Sex-Specific Associations Between Repetitive Head Impact Exposure and Cerebral Blood Flow Among Active Amateur Soccer Players.

Repetitive head impacts (RHIs) in soccer have been associated with long-term risk for neurodegenerative disease. The pathophysiology is largely unknown. This study aims to investigate alterations in cerebral blood flow (CBF) in athletes exposed to RHI compared with athlete controls (CTL). Given that females are known to exhibit higher CBF than males, we also explore sex-specific differences. Finally, we investigate the relationship between CBF and neuropsychological functioning and RHI measures. This study includes 82 amateur athletes (mean age 22.8 ± 1.6 years; 48.9% female). Participants underwent 3T magnetic resonance imaging and completed neuropsychological testing, including questionnaires on stress, resilience, and sleep quality, and computerized assessment of executive function, memory, and processing speed. CBF was assessed using MR pulsed arterial spin labeling. Analysis of covariance was applied to assess the effect of RHI exposure and sex on CBF. Associations between CBF and neuropsychological functioning were analyzed using linear regression models. The analysis was conducted hierarchically, beginning with global gray matter CBF (level 1), followed by cortical and deep gray matter (level 2), and finally brain lobes (level 3). Correction for multiple comparisons was applied at each hierarchical level using false discovery rate, with a significance threshold set at p < 0.05 after correction. We found higher CBF in athletes with RHI exposure (RHI group) compared with athletes with <5 years of exposure to RHI (CTL group; Δ 95% confidence interval [95% CI] = 3.9 [0.5, 7.3] mL/100g/min, p = 0.027). Female athletes with RHI exposure exhibited higher CBF in the global gray matter compared with female CTL (Δ[95% CI] = 6.6 [1.6, 11.5] mL/100g/min, p = 0.013). Among males, individuals with RHI exposure demonstrated higher CBF in the occipital lobe compared with male CTL (Δ[95% CI] = 4.9 [0.3, 9.5] mL/100g/min, p = 0.047). There were no statistically significant associations between CBF and neuropsychological functioning. In the RHI group, years of soccer play were positively associated with whole-brain CBF. Results from this study suggest an association between RHI exposure and higher CBF, a measure of brain activity. Furthermore, we report sex-specific patterns of higher CBF in individuals exposed to RHI, with more widespread elevated CBF in women and more localized higher CBF in men. While these findings highlight the importance of investigating sex-specific effects, there were no associations between CBF and neuropsychological functioning. Future studies are warranted to determine the clinical relevance of the observed sex-specific effects to RHI.