Diffuse axonal injury (DAI) describes a type of traumatic brain injury (TBI). Specifically, it refers to the shearing of the brain’s long connecting nerve fibers, or axons. This can occur when the brain shifts and rotates inside the skull. This damage usually results in a coma and injury to many different parts of the brain.

DAI, also known as traumatic axonal injury, occurs when a sudden violent blow or jolt to the head causes damage to the brain. After the impact, the brain may collide with the inside of the skull, which can result in the shearing of nerve fibers.

This can affect the ability of various brain regions to communicate with other areas, which may lead to neurological problems, as well as coma, long-term impairment, or death.

In this article, we discuss diffuse axonal injury in more detail, including its causes, how doctors grade it, and the outlook for people with this condition.

A person having a brain scan.Share on Pinterest
Getty Images

Traumatic axonal injury or DAI, as it is traditionally known, refers to a type of TBI. This term describes an injury that typically results from blunt trauma to the head and affects how the brain functions. Research shows that there were more than 64,000 TBI-related deaths in the United States in 2020.

Specifically, DAI describes the shearing, or tearing, of nerve fibers known as axons. This trauma usually results from the brain quickly shifting within the skull. Following a sudden impact, mechanical forces cause nerve fibers to stretch and tear.

Axons are the long, thread-like portion of neurons that conduct electrical impulses. They are responsible for communication between nerve cells. As such, damage to axons may impair their ability to communicate and help coordinate bodily functions, which can lead to severe disabilities.

DAI is the most common cause of coma, disability, and persistent vegetative state in people with TBI. Clinically, health experts define DAI as a loss of consciousness that lasts for 6 hours or more after the injury. It may also cause behavioral, social, physical, and cognitive changes in a person that may be temporary or permanent.

DAI is more common in high energy traumatic accidents in which the brain rotates or moves forward or backward inside the skull. Typically, this type of trauma involves accelerating and decelerating motions. If these forces are sufficiently strong, they can damage axons, causing these neuronal interconnections to malfunction or disconnect and affecting many brain areas. DAI commonly affects the following brain areas, which contain axons:

  • frontal lobe white matter
  • temporal lobe white matter
  • corpus callosum
  • brain stem

The leading causes of DAI include:

  • motor vehicle accidents
  • sports-related accidents
  • violence
  • accidental falls, which are more common among older adults
  • shaken baby syndrome

Following the traumatic impact, a person with DAI typically presents with loss of consciousness and poor neurological examination results. Experts use the Glasgow Coma Scale (GCS) to assess the extent of the impairment.

They calculate a value by adding the totals from three different categories to get a score that ranges from a minimum of 3 to a maximum of 15. A lower score indicates a higher level of impairment. A person with DAI will typically have a GCS score of less than 8 for more than 6 hours. The categories for the GCS include:

Eye opening

  • Spontaneous: 4
  • In response to speech: 3
  • In response to pain: 2
  • None: 1

Verbal response

  • Orientated response: 5
  • Confused conversation: 4
  • Inappropriate response: 3
  • Incomprehensible sounds: 2
  • None: 1

Motor response

  • Obeying commands: 6
  • Movement localized to stimulus: 5
  • Withdraws: 4
  • Abnormal muscle bending and flexing: 3
  • Involuntary muscle straightening and extending: 2
  • None: 1

The clinical presentation of DAI depends on the severity of the brain injury. In mild cases of DAI, a person may have symptoms that mimic concussion symptoms, including:

Those with more severe DAI may present with loss of consciousness and stay in a vegetative state. Other neurological manifestations of DAI can include dysautonomia. This term describes when the autonomic nervous system does not work as it should. The symptoms may include:

DAI is a clinical diagnosis. Currently, there are no laboratory tests to diagnose DAI. Healthcare professionals base their diagnosis on a person’s clinical presentation and a GCS score of less than 8 for more than 6 hours.

The results of imaging tests can also help doctors make a diagnosis. These tests may include a brain MRI or diffuse tensor imaging (DTI). A 2020 study suggests that DTI may be a preferable method for detecting DAI, but more research is necessary to confirm this.

Doctors may also use the Adams DAI Classification system to grade DAI. This system combines the pathophysiology and clinical presentation of DAI to provide a score. The grades are as follows:

  • Grade 1, or mild DAI: Microscopic damage to the white matter of the brain, including changes in the cerebral cortex, brain stem, and corpus callosum.
  • Grade 2, or moderate DAI: Larger lesions present in the corpus callosum.
  • Grade 3, or severe DAI: Larger lesions present in both the brain stem and the corpus callosum.

The treatment of DAI is similar to the treatment of other head injuries. The goal of emergency care is to stabilize the person’s condition and prevent any worsening of brain damage. Typically, this involves:

  • ensuring that the airway is open
  • providing ventilation and oxygen
  • maintaining blood pressure

After emergency care, a person may need medications and surgery to help control the symptoms. They may also require rehabilitation. Depending on the extent of the injury, they may need to relearn many everyday tasks, such as how to walk and talk.

Health experts generally do not consider the outlook for people with severe DAI to be good. TBI is a leading cause of mortality and permanent disability worldwide. Evidence highlights the importance of determining an early GCS score and stabilizing oxygen, glucose, and blood pressure levels. A 2020 study also suggests that the extent and location of DAI can help predict individuals at risk of neurodegeneration.

A very small number of those with severe DAI regain their consciousness within the first year after the injury. If a person regains their consciousness and becomes stable, a comprehensive therapeutic program from their brain injury rehabilitation team can help restore their quality of life. This program may include:

The Centers for Disease Control and Prevention (CDC) recommend that people reduce the risk of sustaining a TBI by:

  • wearing a seatbelt whenever riding in or driving a vehicle
  • avoiding driving when under the influence of drugs or alcohol
  • wearing the appropriate protective gear or helmet for the sport or activity
  • evaluating an older adult’s risk of falling and taking steps to reduce their risk
  • keeping the home safe and clutter-free

Diffuse axonal injury describes a severe type of traumatic brain injury. It refers to when trauma causes the brain to shift in the skull, resulting in the shearing of axons. This injury is often fatal. In other cases, a person may remain in a vegetative state or have permanent disability.

Immediate emergency treatment is necessary to stabilize an individual after the injury. Although the outlook for these individuals is usually not positive, a comprehensive therapeutic program can help restore quality of life. To prevent DAI, it is advisable for a person to take suitable safety precautions, such as wearing a seatbelt when traveling in a vehicle.