How Are Brain Contusions Different
from Brain Concussions?


Gary E Cordingley, MD, PhD
Head trauma can damage brain tissue in more than one way. Two types
of brain injury are contusion and concussion, but--contrary to popular
belief--one is not just a worse version of the other.
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