There are several ways to describe brain injuries. The brain is enclosed in the bony vault of the skull. The cerebrospinal fluid surrounds the brain and, most of the time, protects it from impact with the skull. If there is a rapid force applied to the skull or rapid deceleration of the head, the brain may strike the inside of the bony vault.
Brain tissue may stretch or tear because of the rapid movement. This can injure the nervous tissue of the brain directly. If a projectile such as a bullet enters the skull, it can directly injure the brain.
Below is a list of terms and definitions that refer to the different injuries of TBI.
Closed Head Injury– the skull is intact and there is no penetration of the skull. Direct or indirect force to the head can cause this type of injury. This may be caused by rotational and/or deceleration in the case of both direct and indirect force.
Open Head Injury– penetration of the skull with direct injury to the head.
Diffuse Axonal Injury– diffuse cellular injury to the brain from rapid rotational movement. This is often seen in motor vehicle accidents or shaking injuries. The axons are the projections of the brains nerve cells that attach to other nerve cells. They are damaged or torn by the rapid deceleration. The injury is from the shearing force disrupting the axons which compose the white matter of the brain.
Contusion– a bruise to a part of the brain. Like a bruise on the body, this is bleeding into the tissue.
Penetrating Trauma– any object that enters the brain. Causes direct injury by impact and pushing skull fragments into the brain.
Secondary Injury– swelling and release of chemicals that promote inflammation and cell injury or death. This causes swelling in the brain which may increase the intracranial pressure and prevent the cerebrospinal fluid from draining out of the skull. This causes further increase in pressure and brain damage. If this is not controlled or prevented the brain can herniate (push through) the base of the skull and cause respiratory failure and death. The only way to prevent the primary injury is to prevent the trauma. The prevention of this secondary injury is the focus of the acute medical care after injury.
Secondary Injury Includes:
- Intracranial hemorrhage (bleeding inside the skull)
- Brain swelling
- Increased intracranial pressure (pressure inside the skull)
- Brain damage associated with lack of oxygen
- Infection inside the skull, common with penetrating trauma
- Chemical changes leading to cell death
- Increased fluid inside the skull (hydrocephalus)
Acquired Brain Injury– injuries other than congenital, birth trauma, hereditary or degenerative. This includes traumatic brain injury. In the non-traumatic types of acquired brain injury, the brain is usually diffusely injured. These injuries are usually not included in traumatic brain injury but the symptoms span the same spectrum.
Common causes are anoxia and hypoxia. These are lack of oxygen to the brain and insufficient oxygen to the brain. They can occur because of mechanical problems with breathing, with cardiac arrest or bleeding. Drugs and poisoning can also cause acquired traumatic brain injury. Carbon monoxide poisoning is an example of poisoning that may cause brain injury.