Coup-Contra-coup
As stated earlier, the most common cause of closed head injury is
automobile accident which involves acceleration - deceleration injury to
the brain. As one can imagine, in automobile accidents, focal, multifocal,
and diffuse injury to brain tissue may occur. The type and extent of
damage will be directly related to the speed and direction of head
movements (linear or rotational acceleration) and the time and distance of
deceleration. The typical head on automobile accident results in the
individual's head moving forward and stopping (due to hitting the steering
wheel, dashboard, or windshield, or being restrained by the seatbelt and
airbag), and then, after stopping, moving backwards to land against the
headrest. In this scenario, the brain, in fact, moves forward within the
cranium and may rapidly impact against the irregular frontal and temporal
bones which can directly damage associated tissue through contusion
(bruising) or hemorrhage. After the skull and brain have terminated their
forward movement, the brain can bounce backward in the opposite directly
and impact (in this case) the occipital bone. This movement of the brain
inside the skull in the opposite direction of the first impact is referred
to as the contra coup effect. This opposite area of impact is referred to
as the contra coup site, which can in fact, result in as much or more
damage to brain tissue as the original site of impact. In automobile
accidents where the occupant may be thrown in several directions within the
vehicle, there may be multiple impact and contra coup sites. The secondary
effects of such closed head injuries may include hemorrhaging (bleeding)
which can occur intracerebrally from stress to the vascular system, or
hematomas (collections of blood typically noted between the skull and brain
associated with meningial tearing: subdural and epidural hematomas or
subarachnoid hemorrhage), and edema (swelling) of the brain.
Hemorrhage may cause brain tissue necrosis based upon lack of oxygen
saturation (ischemia), increased intracranial pressure (ICP), and the
direct toxic effect of blood on brain tissue when it is not confined to
arteries, vessels, and capillaries (it is treated as a foreign body in the
brain by the immune system). Edema also creates ICP which can also
directly effect brain tissue (which we will discuss later this semester:
Figure: Necrosis of Brain Tissue in the Inferior Frontal Lobes and Anterior Right Temporal Lobe
Secondary to Moderate Closed Head Injury with Hemorrhage