Lumbar Puncture

Overview

Lumbar puncture, also referred to as LP or colloquially as a spinal tap, is the insertion of a needle into the subarachnoid space of the lumbar spine. The procedure can be a method of extracting CSF for analysis, measuring CSF pressure, injecting medication such as chemotherapy agents, or injecting contrast for detailed cross sectional imaging of the spinal canal (myelography). This procedure can often be accomplished at the bedside without imaging guidance. However, factors such as abnormal alignment or bony degenerative changes can make a bedside LP difficult. In these situations fluoroscopic guidance can be very helpful. In pediatric patients ultrasound guidance can be used.

Technique

Any prior spine imaging is reviewed first to get a roadmap of the patient's spinal anatomy and confirm the level of the conus medullaris. The patient is positioned prone on the fluoroscopic examination table. A brief physical exam is performed to palpate for bony landmarks of the lower back. After approximating a skin entry site the patients back is sterilized and draped. The L3/L4 or L4/L5 interspinous/interlaminar space is identified fluoroscopically. A spinal needle is then inserted through the interspinous/interlaminar space. The needle is advanced through the interspinous ligament, ligamentum flavum, and lastly through the dura mater and arachnoid which are sandwiched together. Once the needle is in the subarachnoid space fluid spontaneously flows slowly from the needle. Opening pressures can be measured with a mannometer to report CSF/intracranial pressures. Fluid is then collected and sent to the lab for analysis. Alternatively, contrast can be injected into the spinal canal for cross sectional imaging (myelography) or chemotherapeutic or antibiotics may be injected for therapy.

Indications

CNS infection, meningitis
Suspected subarachnoid hemorrhage
Multiple sclerosis, Guillain-Barré
Carcinomatous meningitis
Therapeutic relief of idiopathic intracranial hypertension (pseudotumor cerebri)
Intrathecal administration of chemotherapy or antibiotics
Injection of contrast media for myelography or for cisternography

Contraindications

Local skin infections over proposed puncture site
Unequal pressures between the supratentorial and infratentorial compartments
Risk for herniation in the setting of an intracranial mass
Increased intracranial pressure (except in pseudotumor cerebri therapy), risk for herniation
Coagulopathy, including anticoagulation therapy (see below for guidelines)
Suspected spinal epidural abscess
Spinal column deformities that prevent safe targeting
Lack of patient cooperation (can be performed with sedation

Risks/Complications

Cerebral herniation: This is the most concerning complication. Assessment of ICP status limits the risk of this occurring.
Post-LP headache: A common complication, reportedly 10-30%. Caused by CSF leak from puncture site with possible tear of the dura. Most often begin within 1-2 days post-LP. Typically worse when upright, better when supine. Treatment is usually conservative unless symptoms are more concerning or persistent for which an epidural blood patch is often placed to stop the CSF leak.
Back pain: Up to 2/3 of patients report back pain of various levels during the procedure. Up to 1/3 report back pain after the procedure which can persist for several days but is very rarely permanent.
Radicular pain or numbness: Most often limited to time during the procedure.
Infection: Local or meningitis.
Bleeding: Usually in patients with coagulopathy. Concerns are blood loss and epidural hematoma that could compress the spinal cord and irritate the meninges.
Late onset of epidermoid tumors of the thecal sac: Exceedingly rare.

Interested in ordering an image guided LP?

Some questions that the Neuroradiologist will ask you to help facilitate the procedure:

1) What is the indication/reason for the LP

2) Has someone on the floor/ER attempted to perform the LP?

3) Is the patient consentable? If not, who is the power of attorney and what is their contact information?

4) What is the INR, PTT and PLT count? We require labs on all inpatients/ER patients. Please refer to lab/medication guidelines for cutoff values.

5) Are there any potential issues that the radiologist should know prior to performing the LP? For example, the LP needs to be performed under conscious sedation or general anesthesia.

6) If the LP is to be done for intrathecal chemotherapy administration, is the chemotherapy ready and who will be available to administer the chemotherapy?

Guidelines for Head CT/MR prior to LP

Recommend Head CT in patients with signs/symptoms of increased intracranial pressure:

New onset seizure
Papilledema
Focal neurologic findings
Altered mental status

American College of Physicians: Practice Guidelines Lumbar Puncture. Physician Information and Education Resource. 2010

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