NICE Guidelines for CT Head Imaging
Perform an immediate non-contrast CT head scan in patients with head injury who have any of the following high-risk features: GCS <15 at any point after injury, loss of consciousness, post-traumatic amnesia, focal neurologic deficit, vomiting (≥2 episodes), severe or persistent headache, signs of skull base fracture, post-traumatic seizure, age ≥65 years, or anticoagulation/antiplatelet therapy. 1
High-Risk Criteria Requiring Immediate CT
The NICE guidelines, as referenced by the American College of Radiology, stratify patients into high-risk categories that mandate immediate imaging to identify life-threatening intracranial injuries 2:
Neurological Status
- GCS <15 at any point after the injury requires immediate CT imaging, as this indicates potential intracranial pathology requiring neurosurgical intervention 1
- Loss of consciousness of any duration is a high-risk feature warranting CT, regardless of current mental status 1
- Post-traumatic amnesia, particularly >30 minutes before impact, significantly increases risk and mandates imaging 1, 3
- Focal neurologic deficits on examination require CT imaging as they may indicate underlying structural damage such as hemorrhage or contusion 1
Clinical Symptoms
- Vomiting ≥2 episodes significantly increases the risk of intracranial injury and requires CT imaging 1, 3
- Severe or persistent headache is an indication for CT imaging 1
- Post-traumatic seizure is a high-risk feature requiring immediate CT 1
Physical Examination Findings
- Signs of basilar skull fracture (Battle's sign, raccoon eyes, hemotympanum, CSF otorrhea/rhinorrhea) warrant immediate CT imaging 1
- Physical evidence of trauma above the clavicles should prompt consideration for imaging 1
Age-Related Considerations
Age ≥65 years is itself a high-risk criterion that warrants head CT when combined with any other risk factor, with elderly patients showing an odds ratio of 19.2 for intracranial injury even with GCS 14-15 1. Elderly patients (>60 years) with GCS 15 and amnesia had a 10% positive CT rate, with some requiring neurosurgical intervention 1.
Anticoagulation Status - Critical Consideration
The NICE guidelines emphasize that anticoagulation status dramatically alters risk stratification 2:
- Warfarin increases intracranial injury risk 1.88-fold and mandates CT imaging regardless of symptom severity 1
- Dual antiplatelet therapy (aspirin + clopidogrel) increases risk 2.88-fold and requires CT imaging 1
- Novel oral anticoagulants (NOACs) including apixaban, rivaroxaban, and dabigatran carry lower but still significant hemorrhage risk and warrant imaging 1, 4
- Clopidogrel or other antiplatelet agents require CT imaging 1
- Aspirin monotherapy alone does not significantly increase risk and is not an absolute indication for CT 1
Timing of CT Imaging
CT imaging should not be delayed if high-risk features are present, with optimal detection of lesions occurring when CT is performed ≥5 hours post-trauma 1. The NICE guidelines recommend that patients with a normal CT but abnormal neurologic examination (GCS <15) should be admitted with documented observations on a half-hourly basis until GCS 15 is achieved 2.
Follow-Up Imaging Indications
When to Repeat CT
- Neurologic deterioration after initially normal or stable CT requires immediate repeat imaging 2, 4
- Failure to achieve GCS 15 after 24 hours despite normal initial CT warrants consideration of repeat CT or MRI 2
- Anticoagulated patients with initial intracranial hemorrhage have a 3-fold increased risk of hemorrhage progression and require routine repeat CT 1, 4
When NOT to Repeat CT
Patients with normal initial CT and stable neurologic examination do not require routine repeat CT, as the risk of deterioration is extremely low (0.006%) 2. A retrospective study of 2,444 ED patients with head trauma found only 0.04% developed intracranial complications within 72 hours after a negative initial CT 2.
Role of MRI
MRI is not indicated for initial evaluation of acute head trauma 2. However, MRI is more sensitive than CT for detecting posterior fossa lesions, diffuse axonal injury, small contusions, and cerebellar infarcts 1. Consider MRI when initial CT is normal but persistent neurologic findings remain, or in the subacute/chronic phase for better characterization of injury 1.
Cervical Spine and Vascular Imaging
CTA of the head and neck should be obtained if there is suspicion of traumatic vascular injury, particularly with neck pain and neurologic symptoms suggesting vertebral artery dissection, with reported sensitivity of 97.7% and specificity of 100% for vascular injury detection 1. Indications include skull base fractures involving the carotid canal, cervical spine fractures, unexplained neurologic deficits, and penetrating head/neck trauma 1.
Common Pitfalls to Avoid
- Failing to obtain CT in elderly patients (≥65 years) with seemingly minor mechanisms - age alone with any other risk factor mandates imaging 1
- Underestimating risk in anticoagulated patients - even minor trauma requires CT in patients on warfarin, NOACs, or dual antiplatelet therapy 1, 4
- Delaying imaging when high-risk features are present - immediate CT is required, not observation 1
- Performing routine repeat CT in stable patients with negative initial CT - this increases costs and radiation exposure without clinical benefit 2, 4
- Using CT reflexively for syncope without head trauma - brain CT should be avoided in uncomplicated syncope 2
Validation and Safety
The Canadian CT Head Rule demonstrated 100% sensitivity for predicting need for neurological intervention using high-risk factors, requiring only 32% of patients to undergo CT 3. External validation studies confirm that a normal early CT in patients with mild head injury (GCS 15) is highly reliable for safe discharge, with only three documented cases of adverse outcomes despite normal CT and GCS 15 at presentation 5.