Acquired Brain Injury Defined
An acquired brain injury (ABI) is an injury to the brain that is not hereditary, congenital, degenerative, or induced by birth trauma. The injury results in a change in neuronal activity, which affects the physical integrity, the metabolic activity, or the functional ability of nerve cells in the brain. An acquired brain injury is an injury to the brain that occurs after birth, where it is presumed there was normal brain development and the injury to the brain was subsequently acquired.
Acquired brain injury (ABI) is an umbrella definition as it includes injuries caused by external physical forces applied to the head, as well as internal insults to the brain. All of the injury causes and pathologies you see in this chart are included as Acquired Brain Injuries.
Three Types of Acquired Brain Injury
Traumatic Brain Injury (TBI)/Traumatic Impact
A traumatic brain injury (TBI) is an alteration in brain function, or other evidence of brain pathology, caused by an external force. With traumatic impact injuries the head is struck by an object or an object strikes the head resulting in either a:
- Open (penetrating) injury
- Closed injury
An open head injury is a penetrating brain injury involving a breach of the skull or breach of the meninges (so that an object penetrates the skull and enters the brain). This type of injury often results in focal injuries (such as epidural or subdural hematomas, or intracerebral hemorrhage). With penetrating injuries (such as a gunshot wound) a major complicating factor can be secondary infection due to the skull/meningeal breach.
Closed head injuries are focal or diffuse non-penetrating brain injuries. They can cause brain lacerations and contusions, or intracerebral hemorrhage within the brain causing focal injuries.
One type of closed head injury is the coup-contrecoup injury. Contusions or lacerations may occur directly beneath the point of impact (coup) and then occur contralateral (opposite side) to the site of impact (contrecoup).
The graphic above shows the head/brain moving forward (linear acceleration) and then striking an object (with rapid linear deceleration of the brain), resulting in frontal lobe focal lesions (this is coup); moving to the right in this graphic, you’ll see the rebound where the head/brain move backwards striking an object causing occipital lobe focal lesions (this is the contrecoup).
Diffuse Axonal Injury (DAI)
With closed head injuries, there can also be more diffuse injury resulting from tearing or shearing of axons, known as a diffuse axonal injury (DAI). DAI is the most common form of damage to the brain structure, resulting from axonal shearing (axons are twisted or disconnected) inhibiting neuron – to – neuron communication.
Non-Traumatic Brain Injury
Non-traumatic brain injuries include stroke, neurotoxic poisoning, hypoxia and anoxia, among others. Hypoxia and anoxia include a lack of oxygen that causes brain cells to die. When they die, they release chemicals that can cause further damage to the brain.