood/anxiety questionnaires, and high-angular-resolution diffusion-weighted brain imaging to evaluate potential changes in white matter microstructure.

Results

Analyses showed that athletes with a history of repetitive, subclinical impacts to the head performed slightly worse on a measure of inhibitory impulse control and had more anxiety symptoms compared to those who never sustained any type of head injury but were otherwise the same as athletes with no history of concussion. Importantly, there were no group differences in cerebral white matter as measured by tract- based spatial statistics (TBSS), nor were there any associations between OSU TBI-ID measures and whole-brain principal scalars and free-water corrected scalars.

Discussion

Our results provide support for the hypothesis that it is not concussion per se, but repetitive head impacts that beget worse outcomes.

Effects of White-Matter Tract Length in Sport-Related Concussion: A Tractography Study from the NCAA-DoD CARE Consortium

Sport-related concussion (SRC) is an important public health issue. White-matter alterations after SRC are widely studied by neuroimaging approaches, such as diffusion magnetic resonance imaging (MRI). Although the exact anatomical location of the alterations may differ, significant white-matter alterations are commonly observed in long fiber tracts, but are never proven. In the present study, we performed streamline tractography to characterize the association between tract length and white-matter microstructural alterations after SRC. Sixty-eight collegiate athletes diagnosed with acute concussion (24-48 h post-injury) and 64 matched contact-sport controls were included in this study. The athletes underwent diffusion tensor imaging (DTI) in 3.0 T MRI scanners across three study sites. DTI metrics were used for tract-based spatial statistics to map white-matter regions-of-interest (ROIs) with significant group differences. Whole-brain white-mater streamline tractography was performed to extract "affected" white-matter streamlines (i.e., streamlines passing through the identified ROIs). In the concussed athletes, streamline counts and DTI metrics of the affected white-matter fiber tracts were summarized and compared with unaffected white-matter tracts across tract length in the same participant. The affected white-matter tracts had a high streamline count at length of 80-100 mm and high length-adjusted affected ratio for streamline length longer than 80 mm. DTI mean diffusivity was higher in the affected streamlines longer than 100 mm with significant associations with the Brief Symptom Inventory score. Our findings suggest that long fibers in the brains of collegiate athletes are more vulnerable to acute SRC with higher mean diffusivity and a higher affected ratio compared with the whole distribution.

Multimodal magnetic resonance imaging of youth sport-related concussion reveals acute changes in the cerebellum, basal ganglia, and corpus callosum that resolve with recovery

Magnetic resonance imaging (MRI) can provide a number of measurements relevant to sport-related concussion (SRC) symptoms; however, most studies to date have used a single MRI modality and whole-brain exploratory analyses in attempts to localize concussion injury. This has resulted in highly variable findings across studies due to wide ranging symptomology, severity and nature of injury within studies. A multimodal MRI, symptom-guided region-of-interest (ROI) approach is likely to yield more consistent results. The functions of the cerebellum and basal ganglia transcend many common concussion symptoms, and thus these regions, plus the white matter tracts that connect or project from them, constitute plausible ROIs for MRI analysis. We performed diffusion tensor imaging (DTI), resting-state functional MRI, quantitative susceptibility mapping (QSM), and cerebral blood flow (CBF) imaging using arterial spin labeling (ASL), in youth aged 12-18 years following SRC, with a focus on the cerebellum, basal ganglia and white matter tracts. Compared to controls similar in age, sex and sport (N = 20), recent SRC youth (N = 29; MRI at 8 ± 3 days post injury) exhibited increased susceptibility in the cerebellum (p = 0.032), decreased functional connectivity between the caudate and each of the pallidum (p = 0.035) and thalamus (p = 0.021), and decreased diffusivity in the mid-posterior corpus callosum (p < 0.038); no changes were observed in recovered asymptomatic youth (N = 16; 41 ± 16 days post injury). For recent symptomatic-only SRC youth (N = 24), symptom severity was associated with increased susceptibility in the superior cerebellar peduncles (p = 0.011) and reduced activity in the cerebellum (p = 0.013). Fewer days between injury and MRI were associated with reduced cerebellar-parietal functional connectivity (p < 0.014), reduced activity of the pallidum (p = 0.002), increased CBF in the caudate (p = 0.005), and reduced diffusivity in the central corpus callosum (p < 0.05). Youth SRC is associated with acute cerebellar inflammation accompanied by reduced cerebellar activity and cerebellar-parietal connectivity, as well as structural changes of the middle regions of the corpus callosum accompanied by functional changes of the caudate, all of which resolve with recovery. Early MRI post-injury is important to establish objective MRI-based indicators for concussion diagnosis, recovery assessment and prediction of outcome.

Effects of docosahexaenoic acid and eicosapentaoic acid supplementation on white matter integrity after repetitive sub-concussive head impacts during American football: Exploratory neuroimaging findings from a pilot RCT

Context

Repetitive sub-concussive head impacts (RSHIs) are common in American football and result in changes to the microstructural integrity of white matter. Both docosahexaenoic acid (DHA) and eicosapentaoic acid (EPA) supplementation exerted neuroprotective effects against RSHIs in animal models and in a prior study in football players supplemented with DHA alone.

Objective

Here, we present exploratory neuroimaging outcomes from a randomized controlled trial of DHA + EPA supplementation in American football players. We hypothesized that supplementation would result in less white matter integrity loss on diffusion weighted imaging over the season.

Design setting participants

We conducted a double-blind placebo-controlled trial in 38 American football players between June 2019 and January 2020.

Intervention

Participants were randomized to the treatment (2.442 g/day DHA and 1.020 g/day EPA) or placebo group for five times-per-week supplementation for 7 months. Of these, 27 participants were included in the neuroimaging data analysis (n = 16 placebo; n = 11 DHA + EPA).

Exploratory outcome measures

Changes in white matter integrity were quantified using both voxelwise diffusion kurtosis scalars and deterministic tractography at baseline and end of season. Additional neuroimaging outcomes included changes in regional gray matter volume as well as intra-regional, edge-wise, and network level functional connectivity. Serum neurofilament light (NfL) provided a peripheral biomarker of axonal damage.

Results

No voxel-wise between-group differences were identified on diffusion tensor metrics. Deterministic tractography using quantitative anisotropy (QA) revealed increased structural connectivity in ascending corticostriatal fibers and decreased connectivity in long association and commissural fibers in the DHA+EPA group compared to the placebo group. Serum NfL increases were correlated with increased mean (ρ = 0.47), axial (ρ = 0.44), and radial (ρ = 0.51) diffusivity and decreased QA (ρ = -0.52) in the corpus callosum and bilateral corona radiata irrespective of treatment group. DHA + EPA supplementation did preserve default mode/frontoparietal control network connectivity (g = 0.96, p = 0.024).

Conclusions

These exploratory findings did not provide strong evidence that DHA + EPA prevented or protected against axonal damage as quantified via neuroimaging. Neuroprotective effects on functional connectivity were observed despite white matter damage. Further studies with larger samples are needed to fully establish the relationship between omega-3 supplementation, RSHIs, and neuroimaging biomarkers.

Trial registration

ClinicalTrials.gov-NCT04796207.

MEG measured delta waves increase in adolescents after concussion

INTRODUCTION

The purpose of this study is to determine if delta waves, measured by magnetoencephalography (MEG), increase in adolescents due to a sports concussion.

METHODS

Twenty-four adolescents (age 14-17) completed pre- and postseason MRI and MEG scanning. MEG whole-brain delta power was calculated for each subject and normalized by the subject's total power. In eight high school football players diagnosed with a concussion during the season (mean age = 15.8), preseason delta power was subtracted from their postseason scan. In eight high school football players without a concussion (mean age = 15.7), preseason delta power was subtracted from postseason delta power and in eight age-matched noncontact controls (mean age = 15.9), baseline delta power was subtracted from a 4-month follow-up scan. ANOVA was used to compare the mean differences between preseason and postseason scans for the three groups of players, with pairwise comparisons based on Student's t-test method.

RESULTS

Players with concussions had significantly increased delta wave power at their postseason scans than nonconcussed players (p = .018) and controls (p = .027).

CONCLUSION

We demonstrate that a single concussion during the season in adolescent subjects can increase MEG measured delta frequency power at their postseason scan. This adds to the growing body of literature indicating increased delta power following a concussion.

White matter abnormalities characterize the acute stage of sports-related mild traumatic brain injury

Sports-related concussion, a form of mild traumatic brain injury, is characterized by transient disturbances of brain function. There is increasing evidence that functional brain changes may be driven by subtle abnormalities in white matter microstructure, and diffusion MRI has been instrumental in demonstrating these white matter abnormalities in vivo. However, the reported location and direction of the observed white matter changes in mild traumatic brain injury are variable, likely attributable to the inherent limitations of the white matter models used. This cross-sectional study applies an advanced and robust technique known as fixel-based analysis to investigate fibre tract-specific abnormalities in professional Australian Football League players with a recent mild traumatic brain injury. We used the fixel-based analysis framework to identify common abnormalities found in specific fibre tracts in participants with an acute injury (≤12 days after injury; n = 14). We then assessed whether similar changes exist in subacute injury (&gt;12 days and &lt;3 months after injury; n = 15). The control group was 29 neurologically healthy control participants. We assessed microstructural differences in fibre density and fibre bundle morphology and performed whole-brain fixel-based analysis to compare groups. Subsequent tract-of-interest analyses were performed within five selected white matter tracts to investigate the relationship between the observed tract-specific abnormalities and days since injury and the relationship between these tract-specific changes with cognitive abnormalities. Our whole-brain analyses revealed significant increases in fibre density and bundle cross-section in the acute mild traumatic brain injury group when compared with controls. The acute mild traumatic brain injury group showed even more extensive differences when compared with the subacute injury group than with controls. The fibre structures affected in acute concussion included the corpus callosum, left prefrontal and left parahippocampal white matter. The fibre density and cross-sectional increases were independent of time since injury in the acute injury group, and were not associated with cognitive deficits. Overall, this study demonstrates that acute mild traumatic brain injury is characterized by specific white matter abnormalities, which are compatible with tract-specific cytotoxic oedema. These potential oedematous changes were absent in our subacute mild traumatic brain injury participants, suggesting that they may normalize within 12 days after injury, although subtle abnormalities may persist in the subacute stage. Future longitudinal studies are needed to elucidate individualized recovery after brain injury.

Repeated Mild TBI in Adolescent Rats Reveals Sex Differences in Acute and Chronic Behavioral Deficits

High school students who participate in contact sports are vulnerable to sustaining multiple concussions and exhibit deficits in cognitive function in both the acute and chronic phases and in emotional behavior in the chronic phase. Further, boys are more likely to suffer cognitive problems whereas girls tend to report depression and anxiety. The effects of repetitive mild TBI in adolescent (35-40-day old) male and female Sprague-Dawley rats on object location and spatial working memory (hippocampal-dependent) and object recognition memory (hippocampal-independent) at 1-and-4-weeks post-injury along with trait-dependent anxiety- and depressive-like behaviors at 5 weeks were examined. Compared to sham-injured rats, male brain-injured rats demonstrated significant impairment in both hippocampal-dependent and -independent memory tasks at both time points, whereas female brain-injured rats only exhibited impairment in these tests at the 4-week time point. In contrast, depressive-like behaviors were present in the forced swim test in only the female brain-injured animals at 5 weeks post-injury; anxiety-like behaviors were not evident in either male or female brain-injured animals. Histological analysis at 6 weeks after injury revealed that repeated mild TBI in male and female adolescent rats resulted in increased reactivity of astrocytes and microglia within the corpus callosum below the impact site and in the stratum oriens and stratum pyramidale of the CA2 region of the dorsal hippocampus. Together, these data are indicative of the differences in the temporal pattern of post-traumatic behavioral deficits between male and female animals and that female animals may be more likely to develop deficits in the chronic post-traumatic period.

Combining MRI and cognitive evaluation to classify concussion in university athletes

Current methods of concussion assessment lack the objectivity and reliability to detect neurological injury. This multi-site study uses combinations of neuroimaging (diffusion tensor imaging and resting state functional MRI) and cognitive measures to train algorithms to detect the presence of concussion in university athletes. Athletes (29 concussed, 48 controls) completed symptom reports, brief cognitive evaluation, and MRI within 72 h of injury. Hierarchical linear regression compared groups on cognitive and neuroimaging measures while controlling for sex and data collection site. Logistic regression and support vector machine models were trained using cognitive and neuroimaging measures and evaluated for overall accuracy, sensitivity, and specificity. Concussed athletes reported greater symptoms than controls (∆R² = 0.32, p < .001), and performed worse on tests of concentration (∆R² = 0.07, p < .05) and delayed memory (∆R² = 0.17, p < .001). Concussed athletes showed lower functional connectivity within the frontoparietal and primary visual networks (p < .05), but did not differ on mean diffusivity and fractional anisotropy. Of the cognitive measures, classifiers trained using delayed memory yielded the best performance with overall accuracy of 71%, though sensitivity was poor at 46%. Of the neuroimaging measures, classifiers trained using mean diffusivity yielded similar accuracy. Combining cognitive measures with mean diffusivity increased overall accuracy to 74% and sensitivity to 64%, comparable to the sensitivity of symptom report. Trained algorithms incorporating both MRI and cognitive performance variables can reliably detect common neurobiological sequelae of acute concussion. The integration of multi-modal data can serve as an objective, reliable tool in the assessment and diagnosis of concussion.

Investigating Brain White Matter in Football Players with and without Concussion Using a Biophysical Model from Multishell Diffusion MRI

BACKGROUND AND PURPOSE

There have been growing concerns around potential risks related to sports-related concussion and contact sport exposure to repetitive head impacts in young athletes. Here we investigate WM microstructural differences between collegiate football players with and without sports-related concussion.

MATERIALS AND METHODS

The study included 78 collegiate athletes (24 football players with sports-related concussion, 26 football players with repetitive head impacts, and 28 non-contact-sport control athletes), available through the Federal Interagency Traumatic Brain Injury Research registry. Diffusion metrics of diffusion tensor/kurtosis imaging and WM tract integrity were calculated. Tract-Based Spatial Statistics and post hoc ROI analyses were performed to test group differences.

RESULTS

Significantly increased axial kurtosis in those with sports-related concussion compared with controls was observed diffusely across the whole-brain WM, and some focal areas demonstrated significantly higher mean kurtosis and extra-axonal axial diffusivity in sports-related concussion. The extent of significantly different WM regions decreased across time points and remained present primarily in the corpus callosum. Similar differences in axial kurtosis were found between the repetitive head impact and control groups. Other significant differences were seen at unrestricted return-to-play with lower radial kurtosis and intra-axonal diffusivity in those with sports-related concussion compared with the controls, mainly restricted to the posterior callosum.

CONCLUSIONS

This study highlights the fact that there are differences in diffusion microstructure measures that are present not only between football players with sports-related injuries and controls, but that there are also measurable differences between football players with repetitive head impacts and controls. This work reinforces previous work showing that the corpus callosum is specifically implicated in sports-related concussion and also suggests this to be true for repetitive head impacts.

Longitudinal white matter microstructural changes in pediatric mild traumatic brain injury: An A-CAP study

In the largest sample studied to date, white matter microstructural trajectories and their relation to persistent symptoms were examined after pediatric mild traumatic brain injury (mTBI). This prospective, longitudinal cohort study recruited children aged 8–16.99 years with mTBI or mild orthopedic injury (OI) from five pediatric emergency departments. Children's pre‐injury and 1‐month post‐injury symptom ratings were used to classify mTBI with or without persistent symptoms. Children completed diffusion‐weighted imaging at post‐acute (2–33 days post‐injury) and chronic (3 or 6 months via random assignment) post‐injury assessments. Mean diffusivity (MD) and fractional anisotropy (FA) were derived for 18 white matter tracts in 560 children (362 mTBI/198 OI), 407 with longitudinal data. Superior longitudinal fasciculus FA was higher in mTBI without persistent symptoms relative to OI, d (95% confidence interval) = 0.31 to 0.37 (0.02, 0.68), across time. In younger children, MD of the anterior thalamic radiations was higher in mTBI with persistent symptoms relative to both mTBI without persistent symptoms, 1.43 (0.59, 2.27), and OI, 1.94 (1.07, 2.81). MD of the arcuate fasciculus, −0.58 (−1.04, −0.11), and superior longitudinal fasciculus, −0.49 (−0.90, −0.09) was lower in mTBI without persistent symptoms relative to OI at 6 months post‐injury. White matter microstructural changes suggesting neuroinflammation and axonal swelling occurred chronically and continued 6 months post injury in children with mTBI, especially in younger children with persistent symptoms, relative to OI. White matter microstructure appears more organized in children without persistent symptoms, consistent with their better clinical outcomes.

Leadership Lessons in Concussion Management for Team Physicians

Over the last decade, with emphasis on concussion awareness and potential long-term deficits, concussions have become a public health concern. Although common, concussions are complex in nature and often require a collaborative treatment approach across multiple disciplines. In an athletic setting, the Team Physician plays a critical leadership role in the organization, management, and provision of care for concussed athletes. However, leadership strategies for the provision of concussion care utilized by the Team Physician have not been adequately described. This manuscript intends to describe advanced planning for concussion management and highlight best practices for the provision of care for the concussed athlete, to assist the Team Physician in coordinating optimal care. Specific emphasis will be placed on outlining a concussion management protocol aligned with evidence-based best practices.

Multiple Past Concussions in High School Hockey Players: Examining Cognitive Functioning and Symptom Reporting

OBJECTIVE

To investigate (1) if there are meaningful differences in baseline preseason cognitive functioning or symptom reporting between high school ice hockey players with and without prior concussions and (2) determine which health history variables predict symptom reporting.

DESIGN

Cross-sectional study.

SETTING

High schools across the state of Maine.

PARTICIPANTS

Participants were 1616 male high school ice hockey players (mean age = 15.6 years; SD = 1.5 years) who completed baseline testing between 2009 and 2015.

INDEPENDENT VARIABLES

Athletes were grouped according to their self-reported concussion history [0 (n = 1136), 1 (n = 321), 2 (n = 112), or 3+ (n = 47) previous concussions].

MAIN OUTCOME MEASURES

Cognitive functioning was measured by the Immediate Post-Concussion Assessment and Cognitive Testing (ImPACT) battery, and symptom ratings were obtained from the Post-Concussion Symptom Scale.

RESULTS

There were no statistically significant differences between groups in cognitive functioning as measured by ImPACT. The group with ≥3 prior concussions endorsed higher total symptom scores, but the effect sizes were small and not statistically significant. In a multivariate model, prior treatment for headaches (not necessarily migraines), prior treatment for a psychiatric condition, and prior treatment for substance/alcohol use all significantly predicted total symptom scores, with concussion history being the weakest independent predictor.

CONCLUSIONS

Players with a history of prior concussions performed similarly to players with no prior concussions on cognitive testing. Health history factors were more strongly associated with symptom reporting than concussion history.

High School Sports-Related Concussion and the Effect of a Jugular Vein Compression Collar: A Prospective Longitudinal Investigation of Neuroimaging and Neurofunctional Outcomes

Sports-related concussion (SRC) can exert serious acute and long-term consequences on brain microstructure, function, and behavioral outcomes. We aimed to quantify the alterations in white matter (WM) microstructure and global network organization, and the decrements in behavioral and cognitive outcomes from pre-season to post-concussion in youth athletes who experienced SRC. We also aimed to evaluate whether wearing a jugular compression neck collar, a device designed to mitigate brain "slosh" injury, would mitigate the pre-season to post-concussion alterations in neuroimaging, behavioral, and cognitive outcomes. A total of 488 high school football and soccer athletes (14-18 years old) were prospectively enrolled and assigned to the non-collar group (n = 237) or the collar group (n = 251). The outcomes of the study were the pre-season to post-concussion neuroimaging, behavioral, and cognitive alterations. Forty-six participants (non-collar: n = 24; collar: n = 22) were diagnosed with a SRC during the season. Forty of these 46 athletes (non-collar: n = 20; collar: n = 20) completed neuroimaging assessment. Significant pre-season to post-concussion alterations in WM microstructural integrity and brain network organization were found in these athletes (corrected p < 0.05). The alterations were significantly reduced in collar-wearing athletes compared to non-collar-wearing athletes (corrected p < 0.05). Concussion and collar main effects were identified for some of the behavioral and cognitive outcomes, but no collar by SRC interaction effects were observed in any outcomes. In summary, young athletes exhibited significant WM microstructural and network organizational, and cognitive alterations following SRC. The use of the jugular vein compression collar showed promising evidence to reduce these alterations in high school contact sport athletes.

Acute Diffusion Tensor and Kurtosis Imaging and Outcome following Mild Traumatic Brain Injury

In this prospective cohort study, we investigated associations between acute diffusion tensor imaging (DTI) and diffusion kurtosis imaging (DKI) metrics and persistent post-concussion symptoms (PPCS) 3 months after mild traumatic brain injury (mTBI). Adult patients with mTBI (n = 176) and community controls (n = 78) underwent 3 Tesla magnetic resonance imaging (MRI) within 72 h post-injury, estimation of cognitive reserve at 2 weeks, and PPCS assessment at 3 months. Eight DTI and DKI metrics were examined with Tract-Based Spatial Statistics. Analyses were performed in the total sample in uncomplicated mTBI only (i.e., without lesions on clinical MRI), and with cognitive reserve both controlled for and not. Patients with PPCS (n = 35) had lower fractional anisotropy (in 2.7% of all voxels) and kurtosis fractional anisotropy (in 6.9% of all voxels), and higher radial diffusivity (in 0.3% of all voxels), than patients without PPCS (n = 141). In uncomplicated mTBI, only fractional anisotropy was significantly lower in patients with PPCS. Compared with controls, patients with PPCS had widespread deviations in all diffusion metrics. When including cognitive reserve as a covariate, no significant differences in diffusion metrics between patients with and without PPCS were present, but patients with PPCS still had significantly higher mean, radial, and axial diffusivity than controls. In conclusion, patients who developed PPCS had poorer white matter microstructural integrity acutely after the injury, compared with patients who recovered and healthy controls. Differences became less pronounced when cognitive reserve was controlled for, suggesting that pre-existing individual differences in axonal integrity accounted for some of the observed differences.

The Natural History of Sport-Related Concussion in Collegiate Athletes: Findings from the NCAA-DoD CARE Consortium

BACKGROUND

Sport-related concussion is recognized as a significant injury with variable recovery rates.

OBJECTIVE

This study defined the acute natural history of sport concussion in male and female collegiate athletes participating in a broad array of sports.

METHODS

We conducted a prospective, longitudinal investigation among collegiate student athletes (n = 34,709) from 30 academic institutions. Primary outcomes included the time (days) from injury until initiation of a return to participation (RTP) protocol and time from injury until medical clearance for unrestricted RTP.

RESULTS

Concussed athletes (n = 1751, 19.2 years, 63.2% male) participating in 22 different sports began the RTP protocol in a median 6.4 (IQR 3.7-11.8) days. Time to initiate the RTP protocol was lengthened by less frequent post-injury assessments, greater initial post-injury symptom severity, limited contact sports participation, practice/training injuries, and three or more prior concussions. The median total RTP duration was 12.8 (IQR 8.7-20.1) days. Total RTP duration was shorter with ADHD medication usage, males, and greater assessment frequency; while greater initial post-injury symptom severity, practice-/training-related injuries, and three or more prior concussions had longer recoveries.

CONCLUSION

Although median recovery times are consistent with previous guidelines, it was not until 1 month post-injury that a preponderance of collegiate athletes were cleared to begin the RTP protocol (92%) or cleared for unrestricted sport participation (85%). Intrinsic and extrinsic factors had a small effect, altering recovery trajectories by up to 2 days, suggesting a largely unified approach to post-injury monitoring and management across all athletes. These data represent a shift from previous classification parameters of normal clinical recovery.

Changes in brain metabolites and resting-state connectivity in collegiate basketball players as a function of play time

BACKGROUND AND PURPOSE

Magnetic resonance (MR) biomarkers are emerging for sports-related traumatic brain injury (TBI), but the effect of play time has not been characterized. Our goal was to characterize brain and inflammatory marker changes as a function of play time.

METHODS

Nine male players (21±2 years old) from a single collegiate basketball team were included. MR imaging (MRI), MR spectroscopy, and plasma were collected pre, mid, and postseason. Game time played was calculated for each subject. Changes in brain volume, diffusion tensor imaging (DTI), metabolites (normalized to total creatine, tCr), temperature, structural and functional connectivity, and inflammatory markers were quantified.

RESULTS

Myo-inositol/tCr in the left frontal white matter and brain temperature in the left frontal lobe varied significantly between time points. Glutamate (Glu/tCr) in the right frontal white matter and N-acetylaspartate in the posterior cingulate cortex (PCC) were negatively associated with minutes played. Midseason play time was associated with stronger blood-oxygen-level-dependent correlations between PCC and occipital areas, and weaker correlations between PCC and superior frontal connectivity. PCC Glu/tCr was positively associated with connectivity between the PCC and posterior supramarginal gyrus at preseason and with connectivity across time points among several right hemisphere regions. Volume, DTI, and inflammatory markers did not vary significantly.

CONCLUSION

Given that MR parameters vary with game play time in the absence of diagnosed injury, play time should be considered as a factor in sports-related TBI research.

White Matter Abnormalities Associated With Prolonged Recovery in Adolescents Following Concussion

Background: Concussion symptoms in adolescents typically resolve within 4 weeks. However, 20 - 30% of adolescents experience a prolonged recovery. Abnormalities in tracts implicated in visuospatial attention and emotional regulation (i.e., inferior longitudinal fasciculus, ILF; inferior fronto-occipital fasciculus, IFOF; uncinate fasciculus; UF) have been consistently reported in concussion; yet, to date, there are no objective markers of prolonged recovery in adolescents. Here, we evaluated the utility of diffusion MRI in outcome prediction. Forty-two adolescents (12.1 - 17.9 years; female: 44.0%) underwent a diffusion Magnetic Resonance Imaging (dMRI) protocol within the first 10 days of concussion. Based on days of injury until medical clearance, adolescents were then categorized into SHORT (<28 days; N = 21) or LONG (>28 days; N = 21) recovery time. Fractional anisotropy (FA) in the ILF, IFOF, UF, and/or concussion symptoms were used as predictors of recovery time (SHORT, LONG). Forty-two age- and sex-matched healthy controls served as reference. Higher FA in the ILF (left: adjusted odds ratio; AOR = 0.36, 95% CI = 0.15 - 0.91, P = 0.030; right: AOR = 0.28, 95% CI = 0.10 - 0.83, P = 0.021), IFOF (left: AOR = 0.21, 95% CI = 0.07 - 0.66, P = 0.008; right: AOR = 0.30, 95% CI = 0.11 - 0.83, P = 0.020), and UF (left: AOR = 0.26, 95% CI = 0.09 - 0.74, P = 0.011; right: AOR = 0.28, 95% CI = 0.10 - 0.73, P = 0.010) was associated with SHORT recovery. In additional analyses, while adolescents with SHORT recovery did not differ from HC, those with LONG recovery showed lower FA in the ILF and IFOF (P < 0.014). Notably, inclusion of dMRI findings increased the sensitivity and specificity (AUC = 0.93) of a prediction model including clinical variables only (AUC = 0.75). Our findings indicate that higher FA in long associative tracts (especially ILF) might inform a more objective and accurate prognosis for recovery time in adolescents following concussion.

Identifying degenerative effects of repetitive head trauma with neuroimaging: a clinically-oriented review

BACKGROUND AND SCOPE OF REVIEW

Varying severities and frequencies of head trauma may result in dynamic acute and chronic pathophysiologic responses in the brain. Heightened attention to long-term effects of head trauma, particularly repetitive head trauma, has sparked recent efforts to identify neuroimaging biomarkers of underlying disease processes. Imaging modalities like structural magnetic resonance imaging (MRI) and positron emission tomography (PET) are the most clinically applicable given their use in neurodegenerative disease diagnosis and differentiation. In recent years, researchers have targeted repetitive head trauma cohorts in hopes of identifying in vivo biomarkers for underlying biologic changes that might ultimately improve diagnosis of chronic traumatic encephalopathy (CTE) in living persons. These populations most often include collision sport athletes (e.g., American football, boxing) and military veterans with repetitive low-level blast exposure. We provide a clinically-oriented review of neuroimaging data from repetitive head trauma cohorts based on structural MRI, FDG-PET, Aβ-PET, and tau-PET. We supplement the review with two patient reports of neuropathology-confirmed, clinically impaired adults with prior repetitive head trauma who underwent structural MRI, FDG-PET, Aβ-PET, and tau-PET in addition to comprehensive clinical examinations before death.

REVIEW CONCLUSIONS

Group-level comparisons to controls without known head trauma have revealed inconsistent regional volume differences, with possible propensity for medial temporal, limbic, and subcortical (thalamus, corpus callosum) structures. Greater frequency and severity (i.e., length) of cavum septum pellucidum (CSP) is observed in repetitive head trauma cohorts compared to unexposed controls. It remains unclear whether CSP predicts a particular neurodegenerative process, but CSP presence should increase suspicion that clinical impairment is at least partly attributable to the individual's head trauma exposure (regardless of underlying disease). PET imaging similarly has not revealed a prototypical metabolic or molecular pattern associated with repetitive head trauma or predictive of CTE based on the most widely studied radiotracers. Given the range of clinical syndromes and neurodegenerative pathologies observed in a subset of adults with prior repetitive head trauma, structural MRI and PET imaging may still be useful for differential diagnosis (e.g., assessing suspected Alzheimer's disease).

The role of diffusion tensor imaging in characterizing injury patterns on athletes with concussion and subconcussive injury: a systematic review

Traumatic brain injury (TBI) is a major public health problem. The majority of TBIs are in the form of mild TBI (also known as concussion) with sports-related concussion (SRC) receiving public attention in recent years.Here we have performed a systematic review of the literature on the use of Diffusion Tensor Imaging (DTI) on sports-related concussion and subconcussive injuries. Our review found different patterns of change in DTI parameters between concussed and subconcussed groups. The Fractional Anisotropy (FA) was either unchanged or increased for the concussion group, while the subconcussed group generally experienced a decrease in FA. A reverse pattern was observed for Mean Diffusivity (MD) - where the concussed group experienced a decrease in MD while the subconcussed group showed an increase in MD. However, in general, discrepancies were observed in the results reported in the literature - likely due to the huge variations in DTI acquisition parameters, and image processing and analysis methods used in these studies. This calls for more comprehensive and well-controlled studies in this field, including those that combine the advanced brain imaging with biomechancial modeling and kinematic sensors - to shed light on the underlying mechanisms behind the structural changes observed from the imaging studies.

A Role for the Amygdala in Impairments of Affective Behaviors Following Mild Traumatic Brain Injury

Mild traumatic brain injury (TBI) results in chronic affective disorders such as depression, anxiety, and fear that persist up to years following injury and significantly impair the quality of life for patients. Although a great deal of research has contributed to defining symptoms of mild TBI, there are no adequate drug therapies for brain-injured individuals. Preclinical studies have modeled these deficits in affective behaviors post-injury to understand the underlying mechanisms with a view to developing appropriate treatment strategies. These studies have also unveiled sex differences that contribute to the varying phenotypes associated with each behavior. Although clinical and preclinical studies have viewed these behavioral deficits as separate entities with unique neurobiological mechanisms, mechanistic similarities suggest that a novel approach is needed to advance research on drug therapy. This review will discuss the circuitry involved in the expression of deficits in affective behaviors following mild TBI in humans and animals and provide evidence that the manifestation of impairment in these behaviors stems from an amygdala-dependent emotional processing deficit. It will highlight mechanistic similarities between these different types of affective behaviors that can potentially advance mild TBI drug therapy by investigating treatments for the deficits in affective behaviors as one entity, requiring the same treatment.

Sensation-Seeking and Impulsivity in Athletes with Sport-Related Concussion

PURPOSE OF REVIEW

Sport-related concussion (SRC) is a significant public health problem. Understanding the behavioral and personal factors that influence risk and incidence of SRC is critically important for appropriate care and management. Sensation-seeking and impulsivity have been posited to be two such factors that may be significantly associated with SRC. We performed a focused review of recent evidence of the relationships between sensation-seeking and impulsivity in athletes with SRC.

RECENT FINDINGS

While the research is relatively limited, extant findings demonstrate a significant relationship between sensation-seeking and contact sport participation and risk of prior and future SRC. Impulsivity appears to be common among athletes competing in high contact sports and may contribute to neural and functional brain changes following SRC; however, causal relationships between impulsivity, contact sport participation, and SRC have not been demonstrated. Both sensation-seeking and impulsivity are significantly associated with SRC in collegiate athletes. Interventions designed to ameliorate high levels of these constructs may prove to be beneficial avenues to reducing SRC risk and improving patient care and outcomes.

Neuroanatomical Substrates and Symptoms Associated With Magnetic Resonance Imaging of Patients With Mild Traumatic Brain Injury

Importance

Persistent symptoms after mild traumatic brain injury (mTBI) represent a major public health problem.

Objective

To identify neuroanatomical substrates of mTBI and the optimal timing for magnetic resonance imaging (MRI).

Design, Setting, and Participants

This prospective multicenter cohort study encompassed all eligible patients from the Collaborative European NeuroTrauma Effectiveness Research in Traumatic Brain Injury (CENTER-TBI) study (December 19, 2014, to December 17, 2017) and a local cohort (November 20, 2012, to December 19, 2013). Patients presented to the hospital within 24 hours of an mTBI (Glasgow Coma Score, 13-15), satisfied local criteria for computed tomographic scanning, and underwent MRI scanning less than 72 hours (MR1) and 2 to 3 weeks (MR2) after injury. In addition, 104 control participants were enrolled across all sites. Data were analyzed from January 1, 2019, to December 31, 2020.

Exposure

Mild TBI.

Main Outcomes and Measures

Volumes and diffusion parameters were extracted via automated bespoke pipelines. Symptoms were measured using the Rivermead Post Concussion Symptoms Questionnaire in the short term and the extended Glasgow Outcome Scale at 3 months.

Results

Among the 81 patients included in the analysis (73 CENTER-TBI and 8 local), the median age was 45 (interquartile range [IQR], 24-59; range, 14-85) years, and 57 (70.4%) were male. Structural sequences were available for all scans; diffusion data, for 73 MR1 and 79 MR2 scans. After adjustment for multiple comparisons between scans, visible lesions did not differ significantly, but cerebral white matter volume decreased (MR2:MR1 ratio, 0.98; 95% CI, 0.96-0.99) and ventricular volume increased (MR2:MR1 ratio, 1.06; 95% CI, 1.02-1.10). White matter volume was within reference limits on MR1 scans (patient to control ratio, 0.99; 95% CI, 0.97-1.01) and reduced on MR2 scans (patient to control ratio, 0.97; 95% CI, 0.95-0.99). Diffusion parameters changed significantly between scans in 13 tracts, following 1 of 3 trajectories. Symptoms measured by Rivermead Post Concussion Symptoms Questionnaire scores worsened in the progressive injury phenotype (median, +5.00; IQR, +2.00 to +5.00]), improved in the minimal change phenotype (median, -4.50; IQR, -9.25 to +1.75), and were variable in the pseudonormalization phenotype (median, 0.00; IQR, -6.25 to +9.00) (P = .02). Recovery was favorable for 33 of 65 patients (51%) and was more closely associated with MR1 than MR2 (area under the curve, 0.87 [95% CI, 0.78-0.96] vs 0.75 [95% CI, 0.62-0.87]; P = .009).

Conclusions and Relevance

These findings suggest that advanced MRI reveals potential neuroanatomical substrates of mTBI in white matter and is most strongly associated with odds of recovery if performed within 72 hours, although future validation is required.

Association of Head Impact Exposure with White Matter Macrostructure and Microstructure Metrics

Prior studies have reported white matter abnormalities associated with a history of cumulative concussion and/or repetitive head impacts (RHI) in contact sport athletes. Growing evidence suggests these abnormalities may begin as more subtle changes earlier in life in active younger athletes. We investigated the relationship between prior concussion and contact sport exposure with multi-modal white matter microstructure and macrostructure using magnetic resonance imaging. High school and collegiate athletes (n = 121) completed up to four evaluations involving neuroimaging. Linear mixed-effects models examined associations of years of contact sport exposure (i.e., RHI proxy) and prior concussion across multiple metrics of white matter, including total white matter volume, diffusion tensor imaging (DTI) metrics, diffusion kurtosis imaging (DKI) metrics, and quantitative susceptibility mapping (QSM). A significant inverse association between cumulative years of contact sport exposure and QSM was observed, F(1, 237.77) = 4.67, p = 0.032. Cumulative contact sport exposure was also associated with decreased radial diffusivity, F(1, 114.56) = 5.81, p = 0.018, as well as elevated fractional anisotropy, F(1, 115.32) = 5.40, p = 0.022, and radial kurtosis, F(1, 113.45) = 4.03, p = 0.047. In contrast, macroscopic white matter volume was not significantly associated with cumulative contact sport exposure (p > 0.05). Concussion history was not significantly associated with QSM, DTI, DKI, or white matter volume (all, p > 0.05). Cumulative contact sport exposure is associated with subtle differences in white matter microstructure, but not gross white matter macrostructure, in young active athletes. Longitudinal follow-up is required to assess the progression of these findings to determine their contribution to potential adverse effects later in life.

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.

Hypobaric Decompression and White Matter Hyperintensities: An Evaluation of the NATO Standard

INTRODUCTION: In their seminal work, McGuire and colleagues reported an increased incidence of white matter hyperintensities (WMH) in a cohort of U2 pilots and hypobaric chamber personnel. WMH burden was higher in U2 pilots with previous reports of decompression sickness (DCS), and McGuire's reports have raised concerns regarding adverse outcomes in the aftermath of hypobaric exposures. Accordingly, a NATO working group has recently revised its standard recommendations regarding hypobaric exposures, including measures to mitigate the risk of WMH. Mandatory recovery time for up to 72 h between repeated exposures has been suggested on the basis of experimental evidence. However, we argue that the evidence is scarce which supports restricting repeated exposures to mitigate WMH. It is plausible that WMH is correlated with DCS and emphasis should be made on limiting the duration of exposures rather than restricting short and repeated exposures. The profiles in the NATO recommendations are meant to mitigate the risk of DCS. Still, they will potentially expose NATO Air Force and Special Operations personnel to flight profiles that can give rise to DCS incidence above 35%. Awaiting reliable data, we recommend limiting the duration of exposures and allowing for short repeated exposures.Ottestad W, Hansen TA, Ksin JI. Hypobaric decompression and white matter hyperintensities: an evaluation of the NATO standard. Aerosp Med Hum Perform. 2021; 92(1):3942.

Increased sensitivity to traumatic axonal injury on postconcussion diffusion tensor imaging scans in National Football League players by using premorbid baseline scans

OBJECTIVE

Statistical challenges exist when using diffusion tensor imaging (DTI) to assess traumatic axonal injury (TAI) in individual concussed athletes. The authors examined active professional American football players over a 6-year time period to study potential TAI after concussion and assess optimal methods to analyze DTI at the individual level.

METHODS

Active American professional football players recruited prospectively were assessed with DTI, conventional MRI, and standard clinical workup. Subjects underwent an optional preseason baseline scan and were asked to undergo a scan within 5 days of concussion during gameplay. DTI from 25 age- and sex-matched controls were obtained. Both semiautomated region-of-interest analysis and fully automated tract-based spatial statistics (TBSS) were used to examine DTI at individual and group levels. Statistical differences were assessed comparing individual DTI data to baseline imaging versus a normative database. Group-level comparisons were also performed to determine if longer exposure to professional-level play or prior concussion cause white matter microstructural integrity changes.

RESULTS

Forty-nine active professional football players were recruited into the study. Of the 49 players, 7 were assessed at baseline during the preseason and after acute concussion. An additional 18 players were assessed after acute concussion only. An additional 24 players had only preseason baseline assessments. The results suggest DTI is more sensitive to suspected TAI than conventional MRI, given that 4 players demonstrated decreased fractional anisotropy (FA) in multiple tracts despite normal conventional MRI. Furthermore, the data suggest individual assessment of DTI data using baseline premorbid imaging is more sensitive than typical methods of comparing data to a normative control group. Among all subjects with baseline data, 1 reduced FA tract (± 2.5 standard deviations) was found using the typical normative database reference versus 10 statistically significant (p < 0.05) reduced FA tracts when referencing internal control baseline data. All group-level comparisons were statistically insignificant (p > 0.05).

CONCLUSIONS

Baseline premorbid DTI data for individual DTI analysis provides increased statistical sensitivity. Specificity using baseline imaging also increases because numerous potential etiologies for reduced FA may exist prior to a concussion. These data suggest that there is a high potential for false-positive and false-negative assessment of DTI data using typical methods of comparing an individual to normative groups given the variability of FA values in the normal population.

The effects of internal jugular vein compression for modulating and preserving white matter following a season of American tackle football: A prospective longitudinal evaluation of differential head impact exposure

The purpose of this clinical trial was to examine whether internal jugular vein compression (JVC)-using an externally worn neck collar-modulated the relationships between differential head impact exposure levels and pre- to postseason changes in diffusion tensor imaging (DTI)-derived diffusivity and anisotropy metrics of white matter following a season of American tackle football. Male high-school athletes (n = 284) were prospectively assigned to a non-collar group or a collar group. Magnetic resonance imaging data were collected from participants pre- and postseason and head impact exposure was monitored by accelerometers during every practice and game throughout the competitive season. Athletes' accumulated head impact exposure was systematically thresholded based on the frequency of impacts of progressively higher magnitudes (10 g intervals between 20 to 150 g) and modeled with pre- to postseason changes in DTI measures of white matter as a function of JVC neck collar wear. The findings revealed that the JVC neck collar modulated the relationships between greater high-magnitude head impact exposure (110 to 140 g) and longitudinal changes to white matter, with each group showing associations that varied in directionality. Results also revealed that the JVC neck collar group partially preserved longitudinal changes in DTI metrics. Collectively, these data indicate that a JVC neck collar can provide a mechanistic response to the diffusion and anisotropic properties of brain white matter following the highly diverse exposure to repetitive head impacts in American tackle football. Clinicaltrials.gov: NCT# 04068883.

Longitudinal white-matter abnormalities in sports-related concussion: A diffusion MRI study

OBJECTIVE

To study longitudinal recovery trajectories of white matter after sports-related concussion (SRC) by performing diffusion tensor imaging (DTI) on collegiate athletes who sustained SRC.

METHODS

Collegiate athletes (n = 219, 82 concussed athletes, 68 contact-sport controls, and 69 non-contact-sport controls) were included from the Concussion Assessment, Research and Education Consortium. The participants completed clinical assessments and DTI at 4 time points: 24 to 48 hours after injury, asymptomatic state, 7 days after return-to-play, and 6 months after injury. Tract-based spatial statistics was used to investigate group differences in DTI metrics and to identify white-matter areas with persistent abnormalities. Generalized linear mixed models were used to study longitudinal changes and associations between outcome measures and DTI metrics. Cox proportional hazards model was used to study effects of white-matter abnormalities on recovery time.

RESULTS

In the white matter of concussed athletes, DTI-derived mean diffusivity was significantly higher than in the controls at 24 to 48 hours after injury and beyond the point when the concussed athletes became asymptomatic. While the extent of affected white matter decreased over time, part of the corpus callosum had persistent group differences across all the time points. Furthermore, greater elevation of mean diffusivity at acute concussion was associated with worse clinical outcome measures (i.e., Brief Symptom Inventory scores and symptom severity scores) and prolonged recovery time. No significant differences in DTI metrics were observed between the contact-sport and non-contact-sport controls.

CONCLUSIONS

Changes in white matter were evident after SRC at 6 months after injury but were not observed in contact-sport exposure. Furthermore, the persistent white-matter abnormalities were associated with clinical outcomes and delayed recovery time.

Autonomic dysfunction following mild traumatic brain injury

PURPOSE OF REVIEW

Between 1.6 and 3.6 million concussions, or mild traumatic brain injuries (mTBI), occur each year, nearly half of which go unreported and untreated. Despite the high incidence, practitioners currently lack both objective gold-standard diagnostic tools and evidence-based treatments to enable optimal care of concussed individuals.

RECENT FINDINGS

This article aims to review recent research on the topic, emphasizing the role of the autonomic nervous system (ANS) in concussion. Current data suggests that ANS dysfunction is often evident following mTBI and accounts for many of the symptoms commonly seen in concussed patients. This link suggests several objective biomarkers that could be used to diagnose and monitor recovery following mTBI. Contrary to conventional wisdom, symptoms and biomarkers of ANS function improve when individuals are exposed to a program of graded exercise as treatment within the first week following concussion.

SUMMARY

ANS dysfunction contributes to concussion symptomatology, an effect likely mediated through diffuse axonal injury, including brainstem structures and pathways mediating normal cerebrovascular autoregulation. Exercise, which enhances ANS function, is a well tolerated and effective method of treatment for both acute concussion patients and those suffering from postconcussion syndrome (PCS). The relationship between the ANS, exercise, and concussion creates an opportunity for the identification of objective biomarkers that can facilitate the diagnosis and treatment of mTBI.

Radiographic and neurobehavioral profile of sports-related concussion associated with scholastic wrestling: a case report

Sports-related concussions (SRCs) are typically characterized by transient neurologic deficits due to physiologic and metabolic brain injury. However, following an SRC, subsequent insults may lead to severe and permanent injury in the affected brain cells. We present the case of a 15-year-old female scholastic wrestler who developed acute encephalopathy, macroscopic white matter injury on imaging, and chronic behavioral changes from inadequate neuro-recovery after a documented SRC. We also compare her case with established SRC data, demonstrating that wrestling-related concussions and repetitive head impacts can produce similar degrees of diffuse neuroinflammation, myelinated axonopathy, blood-brain barrier disruption, and post-concussive symptoms.

Characteristic patterns of white matter tract injury in sport-related concussion: An image based meta-analysis

Sports-related concussion (SRC) is sustained by millions of people per year, yet the spatiotemporal patterns of white matter (WM) injury remain poorly understood. Several SRC studies have implemented the standardised approach Tract-Based Spatial Statistics (TBSS). The aim of this image-based meta-analysis was to identify consensus patterns of SRC-related WM injury across TBSS studies. We included studies comparing the diffusion MRI measurement fractional anisotropy (FA) in SRC or subconcussive injury vs. controls using TBSS, as FA is the most frequently examined diffusion tensor imaging metric. Authors of eligible studies were contacted to request unthresholded statistical map outputs from TBSS, and image-based meta-analyses were performed using Seed-Based d-Mapping. Eight studies contributed to our meta-analyses, comprising 174 SRC or subconcussive injury participants and 160 controls. Our primary meta-analysis (n = 8), encompassing subjects with acute SRC (n = 2), chronic SRC (n = 4) and subconcussive injuries (n = 2) revealed dominant bilateral increased FA in the superior longitudinal fasciculus (SLF) and internal capsule. Subconcussive injury was associated with small clusters of increased and decreased FA in the arcuate fasciculus compared to control. In acute SRC, we found diffuse foci of raised FA at WM/grey matter border-zone associated with the bilateral SLF and right inferior fronto-occipital fasciculus. In contrast, chronic SRC had a pattern of deep WM alteration, asymmetrically located in the right optic radiations and arcuate fasciculus. Our findings represent the most powerful analysis of TBSS data in SRC, supporting the use of this approach to analyse diffusion data. TBSS is sensitive to WM abnormalities resulting from SRC or subconcussive injury over a range of temporal and clinical scenarios. Our data show spatially concordant patterns of WM injury unique to subconcussive, acute and chronic phases, highlighting the future utility of diffusion MRI for concussion diagnosis.

The Association Between Persistent White-Matter Abnormalities and Repeat Injury After Sport-Related Concussion

Objective: A recent systematic review determined that the physiological effects of concussion may persist beyond clinical recovery. Preclinical models suggest that ongoing physiological effects are accompanied by increased cerebral vulnerability that is associated with risk for subsequent, more severe injury. This study examined the association between signal alterations on diffusion tensor imaging following clinical recovery of sport-related concussion in athletes with and without a subsequent second concussion. Methods: Average mean diffusivity (MD) was calculated in a region of interest (ROI) in which concussed athletes (n = 82) showed significantly elevated MD acutely after injury (<48 h), at an asymptomatic time point, 7 days post-return to play (RTP), and 6 months relative to controls (n = 69). The relationship between MD in the identified ROI and likelihood of sustaining a subsequent concussion over a 1-year period was examined with a binary logistic regression (re-injured, yes/no). Results: Eleven of 82 concussed athletes (13.4%) sustained a second concussion within 12 months of initial injury. Mean MD at 7 days post-RTP was significantly higher in those athletes who went on to sustain a repeat concussion within 1 year of initial injury than those who did not (p = 0.048; d = 0.75). In this underpowered sample, the relationship between MD at 7 days post-RTP and likelihood of sustaining a secondary injury approached significance [χ2 (1) = 4.17, p = 0.057; B = 0.03, SE = 0.017; OR = 1.03, CI = 0.99, 1.07]. Conclusions: These preliminary findings raise the hypothesis that persistent signal abnormalities in diffusion imaging metrics at RTP following concussion may be predictive of a repeat concussion. This may reflect a window of cerebral vulnerability or increased susceptibility following concussion, though understanding the clinical significance of these findings requires further study.