Diffuse Axonal Injury (DAI)

Definition: A type of brain injury commonly associated with concussions and mild traumatic brain injuries (mTBI) where the axons (the brain's connecting wires) are stretched and torn.

Mechanism of Injury: DAI occurs when the brain is subjected to forces of acceleration, deceleration, rotation, or angulation. The brain sits in fluid inside the skull and sloshes back and forth during an impact. Because different layers of brain tissue have different densities, they move at different speeds. This shifting and twisting motion creates friction and causes the layers to shear, stretching and tearing the axons.

Severity Matrix: The extent of the injury depends on the level of force and movement. More mild injuries are likely to affect the outer wires of the brain, whereas more significant injuries twist and rotate deeper, affecting the deeper wires.

Clinical Implications:

• DAI is a primary driver behind changes in cognitive processing, thinking, and executive function.
• It is a leading cause of death if severe shearing occurs to the white matter tracts running through the reticular activating system (the stalk of the brain stem).

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