Head injury

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Contents 1 Definition 2 Incidence 3 Classification 4 Principles 4.1 Cerebral perfusion 4.2 Intracranial pressure 5 Types of Brain Injury 5.1 Diffuse Brain Injury 5.2 Focal Brain Injury 6 Immediate management of head injured patients 6.1 Primary Survey 6.2 Secondary Survey 6.3 Investigation 6.4 Brain 6.4.1 Indications for immediate CT head (imaging and results analysed within 1 hour of request for CT): 6.4.2 Indications for CT head within 8 hours (immediate if patient presents 8 hours or more after injury): 6.5 Cervical spine 6.5.1 Indications for immediate CT neck: 7 References

Definition

A head injury is defined as any trauma to the head, which may or may not include trauma to the brain.

For the purposes of this article, the emphasis is on head injury involving the brain.

Incidence

The number of patients attending Emergency Departments in England and Wales is estimated at 700,000 per annum^[1]. It is also estimated that about 114,000 will be admitted for observation (of which 72% are male, and 30% are under 15 years of age). The number of patients requiring neurosurgery after head injury is quoted as 4,000 per annum for the UK^[2], and about 0.2% of patients attending Emergency Departments with head injury will die^[3]. In the context of trauma patients as a whole, head injury accounts for about 50% of all trauma deaths.

Classification

Head injured patients can be broadly classified according to their conscious level, as determined by using the Glasgow Coma Scale (GCS):

Severe head injury	GCS ≤ 8*
Moderate head injury	GCS 9-12
Minor head injury	GCS 13-15

* after initial resuscitation

Of patients attending Emergency Departments with head injury, about 90% will be minor; the majority of fatalities occur in the 10% of patients presenting with moderate or severe head injuries.

It should be noted that the severity of head injury cannot be determined until initial resuscitation has been performed, as the presence of hypovolaemia, hypoxia and/or hypo- or hyperglycaemia can alter the conscious level.

Principles

Brain injury can be further categorised into primary and secondary brain injury. Primary brain injury occurs at the time of the trauma, and consequently cannot be influenced by medical care after the event. Secondary brain injury occurs after the trauma, due to further insult to the brain. This most commonly occurs due to hypoperfusion of the brain, by hypoxaemia in the presence of normal perfusion, or by a combination of the two. It should be remembered, therefore, that secondary brain injury can occur in any trauma patient, regardless of whether or not their initial injuries involved the head.

Cerebral perfusion

The perfusion of the brain is dependent on the systemic blood pressure and the intracranial pressure, in the following way:

Cerebral perfusion pressure = Mean arterial pressure – Intracranial pressure

Consequently, a reduction in the systemic blood pressure or an increase in the intracranial pressure will cause a reduction in cerebral perfusion. Medical management of head injured patients is therefore aimed at maintaining systemic blood pressure by fluid resuscitation and avoidance of increased intracranial pressure.

In addition, the oxygenation of the blood reaching the brain must be maintained. Generally, the use of high flow oxygen is therefore recommended, and other measures such as mechanical ventilation should be instituted quickly if the patient cannot maintain adequate oxygenation.

Intracranial pressure

Intracranial pressure can become raised in head injured patients due to an increase in the volume of the brain (cerebral oedema) or blood within the cranium (intracranial bleed). Initially, in either of these cases the pressure within the cranium is maintained by outflow of blood from venous sinuses and CSF from the subarachnoid space. However, this mechanism is limited by the fact that the cranium is a fixed volume, and once the volume of the cranium is reached by either an expanding brain or haematoma, the pressure will increase rapidly.

This is summarised by the Monroe-Kellie Doctrine:

Intracranial pressure ~ CSF volume + blood volume + brain volume

It should be remembered that a volume as small as 200ml within the cranium can be enough to cause death in an adult patient. Consequently, an expanding haematoma within the cranium must be evacuated rapidly to avoid causing further brain injury. It should also be remembered that hypovolaemic shock present in a head injured patient should not be ascribed to intracranial bleeding, as 200ml blood loss is not enough to cause hypovolaemic shock.

Types of Brain Injury

Diffuse Brain Injury

1. Concussion (or mild traumatic brain injury) – this is a disturbance of cerebral function caused by an acceleration/deceleration type injury. It is essentially an electrical disturbance caused by a release of excitatory neurotansmitters which can last for 7-10 days, which leads to an increase in the metabolic state of the brain. The effects typically last for up to 3 weeks after the injury, and include loss of consciousness, vomiting, confusion, amnesia (anterograde or retrograde), headache and difficulty concentrating on tasks.
2. Diffuse Axonal Injury – this is structural brain injury caused by shearing forces on the brain leading to areas of tearing of axons in the white matter of the brain (most commonly in the frontal and temporal lobes, at the grey-white matter interface). This is usually seen after deceleration-type injuries in which there is a rotational component. Its effects vary from very mild to very severe, with more severely affected patients typically being unconscious. Up to 90% of patients with severe DAI will remain unconscious permanently, with those who do regain consciousness generally being severely neurologically impaired. DAI can be difficult to diagnose initially as it does not tend to show up on CT scans.

Focal Brain Injury

1. Cerebral Contusion – this is bruising of the brain tissue caused by multiple microhaemorrhages from small vessels. It occurs most commonly at the grey-white matter interface (again due to shearing forces) and in the frontal and temporal lobes. CT scans on patients who are unconscious after head injury show contusions in 20% of cases. Contusions after often caused by a direct blow to the head (coup and contrecoup injuries). Contusions generally heal without intervention, but may be associated with attention, memory and emotional problems subsequently (frontal and temporal lobe contusions).
2. Intracranial haemorrhage
   1. Extradural haematoma – this injury occurs when a vessel, often a meningeal artery, is torn as a result of head injury, and bleeds outside the dura mater. The expanding haematoma then compresses the brain, first locally and then more generally due to an increase in intracranial pressure leading to loss of consciousness. The bleed causes the dura mater to strip away from the skull which causes a severe headache; this also causes the haematoma to assume the convex (lentiform) shape seen on CT scanning. Often patients remain conscious for some time after the initial injury, before losing consciousness; they do, however, report a severe headache during the initial stage after the injury. The most common injury pattern is a lateral blow to the head which fractures the temporal bone and tears the middle meningeal artery (70-80% of extradural haematomas). Extradural haematomas must be diagnosed as quickly as possible, as expanding haematomas require neurosurgical drainage and ligation of the bleeding vessel before brain compression causes irreversible damage. Early neurosurgical intervention in these cases is often associated with a good prognosis as there may be little or no primary brain injury.
   2. Subdural haematoma – this is bleeding in the space between the dura mater and the arachnoid mater, which tends to occur when small bridging veins are damaged. The bleeding is usually slower than that seen in extradural haematomas, and tends to come from several small vessels rather than one large vessel. Since this injury occurs more easily if the subdural bridging vessels are longer, and hence more prone to damage from shearing forces, this type of injury is more common in elderly and alcoholic patients (due to brain atrophy) and infants. This injury may present with loss of consciousness, or fluctuating level of consciousness over several days, in addition to headache, seizures, amnesia, vomiting and speech problems. Small haematomas may be managed conservatively, whereas larger haematomas with raised intracranial pressure may require neurosurgical drainage. Recovery from larger traumatic subdural haematomas is associated with a higher rate of neurological sequelae as there is a higher rate of associated primary brain injury compared with extradural haematomas.
   3. Subarachnoid haemorrhage – this is bleeding between the arachnoid mater and the pia mater, often from a single artery. This is usually associated with a severe headache, and may also cause vomiting and loss of consciousness (either transient or ongoing). Early diagnosis is again important, as continued bleeding will cause raised intracranial pressure leading to neurological damage or death. Neurosurgical drainage is much more difficult as these spaces are deep in the brain tissue, but intervention to stop further bleeding (surgical clipping or embolisation of the bleeding vessel) may be possible.
   4. Intracerebral haemorrhage – this is bleeding into the brain matter. This type of injury can cause associated cerebral oedema and, if large, raised intracranial pressure. It is often associated with primary brain injury, and often leads to focal neurological deficit in the affected area. Patients with intracerebral haemorrhage should be managed in a neurosurgical centre as they can sometimes benefit from surgical drainage and management of intracranial pressure.

Immediate management of head injured patients

The aim of medical management of patients immediately after head injury is to prevent secondary brain injury. The two main components of this are to maintain adequate cerebral perfusion and oxygenation, and to avoid (or treat) raised intracranial pressure.

Primary Survey

This is the standard system as used in Advanced Trauma Life Support (ATLS):

Airway & C-Spine Control

Breathing

Circulation and Major Haemorrhage Control

Disability

Exposure

When carrying out the primary survey, it should be remembered that the airway should be protected in comatose patients. It is generally accepted that patients with a GCS of 8 or lower should therefore be managed by endotracheal intubation, with general anaesthesia if required. In addition to this some head injured patients with a GCS higher than 8 may agitated or combative due to cerebral irritation. General anaesthesia and endotracheal intubation should also be considered in these cases.

Patients with injuries which lead to problems with ventilation, generally chest injuries, require prompt treatment of these injuries to avoid cerebral hypoxia. Patients with rib fractures tend to hypoventilate due to pain, so adequate analgesia is important to allow adequate ventilation. Patients who are unable to sustain adequate oxygenation despite adequate analgesia and after correction of other chest injuries, such as haemopneumothorax, may have sustained pulmonary contusions which may be difficult to identify radiologically in the initial hours of hospital care. Mechanical ventilation should also be considered in these cases.

It should also be remembered that patients who have sustained a head injury are at high risk of concomitant neck injury. Consequently these patients should be managed with C-spine immobilisation until such time as C-spine injury can be excluded either clinically or radiologically. In patients with either impaired conscious level or a painful distracting injury C-spine injury cannot be excluded clinically; in these cases not all C-spine injuries can be excluded by plain C-spine radiographs either, so CT scanning of the neck should be considered. This can often be carried out at the same time as CT scanning of the head in these cases.

In patients who have concomitant injuries, fluid resuscitation should be instituted promptly to correct hypovolaemia. However, patients who do not show signs of hypovolaemia should not be treated with rapid intravenous infusions in the presence of head injury, since fluid overload may contribute to cerebral oedema. In this situation, intravenous fluids should be given at a maintenance rate.

Secondary Survey

The secondary survey should be carried out as is usual in patients presenting with multiple injuries. This should include examination of systems and a head to toe external examination. In particular, care should be taken to examine the cervical spine, as head injured patients are at risk of these injuries. It should be remembered that this may be difficult to determine clinically if the patient has impaired consciousness or a painful distracting injury or injuries.

Investigation

For patients with multiple injuries, blood tests and plain radiographs should be carried in the normal way. All patients with a known coagulapathy (history of bleeding, known clotting disorder, current anticoagulant therapy) should also have their clotting measured, in order to determine the level of coagulopathy and consider the need to reverse this.

Brain

In general, the imaging investigation of choice in the Emergency Department setting is a CT scan of the brain. The use of CT scanning has become more common, and has superseded plain radiographs of the skull in suspected skull fractures in addition to its use to image intracranial bleeding.

The indications for CT scanning of the brain and cervical spine were updated in September 2007 (United Kingdom - NICE guideline CG56), and are summarised as follows:

Indications for immediate CT head (imaging and results analysed within 1 hour of request for CT):

• GCS <13 when first assessed in the ED
• GCS <15 when assessed in the ED 2 hours after the injury
• Suspected open or depressed skull fracture
• Sign of skull base fracture (haemotympanum, ‘panda’ eyes, CSF leakage from the ears or nose, Battle’s sign)
• Post-traumatic seizure
• Focal neurological deficit
• >1 episode of vomiting
• Coagulopathy (including anticoagulant treatment) in patient with any amnesia or loss of consciousness since injury

Indications for CT head within 8 hours (immediate if patient presents 8 hours or more after injury):

• Age ≥65 with any amnesia or loss of consciousness since injury
• Amnesia for events more than 30 minutes before injury
• Dangerous mechanism of injury (pedestrian or cyclist struck by a motor vehicle, occupant ejected from a motor vehicle, fall from > 1m or 5 stairs

Cervical spine

In addition to the above guidelines, CT scanning may be required to assess the cervical spine in head injured patients.

Indications for immediate CT neck:

• GCS < 13 on initial assessment
• Patient has been intubated
• Plain film series technically inadequate (for example, desired view unavailable), suspicious or definitely abnormal
• Continued clinical suspicion of injury despite normal X-ray
• Patient is being scanned for multi-region trauma

In the absence of the above findings, the cervical spine should be imaged by 3 view plain radiographs if:

• Patient cannot actively rotate neck to 45 degrees to the left and right (if safe to assess)*
• Not safe to assess range of movement in the neck*
• Neck pain or midline tenderness plus: age ≥ 65 years or dangerous mechanism of injury*
• Definitive diagnosis of cervical spine injury required urgently (for example, prior to surgery)

* see NICE guideline CG56 for details

References

1. ↑ NICE guidelines CG56 (Head injury) page 31.
2. ↑ Society of British Neurological Surgeons 1999.
3. ↑ Kay A, Teasdale G. Head injury in the United Kingdom. World Journal of Surgery 2001; 25(9): 1210-20. PMID 11571960. Full text