Diffuse axonal injury develops most commonly in the setting of angular acceleration of the brain in head injury. This movement causes a shear injury between the gray and white matter with microscopic hemorrhages developing in particular areas of the brain. The shear also disrupts axons, which swell and whose severed ends eventually become the globular structures seen pathologically as the “retraction balls of Cajal.” The earliest changes occur hours after injury and the pathologic changes continue for several days. The clinical manifestations of diffuse axonal injury include a period of unconsciousness (and amnesia) lasting more than 6 hours.

Prognosis for head-injury patients is difficult to predict. The severity of diffuse axonal injury can vary with the severity of head injury. Prognosis for traumatic brain injury also varies with the severity of the injury. In the most severe cases (in which patients who do not die remain in a vegetative state), about one-third of patients recover consciousness by 3 months. However, recovery continues significantly after that, with 46% of patients recovering consciousness by 6 months, and 52% by 1 year. Clinicians must therefore take extreme caution in giving a prognosis for such patients for at least 6 months. The great majority of patients in a vegetative state have diffuse axonal injury on pathological examination of their brains. Thus, when diffuse axonal injury is identified premortem (via head imaging), the same caution must be used in giving a prognosis for diffuse axonal injury.