Traumatic axonal injury has been associated with concussions (also referred to as mild traumatic brain injury), yet the pathological course that leads from injury to recovery or to long-term sequelae is still not known.
It occurs in about half of all cases of severe traumatic brain injury, making it one of the most common traumatic brain injuries. It can also occur in moderate and mild brain injury.
Diffuse axonal injury isn’t the result of a blow to the head. Instead, it results from the brain moving back and forth in the skull as a result of acceleration or deceleration. Automobile accidents, sports-related accidents, violence, falls, and child abuse such as Shaken Baby Syndrome are common causes of diffuse axonal injury. When acceleration or deceleration causes the brain to move within the skull, axons, the parts of the nerve cells that allow neurons to send messages between them, are disrupted. As tissue slides over tissue, a shearing injury occurs. This causes the lesions that are responsible for unconsciousness, as well as the vegetative state that occurs after a severe head injury.
A diffuse axonal injury also causes brain cells to die, which cause swelling in the brain. This increased pressure in the brain can cause decreased blood flow to the brain, as well as additional injury. The shearing can also release chemicals which can contribute to additional brain injury.
The main symptom of diffuse axonal injury is lack of consciousness, which can last up to six hours or more. A person with a mild or moderate diffuse axonal injury who is conscious may also show other signs of brain damage, depending upon which area of the brain is most affected.
Magnetic Resonance Imaging (MRI) - This test is the preferred test for diagnosing diffuse axonal injury.
CT Scan - may result in false negatives, so can’t be relied on to give definitive results when it comes to diffuse axonal injury.
The classification was first proposed by Adams in 1989 5) and divides diffuse axonal injury (DAI) into three grades:
grade I : involves grey-white matter interfaces most commonly : parasagittal regions of frontal lobes, periventricular temporal lobes less commonly : parietal and occipital lobes, internal and external capsules, and cerebellum often inapparent on conventional imaging may have changes on MRS 3
grade II : involves corpus callosum in addition to stage I locations observed in approximately 20% of patients most commonly : posterior body and splenium but does advance anteriorly with increasing severity of injury most frequently unilateral may be seen on SWI 3
grade III : involves brainstem in addition to stage I and II locations most commonly : rostral midbrain, superior cerebellar peduncles, medial lemnisci and corticospinal tracts.
DTI with 3-D fiber tractography can visualize acute axonal shearing injury, which may have prognostic value for the cognitive and neurological sequelae of traumatic brain injury 6).