What are the relative merits of skull radiography and CT scanning in the recently head injured patient?

5.1 Detection of Traumatic Intracranial Lesions by Imaging

Intracranial lesions can be detected radiologically before they produce clinical changes.⁵⁷, ⁵⁸ Early imaging, rather than awaiting neurological deterioration, reduces the delay in the detection and treatment of acute traumatic intracranial injury. This is reflected in better outcomes.^59-62 Exclusion or demonstration of intracranial injury can also guide decisions about the intensity and duration of observation in apparently less severe injuries.⁴⁶ Evidence level III

CT scans can directly answer the key question: is there structural intracranial damage? There is a progressive shift away from skull radiography as a source of circumstantial evidence of intracranial damage, towards CT scanning to provide a definitive answer.^63-67 Disadvantages of performing early CT include the possible hazards and inconvenience of transfer to a scanner, ⁶⁸, ⁶⁹ the occasional need for general anaesthesia to obtain clinically useful images, and the development later of a new significant lesion but this is rare after a 'negative' early scan.^70-72 There is also a need to avoid over- use of this investigation and there is a general duty to reduce radiation dosage when possible. The estimated dose for brain CT (2.0 mSv) is equivalent to one year's background radiation but is considerably more than the dose for three skull films (0.14 mSv).⁷³ Evidence level III and IV

CT scanning is increasingly readily available to patients in General Hospitals.⁶⁴, ⁶⁵, ⁷⁴ Authoritative sources recommend 24 hour access in all Accident and Emergency Departments.¹⁴, ¹⁵, ⁷⁵ Nevertheless, the criteria for the use of skull x-ray and CT scan in patients with less severe injuries provoked most controversy in the development of this guideline. The SIGN guideline development group's conclusions about the indications for the selective use of skull x-ray and CT scan accord with the recommendations of the Royal College of Radiologists,¹⁴ the Society of British Neurological Surgeons,¹³ and the Royal College of Surgeons of England.¹⁵ Evidence level IV

CT scanning, should be readily available, on a 24 hour basis, to A&E Departments responsible for assessing head injured patients.

5.2 Selection of Patients for Imaging

In the absence of evidence from randomised comparisons of the results of different imaging modalities, indications depend upon an assessment of the likely return in different categories of patient. The return can be considered either in terms of the radiological lesions demonstrated or the yield of clinically significant abnormalities, which are typically 10-20% of the former.⁴⁸, ^76-81

5.2.1 Risk factors for an Intracranial Lesion

The most firmly established factors that correlate with the occurrence of a surgically significant intracranial haematoma are the level of consciousness and the presence or absence of a skull fracture.^40-43, ⁴⁷, ⁴⁸, ⁷⁰, ⁷⁸, ⁷⁹, ^81-92 The risks of an intracranial haematoma requiring operative evacuation in head injured patients based on findings on arrival at A&E in one large study are summarised in Table 3.⁴¹ Evidence level III

Table 3

RISK OF AN OPERABLE INTRACRANIAL HAEMATOMA* IN HEAD INJURED PATIENTS (adapted from Teasdale et al, 1990 ⁴¹)

* Data from haematomas that were surgically evacuated

Additional factors modify these risks, but to an extent that has not been quantified. Features include, age over ^{60, 50, 79, 80, 93} injured in an assault or being struck by a vehicle,^{50, 80} headache and vomiting,⁹³ the presence of focal neurological signs,⁴⁷, ⁷⁸ and a history of intake of alcohol,^{42, 51, 94} or anticoagulant treatment.^{95, 96} The Royal College of Radiologists has used these features to categorise head injured patients as at low, medium, high or very high risk of intracranial injury.¹⁴ These correspond broadly to combinations of clinical and skull fracture findings:

• low: GCS 15/15, no fracture
• medium: GCS 15/15, no fracture but history of loss of consciousness
• high: GCS 13 or 14/15, or GCS 15/15 with skull fracture
• very high: GCS 12/15 or less, or clinical deterioration.

Evidence level III and IV

Selection for imaging should be based on known 'risk' factors for the presence of a skull fracture or an intracranial lesion.

5.3 Indications for Skull X-Ray

The indications for skull films need to be considered in the context of the criteria for CT scanning. If an emergency CT scan is planned, there is no reason to carry out skull radiography. If CT scanning is not planned; the need for skull radiographs must be considered.

In the large majority of patients who are conscious (spontaneous eye opening, talking and fully orientated, GCS 15/15) CT scanning is not recommended as a routine unless there is evidence of a skull fracture (see below). In these patients, therefore, it is necessary to decide between a non-selective policy for skull x-ray or an attempt to focus investigation on subgroups likely to have a 'high yield' of fractures. If the patient has persisting impaired consciousness and CT is not planned, skull radiographs are considered to be appropriate in all cases.^13-15 Evidence level IV

Features in the history that increase the prospect of x-ray showing a fracture include:

• persisting impairment of consciousness or neurological signs
• in those who have recovered, a history of loss or consciousness or amnesia, nausea or vomiting
• inadequate history to establish the conscious state.

Clinical signs that correlate with the likelihood of a fracture include:

• a 'full thickness' scalp laceration
• boggy haematoma
• leak of CSF or blood from the nose or ear
• periorbital bruising.^{41, 44, 48, 98-102, 103}

Information about the violence of impact is also relevant, for example a skull fracture is more likely if there has been a fall of more than 60 cm onto a broad hard surface or impact against a small object.⁹⁹ Unfortunately, in features where 'grading' is possible e.g. length of amnesia or severity of impact, there is not sufficient evidence of robust, distinct 'break points' to establish precise 'thresholds' to define when a skull x-ray is or is not appropriate. Evidence level III

Skull films should be carried out if any of the following apply and if CT is not being performed: (a) If the patient is alert and orientated and obeying commands (GCS 15/15) but: the mechanism of injury has not been trivial; or consciousness has been lost; or the patient has loss of memory or has vomited; or the scalp has a full thickness laceration or a boggy haematoma; or the history is inadequate. or (b) If the level of consciousness is impaired (GCS ( 14/15).

5.4 Indications for Head CT

There is a view in some countries that a CT scan should be done in every head injured patient in whom there is any concern whatsoever about an intracranial lesion.^{46, 50, 104, 105} However, over-use of CT scanning has disadvantages that include the time and effort expended in providing emergency immediate 24 hour access, and the possible hazards of transfer and the occasional need for general anaesthesia to obtain satisfactory images. Appropriate use of resources is also a consideration and a realistic balance has to be found.^{14, 82, 84} Evidence level III and IV

The pragmatic view taken by the guideline development group is that CT scanning is appropriate, either as a primary investigation or after a skull x-ray, if the likelihood of yielding an abnormality is 10% or more. This corresponds to the likelihood of identifying a lesion for which surgery is required of at least 1-2%.

The data summarised in Table 3 and data obtained from other studies (see section 5.2) show that this condition is fulfilled either if the patient is conscious but has a skull fracture or has impaired consciousness (GCS 14/15 or less, e.g. confusion or failure to obey commands).

5.4.1 Fully Conscious Patients

In the large number of patients who are fully conscious (GCS 15/15), the risk of an intracranial haematoma is less than 1%. CT scanning is appropriate only if a higher risk is indicated by the presence of other features. The additional feature most clearly justifying CT scanning is the presence of a skull fracture. In the absence of evidence of a skull fracture, other features that may make CT scanning appropriate include persisting severe headache, vomiting or developing neurological signs, and treatment with anticoagulants (see section 5.2). There is some evidence that the features that indicate that a skull x-ray is appropriate can also be used to justify a CT scan without a skull x-ray.^{90, 92, 106} However, the guideline development group considers that this has not to date been established as appropriate in Scottish practice. Evidence level III

5.4.2 Patients with Impaired Consciousness (GCS 3-14/15)

CT scanning shows an abnormality in at least 20% of cases of patients with impairment of consciousness. Some recommend performing CT in all these patients^{13, 77, 88, 104} (see section 5.2). However, the 'positive' yield is increased by selecting those with more profoundly impaired consciousness. The debate is about the speed of obtaining a CT scan in patients with lesser degree of impaired consciousness.

Patients who are confused and/or open their eyes only after a sound stimulus (GCS 13 or 14/15) show an abnormality on CT scanning in about 20-30% of cases. If there is a skull fracture, the yield is even higher. It is therefore widely accepted that if a patient has any impaired consciousness and clinical or radiological evidence of a skull fracture, CT is indicated as an emergency.^{11, 13, 14, 15} When the patient does not have a fracture and especially if there is strong suspicion that consciousness is impaired as a result of alcohol or other drugs, rather than injury, the yield is less and scanning may be more difficult. An option is to decide after assessing the patient's progress during a short period (no more than four hours) of clinical observation. CT scanning is then carried out urgently if the patient fails to improve or there is neurological deterioration. Evidence level III

When the patient's consciousness is markedly depressed (GCS 12/15 or less), there is a sufficiently high likelihood of finding an abnormality that CT scanning is appropriate in all cases. Evidence level III

In considering the rapidity with which CT scanning should be performed, it can be useful to make a broad distinction between scanning as an emergency and urgent scanning. By analogy with use of these terms in surgery, emergency indicates that arrangements for scanning should be initiated immediately and performed as soon as possible after completion of appropriate resuscitation/stabilisation - which will always take priority. Patients who fulfil the criteria for urgent scanning should, if needed, be investigated 'out of hours', and at the most within four hours from the first observation. The investigation should not be delayed until 'normal working hours' because this may detract from the potential benefit resulting from the wider availability of CT.

The above criteria for scanning as an emergency correspond closely with those of the Royal College of Radiologists; likewise, the criteria for scanning urgently correspond with the circumstances in which the Royal College of Radiologists states that CT scanning should be carried out within four hours of admission.¹⁴ Evidence level IV

CT scanning should be done in a patient who has any of the following features: The patient is eye opening only to pain or does not converse (GCS 12/15 or less) A deteriorating level of consciousness or progressive focal neurological signs Confusion or drowsiness (GCS 13/15 or 14/15) followed by failure to improve within at most four hours of clinical observation Radiological/clinical evidence of a fracture, whatever the level of consciousness New focal neurological signs which are not getting worse Full consciousness (GCS 15/15) with no fracture but other features, e.g. severe and persistent headache nausea and vomiting irritability or altered behaviour a seizure

Patients in categories (1) and (2) should be scanned as an emergency.

Patients in categories (3) - (6) should be scanned urgently.

When clinical features point strongly to an intracranial haematoma (e.g. the emergence of focal signs, or a deterioration in consciousness level), there should be discussion with a neurosurgeon about the benefits of transfer promptly to a location which has both CT scanning facilities and an emergency neurosurgical service.

Skull fractures in children, though significantly associated with an increased risk of intracranial injury, are not as discriminating as in adults. In children with a head injury, significant intracranial injury occurs more frequently in the absence of a skull fracture than is the case in adults. Clinical features (e.g. tense fontanelle) are an equally important factor in determining the need for a CT scan to rule out intracranial injury.

In the absence of clinical signs of intracranial injury, observation by experienced paediatric medical and nursing staff in an appropriate unit/ward is an alternative to urgent CT scan

5.4.3 Remote Communities

In remote communities other factors must be taken into account when considering the usefulness of skull films as a triage tool. Where CT is not available locally the finding of a skull fracture (carrying increased risk) may influence the decision to evacuate a patient. However, if a helicopter or plane is needed even to obtain skull films then it is more appropriate to arrange transfer directly to a centre with a CT scanner and neurosurgical facilities Evidence level III

Recommendations for use of radiographic investigations in patients (>5 years old) with a head injury are illustrated in Figure 1.

Figure 1

USE OF RADIOGRAPHIC INVESTIGATIONS IN PATIENTS (>5 YEARS OF AGE) WITH A HEAD INJURY

5.5 Interpretation of Images

Casualty officers have been found to miss 10% of skull fractures in x-rays reviewed by radiologists.⁵⁶ Evidence level III

Doctors who interpret and make clinical decisions based upon skull films or scans should be trained to do so. All imaging should be reviewed by an experienced radiologist as soon as possible.

The growth in CT scanning of head injured patients at general hospitals has been accompanied by consultation about patients whose scans are sent to a tertiary centre for a second opinion. This may be by physical transport of the films or transmission by teleradiology. There is evidence that image transfer influences decision-making and may reduce unnecessary transfers of head injured patients and promote more rapid transfer in appropriate cases.^107-109 Evidence level III

Transport or transmission of images should be used to communicate about patients in whom the appropriate management is not otherwise clear.

5.6 Imaging the Cervical Spine

A head injury may be accompanied by a cervical injury. Even though this is an infrequent event, the need to consider the possibility of spinal injury and to take measures to 'clear the cervical spine' are well-established components of assessment of a head injured patient. The approach depends upon whether or not the patient is conscious and talking and hence able to report any symptoms and co-operate in clinical examination.

Cervical spine films are not considered necessary in conscious patients who are not complaining of pain in the cervical spine, have no neck tenderness, have no clinical evidence of cervical injury or neurological deficit, have not had a "distracting injury", (an injury to another part of the body which draws attention away from the neck injury) and who have a full range of pain-free neck movement.^110-113 Evidence level III

Immobilisation and imaging of the cervical spine is recommended:¹⁷

• if the patient is conscious, but describes the relevant symptoms
• if the mechanism of injury suggests a high risk of cervical injury
• if the patient has neurological signs suggesting spinal injury
• if the patient has impaired consciousness.

Evidence level IV

Plain radiographs of the cervical spine can detect most, but not all cervical spinal injuries and exclusion of injury can be complex, sometimes requiring additional CT of the spine. Detection of unstable ligamentous injuries may depend upon additional flexion and extension radiographs and/or magnetic resonance imaging. In current practice, a balance is usually made between the perceived likelihood of a spinal injury and the extent of investigation employed.

Plain cervical spinal radiographs should be taken (lateral, anteroposterial and transoral) as a single lateral cervical spine radiograph is not sufficient to exclude spinal injury.^{110, 113, 115} It is important to visualise the C7-T1 region and if this is not demonstrated on the plain radiographs the need for computed tomography should be considered.^{110, 113, 116} This may be conveniently performed at the same time as CT head scanning. In patients in deep coma, it is reported that fractures of the upper cervical spine are commonly detected by CT scanning more often than expected from the plain films and therefore the occipito cervical region should be imaged along with the head in patients with GCS <6/15.¹¹⁷ Evidence level III

Lateral radiographs in flexion/extension can be useful in selected circumstances, when an unstable ligamentous injury is suspected, for example, when there are minor degrees of misalignment and/or apparently detached osteophytes. Static flexion/extension views, under medical supervision expose the patient and staff to a significantly lower radiation dose than dynamic fluoroscopy, which has no additional advantages.^{113, 118} Evidence level III

Imaging of the cervical spine, including the cervico-thoracic junction should be carried out: in a fully conscious patient (GCS 15/15) if clinical symptoms or signs or the mechanism of injury indicate the possibility of injury in a patient with persisting impaired consciousness (GCS 14/15 or less) in an unconscious patient, not localising pain (GCS 6/15 or less) CT scanning of the cervical spine down to C2 should be undertaken routinely, at the time of head scanning.