RESUMO
BACKGROUND: Lasting neuroimaging changes after participation in American football are an increasing public health concern. The clinical relevance of imaging findings remains unknown. METHODS: A systematic review was performed with the following inclusion criteria: football players, brain imaging ≥2 years from previous concussion or retirement, and sample size ≥5. Studies were assessed for 1) methodology (control selection, type I error, and recall bias), 2) imaging outcomes, and 3) number of significant statistical comparisons. RESULTS: Sixteen studies (all cross-sectional studies) met the inclusion criteria. Highest level of play included high school (n = 1), college (n = 3), and professional (n = 12). Thirteen of the 16 studies made a total 456 comparisons of brain activity, of which 171 were statistically significant (38%). Nine of 16 studies (56%) had appropriate controls, and 5 of 16 studies (31%) appropriately accounted for type I error. To obtain player concussion history, all studies (16/16) had recall bias or unclear methodology. Imaging outcome measures included structural magnetic resonance imaging (MRI) (29.2%), diffusion tensor imaging (25%), radioactive tracer uptake on positron emission tomography (16.7%), patterns of connectivity on functional MRI (fMRI) (12.5%), transcranial magnetic stimulation (8.3%), arterial spin labeling MRI (4.2%), and metabolic changes on 1H-magnetic resonance spectroscopy (4.2%). CONCLUSIONS: Long-term neuroimaging findings in American football players are heterogeneous in both methodology and findings. Understanding the clinical importance of statistically significant findings is complicated by methodological limitations and study design. Further research is required to correlate imaging findings with clinical outcomes.
