Types of TBI
Early Brain Injury
Early brain injury, or early complications of a head injury, can be diffuse or focal.
Diffuse injuries are characterized by microscopic damage throughout many areas of the brain. Forces exerted on the brain tissues cause damage to the axonsthe "wires" that enable nerve cells to communicate with each other.
A focal brain injury is confined to a specific area of the brain and causes localized damage that can often be detected with a CT scan or x-ray.
Diffuse Axonal Injury
A diffuse axonal injury (DAI) causes shearing of large nerve fibers and stretching of blood vessels in many areas of the brain. In addition to bleeding (hemorrhage), this type of injury can trigger a biochemical cascade of toxic substances in the brain during the days following the initial injury.
DAI occurs throughout the brain, and the frontal and temporal lobes are particularly susceptible. The most prominent manifestation of DAI is impaired cognitive function, resulting in
- impaired memory, and
- varying degrees of inattentiveness.
DAI also can occur in relatively small, but important, nerve centers (or white matter tracts) causing visual field loss or weakness on one side of the body.
Hypoxic-ischemic injury (HII) causes swelling in the brain that restricts the flow of blood-borne oxygen, glucose, and other nutrients. These injuries can be exacerbated by other injuries to the body that further reduce the amount of oxygen entering the bloodstream through the lungs.
Patients with HII and DAI face a poor prognosis and typically experience memory impairment and reduced cognitive function.
Focal Brain Injuries
Focal contusions are bruises that cause swelling, bleeding, and destruction of brain tissue. They typically occur in the frontal and temporal lobes, where memory and behavior centers are located. Less often, they occur in the parietal and occipital lobes. Tiny contusions in the brainstem can interfere with the muscles that control eye movement, resulting in double vision (diplopia).
Symptoms of brain contusion include the following:
- Abnormal sensations
- Behavior impairment
- Loss of some or all vision
- Loss of coordination, weakness (less common)
- Memory impairment
Contusions shrink as swelling diminishes but can leave scars in brain tissue that cause permanent neurological impairment.