This section talks about some of the things that can happen inside the head during and after a brain injury. This section has been written with the assistance of Headway.
We hope to have presented this information in a sensitive manner, but we feel it’s sensible to let you know that the physical processes involved can sometimes make for uncomfortable reading.
If you’re not ready to read on just yet, then this information will be waiting for you when you are.
What happens during a traumatic brain injury?
Traumatic brain injury is caused by an outside force – some kind of blow to the head (read about non-traumatic brain injuries here). There are three types of these injuries:
- Closed head injuries
- Open or penetrating injuries
- Crushing injuries.
Closed head injuries
These are the most common kind of head injuries. The ‘closed’ means simply that there isn’t a break in the skull, and the brain is not exposed. An example might be a collision in a car, where the car stops very suddenly. As the whole body is jolted, the head moves back and forth and the brain bumps around inside the skull.
These collisions taking place inside the head can mean many parts of the brain are affected. This more widespread damage is called diffuse brain injury. Bony ridges inside the skull cause further damage when these collisions take place.
Open or penetrating injuries
These injuries are less common. The ‘open’ means that the skull is cracked and the brain is exposed. This might have happened in some kind of collision or impact. Other reasons for this kind of injury might be a great force, such as an explosion or a gunshot wound. In some circumstances, these kinds of injuries are combined with the rapid deceleration described in ‘closed head injuries’ above.
These are the least common kind of traumatic brain injury (TBI). As the title of the category suggests, these happen when the head is caught between two hard objects. Usually, the skull and the nerve cells of the brain stem are damaged in this kind of injury.
Some severe brain injuries can be a series of events
However it has happened, the first impact to the head may be the start of a chain of events rather than a single incident.
If we think of a blow to the head as the first injury to the brain, then there can sometimes be a second injury. This second injury can happen if the brain doesn’t get the oxygen it needs, perhaps because of blood loss or a blocked airway after an accident.1
There may be other difficulties. The brain responds to injury in the same way the rest of our body does. There may be bleeding, bruising or swelling, and these things can complicate treatment.
What do doctors mean when they talk about intracranial pressure?2
The problem with swelling or bleeding in the brain is that there isn’t any room for it. The skull is a solid box, almost fixed in size when we get past 18 months old.3 When the brain swells or bleeds the result is that there is more pressure inside this solid box.
This is raised intracranial pressure. If there is more fluid in this small space, it can push on the brain and cause damage.4 Intracranial pressure may also lead to other complications.
The flow of blood around the brain might be interrupted. Cerebrospinal fluid – the nourishing liquid which flows around the brain – may also be affected.5
Doctors will monitor intracranial pressure closely6, and there are measures they can take to control it.
A ventilator can help increase the flow of oxygen to the brain. Alternatively, doctors might control the amount of water and salts going into the body to prevent too much fluid being present in the brain.
If this intracranial pressure builds and becomes too high, doctors may attempt to bring it down. This might take the form of draining some fluid from the brain, or in some circumstances, removing a piece of the skull (known as a bone flap) to relieve the pressure.
A ‘shunt’ may also be used. This is where a catheter (a small tube) is used to drain cerebrospinal fluid from the brain into another part of the body. The aim is to lower pressure in the head. In some circumstances, doctors may choose to 'deeply sedate'.
This is where a coma is induced with the aim of reducing stress to the child and managing the intracranial pressure.