Cerebral injury

Head injury may lead to a brief loss of consciousness without associated pathological changes in the brain. The mechanism for the loss of consciousness is not clear.

With more severe head injury, brain damage can occur because of the direct trauma to the brain. This arises from direct disruption of the brain, shearing of axons and intracerebral haemorrhage. These injuries occur at the site of trauma and opposite the site of injury, so-called contre-coup injury. Contre-coup injury results from acceleration/deceleration forces moving the brain within the skull.

There may be secondary brain injury (Fig. 1) due to brain oedema, which causes raised intracranial pressure and can lead to cerebral herniation (p. 48). The raised intracranial pressure, usually associated with hypotension, leads to hypoperfusion of the brain and therefore cerebral ischaemia. Infratentorial lesions can obstruct CSF flow and lead to hydrocephalus.

Fig. 1 Mechanisms of secondary head injury.

Intracranial haematomas

Extradural haematomas occur when the middle meningeal artery bleeds into the extradural space (Fig. 2). This can occur some time after the head injury and should be considered in any patient with deterioration following an apparently good recovery from a head injury.

Fig. 2 CT scan showing an extradural haematoma (arrow) and intracranial haemorrhage (double arrow).

Subdural haematomas occur either acutely, usually with some intracerebral bleeding, or chronically (Fig. 3). The latter occurs when damaged cortical veins ooze into the subdural space.

Fig. 3 CT scan showing a subdural haematoma (arrow) producing some mass effect with displacement of the midline structures.

Intracerebral haematomas (Fig. 2) are the most common, occurring both at the site of direct trauma and at the contre-coup site.

The mass effect of any of these bleeds may lead to cerebral herniation.

Skull fractures

These can be divided into simple and depressed fractures and basal skull fractures. The latter are difficult to see on skull X-rays but are associated with particular physical signs such as periorbital bruising or Battle’s sign (Fig. 4

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