Fluoroscopy-guided lumbar puncture (LP) is a minimally invasive, image-guided diagnostic and therapeutic procedure that involves the removal of a small volume of cerebrospinal fluid (CSF) from, or an injection of medication or other substance (e.g. radiotracer, chemotherapy agents) into the lumbar cistern of the spinal column. In addition to improving success rates, fluoroscopic guidance may reduce the incidence of a so-called traumatic LP.
Fluoroscopic guidance for LP may be required for the following reasons:
- failed attempts without imaging
- for patients who have difficult anatomy due to obesity, prior spine surgery or other reasons
Indications for LP, in general, include 1, 4:
- CSF sampling (for suspected meningitis or encephalitis, or in suspected sub-arachnoid hemorrhage with a normal CT)
- opening pressure measurements
- administration of intrathecal chemotherapy
- administration of contrast (e.g. CT myelography, nuclear medicine CSF leak studies)
There are no absolute contraindications to performing the procedure. However, caution should be used in patients with:
- suspected spinal epidural abscess
- possible raised intracranial pressure
- thrombocytopenia or another bleeding diathesis (including ongoing anticoagulant therapy)
- reason for referral and history of presenting complaint
- relevant medical and surgical history
- review relevant laboratory results and assess for coagulopathies
- review prior imaging, especially lumbar spine images
- discuss the procedure and its potential risks and complications to obtain informed consent
- perform time-out to confirm correct patient, procedure, and site
Positioning/room set up
Correct patient positioning is an important determinant of success in obtaining CSF. LPs can be performed with the patient in the lateral recumbent or prone positions. The prone position is generally preferred for LPs performed under fluoroscopic guidance with the patient being instructed to lie face down. Pillows placed under the abdomen and pelvis may improve patient comfort as well as aid in flexion of the lower lumbar spine.
The lumbar spinous processes of L3, L4, and L5, and the interspaces between can usually be directly identified by fluoroscopy. The conus medullaris (or terminal part) of the spinal cord most commonly ends at the L1/2 intervertebral disc level in children and adults5,6. Thus, the spinal needle can be safely inserted under fluoroscopic guidance at L3-L4 or L4-L5 via a right oblique sublaminar approach since this is well below the conus.
Besides a standard fluoroscopic table, fluoroscopy-guided LP requires the following items:
- sterile dressing
- sterile gloves
- sterile drapes
- antiseptic solution with skin swabs
- lignocaine 1% without epinephrine
- syringe, 3 mL
- needles, 20 and 25 gauge
- spinal needles, 20 and 22 gauge
- three-way stopcock
- three plastic test tubes, numbered 1-3, with caps
- syringe, 10 mL
- pulse oximetry +/- ECG leads and other monitoring devices if sedation is required or in seriously ill patients.
Following informed consent, the patient should be placed in the prone or prone oblique position on a standard fluoroscopic table. Lignocaine 1% is then administered for local anesthesia.
Once numb, a spinal needle is inserted under strict aseptic conditions using intermittent-pulse fluoroscopy to identify the appropriate site for the LP (often L2-L3 or L3-L4 intervertebral space). The course of the advancing needle is monitored during the procedure until the subarachnoid space is entered via left or right oblique sublaminar approach, which is confirmed by the reflux of clear CSF. Needle position can be assessed with a lateral projection if there is uncertainty about depth.
Opening pressure measurement
The technique for correctly measuring opening pressure is somewhat controversial, despite some evidence that prone and lateral decubitus positioning leads to the same results 2. The three generally encountered approaches are 3:
- needle inserted into CSF prone, measurement prone (most common)
- needle inserted into CSF prone, measurement lateral decubitus (patient rotated with the needle in situ)
- needle inserted into CSF in lateral decubitus, measurement lateral decubitus
Although not most common, the third (lateral decubitus option) has the advantage that it mimics traditional ward positioning and does not require the decision of whether or not to add needle length to the prone opening pressure, which is another variably performed step in calculations 3.
Finally, the required amount of CSF is collected in test tubes and sent to a laboratory for investigations.
- patient to rest supine on the bed (varies by institution but typically up to 4 hours)
- pain score assessed immediately and 15-20 minutes post procedure
- observe for 20-30 minutes for any immediate complications
Complications associated with LP occur rarely. However, minor and major complications can occur even when good technique and standard infection control measures are used. These complications include:
- post-LP headache (in up to 33% 1)
- infection (or spinal abscess)
- bleeding (e.g. from vertebral artery puncture)
- minor neurologic symptoms, e.g. transient pain/numbness/paralysis
- back pain
- cerebral herniation (rare)
- late onset of epidermoid cysts of the thecal sac
- failure to obtain a specimen / need to repeat LP/ Traumatic tap (common)
- 1. Cauley KA. Fluoroscopically Guided Lumbar Puncture. AJR Am J Roentgenol. 2015;205 (4): W442-50. doi:10.2214/AJR.14.14028 - Pubmed citation
- 2. Abel AS, Brace JR, McKinney AM, Friedman DI, Smith SD, Westesson PL, Nascene D, Ott F, Lee MS. Effect of patient positioning on cerebrospinal fluid opening pressure. Journal of neuro-ophthalmology : the official journal of the North American Neuro-Ophthalmology Society. 34 (3): 218-22. doi:10.1097/WNO.0000000000000074 - Pubmed
- 3. Abel AS, Brace JR, McKinney AM, Harrison AR, Lee MS. Practice patterns and opening pressure measurements using fluoroscopically guided lumbar puncture. AJNR. American journal of neuroradiology. 33 (5): 823-5. doi:10.3174/ajnr.A2876 - Pubmed
- 4. Doherty CM, Forbes RB. Diagnostic Lumbar Puncture. Ulster Med J. 2014 May;83(2):93-102. PMID: 25075138; PMCID: PMC4113153.
- 5. Wilson DA, Prince JR. John Caffey award. MR imaging determination of the location of the normal conus medullaris throughout childhood. AJR Am J Roentgenol. 1989;152 (5): 1029-32.
- 6. Soleiman J, Demaerel P, Rocher S et-al. Magnetic resonance imaging study of the level of termination of the conus medullaris and the thecal sac: influence of age and gender. Spine. 2006;30 (16): 1875-80.
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