Head Injury - Disorders of consciousness and memory

Head Injury

Definition

Head injury is one of the most common causes of death and disability in young men, mainly due to road traffic accidents.

Incidence

Common; based on hospital attendances and admissions the incidence is ∼250 per 100,000 population.

Age

Young > old

Sex

M > F

Aetiology

The main aetiological causes of head injury are road traffic accidents and alcohol:

Non-penetrating trauma: As a result of acceleration/ deceleration to the head, rotational and shearing forces act on the brain.

Penetrating trauma: Penetration of the skull by an external object such as a bullet.

Pathophysiology

The pathology of head injury can be divided into two groups:

Primary brain damage:

i.            Cerebral contusions occur as the brain moves within the skull, causing bruising of the brain, particularly on the side of the trauma (coup lesion) and on the opposite side of the brain (contrecoup). Con-tusions heal by gliosis stained with haemosiderin.

ii.            Diffuse axonal injury due to shearing forces causing damage to cortical white matter tracts. Patients who survive such injury may have severe brain damage.

Secondary brain damage occurs after the initial trauma, and is the result of problems in maintaining blood and oxygen supply to the brain due to hypoxia (e.g. airway obstruction, respiratory failure) or mass effect from haematoma. The degree of secondary brain damage can be influenced by medical or surgical treatment, whereas primary brain damage occurs at the time of injury and therefore can only be influenced by other factors such as car design to reduce pedestrian injury. Following trauma, the brain is much more susceptible to hypoxia and hypotension due to disruption of autoregulation and impaired vascular supply.

Clinical features

In a mild injury the patient is stunned or dazed for a few seconds or minutes. Loss of consciousness is transient and following this the patient remains alert with no amnesia. In more severe injuries, there is persistent post-traumatic amnesia. Neurological signs including papilloedema (although rare) and any evidence of penetrating injury or skull fracture should be looked for. Patients may have other injuries depending on the nature of the accident or trauma. The Glasgow Coma Scale is used to assess the level of consciousness (see Table 7.10).

Macroscopy/microscopy

Early contusions appear as petechial haemorrhages. Over a period of several hours there is oozing of blood and the contusions become haemorrhagic with swelling of the brain. Petechial haemorrhage may occur in the corpus callosum and brain stem.

Axonal damage appears as swollen torn ends of the axon.

Complications

Short term: Vascular, e.g. meningeal artery tear, causing extradural haematoma, or dural vein tear causing a subdural haematoma. Subarachnoid and intracerebral haemorrhage may also occur. Headache, dizziness and depression are common after a head injury.

Long term:

·        Posttraumatic epilepsy.

·        Chronic traumatic encephalopathy (the punch drunk syndrome seen in professional boxers).

·        Benign positional vertigo.

·        Hydrocephalus.

Management

Resuscitation including intubation and ventilation as required. If neck injury is suspected, the patient should be immobilised until a spinal cord injury or unstable cervical spine has been excluded.

Assessment of the severity of coma by the Glasgow Coma Scale, and full neurological and general examination. The decision to admit for observation is based on the history and assessment at presentation. In these cases, it is important to continue at least hourly neurological observations (vital signs, GCS and pupillary sizes/responses). Osmotic diuretics such as mannitol may also be used to reduce brain oedema.

Investigations including routine investigations (FBC, U&Es and clotting) and a CT brain where indicated.

In severe cases initial management may include admission to intensive care for intracerebral pressure monitoring and management, e.g. with mannitol and diuretics.

All patients require close monitoring to check for development of complications that require urgent treatment. CT brain is urgently indicated if

·        level of consciousness depressed (A GCS score of <8 following resuscitation).

·        the GCS score falls despite initial management. presence of skull fractures.

·        the patient is difficult to assess, e.g. due to alcohol or drug intoxication.

Urgent neurosurgical assistance is required in the case of a depressed skull fracture, or expanding intracranial haemorrhage, particularly extradural haematomas or acute subdural haematomas.

Prognosis

Recovery may take weeks to months. Prolonged coma can still be followed by good recovery. 10 per 100,000 people die annually and the prevalence of survivors with a persisting disability or impairment is 100 per 100,000.