When to Order a CT Scan in Clinical Practice
Non-contrast head CT is the recommended first-line imaging study for patients with acute head trauma, regardless of severity, as it provides rapid assessment of potentially life-threatening intracranial injuries that may require urgent intervention. 1
Head Trauma
Indications for Immediate CT Head
- Moderate to severe head trauma (GCS ≤12)
- Mild head trauma (GCS 13-15) with any of the following:
- Loss of consciousness or amnesia
- Headache
- Vomiting
- Age >60 years
- Drug or alcohol intoxication
- Deficits in short-term memory
- Physical evidence of trauma above the clavicles
- Seizure
- Focal neurologic deficit
- Anticoagulation or bleeding disorder
Timing Considerations
- CT should be performed as soon as possible after injury, as early detection of intracranial hemorrhage is critical for timely intervention 1
- For patients presenting >24 hours after injury, CT remains indicated if any of the above criteria are present, though sensitivity may be reduced (70% vs 98% for those presenting within 24 hours) 2
Follow-up Imaging
- Repeat CT is indicated for patients with:
- Positive initial findings requiring monitoring
- New or progressive neurologic deficits
- Unchanged neurologic examination after a negative or unremarkable initial head CT only when clinically indicated 3
Neurological Emergencies
Suspected Stroke
- Non-contrast CT head should be performed immediately for patients with suspected stroke to rule out hemorrhage before considering thrombolysis 3
- CT angiography (CTA) should be considered when vascular abnormalities are suspected
Suspected Subarachnoid Hemorrhage (SAH)
- Patients with suspected SAH should have a non-contrast CT scan immediately on arrival to hospital 3
- If CT is negative but clinical suspicion remains high:
- For CT performed within 6 hours of headache onset and read by a neuroradiologist: no further imaging needed
- For CT performed after 6 hours, lower generation CT, or if not read by an experienced radiologist: lumbar puncture should be performed 3
Suspected Encephalitis
- MRI is preferred over CT for suspected encephalitis
- If MRI is not immediately available, CT should be performed to rule out contraindications to lumbar puncture or other mass lesions 3
- Clinical assessment, not CT, should be used to determine if it is safe to perform a lumbar puncture 3
Other Clinical Scenarios
Seizures
- For new-onset seizures with return to normal baseline:
Foreign Body Ingestion/Esophageal Emergencies
- CT scan should be performed in patients with suspected perforation or other complications that may require interventional endoscopy or surgery 3
- CT has 90-100% sensitivity for detecting fish bone impaction compared to 32% for plain X-ray 3
Sudden Hearing Loss
- MRI is preferred over CT for evaluation of sudden sensorineural hearing loss
- CT is not recommended for isolated sudden hearing loss due to radiation exposure and low yield 3
Avoiding Overuse
- Studies show CT overuse rates of approximately 15% for mild head trauma 4
- To minimize unnecessary radiation exposure:
- Adhere to evidence-based guidelines
- Consider patient age (younger patients have higher lifetime risk from radiation)
- Avoid routine repeat CT in the absence of neurologic deterioration 3
Special Considerations
- Contrast-enhanced CT is not recommended for initial head trauma evaluation as it may obscure subtle hemorrhages 1
- MRI is more sensitive than CT for detecting subacute and chronic subdural collections, parenchymal injuries, and posterior fossa or brainstem lesions 1, 5
- For suspected vascular injuries, CT angiography or venography should be considered 1
By following these evidence-based guidelines, clinicians can appropriately utilize CT imaging to improve patient outcomes while minimizing unnecessary radiation exposure and healthcare costs.