Plain Skull X-ray (SXR)

Headache and head trauma are common presenting problems in both primary care and the Accident and Emergency Department.
It is now well recognised that only in a small proportion of cases are plain skull films appropriate and likely to aid management decisions. In light of the amounts of unnecessary radiation to which patients are exposed by the use of inappropriate x-rays, the Ionising Radiation (Medical Exposure) Regulation (IRMER) states that practitioners must ascertain that the net clinical benefit of each x-ray film justifies the risk involved in undergoing the procedure.

The majority of plain skull films are performed following trauma to the head, and in order to aid decisions as to which patients might benefit from these x-rays, several groups have audited past results from many radiology departments.^1,2,3 From these and other studies it became clear that whilst intra-cranial injury is more likely if there is a skull fracture, significant intracranial injury may also occur in the absence of a fracture,and a normal skull x-ray may give a false sense of reassurance.

Several guidelines have been produced in an attempt to aid the decision as to when a plain skull film may be helpful in both acute and non-acute situations.^4,5,6

The risk of intracranial injury is the main consideration when planning further imaging of the skull.
The Royal College of Radiologists has defined four categories of risk for intracranial injury following head trauma as follows:⁴

• Low risk: Glasgow Coma Scale (GCS) 15/15, no fracture.
• Medium risk: GCS 15/15 , no fracture, but history of loss of consciousness.
• High risk: GCS 13-14/15,or GCS 15/15 with a skull fracture.
• Very high risk: GCS <13/15, or deterioration in clinical condition.

If the risk of intracranial injury is sufficiently high to warrant the performance of an emergency CT scan, then plain skull films should not be routinely carried out in addition as they will not influence management further. If the GCS is 15/15 i.e. the patient is fully conscious, orientated and obeying commands and CT scanning is not going to be carried out, plain skull films should be carried out in the following situations:^6,7

• The mechanism of the injury has not been trivial and/or has involved a fall from a significant height.
• Consciousness has been lost
• The patient has loss of memory
• The patient has vomited since the event
• The scalp has a full thickness laceration
• A boggy haematoma or scalp bruise is evident
• The child is under the age of 5 and non-accidental injury is suspected
• The history is inadequate

The Royal College of Radiologists have collated the available evidence and made the following recommendations as to when the use of plain skull films may be the most appropriate investigation to aid diagnosis:⁴:

• The presence of a palpable vault abnormality which feels bony
• As part of an imaging protocol for specific clinical problems after discussion with radiologists e.g. skeletal survey for myeloma
• Facial views are of use following trauma to facial skeleton or mandible
• Facial views may be of use following trauma to the orbit, or possibility of metallic foreign body

Skull films are not indicated routinely for the following indications:

• Headache
• Possible pituitary problems - ( CT/MRI preferred)
• Possible space occupying lesion
• Epilepsy
• Dementia or memory loss
• Middle or inner ear problems
• Nasal trauma - coned views may be requested by appropriate specialist
• Sinus disease - mucosal thickening is a common incidental finding and not diagnostic
• Temporal mandibular joint dysfunction - will not show disc abnormality which is the most common cause of dysfunction.

Skull films should be interpreted wherever possible, by a doctor with specialist training and/or considerable experience in interpreting such films. In untrained hands approximately 10% of bony abnormalities are not recognised. The absence of a fracture on a skull film does not rule out the possibility of an operable intracranial haematoma in head injured patients. All such findings must be taken in the context of the clinical condition of the patient e.g. patients with a GCS of 3-8 and no fracture still have a 1 in 27 risk of having an operable intracranial haematoma.⁸