Diffuse axonal injury (DAI) is a frequent result of traumatic deceleration injuries and a frequent cause of persistent vegetative state in patients. In fact, DAI represents approximately one half of all intra-axial traumatic lesions. This lesion is the most significant cause of morbidity in patients with a traumatic brain injuries, which most commonly result from high-speed motor vehicle accidents. DAI typically consists of several focal white-matter lesions measuring 1-15 mm in a characteristic distribution.
Classically, DAI has been considered a primary-type injury, with damage occurring at the time of the accident. Research has shown that another component of the injury comprises the secondary factors (or delayed component), since the axons are injured, secondary swelling occurs, and retraction bulbs form. Of patients with DAI, 80% demonstrate multiple areas of injury on computed tomography (CT) scans.
The degree of microscopic injury usually is considered to be greater than that seen on diagnostic imaging, and the clinical findings reflect this point. DAI is suggested in any patient who demonstrates clinical symptoms disproportionate to his or her CT-scan findings. DAI results in instantaneous loss of consciousness, and most patients (>90%) remain in a persistent vegetative state, since brainstem function typically remains unaffected. DAI rarely causes death.
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