What are coup and contrecoup injuries?
In brain trauma, a coup injury (pronounced coo) occurs on the side of the brain where it initially impacts the inner skull. A contrecoup injury (pronounced contra coo) occurs on the opposite side of the brain from where the coup injury happened and is the result of the brain recoiling from the original coup injury. Inertia forces to the head play a role in this type of injury. Coup and contrecoup injuries can occur individually or together.
When they occur together, they constitute a coup contrecoup (pronounced coo contra coo) brain injury. These terms refer to the mechanism of injury. In other words, they are used to describe how particular sites within the brain become injured during a traumatic event and are not descriptive of injury classification or degree.
Coup and contrecoup injuries are considered “focal” brain injuries (those that occur in a specific spot in the brain) and non-penetrating but can cause a wider area of damage when diffuse axonal injury (DAI) is involved. Most brain injuries are the result of contact with outside objects, meaning something encounters the head. There does not have to be a head impact, however, for a coup contrecoup injury to occur. Shaken babies, for example, can have these injuries even if the head is never struck by or contacts an object. The movement of the brain within the skull is enough to cause the injuries.
As a simple example of coup and contrecoup injuries, imagine shaking ice cubes in a glass. If you shake the glass hard enough, you can make the ice cubes hit both sides of the glass with one sharp movement of your hand. The ice impacts the first side of the glass hard enough to bounce and hit the other side of the glass. The same is true of the brain during a traumatic injury. The brain is the ice cubes and the skull is the glass.