The contrecoup-coup phenomenon: a new understanding of the mechanism of closed head injury.

A common observation in closed head injuries is the contrecoup brain injury. As the in vivo brain is less dense than the cerebrospinal fluid (CSF), one hypothesis explaining this observation is that upon skull impact, the denser CSF moves toward the site of skull impact displacing the brain in the opposite direction, such that the initial impact of the brain parenchyma is at the contrecoup location. A simple model was developed consisting of a balloon filled with water of density 1.00 g/mL enclosed in a clear plastic jar containing salt water of density 1.04 g/mL, simulating the same relative densities of the CSF and brain. The initial movement of the balloon, modeling the brain, was toward the contrecoup location with subsequent movement toward the coup location. The pattern of brain injury in which the contrecoup injury is greater than the coup injury is a result of initial movement of the brain in the contrecoup location. During the process of closed head injury, the brain parenchyma is initially displaced away from the site of skull impact and toward the contrecoup site resulting in the more severe brain contusion.