CT Head Scanning Indications

oPatientPlus articles are written by UK doctors and are based on research evidence, UK and European Guidelines. They are designed for health professionals to use, so you may find the language more technical than the condition leaflets.

Computed axial tomography (commonly termed CT scanning - as here) was first used at the Atkinson Morley Hospital in London in 1972. CT scans rapidly became the mainstay of the diagnosis of structural brain disease until the advent of magnetic resonance imaging (MRI) during the late 1980s. However, CT remains an extremely valuable method of investigation, particularly in the acute situation and because of the very high expense of MRI systems. CT scans have a relatively high radiation dose so should be avoided in pregnancy. Claustrophobia is less of a problem compared with MRI.

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  • CT remains the investigation for the diagnosis and management of many central nervous system diseases.
  • MRI is superior in the posterior fossa and parasellar region and for the assessment in multiple sclerosis, epilepsy and tumours.
  • CT is superior to MRI in the assessment of head injury.
  • Indications for CT imaging, CT angiography, and CT venography include:


  • Acute stroke:
    • CT scan as soon as possible and within 48 hours to rule out haemorrhage.
    • CT scanning is reliable in excluding primary intracerebral haemorrhage as a cause of acute stroke, provided it is performed within about a week of onset.
    • A CT scan is particularly important in those patients who are being evaluated for thrombolysis or carotid endarterectomy.
    • The CT signs of ischaemia are more subtle and detection of acute infarction is variable depending on the timing of the examination.
    • The area of infarction matures over the first week or more with the development of progressively better defined low attenuation and loss of volume in the damaged area.
  • Transient ischaemic attack (TIA): can help to distinguish infarction from haemorrhage and also differentiate from other causes such as extracerebral haemorrhage or glioma.
  • Acute subarachnoid haemorrhage: CT will provide evidence of subarachnoid haemorrhage in 98% of cases if performed within 48 hours. CT is indicated in acute headache with focal neurological signs, nausea, vomiting or Glasgow Coma Scale (GCS) below 14. MRI is better for inflammatory causes of acute headache.
  • Acute head injury: CT the head in every severe head injury (GCS less than or equal to 8) and every moderate head injury (GCS 9-12). This should be done as soon as possible and within an hour after arrival to hospital.[2] The role of CT scanning in mild head injury is controversial.[3] The National Institute for Health and Clinical Excellence (NICE) and the Scottish Intercollegiate Guidelines Network (SIGN) now recommend:[4][5]
    CT Scan in Head Injuries[4][5]
    Selection of adults for CT ScanSelection of children (under 16 years) for CT Scan
    Urgent scan if any of the following (results within 1 hour):
    • Glasgow Coma Scale (GCS) <13 when first assessed or GCS <15 two hours after injury
    • Suspected open or depressed skull fracture
    • Signs of base of skull fracture*
    • Post-traumatic seizure
    • Focal neurological deficit
    • >1 episode of vomiting (SIGN guidance suggests 2 distinct episodes of vomiting)
    • Coagulopathy + any amnesia or loss of consciousness since injury

    A CT scan is also recommended (within 8 hours of injury) if there is either:
    • More than 30 minutes of amnesia of events before impact
    • Or any amnesia or loss of consciousness since injury if:
      • Aged ≥65 years
      • Coagulopathy or on warfarin
      • Dangerous mechanism of injury
        • Road traffic accident (RTA) as a pedestrian
        • RTA - ejected from car
        • Fall >1 m or >5 stairs

    Urgent scan if any of the following:
    • Witnessed loss of consciousness >5 minutes
    • Amnesia (antegrade or retrograde) >5 minutes
    • Abnormal drowsiness
    • ≥3 Discrete episodes of vomiting
    • Clinical suspicion of nonaccidental injury
    • Post-traumatic seizure (no PMH of epilepsy)
    • GCS <14 in emergency room
      (Paediatric GCS <15 if aged <1)
    • Suspected open or depressed skull fracture or tense fontanelle
    • Signs of base of skull fracture*
    • Focal neurological deficit
    • Aged <1 - bruise, swelling or laceration on head >5 cm
    • Dangerous mechanism of injury (high-speed RTA, fall from >3 m, high-speed projectile)
    *Signs of basal skull fracture: haemotympanum, 'panda' eyes (bruising around the eyes), cerebrospinal fluid (CSF) leakage (ears or nose) or Battle's sign (bruising which sometimes occurs behind the ear in cases of basal skull fracture).
  • Space-occupying lesions: suspected tumour or mass, eg cerebral abscess. MRI is more sensitive for early tumours and posterior fossa lesions but CT is usually adequate for supratentorial lesions. MRI may miss calcification.
  • Suspected hydrocephalus or shunt revision. MRI may be more appropriate for children. Ultrasound is the first choice for infants.
  • Chronic headache. CT or MRI are not usually useful if there are no focal neurological signs but are more likely to detect an abnormality if there is:
    • Recent onset and a progressive worsening of symptoms and frequency or a change in their pattern
    • Association with the onset of epilepsy (especially focal epilepsy)
    • Change in personality
    • Associated dizziness, lack of co-ordination, tingling or numbness
    • History of recent head injury, or falls (to exclude subdural haemorrhage)
  • Intracranial infection: to exclude raised intracranial pressure prior to lumbar puncture (but only if there is considered to be a high risk of coning). In cases of childhood bacterial meningitis, CT is accurate in the diagnosis of intracranial complications of bacterial meningitis and is indicated mainly in children with persistent neurological dysfunction such as complex seizure disorder, and is of little value in children with prolonged fever alone.[6]
  • Detection or evaluation of calcification: For example, the radiological hallmark of an oligodendroglioma is calcification, which is best detected on CT scanning. Calcification may be invisible on MRI.
  • Other: mental status change, increased intracranial pressure, headache, acute neurological deficits, congenital lesions (eg craniosynostosis, macrocephaly, and microcephaly), evaluation of patients with psychiatric disorders and brain herniation. In the assessment of psychosis, CT scan should be reserved for those with recent onset, rapid unexplained deterioration, focal neurological signs, recent head injury before onset or if there has been urinary incontinence or gait disturbance early in the illness.
  • Secondary indications (eg when access to MRI is not available): diplopia, cranial nerve dysfunction, seizures, apnoea, syncope, ataxia, suspicion of neurodegenerative disease, developmental delay, neuroendocrine dysfunction, encephalitis, vascular occlusive disease or vasculitis (including use of CT angiography and/or venography), aneurysm, cortical dysplasia, and migration anomalies.


  • Middle or inner ear symptoms, including vertigo. If felt necessary following specialist assessment. MRI is much better, especially for acoustic neuromas.
  • Sinus disease if there has been failure of maximal medical treatment, complications, eg orbital cellulitis or suspicion of malignancy.
  • Congenital anomalies, benign and malignant neoplasms, trauma, vascular malformations, evaluation of palpable masses, planning and follow-up of radiotherapy.[7]
  • Orbital lesions, including eye trauma in which there may be an associated facial fracture. Ultrasound may be appropriate for intraocular lesions. CT scan may also be indicated for strong suspicion of an intraocular foreign body that has not been shown on X-ray.
  • Fractures of the temporal bone, skull, and face.
  • Evaluation of the skull base including primary and secondary bone lesions.
  • Cranio-maxillofacial surgery: the CT scan delineates lesions in the oral and maxillofacial complex to aid in planning surgical treatment. CT-based 3D models allow precise preoperative diagnosis and operation planning.[8]
  • Secondary indications (eg when access to MRI is not available): evaluation of lesions involving the orbit, larynx, pharynx, oral cavity and soft tissue spaces of the face.

Further reading & references

  1. Making the best use of clinical radiology services, Royal College of Radiologists (2007)
  2. Hammell CL, Henning JD; Prehospital management of severe traumatic brain injury. BMJ. 2009 May 19;338:b1683. doi: 10.1136/bmj.b1683.
  3. Haydel MJ, Preston CA, Mills TJ, et al; Indications for computed tomography in patients with minor head injury. N Engl J Med. 2000 Jul 13;343(2):100-5.
  4. Triage - assessment - investigation and early management of head injury in infants, children and adults; NICE Clinical Guideline (September 2007)
  5. Early Management of Patients with a Head Injury; Scottish Intercollegiate Guidelines Network - SIGN (May 2009)
  6. Daoud AS, Omari H, al-Sheyyab M, et al; Indications and benefits of computed tomography in childhood bacterial meningitis. J Trop Pediatr. 1998 Jun;44(3):167-9.
  7. Santler G, Karcher H, Ruda C; Indications and limitations of three-dimensional models in cranio-maxillofacial surgery. J Craniomaxillofac Surg. 1998 Feb;26(1):11-6.
  8. Exadaktylos AK, Stettbacher A, Bautz PC, et al; The value of protocol-driven CT scanning in stab wounds to the head. Am J Emerg Med. 2002 Jul;20(4):295-7.

Disclaimer: This article is for information only and should not be used for the diagnosis or treatment of medical conditions. EMIS has used all reasonable care in compiling the information but make no warranty as to its accuracy. Consult a doctor or other health care professional for diagnosis and treatment of medical conditions. For details see our conditions.

Original Author:
Dr Colin Tidy
Current Version:
Last Checked:
Document ID:
2023 (v24)