How Are Brain Contusions Different from Brain Concussions?
For a problem as pervasive as traumatic brain injury one would
think that the different forms it can take would be widely known
and understood. However, in my practice of community-based
neurology I find this is not the case. Patients and their
families are seldom familiar with the concepts of cerebral
(brain) contusion and concussion, and a common error is to
believe that they are basically the same, except that a
contusion is a more severe form of a concussion.
Before exploring the differences between these two terms, let's
first acknowledge how they are alike:
* Both are due to head trauma.
* Both are common.
* Both are serious.
But that's where the similarities end. The differences between
cerebral contusions and concussions can be boiled down to two
basic concepts:
* Contusions are localized, while concussions are widespread.
* Contusions are macroscopic, while concussions are microscopic.
To flesh out these concepts more fully we'll need to discuss
brain anatomy, brain physiology and brain-imaging technologies.
A contusion is a bruise. At one time or another everyone has
bruised himself or herself, as, for example, when they banged a
forearm against a hard object. This caused bleeding within or
beneath the skin. In the days following the injury it turned
purple and perhaps a variety of other colors as the body's
repair mechanisms degraded and absorbed the red blood cells that
had escaped from the injured blood vessels.
The same thing can happen to the brain, except that the bruises
are not located in a place the eye can see. However, with the
help of imaging technology the bruises (contusions) can be made
visible. To a close approximation, computed tomographic (CT)
scans and magnetic resonance (MR) scans can "see" a level of
detail corresponding to what the naked eye can see, except that
the information is presented like slices of a loaf of bread,
shown one slice at a time. "Macroscopic" means that the naked
eye can see the contusions (with the help of a scanner). If a
similar process occurs at a "microscopic" level, it is too small
for the eye (and scanner) to see.
CT scans are more useful than MR scans in evaluating patients
with acute brain trauma because seriously ill patients can be
better monitored while receiving CT scans and because fresh
hemorrhages are more apparent. In images created by CT scanners
fresh blood appears intensely white, while normal brain tissue
appears gray.
Although contusions can be multiple, they occur in single
locations. That's what "localized" implies. So a brain contusion
is both macroscopic and localized. One common pattern of
contusions is "coup-contrecoup." When a moving head is abruptly
stopped (as occurs during a fall when it strikes the ground) the
brain nearest the point of impact bashes against the inner
surface of the hard skull, producing a contusion. That is the
"coup" injury. But then there is either a bounce-back of the
brain within the skull or a suddenly created vacuum that
produces a second "contrecoup" contusion on the opposite pole of
the brain.
Contusions can occur in large enough numbers to produce a
"salt-and-pepper" appearance on CT scans. Adjacent contusions
can also coalesce via further oozing of blood to produce larger
blood-deposits. If a collection of blood becomes large enough to
compress and distort the rest of the brain, it might require
surgical removal.
It is important to realize that injury to brain tissue is not
limited to that produced by bleeding. The same physical blow
that disrupts blood vessels is also capable of damaging the
brain cells directly.
Now let's contrast these findings with what occurs in a cerebral
concussion. In a pure concussion there is no macroscopic,
localized collection of blood. Any bleeding that occurs is at a
scale that escapes detection by the eye (helped by the scanner).
In a concussion there is diffuse, widespread, homogeneous
impairment of brain tissue, but nothing that shows as a
macroscopic, localized abnormality on a scan.
In fact, it may not be fair to imply that even a microscope
could see the changes that occur in a concussion. Although in
severe concussions there can be a physical snapping-in-two of
axons (the long extensions that brain cells use to communicate
with each other) a concussion disrupts the physiology
(functioning) of brain cells more than their anatomy
(structure). That is, the trauma makes large numbers of brain
cells sick without actually killing them. While sick, the brain
cells under-perform. As a result, the victim of a concussion
might lose consciousness or become confused. Because emotions
are also produced by interactions among brain cells, the
concussed patient might show tearfulness, irritability or other
changes in behavior as a result of the injury.
While a person with traumatic brain injury might experience
contusion without concussion, or concussion without contusion,
having one does not preclude having the other, and it is common
for both to occur together. So while cerebral contusions and
concussions are different from each other, a victim of head
trauma might be unlucky enough to have both.
(C) 2005 by Gary Cordingley