A contusion or bruise is caused by a force or blow that damages or destroys blood vessels. Coup and contrecoup injuries are contusions resulting from a strong blow to the head, causing the brain to slam against the inside of the skull. Coup injuries are brain contusions occurring at the point of impact. Contrecoup injuries result when the brain impacts the side of the skull opposite the point of impact. Many blows to the head result in damage to the brain on opposite sides of the head. This is a specific type of closed-head injury and occurs when the force impacting the head is not only great enough to cause a contusion at the site of impact, but also is able to move the brain and cause it to slam into the opposite side of the skull, which causes the additional contusion.
The telling and defining feature of the coup-contrecoup injury is damage to the brain on opposite sides: the side that received the initial impact (coup) or blow and the side opposite the initial impact (contrecoup). This occurs when the force of the initial blow is great enough to cause brain damage at the site of initial impact between the skull and brain and is also great enough to cause the brain to move in the opposite direction and hit the opposite side of the skull, causing damage at that site.
The brain is less dense than the cerebrospinal fluid (CSF), and one idea is that upon skull impact, the denser CSF moves toward the site of skull impact pushing the brain in the opposite direction, and into the skull.
Coup-contrecoup injuries can be caused by automobile accidents, or abusive or violent events (such as violently shaking a baby). Coup-contrecoup injuries often cause additional complications such as hematomas (brain bleeding), brain swelling, disruptions to the flow of cerebrospinal fluid (which surrounds, protects, and nourishes the brain), and problems with skull fragments compressing or entering brain tissue.
Frontal (behind the forehead) and temporal lobe (underneath the temples) are the most common form of coup-contrecoup injuries, resulting in problems with making decisions, and speaking and understanding language. Other symptoms of coup-contrecoup injuries depend on the specific brain structures that are injured and can include impaired concentration, memory, swallowing, balance and coordination; muscle weakness or paralysis; and sensory changes. The damage caused by coup-contrecoup injuries is usually irreversible, so treatment is designed to prevent further damage by addressing associated medical conditions. In some cases, neurosurgery or medications may be used to decrease brain bleeding or brain swelling.