A 38-year-old woman presents with acute severe headache, neck stiffness, and fever. Clinical suspicion for meningitis is high. Which is the most appropriate first imaging investigation before lumbar puncture?

Explanation

## Investigation of Choice Before Lumbar Puncture in Suspected Meningitis ### Clinical Context A patient with signs of meningitis (headache, neck stiffness, fever) requires imaging before lumbar puncture to exclude contraindications such as increased intracranial pressure, mass effect, or herniation risk. ### Why Non-Contrast CT Head? **Key Point:** Non-contrast CT is the fastest, most readily available imaging modality to rule out contraindications to lumbar puncture (mass lesions, midline shift, uncal herniation). **High-Yield:** Non-contrast CT is preferred because: - **Speed:** Obtained within minutes; critical in acute meningitis - **Availability:** Present in all emergency departments - **Sensitivity for mass effect:** Detects hemorrhage, edema, midline shift, and herniation - **No contrast delay:** Avoids treatment delays - **No need for IV access:** Faster patient processing ### Contraindications to Lumbar Puncture (Detected on Non-Contrast CT) - Intracranial mass or space-occupying lesion - Midline shift >5 mm - Uncal or transtentorial herniation - Significant cerebral edema - Hydrocephalus with mass effect ### Comparison of Imaging Modalities | Modality | Indication | Timing | Limitation | |---|---|---|---| | **Non-contrast CT** | Rule out contraindications to LP | Immediate | Lower sensitivity for inflammation, subtle lesions | | **MRI with contrast** | Detailed assessment of meningitis; better for complications | 30–60 min | Too slow for acute decision-making | | **CT with contrast** | Not needed for LP decision | Adds 10–15 min | Delays treatment | | **Skull X-ray** | Obsolete in modern practice | Not applicable | No role in acute meningitis | ### Clinical Pearl **Mnemonic: STAT CT for Meningitis — Speed, Trauma/mass, Acute decision, Treatment delay avoidance** In meningitis, time is brain. Non-contrast CT takes <5 minutes and answers the critical question: "Is LP safe?" If CT is normal, LP proceeds immediately. If CT shows contraindications, imaging-guided intervention (ventriculostomy, osmotic therapy) is pursued instead. ### Guideline Recommendation American Academy of Neurology (AAN) and CDC guidelines recommend **non-contrast CT before LP** in patients with: - Focal neurologic signs - Papilledema - Immunocompromise - Recent head trauma - Signs of increased ICP ### Sequence After Imaging 1. **Non-contrast CT normal** → Proceed to LP immediately 2. **Non-contrast CT abnormal** → Defer LP; start empiric antibiotics and consider alternative diagnosis or imaging-guided sampling 3. **After LP (if done)** → MRI with contrast can be obtained for detailed assessment of meningitis complications