Traumatic brain injury (TBI) refers to damage or destruction
of brain tissue due to a blow to the head, resulting from an assault,
a car accident, a gunshot wound, a fall or the like. The damage to
the brain associated with the two types of injury that occur -- closed
head injury and open head injury -- is discussed below. It is important
to understand this, as the brain area that is injured and the extensiveness
of injury help predict the type of long-term effects that will emerge
in the lives of persons with TBI.
In closed head injury, damage occurs because
in the car accident (or fall or the like) the person receives a blow
to the head, which whips the head forward and back or from side to
side, causing the brain to collide at high velocity with the bony
skull in which it is housed. This jarring bruises brain tissue and
tears blood vessels, particularly where the inside surface of the
skull is rough and uneven; damage occurs at (and sometimes opposite)
the point of impact.
Thus, specific areas of the brain -- most often the frontal and temporal
lobes -- are damaged as a result of this harsh shaking/rotating of
the gelatinous brain tissue within its jagged casing and the subsequent
bleeding/swelling within the brain. This focal damage often
can be detected through MRI and CAT scans.
In closed head injury, the rapid movement of the brain
can also stretch and injure neuronal axons -- the long thread-like
arms of nerve cells in the brain that link cells to one another, that
link various parts of the brain to each other and that link the brain
to the rest of the body.
This diffuse axonal injury interrupts functional communication within
and between various brain regions and sometimes between the brain
and other body parts. However, this type of diffuse damage cannot be detected through currently available imaging technology.
It's existence is very clear, however, in the wide-spread effects
it has on the individual's functioning.
In sum, after a closed head injury, damage can occur
both in specific brain areas (due to bruising and bleeding) and also
be diffused throughout the brain (due to stretched or destroyed axons).
The results of a closed head injury tend to affect broad areas of
the individual's functioning, primarily due to the diffuse axonal
injury.
The extent of damage is correlated with the force of the blow to the
head; for example, a head forced into a car windshield at high speed
will tend to sustain more tissue damage than when the car is travelling
at a slower speed, all other factors being held constant. Finally,
as the name implies, a closed head injury involves no penetration
of the individual's skull.
Open head injury, the second type of TBI, occurs
when the skull is penetrated, for example by a bullet. Damage
following open head injuries tends to be focal, not diffuse, and the
implications for subsequent impairment tend, also, to be focal and
limited. However, such injuries can be as severe as closed head injuries,
depending on the destructive path of the bullet or other invasive
object within the brain.
Wayne Gordon, Ph.D.
Chief Psychologist and Coordinator of Research
Professor, Department of Rehabilitation Medicine
Mount Sinai Medical Center
New York, NY
