Lumbar Puncture: Why it is used?
It is used to do the following
- Evaluate intracranial pressure and CSF composition (see Table: Cerebrospinal Fluid Abnormalities in Various Disorders)
- Therapeutically reduce intracranial pressure (eg, idiopathic intracranial hypertension)
- Administer intrathecal drugs or a radiopaque contrast agent for myelography
Relative contraindications include
- Infection at the puncture site
- Bleeding diathesis
- Increased intracranial pressure due to an intracranial mass lesion, obstructed CSF outflow (eg, due to aqueductal stenosis or Chiari I malformation), or spinal cord CSF blockage (eg, due to tumor cord compression)
- If papilledema or focal neurologic deficits are present, CT or MRI should be done before lumbar puncture to rule out presence of a mass that could precipitate transtentorial or cerebellar herniation (see Figure: Brain herniation.).
Lumbar Puncture Procedure
| For the procedure, the patient is typically in the left lateral decubitus position. A lumbar puncture needle with stylet is inserted into the L3-to L4 or L4-to-L5 interspace (the L4 spinous process is typically on a line between the posterior-superior iliac crests); the needle is aimed rostrally toward the patient’s umbilicus and always kept parallel to the floor. Entrance into the subarachnoid space is often accompanied by a discernible pop; the stylet is withdrawn to allow CSF to flow out.
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