Diffuse axonal injury (DAI) is a brain injury in which scattered lesions occur over a widespread area in white matter tracts as well as grey matter. 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.