Does a patient with altered mental status always require a computed tomography (CT) scan of the head?

CT Scanning in Patients with Reduced Consciousness

Not every patient with reduced consciousness requires a CT scan, but the decision must be guided by specific clinical risk factors rather than blanket imaging of all patients. 1

Risk-Stratified Approach to CT Imaging

The 2024 American College of Radiology guidelines provide clear direction that CT head without contrast is the first-line imaging test for altered mental status when acute intracranial pathology is suspected, but emphasize that the decision falls on clinical judgment rather than automatic imaging. 1

High-Risk Features Requiring CT Scan

You must obtain a CT scan when any of these risk factors are present: 1

• Focal neurologic deficit on examination
• History of recent falls or head trauma
• Anticoagulation therapy (warfarin, DOACs, antiplatelet agents)
• Signs of elevated intracranial pressure (papilledema, Cushing's triad)
• Significant deterioration of consciousness (not just baseline confusion)
• Older age with acute change
• History of malignancy
• Headache, nausea, or vomiting accompanying the altered mental status 1

Low-Yield Scenarios

The diagnostic yield of CT is very low in elderly patients with new-onset delirium who lack the above risk factors. 1 In these cases, the low yield must be weighed against the small but real risk of missing preventable morbidity from conditions like subdural hematoma, stroke, or tumors. 1

Critical Pitfall: The Limitations of Clinical Examination

A normal or near-normal neurological examination cannot exclude serious intracranial pathology. This is a crucial point that contradicts common clinical intuition. Research demonstrates that 18.4% of mild head injury patients with relatively normal neurological examinations had intracranial lesions on CT, and 5.5% required surgery. 2 Another study found that among patients with minor head injury (GCS 13-15), none with normal CT scans deteriorated, but CT scanning had 100% sensitivity for detecting lesions requiring craniotomy. 3

Notably, 70% of patients with missed ischemic stroke diagnoses presented with altered mental status rather than classic focal deficits. 1 This underscores that absence of focal findings does not rule out stroke.

When to Consider MRI Instead

MRI should be considered as a second-line test when initial CT is unrevealing but clinical suspicion remains high, particularly for: 1

• Suspected ischemia (MRI detects small cortical infarcts missed by CT)
• Encephalitis or meningitis
• Subtle subarachnoid hemorrhage
• Known malignancy, HIV, or endocarditis (may be first-line in clinically stable patients) 1

MRI changed clinical management in 76% of ICU patients with acute disorders of consciousness, including revised diagnoses in 20% and changes in level of care in 21%. 1

Practical Algorithm

For patients presenting with reduced consciousness:

1. Assess for high-risk features listed above 1
2. If ANY high-risk feature present → obtain CT head without contrast immediately 1
3. If NO high-risk features in elderly delirium → clinical judgment required, weighing low yield against medicolegal and safety concerns 1
4. If CT negative but symptoms persist/worsen → consider MRI brain 1, 4
5. Document your clinical reasoning for imaging decisions, as physician reassurance, patient expectations, and medicolegal concerns influence practice patterns 5

Special Consideration: Postictal States

In patients with known epilepsy presenting with altered consciousness and tongue trauma (pathognomonic for seizure), observation with serial neurological examinations may be appropriate without immediate CT if there are no high-risk features. 4 However, if deficits persist beyond 24-48 hours or worsen, MRI is recommended to evaluate for occult stroke. 4

The key principle: CT scanning should be risk-stratified based on specific clinical features rather than applied universally or withheld categorically. 1