Introduction

Head injury can be defined as any alteration in mental or physical functioning related to a blow to the head. The most affected are young adults and societal cost is significant (emotional and financial), estimated at $25 billion per annum in the USA alone, excluding inpatient costs.

Classification

1. ▪ Neurological impairment: mild (GCS 14–15), moderate (GCS 9–13) or severe (GCS 3–8). See Trauma Scoring Systems Chapter for GCS.

2. ▪ Anatomical: focal (extradural, subdural and intra-cerebral haematoma) vs. diffuse (concussion, multiple contusions, diffuse axonal injury (DAI), hypoxic injury).

3. ▪ Mechanism: blunt vs. penetrating.

Incidence

180–220 cases per 100 000 population (US), approximately 600 000 each year. Of these 10% are fatal, 75% are minor, the remainder equally divided between moderate and severe. Males are affected more than females (2:1) and it is commoner in the under 35s.

Aetiology

Road accidents are the commonest cause. Also falls, occupational injuries, sports and leisure accidents. Violence and penetrating trauma increases in cities with a population >100 000.

Pathophysiology concepts

Monro-Kelly doctrine: total intra-cranial volume (1500 ml) is fixed due to the inelastic nature of the skull and is composed of brain (85–90%), blood (10%), and CSF (<3%). Cerebral oedema, haemorrhage, focal haematoma and hydrocephalus increase these components. An increase in one of these compartments will require a compensatory decrease in the others in order to maintain intracranial pressure (ICP). Normal ICP=10–15 mmHg. At the point where the compensatory mechanisms are exhausted, ICP exponentially rises (see Figure 21).