What Is a Diffuse Axonal Injury?

A diffuse axonal injury (DAI) is a type of brain injury that causes tears in the brain's long connecting nerve fibers, called axons. This injury occurs due to a blunt injury that causes the brain to rotate and shift rapidly inside the skull. Up to 50% of traumatic brain injuries (TBIs) requiring hospital admission are diffuse axonal injuries (DAI).

This article will review the types of diffuse axonal injury as well as its symptoms, causes, diagnosis, and treatment options.

Types of Diffuse Axonal Injury

To understand the different types of DAIs, it is first important to explain that there are two ways a TBI can occur:

• A closed brain injury: a TBI with no puncture through the skull, such as an intracranial hemorrhage or a concussion
• A penetrating brain injury: a TBI with a puncture in the skull, such as a bullet or knife wound inside the brain

A diffuse axonal injury is a closed brain injury because it occurs inside the skull without a penetrating force.

The Adams DAI classification system is one way healthcare providers grade DAIs and determine their overall severity. This grading system looks at brain injuries in the following areas:

• The cerebral cortex: the outermost portion of the brain, covering two cerebral hemispheres. This is the "gray matter" portion of the brain associated with the highest levels of mental capacity.
• The brain stem: the part of the brain that connects to the spinal cord.
• The corpus callosum: the brain area consisting of white matter tracts connecting the left and right cerebral hemispheres.

The Adams DAI classification system analysis the pathophysiology and clinical presentation of the DAI to determine one of the following grades:

• Grade 1 (mild DAI): involves damage to the white matter of the brain, including changes in the cerebral cortex, brain stem, and corpus callosum
• Grade 2 (moderate DAI): large lesions visible in the corpus callosum
• Grade 3 (severe DAI): large lesions present in the brain stem and the corpus callosum
  

Diffuse Axonal Injury Symptoms

DAI typically presents as a loss of consciousness, or coma, that can occur as the result of a traumatic brain injury (TBI).

Those with a mild DAI may exhibit symptoms similar to those with a concussion. These symptoms may include:

• Headache
• Dizziness
• Nausea
• Vomiting
• Fatigue
• Sleep issues
• Trouble balancing

In patients who receive a severe TBI diagnosis, about 40–50% of them also receive a DAI diagnosis. Patients with moderate or severe DAI usually present with a loss of consciousness and remain in a continuous vegetative state.

Causes

The most common cause of DAI involves high-speed car accidents. These accidents present a high risk of rapid rotation or a sudden acceleration/deceleration motion of the brain inside the skull. This aggressive and forceful brain movement leads to tears in the brain's long connecting nerve cell fibers.

Other causes for DAI include:

• A fall
• A sports injury
• Child abuse, or shaken baby syndrome
• Physical abuse or a violent assault
• Blast injuries from explosions
  

Diagnosis

Healthcare providers use several tests to diagnose all types of TBIs, including DAIs. In most cases, several diagnostic tests can diagnose and form a treatment plan.

Imaging tests that can diagnose a DAI include:

• Computerized tomography (CT) scan: takes X-ray "slices" from many angles to create a complete brain image. It can quickly show whether the brain is bleeding, bruised, or has sustained other damage.
• Magnetic resonance imaging (MRI): MRI is the modality of choice for assessing a suspected DAI, even in patients with a normal CT scan. In recent years, MRI use in diagnoses and prognoses of DAI has increased.
  

Patients with a DAI are more commonly in a state of unconsciousness, at least for several hours. However, if a healthcare provider suspects a mild DAI or another type of brain injury and the patient is awake, they may perform a test called the Glasgow Coma Scale. The better the patient performs on the test, the higher the score and the less severe the DAI.

The healthcare provider gives this test to the patient and allows them to measure the patient's functioning in three areas:

• Eye-opening response
• Verbal response
• Motor response

A healthcare provider rates a person’s responses in these categories and calculates a score of 3–15 points. The better the patient performs on the test, the higher the score and the less severe the DAI. A lower score points to a lower chance of recovery.

Treatment

Treatment for DAIs focuses on reducing swelling using steroids. For mild to moderate DAIs, treatment is similar to that of a person with a concussion, with rest and rehabilitation. If a person is in a coma or vegetative state because of a more severe DAI, rehabilitation will be necessary to return to functioning. Treatment also helps prevent secondary injuries, which can be dangerous.

People who regain consciousness after a DAI require intensive rehabilitation, including:

• Physical therapy
• Occupational therapy
• Speech therapy
  
• Vocational counseling
• Cognitive therapy
• Psychological counseling

Depending on the severity of the DAI, individual treatment may be temporary or lifelong.

Prognosis

Tears in the brain from a DAI can be microscopic and cause brain damage, resulting in mild to moderate trauma that may heal over time. However, the tears from a DAI can also be large, which can be deadly.

The severity of a DAI's symptoms largely depends on the affected brain areas, the amount and size of tearing in the brain, and whether any other injuries, such as other traumatic brain injuries, also occurred. Brain damage may be temporary or permanent, and healthcare providers give prognoses individually.

Summary

A diffuse axonal injury is a type of TBI from a blunt injury that causes the brain to rotate and shift rapidly inside the skull. This rapid acceleration and deceleration motion leads to the shearing of the brain's long connecting nerve cell fibers. The Adams DAI classification system is one way that healthcare providers grade a DAI and determine overall severity: grade 1 (mild), grade 2 (moderate), and grade 3 (severe).

High-velocity motor vehicle accidents most commonly cause DAIs. However, they can also result from falls, sports injuries, child abuse, violent assault, or blast injuries from explosions. Healthcare providers use CT scans, MRIs, and the Glasgow Coma Scale to diagnose DAIs and form treatment plans.