Alex Hill of Green Island School asks :-

Why does your brain swell when you break your skull?

Robin Fraser, a retired pathologist at the Otago University School of Medicine in Christchurch, responded.

The brain is a soft organ with a huge blood supply with many tiny capillaries taking oxygen and nutriment to multiple highly active brain cells. Any bump or trauma may make those capillaries leaky with blood or fluid entering the soft surroundings.

The brain is contained by the rigid skull, cranium or brain-box so that any leaking leads to a rapid rise in pressure. If the brain is slightly smaller than the cranial cavity before the trauma (as in old age or alcoholism) it is more mobile, and blood vessels from the bones to the "skin" of the brain (dura or meninges) may tear and a real haemorrhage occurs which rapidly increases in volume. This is know as an extradural (more common in skull fracture) or sub-dural haematoma or large collection of blood. A burr hole in the overlying skull is urgently required to release the pressure.

The terrible danger of raised intra-cranial haemorrhage is that the pressure pushes the brain through the tight openings of the brain box, thus causing herniation of the brain which presses on the mid-brain with its heart and breathing centres, leading to sudden death.

Another problem of brain trauma is concussion or temporary loss of consciousness. Following this the airways may be kinked and the oxygen in the blood will fall, and the carbon dioxide builds up. This makes the vessels in the brain dilate, up goes the intra-cranial pressure and a vicious cycle develops with death. A good airway in the "recovery" position is essential in a person with head injury.