Should You Perform a Lumbar Puncture in Hydrocephalus?
Lumbar puncture in hydrocephalus is generally safe and should be performed in specific clinical contexts, particularly when evaluating for underlying infection, assessing shunt function, or predicting response to surgical intervention—but it is contraindicated when there is significant mass effect, obstructive hydrocephalus, or signs of impending herniation.
Clinical Decision Framework
When LP is Indicated and Safe
In infectious/inflammatory hydrocephalus contexts:
- Lumbar puncture has a low risk even when hydrocephalus is present and should be undertaken as part of neurosurgical collaboration 1
- In coccidioidal meningitis with hydrocephalus, LP is explicitly recommended for diagnosis and pressure management, with repeated LPs used therapeutically to reduce intracranial pressure 1
- For patients with intracranial devices (ventriculostomies, shunts) who develop fever or altered mental status, CSF should be obtained—either from the device reservoir or via lumbar puncture 2
In normal pressure hydrocephalus (NPH):
- LP with CSF removal (typically 40-50 mL) serves as both a diagnostic and prognostic tool 3, 4, 5
- Improvement in gait, cognition, or urinary symptoms after LP strongly predicts favorable response to shunt surgery 3, 4, 5
- The volume removed matters less than the clinical response; even standard-volume taps are effective 6
In posthemorrhagic hydrocephalus in premature infants:
- Serial LPs can provide temporary benefit if communication exists between ventricles and lumbar space 7
- However, routine serial LP is NOT recommended to prevent shunt placement or halt progression 8
Absolute Contraindications to Immediate LP
Do NOT perform LP when any of the following are present 9:
- Moderate to severe impairment of consciousness (GCS <13) or fall in GCS >2
- Focal neurological signs (excluding isolated cranial neuropathies)
- Abnormal posturing
- Papilledema
- Unequal, dilated, or poorly responsive pupils
- Recent seizures until patient stabilized
- Relative bradycardia with hypertension (Cushing's triad)
- Coagulopathy (platelets <100 × 10⁹/L, abnormal coagulation studies, anticoagulation therapy)
- Local infection at LP site
- Respiratory insufficiency
When to Image Before LP
Obtain CT scan before LP if:
- New focal neurologic findings suggesting disease above the foramen magnum 2
- Any of the contraindications listed above are present 9
- Clinical suspicion for mass lesion or obstructive hydrocephalus
Key principle: A noncontrast CT is adequate to exclude mass lesions or obstructive hydrocephalus that would contraindicate LP 2. However, CT is NOT a reliable tool for diagnosing raised intracranial pressure itself 9—clinical assessment takes precedence.
Context-Specific Guidance
Subarachnoid Hemorrhage with Hydrocephalus
In aneurysmal SAH patients with CT evidence of clinically symptomatic hydrocephalus, the priority is urgent external ventricular drain (EVD) placement, not LP 10. LP plays no role in acute SAH management.
Infectious Meningitis with Hydrocephalus
In coccidioidal or cryptococcal meningitis with elevated intracranial pressure (≥250 mm H₂O), repeated therapeutic LPs are first-line management to reduce pressure by removing sufficient CSF to lower pressure to 50% of opening pressure or 200 mm H₂O, whichever is greater 1. This should be repeated daily for at least 4 days until pressure stabilizes.
Critical Care Patients
In febrile ICU patients with altered consciousness but no focal findings and no immune compromise or CNS instrumentation, the yield of LP may be low 2. However, if bacterial meningitis is suspected and LP is delayed for imaging, start empirical antibiotics after blood cultures 2.
Common Pitfalls to Avoid
Don't rely on imaging alone to assess ICP: There may be few or no radiographic changes with acute increased intracranial pressure 1
Don't assume normal opening pressure excludes pathology: Ventricular fluid pressure may be normal in some cases of meningitis; this finding alone should not exclude diagnosis 1
Don't delay necessary LP excessively: If LP cannot be performed initially due to contraindications, reassess every 24 hours and perform when safe 9
Don't perform routine serial LPs in neonatal posthemorrhagic hydrocephalus: This does not reduce shunt need or prevent progression 8