• primary brain injury may be focal (contusion/haematoma) or diffuse (diffuse axonal injury)

• diffuse axonal injury occurs as a result of mechanical shearing following deceleration, causing disruption and tearing of axons

• intra-cranial haematomas can be extradural, subdural or intracerebral, while contusions may occur adjacent to (coup) or contralateral (contre-coup) to the side of impact

• secondary brain injury occurs when cerebral oedema, ischaemia, infection, tonsillar or tentorial herniation exacerbates the original injury. The normal cerebral auto regulatory processes are disrupted following trauma rendering the brain more susceptible to blood flow changes and hypoxia

• the Cushings reflex (hypertension and bradycardia) often occurs late and is usually a pre terminal event

• NICE pathway for adults attending ED with head injury:

Extradural bleed

Subdural bleed

Subarachnoid bleed

Intracerebral bleed

Intraventricular bleed

Investigations

CT head immediately if:

• GCS < 13 on initial assessment
• GCS < 15 at 2 hours post-injury
• suspected open or depressed skull fracture
• any sign of basal skull fracture (haemotympanum, 'panda' eyes, cerebrospinal fluid leakage from the ear or nose, Battle's sign).
• post-traumatic seizure.