Types of brain injury

Brain injuries can be classified as either closed (diffuse) or open (penetrating).

Closed (diffuse) injuries are the most common and happen when violent forces cause the brain to be shaken about inside the skull, causing in either case 'diffuse axonal damage' or even physical damage to the brain in contact with the inside of the skull; for example, in a bad car crash the head may hit the windscreen or the dashboard.

It is not necessary for the skull to actually hit anything for this type of damage to be sustained.

Primary brain injury results from the mechanical effect of forces applied to the skull and brain. Secondary damage is caused by complications of the primary injury (such as raised intracranial pressure, blood clots, low blood pressure and lack of oxygen). Many very severe brain injuries are caused without damage to the skull.

Open (penetrating) injuries or fractures are usually caused by a blunt or sharp trauma or crushing. Such injuries, by their nature, are usually identified at an early stage.

The presence or absence of a fracture is not a reliable indication to what is called 'outcome'; some people recover well despite serious fracture; likewise there can be a crippling disability caused by trauma which does not fracture the skull. It is not even enough to ask whether there has been a severe blow to the head, because it is quite possible for serious injury to the brain to result from an acceleration/deceleration injury (sometimes called a 'contre coup' injury).

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