Mathematical Modeling of Diffuse Brain Injury: Correlations of Foci and Severity of Brain Strain with Clinical Symptoms and Pathology

To address the relationships of clinical symptoms and pathology and the location and magnitude of brain strains, the Wayne State University human head finite element model was used with loading conditions posited to produce severe concussion (AIS 3) and mild, moderate and severe diffuse axonal injury (DAI) (AIS 4 ‐ AIS 5). Sinusoidal accelerations with peak thresholds of 8,100, 11,000, 14,000 and 16,000 rad/s, respectively, were applied in sagittal, coronal and oblique planes to evaluate the effect of loading directions on brain strain distribution. Large maximum principal strains were consistently found in the thalamus, midbrain, corpus callosum and hippocampus. These areas seem to correlate well with observed clinical symptoms of memory dysfunction and altered awareness associated with concussion. Together with our previous study, 0.35 brain strain appeared to be a tissue injury tolerance for concussive injuries (severities of AIS 1‐3), with the brain volume involvement of 5%, 20%, and 35% to be the thresholds for mild, classic and severe cerebral concussion, respectively. 0.50 brain strain would result in more widespread axonal pathology, with 10%, 20% and 30% volumetric involvement being the thresholds, respectively, for mild, moderate and severe DAI. These proposed regional strain estimates can be used to allow the assessment of risk and outcome for the whole spectrum of diffuse brain injury.