What can a non-contrasted Computed Tomography (CT) head show in a patient with altered mental status?

Non-Contrast CT Head Findings in Patients with Altered Mental Status

A non-contrasted CT head in a patient with altered mental status can reveal several critical intracranial pathologies including ischemic and hemorrhagic stroke, subdural hematoma, subarachnoid hemorrhage, hydrocephalus, mass effect, cerebral tumors, and evidence of infection such as encephalitis or meningitis. 1

Common Pathologies Detectable on Non-Contrast Head CT

Hemorrhagic Conditions

• Intracranial hemorrhage - readily visible as hyperdense areas
• Subdural hematoma - crescent-shaped collection along the cerebral convexity
• Subarachnoid hemorrhage - blood in the subarachnoid spaces, often in the basal cisterns
• Intraventricular hemorrhage - blood within the ventricular system

Ischemic Conditions

• Acute/subacute ischemic stroke - may appear as subtle hypodensity, loss of gray-white matter differentiation, or sulcal effacement
• Chronic infarcts - encephalomalacia or volume loss in vascular territories

Space-Occupying Lesions

• Brain tumors (primary or metastatic) - may appear as masses with surrounding edema
• Brain abscesses - ring-enhancing lesions with surrounding edema
• Mass effect - midline shift, ventricular compression, or herniation syndromes

Other Findings

• Hydrocephalus - enlarged ventricular system
• Cerebral edema - diffuse or focal brain swelling
• Evidence of increased intracranial pressure - effaced sulci, compressed ventricles

Diagnostic Yield of Non-Contrast Head CT

The diagnostic yield of non-contrast head CT in altered mental status varies significantly:

• In general hospital settings: 13% of scans show clinically significant findings 2
• In ICU patients: approximately 22.8% of scans reveal acute communicable findings 3
• Yield ranges from 2% to 45% depending on patient selection criteria 1

Risk Factors Associated with Abnormal CT Findings

Patients with the following risk factors have higher likelihood of abnormal CT findings:

• Focal neurological deficits (OR 1.82) 4
• Decreased level of consciousness (GCS <15) (OR 1.90) 4
• History of anticoagulant use (OR 3.59) 4
• History of antiplatelet use (OR 2.20) 4
• Headache (OR 3.37) 4
• Advanced age (≥73 years) 5
• History of recent falls or head injury 1
• Hypertension 1
• Signs of elevated intracranial pressure 1

Clinical Approach to CT Head Interpretation

When reviewing a non-contrast head CT in a patient with altered mental status:

1. Systematically evaluate:

   • Bone windows for fractures
   • Brain parenchyma for densities (hyper/hypodense lesions)
   • Ventricular system for size and symmetry
   • Midline structures for shift
   • Basal cisterns for effacement

2. Remember limitations:

   • Early ischemic changes may not be visible in the first 6-12 hours
   • Small lesions in the posterior fossa may be obscured by beam-hardening artifacts
   • Certain conditions like encephalitis may show subtle or no findings on CT

Important Considerations

• Non-contrast head CT is the first-line neuroimaging test for altered mental status due to its rapid acquisition and availability 1
• MRI has higher sensitivity for detecting ischemia, encephalitis, and subtle cases of subarachnoid hemorrhage when CT is negative but clinical suspicion remains high 1
• CT without contrast is sufficient as initial imaging; contrast-enhanced CT does not add significant value as a first-line test in the acute setting 1
• The yield of CT head has been declining over time (19.8% before 2000 vs. 11.1% after 2000) 2, suggesting improved clinical selection

Pitfalls to Avoid

• Don't assume a normal CT excludes all intracranial pathology - consider MRI for suspected conditions with limited CT visibility
• Avoid attributing altered mental status solely to metabolic causes without appropriate neuroimaging, especially in high-risk patients
• Remember that patients may not have clinical signs on examination that predict focal pathology 1
• Be aware that approximately 7.4% of patients with altered mental status but no focal deficits may still have acute changes on imaging 1

Non-contrast head CT remains a crucial initial diagnostic tool in evaluating patients with altered mental status, with its greatest utility in patients with specific risk factors that increase the likelihood of intracranial pathology.