In an older adult with fever and acute delirium but no focal neurologic deficits, trauma, or anticoagulation, is an emergent head CT required?

Head CT in Febrile Delirium Without High-Risk Features

In an older adult with fever and acute delirium but no focal neurologic deficits, trauma, or anticoagulation, emergent head CT is generally not required and has extremely low diagnostic yield (1.7%-2.7%), though clinical judgment must weigh this against medicolegal concerns and the possibility of occult pathology. 1, 2, 3

Risk Stratification Framework

The decision to obtain head CT should be based on the presence or absence of specific high-risk features rather than automatic imaging for all delirious patients 1, 4:

High-Risk Features Requiring Immediate CT (Any Present = Image)

• Focal neurologic deficit on examination - strongest predictor of abnormal CT (OR 101.8) 4, 5
• Recent falls or head trauma 1, 4
• Anticoagulation therapy (warfarin, DOACs, or antiplatelet agents) 1, 4
• Signs of elevated intracranial pressure (papilledema, Cushing's triad) 4
• Significant deterioration of consciousness (GCS <13-14) 1, 4, 3
• History of malignancy 1, 4
• Headache, nausea, or vomiting accompanying the altered mental status 1, 4

Your Clinical Scenario: Low-Risk Profile

For febrile delirium without any high-risk features listed above, the diagnostic yield of head CT drops to 1.7%-2.7% 2, 6, 3. The American College of Radiology acknowledges that in elderly patients with new-onset delirium lacking these risk factors, the yield is very low, and determination falls on clinical judgment 1.

Evidence-Based Diagnostic Yields

The most recent systematic reviews and meta-analyses demonstrate:

• Overall yield in ED/inpatient delirium: 13% (but this includes high-risk patients) 7
• Yield in delirium without focal deficits: 7.4% 1
• Yield when excluding trauma, falls, anticoagulation, and focal deficits: 1.7%-2.7% 6, 3
• Only 4.7% of delirious elderly ED patients had acute CT findings, and 30.8% of those had focal neurologic deficits 2

Recommended Approach for Febrile Delirium

Step 1: Focus on Infectious/Metabolic Workup First

Since fever is present, prioritize evaluation for:

• Sepsis (most common cause of AMS in elderly, 29.1% of cases) 3
• Urinary tract infection
• Pneumonia
• Meningitis/encephalitis (requires lumbar puncture if suspected, not CT as first test) 1
• Metabolic derangements

Step 2: Defer CT Initially If All True:

• GCS ≥13-14 3
• No focal neurologic deficits 5
• No anticoagulation 1
• No recent trauma/falls 1
• No signs of elevated ICP 4
• Clear infectious/metabolic etiology identified 1

Step 3: Obtain CT If:

• Delirium persists or worsens despite treatment of identified cause (fever/infection) after 24-48 hours 1, 4
• Any new high-risk feature develops 1, 4
• Clinical suspicion for intracranial infection (meningitis/encephalitis) - though contrast-enhanced imaging or MRI may be more appropriate 1

Critical Pitfalls to Avoid

Do not assume normal examination excludes intracranial pathology entirely - 70% of missed ischemic strokes present with altered mental status rather than focal deficits 8, 4. However, this risk must be balanced against the 1.7%-2.7% yield in truly low-risk patients 6, 3.

Do not reflexively order CT based solely on age and confusion - this leads to overutilization with minimal benefit 2, 7. The yield has declined over time (19.8% pre-2000 vs. 11.1% post-2000) 7.

Anticoagulation alone without other features is NOT strongly predictive - one study found OR 1.2 (not statistically significant) 5. However, ACR guidelines still list it as a risk factor requiring imaging 1, 4.

When to Consider MRI Instead

If CT is performed and negative but delirium persists beyond 24-48 hours, MRI brain without contrast should be obtained as second-line imaging 1, 8, 4. MRI has higher sensitivity for:

• Small ischemic infarcts 8, 9
• Encephalitis 1, 8
• Subtle subarachnoid hemorrhage 1
• MRI changes management in 76% of patients with acute consciousness disorders 8, 4

Practical Algorithm Summary

1. Assess for high-risk features (focal deficits, trauma, anticoagulation, GCS <13-14, ICP signs, malignancy history) 1, 4
2. If ANY high-risk feature present → Immediate non-contrast head CT 1
3. If NO high-risk features + fever present → Pursue infectious/metabolic workup, defer CT 1, 6, 3
4. If delirium persists/worsens despite treating infection → Obtain CT or MRI 1, 4
5. If CT negative but symptoms persist >24-48 hours → Consider MRI brain 1, 8, 9