Adult Minor Head Injury - CT Decision Rules

Key Points

• Use a validated head-CT decision rule only in the population for which it was developed.
• The Canadian CT Head Rule is preferred by ACEP for many adults with minor head injury because of its balance of sensitivity and specificity.
• Noncontrast CT is the acute imaging test of choice for suspected intracranial hemorrhage.
• Anticoagulation and focal neurologic findings lower the threshold for imaging and may place the patient outside simple decision-rule use.
• A normal CT does not exclude concussion.
• Routine repeat CT after a negative scan is not necessary for every stable anticoagulated patient.
• Discharge instructions and return precautions are part of the imaging strategy because some symptoms evolve after the ED visit.
• Do not let a normal scan substitute for a documented neurologic examination.

Algorithm

1. Stabilize ABCs and determine whether injury is truly minor or part of major trauma.
2. Document GCS, loss of consciousness or amnesia, vomiting, seizure, skull-fracture signs, focal deficits, medications, and mechanism.
3. If eligible, apply the Canadian CT Head Rule or another validated tool correctly.
4. Obtain noncontrast head CT when rule criteria, anticoagulation context, neurologic findings, or clinical judgment indicate.
5. Consult neurosurgery and reverse anticoagulation promptly for clinically significant hemorrhage when appropriate.
6. Observe or admit patients with neurologic change, persistent symptoms, intoxication preventing assessment, or unreliable follow-up.
7. Discharge selected patients with negative imaging and baseline examination using written concussion and hemorrhage precautions.
8. Arrange follow-up for persistent post-concussive symptoms or functional limitations.

Clinical Synopsis & Reasoning

Minor head injury is common, but most patients do not have clinically important intracranial hemorrhage. The imaging task is therefore to identify the small subgroup in whom CT changes acute management without scanning every person with a bump to the head. Begin with a careful history of mechanism, loss of consciousness, amnesia, vomiting, seizure, anticoagulant or antiplatelet use, intoxication, and prior neurosurgery. Examination should document Glasgow Coma Scale, pupils, focal neurologic findings, signs of basilar or depressed skull fracture, cervical spine symptoms, and evidence of other trauma.

The Canadian CT Head Rule is one of the best validated tools for adults with minor head injury and a GCS of 13 to 15 after witnessed loss of consciousness, definite amnesia, or witnessed disorientation. High-risk features include failure to reach GCS 15 within 2 hours, suspected open or depressed skull fracture, signs of basilar skull fracture, at least two episodes of vomiting, and age 65 years or older. Additional medium-risk features help identify clinically important brain injury, including dangerous mechanism and substantial retrograde amnesia. The tool has inclusion and exclusion criteria and should not be applied mechanically outside the population in which it was validated.

The New Orleans Criteria and NEXUS Head CT instrument are alternatives, but they differ in sensitivity and specificity. ACEP guidance supports use of the Canadian CT Head Rule in appropriate adults because it can reduce unnecessary imaging. Patients receiving anticoagulants or many antiplatelet regimens were not the target population for some classic rules and generally require a lower threshold for CT. Clinical judgment also overrides a rule when there is a focal deficit, worsening headache, seizure, suspected abuse, penetrating injury, or another feature not captured by the instrument.

Treatment Strategy & Disposition

Noncontrast head CT is the first-line test when acute intracranial hemorrhage or skull fracture is a concern. It is fast, widely available, and sensitive for clinically important acute blood. MRI is not the routine first test for uncomplicated minor head injury, but it may help later when persistent neurologic symptoms are unexplained by CT or when diffuse axonal injury is suspected.

Disposition depends on imaging, neurologic stability, social support, intoxication, and the ability to return for worsening symptoms. A patient with a normal CT and baseline neurologic examination can often be discharged if there is no other reason for observation. Routine repeat CT is not indicated in every stable anticoagulated patient with an initially negative scan; current ACEP guidance supports individualized observation and repeat imaging rather than an automatic protocol. Patients with intracranial hemorrhage, declining GCS, new deficit, persistent vomiting, uncontrolled symptoms, or unreliable follow-up need observation, specialty consultation, or admission.

Imaging does not diagnose or exclude concussion. Provide written instructions about expected cognitive and somatic symptoms, graded return to activity, driving and work precautions, and red flags such as worsening headache, repeated vomiting, confusion, seizure, weakness, or unusual drowsiness. Avoid unnecessary prolonged strict rest. Anticoagulant management should be individualized when hemorrhage is present, including reversal when indicated.

Epidemiology / Risk Factors

• Minor head trauma is among the most common reasons for emergency neuroimaging.
• The great majority of mild traumatic brain injuries do not contain a lesion requiring neurosurgical intervention.
• Older adults are increasingly represented because of falls and antithrombotic use.
• Decision rules can reduce CT use without sacrificing safety when correctly applied.

Investigations

Typical High Risk Clues

Pharmacology

Prognosis / Complications

• Most adults with minor head injury and a negative CT recover without a delayed clinically important hemorrhage.
• Concussion symptoms can last days to weeks despite normal structural imaging.
• Prognosis worsens with intracranial bleeding, advanced age, anticoagulation, recurrent falls, and preexisting neurologic disease.
• Persistent post-concussive symptoms benefit from structured follow-up rather than repeated reassurance alone.

Patient Education / Counseling

• Explain why CT is or is not recommended using the specific risk features present.
• A normal CT means no acute structural injury was seen; it does not mean the patient cannot have concussion symptoms.
• Avoid alcohol, sedatives, driving, or risky activity until cognition and balance have recovered sufficiently.
• Return immediately for repeated vomiting, worsening headache, increasing confusion, seizure, new weakness or numbness, or inability to awaken normally.
• Give a graded return-to-work and activity plan and arrange follow-up when symptoms persist.
• Patients on anticoagulants should receive explicit medication and delayed-bleeding instructions.

Notes

Decision tools are aids, not substitutes for inclusion criteria and clinical judgment. A frequent error is to memorize isolated criteria while forgetting that the rule was validated in a specific minor-head-injury population.

Another common error is to treat imaging as the endpoint of care. The patient with a negative CT still needs concussion education, fall-risk assessment when relevant, and a plan for recurrent or worsening symptoms.

References

1. American College of Emergency Physicians: 2023 Clinical Policy for Mild Traumatic Brain Injury — Link
2. American College of Radiology Appropriateness Criteria: Head Trauma — Link