Brain injuries can be unusual in their presentation. There can be brain injuries due to a fracture of the skull but brain injuries are just as likely to happen in situations where the skull is not fractured. How does this happen? The brain is attached to the body by the brainstem and spinal cord at the base of the brain. The rest of the brain is loosely attached to the skull by means of blood vessels and a membrane around the brain, called the dura mater. These connections aren’t very secure.
When a brain injury happens, there are forces on the brain that cause the brain to slosh around in the skull, thus breaking the delicate blood vessels and causing bleeding around the brain. There can be bruising of the brain at the place of impact. This is called a coup injury and comes because of direct brain trauma to the brain.
There is another injury that is possible. This is called a contracoup injury to the brain and occurs directly opposite the coup injury. How does this occur? Imagine the brain is a ball tethered at the base. It is still wobbly but will not disconnect from the base. Striking the ball on one side causes it to push against the opposite side. This is what happens in a contracoup injury.
The end result is bleeding and swelling at two injury areas of the brain: the coup area and the contracoup area. Sometimes the contracoup area can be more significant than the coup area, making it difficult to know which is which.
One study looked at the patterns that occur in a contracoup injury as well as the prevalence of these types of injury. They looked particularly at fractures of the temporal bone with the assumption that the coup injury occurred at the site of the fracture. The study was a prospective study of all patients who sustained a traumatic brain injury at a major hospital in Malaysia. The study took place over an 18 month period of time. CT scans of the head were performed on all patients suspected of having a traumatic brain injury, based on the clinical findings and on the patient’s Glasgow Coma Scale. Patients who were discovered to have a traumatic brain injury were selected for the study and received additional CT scans of the head to look for Contracoup injury, which do not always show up right away. To be included in the study, the patient had to have a single temporal lobe fracture but not fractures on both sides.
The researchers looked for the presence of a contracoup injury along with its location, type, size, severity and outcome. They found 1579 patients with head injuries but only 81 of these met the criteria and had temporal bone fractures. The incidence of contracoup injuries with temporal fractures was found to be 13.6 percent. If the petrous temporal bone was fractured, the incidence of contracoup injuries was higher. The most common type of contracoup injury is a cerebral contusion. Other injuries included extradural hematoma and a subdural hematoma. The doctors concluded that contracoup injuries are not terribly rare and are especially associated with petrous temporal lobe fracture.