Diffuse axonal injury
| Diffuse axonal injury | |
|---|---|
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| Susceptibility weighted image (SWI) of diffuse axonal injury in trauma at 1.5 teslas (right) | |
| Classification and external resources | |
| eMedicine | radio/216 |
| MeSH | D020833 |
Diffuse axonal injury (DAI) is a brain injury in which damage in the form of extensive lesions in white matter tracts occurs over a widespread area. DAI is one of the most common and devastating types of traumatic brain injury, and is a major cause of unconsciousness and persistent vegetative state after severe head trauma. It occurs in about half of all cases of severe head trauma and may be the primary damage that occurs in concussion. The outcome is frequently coma, with over 90% of patients with severe DAI never regaining consciousness. Those who do wake up often remain significantly impaired.
DAI can occur in every degree of severity from very mild or moderate to very severe.Concussion may be a milder type of diffuse axonal injury.
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 car 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: 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 each other, 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.
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