August 23, 2014

What are the Causes of TBI?

The number of people with Traumatic Brain Injury (TBI) is difficult to assess accurately but is much larger than most people would expect.  According to the CDC (United States Centers for Disease Control and Prevention), there are approximately 1.5 million people in the U.S. who suffer from a traumatic brain injury each year.  50,000 people die from TBI each year and 85,000 people suffer long term disabilities.  In the U.S., more than 5.3 million people live with disabilities caused by TBI.  Patients admitted to a hospital for TBI are included in this count, while those treated in an emergency room or doctor’s office are not counted.

The causes of TBI are diverse.  The top three causes are: car accident, firearms and falls.  Firearm injuries are often fatal: 9 out of 10 people die from their injuries.  Young adults and the elderly are the age groups at highest risk for TBI. Along with a traumatic brain injury, persons are also susceptible to spinal cord injuries which is another type of traumatic injury that can result out of vehicle crashes, firearms and falls. Prevention of TBI is the best approach since there is no cure.

Mechanisms of Injury

These mechanisms are the highest causes of brain injury: Open head Injury, Closed Head Injury, Deceleration Injuries, Chemical/Toxic, Hypoxia, Tumors, Infections and Stroke.

1. Open Head Injury

  • Results from bullet wounds, etc.
  • Largely focal damage
  • Penetration of the skull
  • Effects can be just as serious as closed brain injury

2. Closed Head Injury

  • Resulting from a slip and fall, motor vehicle crashes, etc.
  • Focal damage and diffuse damage to axons
  • Effects tend to be broad (diffuse)
  • No penetration to the skull

3. Deceleration Injuries (Diffuse Axonal Injury)

The skull is hard and inflexible while the brain is soft with the consistency of gelatin.  The brain is encased inside the skull.  During the movement of the skull through space (acceleration) and the rapid discontinuation of this action when the skull meets a stationary object (deceleration) causes the brain to move inside the skull.  The brain moves at a different rate than the skull because it is soft.  Different parts of the brain move at different speeds because of their relative lightness or heaviness.  The differential movement of the skull and the brain when the head is struck results in direct brain injury, due to diffuse axonal shearing, contusion and brain swelling.

Diffuse axonal shearing: when the brain is slammed back and forth inside the skull it is alternately compressed and stretched because of the gelatinous consistency.  The long, fragile axons of the  neurons (single nerve cells in the brain and spinal cord) are also compressed and stretched.  If the impact is strong enough, axons can be stretched until they are torn.  This is called axonal shearing.  When this happens, the neuron dies.  After a severe brain injury, there is massive axonal shearing and neuron death.

4. Chemical / Toxic

  • Also known as metabolic disorders
  • This occurs when harmful chemicals damage the neurons
  • Chemicals and toxins can include insecticides, solvents, carbon monoxide poisoning, lead poisoning, etc.

5. Hypoxia (Lack of Oxygen)

  • If the blood flow is depleted of oxygen, then irreversible brain injury can occur from anoxia (no oxygen) or hypoxia (reduced oxygen)
  • It may take only a few minutes for this to occur
  • This condition may be caused by heart attacks, respiratory failure, drops in blood pressure and a low oxygen environment
  • This type of brain injury can result in severe cognitive and memory deficits

6. Tumors

  • Tumors caused by cancer can grow on or over the brain
  • Tumors can cause brain injury by invading the spaces of the brain and causing direct damage
  • Damage can also result from pressure effects around an enlarged tumor
  • Surgical procedures to remove the tumor may also contribute to brain injury

7. Infections

  • The brain and surrounding membranes are very prone to infections if the special blood-brain protective system is breached
  • Viruses and bacteria can cause serious and life-threatening diseases of the brain (encephalitis) and meninges (meningitis)

8. Stroke

  • If blood flow is blocked through a cerebral vascular accident (stroke), cell death in the area deprived of blood will result
  • If there is bleeding in or over the brain (hemorrhage or hematoma) because of a tear in an artery or vein, loss of blood flow and injury to the brain tissue by the blood will also result in brain damage.