Traumatic brain injury from accidents, falls and violent attacks is the leading cause of death and disability amongst young adults, and it is a growing problem amongst older people, too. So what actually happens inside your skull when you have a traumatic brain injury? We asked leading expert Professor David Menon from the University of Cambridge in the UK.
"What most lay people think about is if you have a traumatic brain injury you have a bang on the side of your head, there's a local injury to the skull, and maybe the underlying brain is injured. That does happen, particularly if there's a fracture of the skull, and the skull is driven into the brain. But that's unusual," says Menon.
He adds: "The two sorts of things that are much more common is that with high velocity injuries the brain is moving and the skull is moving, and then when the skull impacts something it stops moving. But the brain continues to move and hits it, the inside of the skull. The inside of the skull tends to be very rigid, and has sharp points on it, so that movement against the inside surface of the skull can cause bruising of the surface of the brain, what we call a contusion. It can also cause tearing of blood vessels and cause bleeding on the surface of the brain or inside the brain. Now all of these are abnormalities we can see on Cat scans, the routine scans that we get when patients come in."
Menon concludes by saying: "The third kind of injury can be a hidden kind of injury on conventional scanners. And that is a tearing of nerve fibres. So all the nerve fibres that come up from the spinal cord and go into the brain and fan out into the brain, and similarly all the nerve fibres that come down from the brain and go into the spinal cord, are individual stalks that are coming down. When there's a rapid acceleration, or deceleration, when the brain suddenly starts moving and stops moving, then these can tear, and cause what we call traumatic axonal injuries. So the axon is the nerve fibre. Those are not picked up easily on Cat scans. They show up on MRI, either directly or because of the blood vessels that tear alongside, and they are probably the most important cause of severe disability."