A traumatic brain injury (TBI) occurs when the head is subject to a sudden force, which causes damage to the brain. There need not be a fracture of the skull in order for a serious, or even fatal, brain injury to occur. This is true because of the anatomy of the brain.
While the brain sits inside the skull, it is not physically attached to the skull. Instead, the brain is enclosed within spinal fluid. Thus, if the head sustains a sudden blow, such as falling onto the floor or from striking a part of a motor vehicle, the skull itself may not fracture but the brain may be suddenly slammed against the side of skull. This can cause injury to the brain.
In addition, the brain may actually then “bounce back” against the skull and hit the opposite side of the skull, causing what doctors call a “contra coup” injury to the brain. A brain injury, which occurs when the head sustains an impact but the skull does not break, is called a “closed head injury.” Brain injuries also occur when an object penetrates the skull and enters the brain tissue. In addition to causing injury to the brain, a skull fracture may also allow infection to leak into the brain fluid, causing damage to the brain.
Brain injuries can result from injuries not only to the brain tissue itself but also the blood vessels within the brain.