Post-Concussion Brain Changes Relative to Pre-Injury White Matter and Cerebral Blood Flow, 2025, Churchill, Hutchison, Graham, Schweizer

Post-Concussion Brain Changes Relative to Pre-Injury White Matter and Cerebral Blood Flow
Nathan W. Churchill, Michael G. Hutchison, Simon J. Graham, Tom A. Schweizer

BACKGROUND AND OBJECTIVES
Medical clearance for return to play (RTP) after sports-related concussion is based on clinical assessment. It is unknown whether brain physiology has entirely returned to preinjury baseline at the time of clearance. In this longitudinal study, we assessed whether concussed individuals show functional and structural MRI brain changes relative to preinjury levels that persist beyond medical clearance. Secondary objectives were to test whether postconcussion changes exceed uninjured brain variability and to correlate MRI findings with clinical recovery time.

METHODS
For this prospective observational study, healthy athletes without a history of psychiatric, neurologic, or sensory-motor conditions were recruited from a single university sport medicine clinic. Clinical and MRI data were collected at preseason baseline, and those who were later concussed were reassessed at 1–7 days after injury, RTP, 1–3 months after RTP, and 1 year after RTP. A demographically matched control cohort of uninjured athletes was also reassessed at their subsequent preseason baseline. Primary outcomes were postconcussion changes in MRI measures of cerebral blood flow (CBF), white matter mean diffusivity (MD), and fractional anisotropy (FA), evaluated using mixed models. Secondary outcomes were group differences in MRI change scores and correlations of change scores with days to RTP.

RESULTS
Of the 187 athletes enrolled in the study, 25 had concussion with follow-up imaging (20.3 ± 1.5 years, 56% male, 44% female) and were compared with 27 controls (19.7 ± 1.8 years, 44% male, 56% female). Concussed athletes showed statistically significant changes from baseline, including decreased frontoinsular CBF (mean and 95% CI −8.97 [−12.80, −5.01] mL/100 g/minute, z = −4.53), along with increased MD (1.94 × 10−5 [1.26, 2.69] × 10−5, z = 5.48) and reduced FA (−7.30 × 10−3 [-9.80, −5.05] × 10−3, z = −6.07) in the corona radiata and internal capsule. Effects persisted beyond RTP, although only CBF changes exceeded longitudinal variability in controls. For participants with longer recovery periods, significantly greater changes in medial temporal CBF were also seen (ρ = 0.64 [0.44, 0.81], z = 6.80).

DISCUSSION
This study provides direct evidence of persistent postconcussion changes in CBF and white matter at RTP and up to 1 year later. These results support incomplete recovery of brain physiology at medical clearance, with secondary analyses emphasizing the sensitivity of CBF to clinical recovery.

Link | PDF (Neurology) [Paywall]

 

Editorial in Uncovering Subclinical Neural Alterations in Sport-Related Concussion (2025, Neurology)

Some quotes from the editorial —

 

AI Summary (Gemma3:12b) —

Results
1. Overview

The study compares a group of concussed athletes to a control group (presumably uninjured athletes). The researchers are looking at changes in brain structure and how these changes relate to the time it takes for the athletes to return to play (RTP). The study follows participants through several time points: Symptomatic Injury (SYM), Return to Play (RTP), 1-3 Months Out (1-3MO), and 1 Year Out (1YR).

2. Key Findings (Neuroimaging)

The study used three main MRI measures:

• Mean Diffusivity (MD): This reflects the average size of water molecules diffusing in the brain tissue. Changes in MD can indicate changes in tissue integrity, often related to swelling or damage.
• Fractional Anisotropy (FA): This measures the directionality of water diffusion. Higher FA indicates more organized tissue (like in healthy white matter). Lower FA suggests disruption of this organization.
• Cerebral Blood Flow (CBF): This measures the amount of blood flowing to the brain.

Here's a summary of the findings for each measure:

• Mean Diffusivity (MD):
  • Significant increases in MD were observed in the left corona radiata and internal capsule at SYM, RTP, and 1-3MO. This suggests swelling or damage in these areas.
  • The increases were no longer significant at 1 year.
  • Concussed athletes showed greater increases in MD compared to controls, but the difference wasn't statistically significant.
• Fractional Anisotropy (FA):
  • Significant decreases in FA were observed in the left corona radiata and internal capsule at SYM and RTP. This indicates disruption of white matter organization.
  • The decreases were no longer significant at 1 year.
  • Concussed athletes showed greater decreases in FA compared to controls, but the difference wasn't statistically significant.
• Cerebral Blood Flow (CBF):
  • Significant changes in CBF were observed in medial temporal areas (right fusiform gyrus, left parahippocampal gyrus, and left hippocampus) at SYM, RTP, and 1 year.

3. Analysis of Neuroimaging and Recovery Time

• The study found a significant positive correlation between CBF in specific medial temporal areas and the time it took for athletes to return to play. This means that lower CBF in these areas was associated with longer recovery times.
• Exploratory analyses also found associations between MRI measures and clinical change scores (how athletes' symptoms changed over time).

Overall Focus: This study investigates brain changes after concussion using advanced MRI techniques (CBF - Cerebral Blood Flow, MD - Mean Diffusivity, FA - Fractional Anisotropy) and compares them to changes in a control group. The goal is to understand the recovery process and identify potential biomarkers for clinical outcomes.

Discussion
Key Findings:

• Significant Longitudinal Changes: The study found significant changes in CBF, MD, and FA after concussion, even at the point of return to play (RTP).
• CBF as a Biomarker: Changes in CBF, particularly in the medial temporal region, were significantly different from those in the control group and correlated with the time it took for athletes to be medically cleared. This suggests CBF changes may be a biomarker for more severe clinical outcomes.
• MD & FA Less Specific: While MD and FA showed changes after concussion, these changes weren't consistently distinguishable from normal variations seen in the control group. This suggests they may be influenced by factors beyond concussion, like physical exertion and stress.
• Comparison to Controls: While CBF changes were distinct, MD and FA changes were not significantly different from those seen in the control group, indicating they may be influenced by factors beyond concussion.
• Recovery Process: The study provides insights into the recovery process, highlighting that while brain changes occur, they don't always translate to noticeable behavioral deficits.

In essence, the study reinforces the importance of CBF as a potential biomarker for concussion recovery while acknowledging the complexity of interpreting changes in other brain measures and highlighting the need for further research to better understand the long-term effects of concussion.