Lumbar puncture

Question 1

Define lumbar puncture.

Answer 1

Spinal tap; CSF if taken from the spine in the lower back through a hollow needle, done for diagnostic purposes.

Question 2

What are the indications for a lumbar puncture?

Answer 2

• Suspicion of meningitis
• Suspicion of subarachnoid hemorrhage (SAH)
• Suspicion of central nervous system (CNS) diseases such as Guillain-Barré syndrome and carcinomatous meningitis
• Therapeutic relief of pseudotumor cerebri

Question 3

List some contraindications to LP.

Answer 3

• Infection at needle insertion site
• Raised ICP
• Cardiorespiratory compromise
• Bleeding diathesis (tendency)

Question 4

Why should you obtain a CT prior to LP?

Answer 4

Raised ICP (suspect in severe headache, low GCS, falling pulse, rising BP, vomiting, focal neurology or papilloedema) can lead to coning of the brainstem so should obtain CT before LP (unless routine e.g. for idiopathic intracranial hypertension)

Question 5

What are the common complications of a lumbar puncture?

Answer 5

• Post-dural puncture headache (10-30%) within 24hrs- usually resolves within 3-4 days.
• Infection
• Bleeding
• Cerebral herniation (rare, check for raised ICP)
• Minor/transient neurological symptoms e.g. paraesthesias, radiculopathy

Question 6

Describe the LP procedure.

Answer 6

• Patient hugs knees to chest and lies on their left side
• Aseptic technique is used
• Landmarks - at iliac crest level L3/4 or one below (spinal cord ends at L1/2)
• Needle (25G then 21G) is inserted perpendicular or slightly towards umbilicus. Feel resistance of spinal ligaments then dura. CSF should fill the needle when stilette is withdrawm
• CSF is connected in 10 drops in 3 tubes

Question 7

What layers do you have to go through during an LP?

Answer 7

1. Skin
2. Subcutaneous tissue
3. Supraspinous ligament
4. Interspinous ligament
5. Ligamentum flavum
6. Epidural space
7. Dura mater
8. Arachnoid mater
9. Subarachnoid space - CSF is found here