In a patient with suspected meningitis and differential diagnoses of intracerebral space-occupying lesion or subarachnoid hemorrhage, what are the absolute contraindications to performing a lumbar puncture?

Absolute Contraindications to Lumbar Puncture in Suspected Meningitis

There are NO true "absolute" contraindications to lumbar puncture in suspected meningitis—rather, there are clinical scenarios where LP must be delayed until after CT imaging and/or stabilization, but even then LP may still be performed if imaging is reassuring. The key is identifying patients at high risk for brain herniation who require CT before LP 1, 2.

Clinical Features Requiring CT Before LP

Perform CT head before LP if ANY of the following are present 1, 2:

Neurological Signs

• Altered consciousness: GCS ≤12 (some use ≤11) 2, 3
• Inability to answer 2 consecutive questions correctly or follow 2 consecutive commands 1
• Focal neurological deficits:
  • Gaze palsy
  • Abnormal visual fields
  • Facial palsy (except CN VI or VII palsy, which are NOT contraindications) 1
  • Arm or leg drift
  • Abnormal language
• New-onset seizure within 1 week of presentation 1
• Papilledema 1

Patient History

• Age ≥60 years 1
• History of CNS disease: mass lesion, stroke, focal infection, CSF shunts, hydrocephalus, prior neurosurgery 1
• Immunocompromised state: HIV/AIDS, immunosuppressive therapy, transplantation 1

Situations Where LP Should Be Delayed/Avoided Regardless of Imaging 2

Do NOT perform LP in these scenarios:

1. Cardiorespiratory compromise or instability
2. Signs of severe sepsis or rapidly evolving rash (meningococcemia)
3. Infection at the LP site
4. Coagulopathy or anticoagulation 2:
   • Platelets <40 × 10⁹/L or rapidly falling
   • INR >1.4 on warfarin
   • Within 12 hours of prophylactic LMWH
   • Within 24 hours of therapeutic LMWH
   • Within 7 days of clopidogrel (unless reversed)
   • Aspirin/NSAIDs are NOT contraindications

Critical Management Algorithm

If ANY high-risk features are present:

1. Start empiric antibiotics immediately (ceftriaxone + ampicillin + dexamethasone) 4
2. Obtain urgent CT head
3. If CT shows mass effect, midline shift, or herniation: DO NOT perform LP 5
4. If CT is normal: LP may still be unsafe if clinical signs of impending herniation persist 3

If NO high-risk features present:

• Proceed directly to LP without CT 2, 4
• The 2009 Swedish guideline change removing altered consciousness as a mandatory CT indication resulted in antibiotics started 1.2 hours earlier and reduced mortality from 11.7% to 6.9% 2

Key Pitfalls to Avoid

• A normal CT does NOT guarantee LP safety in patients with severely altered consciousness or brainstem signs—CT does not detect raised intracranial pressure directly 2, 3
• Never delay antibiotics for imaging or LP—if LP is contraindicated, start empiric treatment immediately 4, 6
• The risk of herniation from LP is approximately 5-6% in bacterial meningitis, accounting for 30% of mortality 3
• Prolonged seizures may transiently increase intracranial pressure; some delay LP 30 minutes after brief seizures 1

Context for SAH and Space-Occupying Lesions

In your specific scenario with differentials of intracerebral mass or SAH:

• If SAH is suspected, CT head is the primary diagnostic test (not LP initially)
• If space-occupying lesion is suspected, CT must be performed before LP to assess for mass effect 5
• SAH complicating bacterial meningitis is rare (0.9%) but carries 54% mortality 7
• Imaging findings that absolutely contraindicate LP include: supratentorial mass with herniation/significant midline shift, medium-to-large posterior fossa masses, obstructive hydrocephalus, or severe global edema with mass effect 5