Traumatic Brain Injury — Part 1: Classification & CT Imaging Decision Rules

1. Glasgow Coma Scale

The Glasgow Coma Scale (GCS) remains the most widely used clinical tool for standardized assessment of consciousness after traumatic brain injury. Originally described in 1974 and subsequently refined, the GCS evaluates three independent behavioral responses — eye opening, verbal response, and motor response — yielding a composite score from 3 (deepest coma) to 15 (fully alert).¹

1.1 Complete GCS Scoring Table

Total GCS = E + V + M (Range: 3–15)

Clinical Pearl: When reporting GCS, always document the individual components (e.g., E3V4M5 = GCS 12) rather than the composite score alone. The motor component is the strongest independent predictor of outcome and should be given particular attention. An intubated patient cannot be assessed for verbal response — record as E_VTM_ where T denotes intubation.¹

1.2 GCS-Pupils Score (GCS-P)

The GCS-Pupils Score extends the traditional GCS by incorporating pupillary reactivity, providing improved prognostic discrimination. The Pupil Reactivity Score (PRS) is subtracted from the GCS total.²

GCS-P = GCS − PRS (Range: 1–15)

1.3 Pediatric GCS Modifications

For pre-verbal children (< 2 years), a modified verbal scale is required.³

2. TBI Classification by Severity

2.1 GCS-Based Classification

2.2 Key Definitions and Subgroups

Mild TBI (GCS 13–15) encompasses a wide spectrum from simple concussion to patients with traumatic intracranial hemorrhage. Within this group, patients with GCS 13 have significantly higher rates of neurosurgical intervention than those with GCS 15 and should be managed more cautiously.⁴

• “Complicated” mild TBI: GCS 13–15 with intracranial pathology on CT (contusion, hemorrhage, or skull fracture). These patients have outcomes more similar to moderate TBI and warrant admission and observation.
• “Uncomplicated” mild TBI: GCS 13–15 with normal CT. Low risk of deterioration; may be candidates for ED observation and discharge with appropriate precautions.

Moderate TBI (GCS 9–12) requires admission to an ICU-level or step-down setting with serial neurologic examinations. Approximately 10–20% of patients with moderate TBI will deteriorate to severe TBI and require intubation or surgical intervention.

Severe TBI (GCS 3–8) constitutes a neurological emergency. By definition, these patients cannot follow commands and nearly always require endotracheal intubation for airway protection. GCS should be assessed after resuscitation and before administration of sedatives or paralytics when possible.¹

2.3 Mechanism-Based Classification

2.4 Time-Based Classification

3. CT Imaging Decision Rules for Minor Head Injury

The decision to obtain CT imaging in patients with mild TBI (GCS 13–15) is one of the most common clinical dilemmas in emergency medicine. Several validated clinical decision rules exist to identify patients who require imaging while minimizing unnecessary radiation exposure, particularly in children.^{5 6 7 8}

3.1 Canadian CT Head Rule

The Canadian CT Head Rule applies to patients with minor head injury defined as: witnessed loss of consciousness, definite amnesia, or witnessed disorientation in a patient with GCS 13–15. The rule was derived and validated in a prospective cohort of 3,121 patients and subsequently validated externally in multiple settings.⁵

Inclusion Criteria:

• GCS 13–15
• Age ≥ 16 years
• Injury within the preceding 24 hours
• Witnessed loss of consciousness, definite amnesia, or witnessed disorientation

Exclusion Criteria:

• Age < 16 years
• Anticoagulant use or known bleeding disorder
• Obvious open or depressed skull fracture
• Focal neurologic deficit
• Unstable vital signs
• Seizure before assessment in the ED
• Returned for reassessment of same head injury
• Pregnant

High-Risk Criteria (for neurosurgical intervention)

CT is required if any ONE of the following is present:

Medium-Risk Criteria (for brain injury on CT)

CT is required if any ONE of the following is present:

Performance Characteristics:

3.2 New Orleans Criteria (NOC)

The New Orleans Criteria apply to patients with minor head injury defined as: loss of consciousness with GCS 15 and normal neurological examination. The rule was derived from 520 patients and validated in 909 patients.⁶

Inclusion Criteria:

• GCS 15
• Loss of consciousness after blunt head trauma
• Normal neurological examination
• Age ≥ 3 years

Exclusion Criteria:

• Penetrating trauma
• GCS < 15
• Focal neurologic deficit
• Obvious skull fracture

CT is required if ANY ONE of the following is present:

Performance Characteristics:

3.3 PECARN Pediatric Head CT Decision Rule

The Pediatric Emergency Care Applied Research Network (PECARN) rule is the largest and most rigorously validated clinical decision rule for pediatric head injury, derived from a prospective cohort of 42,412 children across 25 emergency departments. It uses a two-algorithm approach stratified by age.⁸

Algorithm for Children < 2 Years of Age

Step 1 — Is the patient at HIGH risk? (CT recommended)

Step 2 — If NO high-risk findings, assess for INTERMEDIATE risk:

• If NONE of the above present: ciTBI risk < 0.02%. CT not recommended. Observation is appropriate.
• If ONE OR MORE present: ciTBI risk ~0.9%. Observation vs. CT based on clinical judgment, parental preference, age < 3 months, worsening symptoms, physician experience, and multiple findings.

*Severe mechanism: MVC with patient ejection, death of another passenger, or rollover; pedestrian or bicyclist without helmet struck by motorized vehicle; fall > 3 feet (0.9 m); head struck by high-impact object.

Algorithm for Children ≥ 2 Years of Age

Step 1 — Is the patient at HIGH risk? (CT recommended)

Step 2 — If NO high-risk findings, assess for INTERMEDIATE risk:

• If NONE of the above present: ciTBI risk < 0.05%. CT not recommended.
• If ONE OR MORE present: ciTBI risk ~0.8%. Observation vs. CT based on clinical judgment, worsening symptoms, and number/combination of findings.

Clinically important TBI (ciTBI) is defined as: death from TBI, neurosurgical intervention, intubation > 24 hours for TBI, or hospital admission ≥ 2 nights for TBI with abnormal CT findings.

Performance Characteristics (PECARN):

Clinical Pearl: The PECARN rule identifies a very-low-risk group (< 0.05% ciTBI risk) in whom CT can be safely avoided. For the intermediate-risk group, an initial period of observation (4–6 hours) with serial examinations is a reasonable alternative to immediate CT, as most children with ciTBI will develop signs within this window.⁸

3.4 Comparison of Adult Minor Head Injury Decision Rules

3.5 Additional CT Decision Tools

UK Head Injury Guidelines

The international guidelines for head injury from the United Kingdom recommend CT within 1 hour for any of the following in adults.⁹

• GCS < 13 on initial assessment
• GCS < 15 at 2 hours after injury
• Suspected open or depressed skull fracture
• Any sign of basal skull fracture
• Post-traumatic seizure
• Focal neurological deficit
• More than 1 episode of vomiting

CT within 8 hours (or immediately if presenting > 8 hours post-injury) for:

• Age ≥ 65 with loss of consciousness or amnesia
• Coagulopathy (including therapeutic anticoagulation) with loss of consciousness or amnesia
• Dangerous mechanism with loss of consciousness or amnesia
• More than 30 minutes retrograde amnesia of events before impact

NEXUS II Head CT Criteria

Sensitivity 98.3% for significant intracranial injury; specificity 13.7%.¹⁰

4. CT Interpretation in TBI

4.1 Marshall CT Classification

The Marshall Classification provides a standardized system for categorizing CT findings in TBI and correlates with outcome.¹¹

4.2 Rotterdam CT Score

The Rotterdam CT Score provides a numerical score (1–6) with better prognostic discrimination than the Marshall Classification.¹²

4.3 Helsinki CT Score

An alternative scoring system incorporating subdural hematoma thickness, intracerebral hemorrhage volume, and suprasellar cistern status. Provides 6-month outcome prediction with discriminatory ability comparable to the Rotterdam score.¹³

4.4 Key CT Findings by Injury Type

5. Indications for Repeat CT Imaging

5.1 Routine Repeat CT

The role of routine (protocol-driven) repeat CT in TBI remains debated. Current evidence suggests.¹⁴

Repeat CT is indicated for:

• Any neurological deterioration (decline in GCS by ≥ 2 points, new pupillary asymmetry, new focal deficit)
• Failure to improve as expected
• Patients on anticoagulation (repeat at 6–24 hours even if stable)
• After neurosurgical intervention (to assess adequacy of evacuation)
• Prior to ICP monitor or EVD removal

Routine repeat CT may NOT be necessary for:

• Neurologically stable patients with small contusions or traumatic SAH who are not on anticoagulants
• Patients with normal initial CT and improving clinical status

Practical Recommendation: The decision to repeat CT should be driven by clinical change rather than a fixed protocol in most patients. Exceptions include anticoagulated patients and those with injury types known to expand (contusions, small subdural hematomas).¹⁴

5.2 CT Angiography Indications in TBI

CT angiography of the head and neck should be considered in the following scenarios to evaluate for blunt cerebrovascular injury (BCVI).¹⁵

6. Special Considerations in Imaging

6.1 Anticoagulated Patients

Patients on anticoagulant or antiplatelet therapy represent a high-risk subgroup that is excluded from or not adequately addressed by most clinical decision rules. Current evidence supports a low threshold for CT imaging in these patients.¹⁶

• Warfarin: CT recommended for any head injury with loss of consciousness or amnesia, regardless of GCS score. Repeat CT at 6–24 hours is recommended even if the initial CT is normal, given the risk of delayed hemorrhage.
• Direct oral anticoagulants (DOACs): CT recommended as for warfarin. Risk of delayed hemorrhage is lower than with warfarin but not negligible.
• Antiplatelet agents: CT is recommended for patients on dual antiplatelet therapy or combined antiplatelet-anticoagulant therapy with any head injury. Single antiplatelet therapy (aspirin or clopidogrel alone) in the setting of GCS 15 and no other risk factors has a low but non-zero risk of intracranial hemorrhage.

6.2 Elderly Patients

Patients aged ≥ 65 years have a significantly higher rate of intracranial hemorrhage following minor head injury, even with trivial mechanisms. Cerebral atrophy increases subdural space, placing bridging veins on greater stretch. The threshold for imaging should be lower in this population.¹⁷

6.3 MRI in TBI

MRI is more sensitive than CT for detecting diffuse axonal injury, small contusions, brainstem lesions, and ischemic injury. However, MRI is not the initial imaging modality of choice in acute TBI due to longer acquisition times, limited availability, and challenges monitoring unstable patients in the scanner. MRI is most useful in.¹⁸

• Patients whose neurologic examination is worse than expected from CT findings
• Suspected diffuse axonal injury (GCS disproportionately low relative to CT)
• Prognostication in severe TBI (extent of DAI correlates with outcome)
• Subacute phase evaluation