Coup contrecoup injury

In head injury, a coup injury occurs under the site of impact with an object, and a contrecoup injury occurs on the side opposite the area that was hit. Coup and contrecoup injuries are associated with cerebral contusions, a type of traumatic brain injury in which the brain is bruised. Coup and contrecoup injuries can occur individually or together. When a moving object impacts the stationary head, coup injuries are typical, while contrecoup injuries are produced when the moving head strikes a stationary object.

Coup and contrecoup injuries are considered focal brain injuries, those that occur in a particular spot in the brain, as opposed to diffuse injuries, which occur over a more widespread area.

The exact mechanism for the injuries, especially contrecoup injuries, is a subject of much debate. In general, they involve an abrupt deceleration of the head, causing the brain to collide with the inside of the skull. It is likely that inertia is involved in the injuries, e.g. when the brain keeps moving after the skull is stopped by a fixed object or when the brain remains still after the skull is accelerated by an impact with a moving object. Additionally, movement of cerebrospinal fluid following a trauma may play a role in the injury.

Coup injury may be caused when, during an impact, the skull is temporarily bent inward and impacts the brain. When the skull bends inward, it may set the brain into motion, causing it to collide with the opposite side of the skull; this will result in a contrecoup injury. The injuries can also be caused solely by acceleration or deceleration, in the absence of an impact. In injuries associated with acceleration or deceleration but with no impact, the brain is thought to bounce off the inside of the skull and hit the opposite side, potentially resulting in both coup and contrecoup injuries. In addition to the skull, the brain may also impact the tentorium, causing a coup injury. Contrecoup injury may be produced by tensile forces.

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