Head injuries are very common with over 15000 hospital admissions in the UK each year

All ages are affected, with mode of injury varying from simple falls (22-43%), sporting injuries, to road traffic accidents (25%), and assaults (30-50%).

Alcohol is involved in 65% of cases.

Classification may be by:

Mechanism of injury: blunt, penetrating

Severity of injury: mild, moderate, severe by GCS (Glasgow Coma Scale)

Lesion type: Extradural haematoma (EDH), Acute Subdural haematoma (ASDH), and Diffuse Axonal Injury (DAI).

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The Monro Kellie Doctrine 

The skull has a fixed capacity

Its contents are: brain, CSF, intravascular blood, space occupying haematoma with swelling

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Outcome is usually recorded at 1y. Unfortunately even initially mild injuries can have poor outcomes.

This is a very dangerous condition, associated with head injury. It commonly affects older patients. Risk factors include alcohol, and anticoagulant medication. Following the head injury, there may be headache and vomiting, with a slow deterioration into coma as the clot volume increases exerting pressure on the brain. Sometimes there is coma from outset, indicative of a significant primary brain injury. The prognosis is much worse than in EDH. This injury results in a driving suspension. 

Surgery usually requires a much bigger opening in the skull (craniotomy), the dura is opened widely, and the clot washed out. If a bleeding point is identified, this can be coagulated. Sometimes, especially if the brain is swollen, the bone flap may not be replaced at the end (ie decompressive craniectomy). In these cases, if recovery is good enough the skull defect may be repaired subsequently (cranioplasty)

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EDH are almost always a consequence of significant trauma - with a skull fracture. Most are due to meningeal artery laceration from the fractured bone. There is typically a "lucid interval" - meaning that there is initial loss of consciousness from the impact, then recovery, before a deterioration to drowsiness or coma from the pressure from the developing blood clot. A pure EDH is not associated with underlying brain injury - so prognosis is good.

Minimising the time to surgery is crucial. Delays to recognition and surgery can result in a secondary brain injury, which worsens outcome.

In older people, the dura mater is fiercely adherent to the inner surface of the skull, so significant EDH are rare.

Rarely a skull fracture can result in a tear of a dural venous sinus - this can result in EDH in 2 separate compartments.

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Diffuse brain (axonal) injury is a devastating condition following head injury. It is a consequence of the brain shaking within the skull. Bruising occurs due to shear forces. Bruising can evolve into blood clots. There may be swelling around these injured ares, leading to increased pressure within the skull, and secondary brain injury.

Autoregulation is a feature of healthy brain - reflecting its ability to take whatever oxygen and nutrients it needs from the blood, independent of the blood flow. Injured brain loses its capacity to autoregulate. 

Measurement of intracranial pressure allows for interventions to lower the pressure back towards normal, and cerebral perfusion pressure may be maintained.

Simple measures include maintaining adequate blood pressure and oxygenation, and avoiding venous congestion, by appropriate use of positioning and judicious use of cervical collars.

Surgical interventions include clot evacuation, CSF drainage, and decompresssive craniectomy  to reduce high pressures.