Traumatic brain injury: definition and causes

Traumatic brain injury (TBI) is damage to the brain as a consequence of external blunt force or penetrating trauma to the head.  As a result, the injured person experiences impairments in one or more of the following areas: physical impairments; cognitive impairments; or behavioral-emotional impairments.
These impairments can be temporary or permanent, and can leave the victim partially or totally disabled.


TBI can occur after a host of situations including motor vehicle accidents, sports injuries, gunshot wounds, explosions, and falls. A blow to the head, the head striking an object, or the rapid acceleration and deceleration of the brain in a whiplash type injury are the major causes. In each of these events, the brain can be injured by direct impact of the head with another object, like the head rest, windshield or airbag, or the brain can be injured when the head is shaken violently and the brain moves, twists, and stretches inside of the skull damaging brain cells.

Although the skull protects the brain from being crushed by outside forces, the skull itself can contribute to brain injuries when the head hits an object or is shaken. The brain is a soft organ with the consistency of soft butter.  Brain damage can occur from the contact of the soft brain with the sharp interior of the skull at the side of the initial contact and at the opposite side of the brain, as the brain rebounds back and forth like water sloshing in a shallow pan. This movement of the brain within the skull is commonly referred to as “coup” and “contracoup.”

Once the brain is jarred against the inside of the skull, nerves in the brain become stretched or deformed, which can lead to organic changes that interfere with the brain’s normal functioning.

Contrary to common beliefs, doctors generally agree that:

  • A person need not have been rendered unconscious in order to sustain TBI.
  • A person need not have struck his or her head in order to sustain TBI.
  • X-rays, CT scans, MRI exam or EEG studies do not always reveal TBI.
  • A person may have a brain injury that was not diagnosed when he or she was treated in the hospital after an accident.


Causes of brain injury other than trauma

The brain can be injured by circumstances other than a blow or shaking.  Although not technically traumatic brain injury, the brain can be injured by oxygen deprivation (“hypoxic” or “anoxic” brain damage) or exposure to chemical neurotoxins that kill brain cells. Such injuries can be caused by anesthesia errors during surgery, obstetrical errors during labor and delivery, and errors in prescribing or dispensing medications, for example.