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Mild brain injury - a brain injury to someone who is not you or someone you care about

Primary TBI represents the irreversible mechanical insult sustained at the moment of impact. It results from linear and rotational forces producing tissue deformation, vascular disruption, and axonal shearing. Rotational acceleration is particularly implicated in diffuse axonal injury due to differential movement between gray and white matter structures. Accurate classification of primary injury type is essential for prognosis, monitoring for secondary complications, and guiding acute management.

Secondary injury involves processes such as negative neuroplasticity, impaired blood flow regulation, mitochondrial, metabolic dysfunction, neuroinflammation, oxidative stress, and blood–brain barrier disruption, along with glial cell dysfunction, reduced neurogenesis, demyelination, and accumulation of abnormal proteins such as tau. It also extends beyond the brain to include hormonal, psychological, cervical spine, vestibular, and brain–gut axis dysfunction, reflecting the whole-body impact of TBI. These changes are not caused by the original trauma itself, but by the body’s response to it and they play a major role in driving symptoms, recovery, and long-term outcomes.

Importantly, many of these secondary processes are dynamic and potentially modifiable, making secondary injury a critical target for early recognition and intervention.