Diffuse Axonal Injury - Mechanism

Mechanism

Unlike brain trauma that occurs due to direct impact and deformation of the brain, DAI is the result of traumatic shearing forces that occur when the head is rapidly accelerated or decelerated, as may occur in auto accidents, falls, and assaults. It usually results from rotational forces or severe deceleration. Vehicle accidents are the most frequent cause of DAI; it can also occur as the result of child abuse such as in shaken baby syndrome.

The major cause of damage in DAI is the disruption of axons, the neural processes that allow one neuron to communicate with another. Tracts of axons, which appear white due to myelination, are referred to as white matter. Acceleration causes shearing injury, which refers to damage inflicted as tissue slides over other tissue. When the brain is accelerated, parts of differing densities and distances from the axis of rotation slide over one another, stretching axons that traverse junctions between areas of different density, especially at junctions between white and grey matter. Two thirds of DAI lesions occur in areas where grey and white matter meet.