Lumbar Puncture

Indications

• Diagnostic:
  • Suspected CNS infections (bacterial, viral, fungal, TB meningitis, encephalitis).
  • Subarachnoid hemorrhage (SAH) w/ negative head CT (eval for xanthochromia).
  • Autoimmune/inflammatory CNS disorders (Multiple Sclerosis, Guillain-Barré syndrome, Neuro-Behcet).
  • Idiopathic Intracranial Hypertension (IIH / pseudotumor cerebri) — diagnostic & therapeutic opening pressure measurement.
  • Carcinomatous meningitis / CNS malignancy staging.
• Therapeutic:
  • Intrathecal administration of medications (chemotherapy, Abx, baclofen).
  • Large-volume CSF removal for IIH or Normal Pressure Hydrocephalus (tap test).
  • Spinal anesthesia / myelography.

Contraindications & Pre-Procedure Evaluation

• Absolute Contraindications:
  • Infection at the needle insertion site (skin/soft tissue infection, epidural abscess).
• Relative Contraindications / Risk of Brain Herniation:
  • Signs of ↑ ICP / Mass Effect: Space-occupying lesion, midline shift, posterior fossa mass.
  • Risk: Uncal or tonsillar herniation post-LP.
  • Indications for Non-contrast Head CT prior to LP:
    • Focal neuro deficits.
    • New-onset seizure (within 1 week).
    • Papilledema.
    • Altered mental status / depressed consciousness.
    • Immunocompromised state (HIV, immunosuppressive therapy, post-transplant).
    • Hx of CNS disease (stroke, mass, focal infection).
• Coagulopathy / Bleeding Risk:
  • Thrombocytopenia (Plt < 50,000/mm³) or INR > 1.5.
  • Severe bleeding disorder or active anticoagulation (hold anticoagulants per protocol to prevent epidural hematoma).
• Critical Management Note:
  • If bacterial meningitis is suspected and CT is required prior to LP: Obtain blood cultures & administer empiric IV Abx + dexamethasone IMMEDIATELY before CT scan. Do NOT delay Abx for neuroimaging or LP.

Anatomical Landmarks & Layers Traversed

• Landmarks:
  • L3/L4 or L4/L5 interspinous space (line connecting supracristal plane / highest points of iliac crests aligns w/ L4 spinous process).
  • Spinal cord terminates at L1-L2 in adults (conus medullaris); L2-L3 in infants. Safe insertion is below L2.
• Anatomical Layers Traversed (Outer to Inner):
  1. Skin
  2. Subcutaneous tissue
  3. Supraspinous ligament
  4. Interspinous ligament
  5. Ligamentum flavum (1st “pop” felt)
  6. Epidural space (contains internal vertebral venous plexus)
  7. Dura mater (2nd “pop” felt into subarachnoid space)
  8. Arachnoid mater
  • Note: Does NOT pierce the Pia mater.

Technique & Opening Pressure

• Positioning: Lateral decubitus position w/ knees/hips flexed (preferred for accurate opening pressure [OP] measurement) or sitting position.
• Opening Pressure Measurement:
  • Measured w/ manometer in lateral decubitus position w/ legs extended.
  • Normal OP: 6-20 cm H2O (10-20 cm H2O standard; > 25 cm H2O diagnostic for IIH).
• CSF Collection:
  • Tube 1: Cell count & differential.
  • Tube 2: Glucose & protein.
  • Tube 3: Gram stain, culture, PCR (HSV, VZV, enterovirus), fungal/TB studies.
  • Tube 4: Cell count & differential (comparison w/ Tube 1 to diff traumatic tap vs true hemorrhage), special studies (Oligoclonal bands, cytology).

Complications

• Post-Lumbar Puncture Headache (PLPH): c
  • Etiology: Persistent CSF leakage through dural puncture site -> low CSF pressure -> traction on pain-sensitive meningeal structures.
  • Clinical Presentation: Positional headache (worse when sitting/standing, rapidly relieved w/ recumbency); may assoc w/ nausea, neck stiffness, tinnitus.
  • Prevention: Use small-caliber, non-cutting/pencil-point (atraumatic) needles; orientation of bevel parallel to dural fibers.
  • Management:
    • Conservative (First-line): Bed rest, aggressive oral/IV hydration, simple analgesics, oral/IV caffeine (vasoconstricts adenosine receptors).
    • Refractory (> 48 hrs or severe): Epidural Blood Patch (inject autologous blood into epidural space to seal defect).
• Brain Herniation:
  • Precipitated by LP in presence of ↑ ICP / intracranial mass lesion.
  • Prevention: Neuroimaging (CT) prior to LP in high-risk patients.
• Spinal / Epidural Hematoma:
  • Secondary to vascular injury during LP in patients w/ coagulopathy or on anticoagulants/antiplatelets.
  • Symptoms: Rapidly progressive lower extremity weakness, sensory deficit, bowel/bladder dysfunction (cauda equina syndrome).
  • Dx: Urgent MRI spine. Management: Urgent surgical decompression.
• Infection:
  • Meningitis, epidural abscess, discitis due to poor aseptic technique.
• Cortical Vein / Dural Sinus Thrombosis:
  • Rare complication secondary to CSF hypotension and altered venous flow dynamics.