Brain Contusions—Coup and Contrecoup Injuries
A brain contusion on the same side of the head as the surface impact site (abrasions and lacerations) is referred to as a coup contusion. In the opposite pattern, called a contrecoup contusion, the brain injury, paradoxically, is on the opposite side of the head from the surface injury. As a rule, coup contusions occur when a moving object strikes the head. The kinetic energy of the moving object translates to the brain underlying the point of impact and causes contusion on that side of the brain. A windshield may be that moving object.
In contrast, a contrecoup contusion is typically caused by a moving head striking a non-moving object. This is because the movement of the head causes the brain to be pushed to the opposite side of the skull from the point of impact. Contusions in those cases occur on the opposite side of the brain from the impact site on the surface of the head.
Severe head injuries frequently, but not universally, produce rapid loss of consciousness. Conversely, even minor head injuries can cause immediate loss of consciousness, such as with sports-related concussions. This is because any impact injury to the head can cause force waves to travel through the very soft brain tissue and disrupt function in other areas. Nonetheless, the more severe an injury the more likely the risk of loss of consciousness.