For an 82‑year‑old woman presenting to the emergency department with new‑onset paranoid delusions and no memory loss, should a head CT or MRI be obtained even though none was performed in the ED?

Yes, obtain a head CT now for this 82-year-old woman with new-onset paranoid delusions

A non-contrast head CT should be obtained as the initial neuroimaging study for this patient, even though it was not performed in the ED. While the diagnostic yield may be modest, the potential for detecting life-threatening but treatable intracranial pathology in an elderly patient with new psychiatric symptoms justifies imaging 1.

Why Imaging is Indicated

Age and New-Onset Psychiatric Symptoms are Red Flags

An 82-year-old presenting with new-onset paranoid delusions without prior psychiatric history represents a concerning clinical scenario. The 2024 ACR Appropriateness Criteria emphasize that elderly patients with new-onset delirium or altered mental status warrant neuroimaging unless the etiology is clearly non-neurologic and risk of intracranial pathology is low 1.

Diagnostic Yield in Elderly Patients

The evidence shows:

• In elderly patients with altered mental status, abnormal brain imaging occurs in 15.6% to 16.5% of cases 1, 2
• Critical findings include intracranial hemorrhage, ischemic stroke, subdural hematoma, tumors, and infections 1
• Notably, 70% of patients with missed ischemic stroke initially presented with altered mental status rather than classic focal deficits 1

The "No Focal Deficit" Pitfall

The absence of focal neurologic findings does not exclude serious intracranial pathology. Studies show that 7.4% of patients with altered mental status but no focal deficits still had acute changes on imaging 1. Case reports document occipital lobe strokes presenting solely as delusional parasitosis 3 and temporal lobe hypoperfusion manifesting as isolated hallucinations and delusions 4.

Recommended Imaging Approach

First-Line: Non-Contrast Head CT

Start with a non-contrast head CT because it:

• Can be performed rapidly and safely in all patients 1
• Effectively detects hemorrhage, mass effect, hydrocephalus, and large infarcts
• Serves as appropriate initial screening in the acute setting 1

When to Add MRI

Consider brain MRI without contrast as a second-line study if:

• The head CT is unrevealing but clinical suspicion remains high
• You need higher sensitivity for subtle ischemia, encephalitis, or small lesions 1
• The patient has known malignancy, HIV, or endocarditis (MRI may be first-line) 1

MRI changed clinical management in 76% of patients with altered consciousness in one study, including revised diagnoses in 20% and altered levels of care in 21% 1. However, this benefit was greatest in stroke patients who typically have focal deficits.

Risk Stratification Considerations

High-Risk Features Present in This Case

• Advanced age (82 years) - consistently associated with higher yield 1
• New-onset psychiatric symptoms - warrants organic workup 3

Additional Risk Factors to Assess

• History of falls or head trauma
• Anticoagulation or antiplatelet use
• Hypertension
• Known malignancy
• Deteriorating level of consciousness 1

Important caveat: While anticoagulation is often cited as a risk factor, meta-analysis showed it was not significantly associated with abnormal head CT (OR 1.2,95% CI 0.4-3.3) 2. However, clinical practice still considers it relevant.

Balancing Low Yield Against Preventable Morbidity

The ACR guidelines acknowledge the tension: "the low diagnostic yield of CT in this setting must be weighed against the risk of possible, preventable morbidity" 1. In an 82-year-old with new psychiatric symptoms:

• The stakes are high: Missing a subdural hematoma, tumor, or stroke could result in death or permanent disability
• The intervention is low-risk: Non-contrast CT has minimal risk beyond radiation exposure
• Alternative diagnoses remain possible: Even if imaging is negative, you've ruled out structural causes and can pursue metabolic, infectious, or medication-related etiologies with greater confidence

Practical Algorithm

1. Obtain non-contrast head CT now (first-line imaging)
2. If CT shows acute abnormality: Manage accordingly (neurosurgery consult for hemorrhage, neurology for stroke, etc.)
3. If CT is negative but suspicion remains high: Consider brain MRI without contrast for subtle ischemia, encephalitis, or small masses
4. Simultaneously pursue non-imaging workup: Metabolic panel, medication review, infection workup, toxicology as clinically indicated

The decision to image should not substitute for clinical reasoning, but in an elderly patient with new-onset delusions and no clear alternative explanation, the potential to detect treatable intracranial pathology justifies neuroimaging 1, 3.