Lumbar Puncture TutorialThis module will teach you how to perform lumbar punctures under fluoroscopy utilizing 3D models correlated with fluoroscopic images. This was adapted from the original iBook "Lumbar Punctures in 3D". Scroll down or select your desired section:
You’ve just received an LP request. The following are good questions to ask:
Have you already attempted the procedure and failed? If not, what is the reason it requires fluoroscopy? Lumbar punctures under fluoroscopy involve radiation to the patient and are more expensive than those performed at bedside. Moreover, most radiology departments are not adequately staffed to perform every lumbar puncture.
Is the patient consentable? If not, who can you consent? (Get a phone number) If no one is available for consent, you can do a 2 physician consent.
Is the patient too altered to tolerate the procedure? Fluoroscopy will not change that.
Anti-coagulation parameters: Your institution should have a policy on this, and the latest JVIR guidelines provide a good starting point. INR, platelets, and anti-coagulation medications are common questions.
Review any recent brain imaging. If there is an intracranial mass with early herniation, you could worsen the herniation by removing CSF. If you are doing the study for intracranial hypertension or papilledema and the patient does not have any head imaging, they should probably at least get a CT before doing the procedure.
Review any recent lumbar spine cross-sectional imaging. This will help you select an appropriate level based on degenerative disease or other pathology such as a soft tissue abscess.
How much CSF should you collect? This is based on the labs requested. Contact your local laboratory to find out what volumes they prefer. The ARUP labs website is also useful for a starting point – you can search for any test and they detail the amount required. Here are some rough guidelines:
- Cell count: 1 cc
- Culture: 1 cc
- PCR (e.g. for HSV): 1 cc
- Glucose and Protein: 2-3 cc
- Pathology or cytology: full tube (7-10 cc)
Some useful points when obtaining LP consent:
The most common complication is a post-procedure headache caused by pressure alteration after removing CSF. Risk factors include female gender, younger age (20-40), and history of prior LP headache. It is common practice for patients to lie flat for 45 minutes after the procedure, though studies suggest this does not reduce incidence of headaches. If they get a headache, encourage them to drink lots of fluids. There is about 150 mL of CSF in the body, and you make about 20 mL/hour. That means you will replace the volume removed in about an hour, and you turn over your entire CSF volume about three times per day.
CSF leak is another potential complication. Using the smallest gauge needle possible and entering the thecal sac with a longitudinal bevel orientation decrease the risk of CSF leak.
Bleeding, infection, and damage to surrounding structures are all very small risks.
Anatomy and Level Selection
Meninges and Epidural Space
Just like in the brain, the spinal cord is surrounded by meninges (dura and arachnoid). Some important points:
- Lesion location is classically described as extradural (outside the dura), intradural extramedullary (inside the dura but outside the spinal cord), and intradural intramedullary (inside the cord).
- The intradural extramedullary space (a.k.a intrathecal or subarachnoid space) contains the CSF and nerve roots and spinal cord.
- The epidural space surrounds the dura and extends along the nerves through the foramina. The epidural space contains semi-liquid fat, lymphatics, arteries, loose areolar connective tissue, the spinal nerve roots, and an extensive plexus of veins. Visualizing the boundaries of the epidural space is important for the accurate needle placement for certain types of spine injections.
- The dorsal epidural space in the adult measures about 0.4 mm at C7-T1, 4.1 mm at T11-12, and 4-7 mm in the lumbar region.
- The epidural space is bounded superiorly by the fusion of the spinal and periosteal layers of the dura mater at the foramen magnum. Inferiorly, it is bound by the sacrococcygeal membrane. The space is bounded anteriorly by the posterior longitudinal ligament, vertebral bodies and discs while the pedicles and intervertebral foraminae form the lateral boundary. The ligamentum flavum, capsule of facet joints and the laminae form the posterior boundary of the epidural space.
- With degenerative disease, thickening and calcification of the ligamentum flavum can narrow the dorsal epidural space.