Neuroanatomical differences in Australian rules footballers following mild traumatic brain injury

2158 

Abstract Submission 

Jackson Lee^1,2, Remika Mito^1,3, Heath Pardoe^1,4, Donna Parker¹, Mangor Pedersen⁵, David Abbott^1,4, Graeme Jackson^1,4,6

¹The Florey Institute of Neuroscience and Mental Health, Melbourne, VIC, Australia, ²Department of Anatomy and Physiology, The University of Melbourne, Melbourne, VIC, Australia, ³Department of Psychiatry, The University of Melbourne, Melbourne, VIC, Australia, ⁴Florey Department of Neuroscience and Mental Health, University of Melbourne, Melbourne, VIC, Australia, ⁵Auckland University of Technology, Auckland, New Zealand, ⁶Department of Neurology, Austin Health, Melbourne, VIC, Australia

Jackson Lee  
The Florey Institute of Neuroscience and Mental Health|Department of Anatomy and Physiology, The University of Melbourne
Melbourne, VIC, Australia|Melbourne, VIC, Australia

Remika Mito  
The Florey Institute of Neuroscience and Mental Health|Department of Psychiatry, The University of Melbourne
Melbourne, VIC, Australia|Melbourne, VIC, Australia

Heath Pardoe  
The Florey Institute of Neuroscience and Mental Health|Florey Department of Neuroscience and Mental Health, University of Melbourne
Melbourne, VIC, Australia|Melbourne, VIC, Australia

Donna Parker  
The Florey Institute of Neuroscience and Mental Health
Melbourne, VIC, Australia

Mangor Pedersen, Associate Professor  
Auckland University of Technology
Auckland, New Zealand

David Abbott, PhD  
The Florey Institute of Neuroscience and Mental Health|Florey Department of Neuroscience and Mental Health, University of Melbourne
Melbourne, VIC, Australia|Melbourne, VIC, Australia

Graeme Jackson  
The Florey Institute of Neuroscience and Mental Health|Florey Department of Neuroscience and Mental Health, University of Melbourne|Department of Neurology, Austin Health
Melbourne, VIC, Australia|Melbourne, VIC, Australia|Melbourne, VIC, Australia

Australian rules football is a full-contact sport played with intensity, in which players are exposed to one of the highest rates of concussion (a type of mild traumatic brain injury (mTBI)), across sporting codes in Australia¹. The wellbeing of athletes exposed to repeated mTBI and sub-concussive impacts is of growing concern given the association with long-term neurodegenerative consequences^2-3. Previous work has highlighted changes in white matter microstructure and functional connectivity in professional Australian rules footballers following mTBI^4-5, however, these footballers may also exhibit observable changes in standard structural brain measures. Here, we explored differences in structural brain measures in professional Australian rules footballers with a recent mTBI. We hypothesised that footballers would exhibit differences in volume and thickness measures, particularly in the hippocampus, which has well-documented vulnerability to mTBI^6-7.

Professional male footballers from the Australian Football League (AFL), who had sustained an mTBI within 3 months prior to MRI acquisition, were included and categorised into either an acute mTBI group (n=17, ≤12 days since mTBI), or a sub-acute mTBI group (n=14, >12 days since mTBI). Healthy male age-matched controls with no history of head trauma were also included (n=37).

T1-weighted MRI data were acquired at 3T on either a Siemens Trio or Skyra using an MPRAGE sequence (0.9mm isotropic voxels, inversion time=900ms, flip angle=9°, TR/TE=1900/2.5ms). All T1-weighted MRI scans were processed using FreeSurfer (v7.3.2). Estimated total intracranial volume (eICV), whole brain volume, hippocampal and amygdala volumes, and cortical thickness were quantified using FreeSurfer's recon-all pipeline⁸. Hippocampal subfield volumes were obtained using FreeSurfer's hippocampus and amygdala nuclei subregion segmentation pipeline⁹. All outputs were manually inspected and edited where necessary using FreeView, and group-level comparisons made using multiple linear regression (adjusting for age and eICV). For subfield and thickness analyses, False Discovery Rate (FDR) correction was performed to correct for multiple comparisons.

In a subset of mTBI participants (n=26), cognitive screening was performed using the CogSport computerised battery¹⁰. Normalised scores from the one-back and continuous learning tests (which assess working memory and learning, respectively) were used to examine the relationship between hippocampal volume and cognitive function post-mTBI (using Pearson's correlation).

Compared to controls, both mTBI groups exhibited significantly smaller whole brain volume (acute: p=0.013; sub-acute: p=0.008) and right hippocampal volumes (acute: p=0.031; sub-acute mTBI: p=0.012). The acute mTBI cohort also exhibited significantly smaller right amygdala volume (p=0.018) and thinner right rostral anterior cingulate thickness compared to controls (FDR-corrected p=0.010). At the hippocampal subfields, the sub-acute mTBI group exhibited significantly smaller right subicular complex volume compared to controls (FDR-corrected p=0.035). A similar trend was seen in the acute mTBI group at the right subicular complex; however, this did not survive FDR correction (FDR-corrected p=0.063).

There was a significant positive correlation between footballers' cognitive learning scores, and hippocampal volume bilaterally (left: r(23)=0.44, p=0.030; right: r(23)=0.40, p=0.046).

Here, we provide evidence of subtle structural brain differences in Australian rules footballers following a recent mTBI, namely at the whole brain level, and at the hippocampus and amygdala (right more than left). Longitudinal research is needed to assess if these subtle differences may be early signatures of long-term neurodegenerative changes, and whether quantifying these structural MRI changes in individuals may be a clinically viable tool in future.

Cortical Anatomy and Brain Mapping

Subcortical Structures ¹

Neuroanatomy Other ²

Anatomical MRI

MRI

Segmentation

STRUCTURAL MRI

Trauma

Other - Concussion