Making a Difference #3: The Mechanics of Injury

From skull fractures to focal sheer injuries, brain injuries can have significantly different outcomes.

[Module 3: The Mechanics of Injury] [♪music♪] What I'd like to talk to you about now is how the brain is injured. There are 4 primary ways that the brain can be injured: a skull fracture, a contusion from a coup or contra-coup injury, a diffuse axonal injury (DAI), or a focal shear injury. A skull fracture is exactly what it sounds like. You are actually fracturing or breaking the skull, which is the bony covering over the brain and actually protects the brain. Unfortunately, when the skull is fractured, what can happen is that small pieces of bone can be embedded into the brain, and this will cause great injury to that area. Another way that you can sustain an injury to your brain is called a coup-contracoup injury. This type of injury frequently occurs when you have a car accident. When you have a car accident and you stop suddenly, you are usually thrown forward. At this point in time, your head can hit the dashboard, and you would typically think that this is where the injury would occur; and there is damage to the brain at that point, but the other thing that happens is then your head is thrown back, and your brain is then pushed back to the back part of the skull, and as a result of your brain hitting that back part of the skull: it sustains another injury. So coup is when you hit something and contra-coup is an injury at the opposite end of the brain. Another type of injury is called a diffuse axonal injury (DAI), and this also frequently occurs as a result of car accidents. What happens in this type of injury is that the brain is rotating inside the head and as a result of these rotational forces, it's causing stretching and snapping of axons in the brain, and axons are the part of the brain that send messages everywhere, so it is as though you were to go into a computer and snip a wire, and therefore, the information could not get through from point A to point B. Well, in diffuse axonal injury, these types of shearing and tearing of axons is occurring all over the brain, and that's what we mean by "diffuse." In a focal shear injury, this is when there is rupture of the axons around a particular area that has been injured, and this can continue to occur after the injury has happened. In addition to these types of injuries that occur by actual forces on the brain, there are different types of injuries, or what we call secondary injuries that occur. Those three types of injuries are cerebral edema, hydrocephalus, and hematomas. In cerebral edema, what is happening is that the brain is swelling, and as a result, there is no room in the skull for the brain and so it begins to compress brain tissue. In hydrocephalus, the area of the brain which houses the cerebro-spinal fluid-- which are the ventricles--begin to enlarge, and this area is in the center of the brain. What is happening is that cerebro-spinal fluid cannot drain out of the brain for some reason, and it begins to collect in the ventricles and these begin to enlarge and once again, tissue is squeezed because there's not enough room in the brain for this type of swelling to occur. Another type of injury is the hematoma. When we think about a hematoma, what we think about is bleeding, and this is caused by bleeding in the brain. And once this blood is released, it can cover the brain and it can not only cause pressure in the brain, but the contact of the blood with the brain tissue will also cause injury. In terms of brain damage, many people often confuse a stroke with a traumatic brain injury (TBI). Let me explain the difference to you. In a stroke, there is a single discrete area of the brain that is affected and the damage to that area of the brain is complete. Strokes can be caused by either a blockage of a blood vessel-- which is the most common type of stroke-- or a rupture of a blood vessel such as an aneurysm. In this type of injury, then, the blood is released into the brain. In a traumatic brain injury (TBI), the injury usually occurs to the entire brain and it can be diffuse and global. In addition to the diffuse injury, you can have damage to scattered neurons and there are also focal injuries due to bruising and bleeding in localized areas. In a stroke, patients whose stroke was due to the same blood vessel damage will have similar problems. Those two patients will look very much alike. In brain injury, however, diffuse injuries vary greatly from one individual to the next, so no two traumatic brain injury survivors will be exactly alike. Some similarities may be related to the frequency of frontal lobe injuries which happen quite a bit in car accidents. But the types of difficulties that people can suffer and the types of affects that you will see after the injury may be very, very different even though people have sustained a similar injury. [Fact] [♪music♪] It's unfortunate, but in Texas, more than 442,000 people are living with a disability as a result of a traumatic brain injury. That is about 2% of the population of the state. [End of Module 3]
Posted on BrainLine April 8, 2011.

Produced by Texas Department of State Health Services and the Texas Traumatic Brain Injury Advisory Council.