Lumbar puncture
This classic procedure is performed for two main purposes: analysis of CSF composition and therapeutic reduction of intracranial pressure.
To safely perform the puncture, it is critical to correctly determine the insertion point. The surgeon relies on a horizontal line drawn through the highest points of the iliac crests (crista iliaca). This line serves as a reliable projection landmark indicating the L3–L4 interspinous space. The puncture is performed precisely here. The procedure requires a special long needle, which must be equipped with a stylet to prevent tissue from clogging the needle lumen.
Suboccipital (cisternal) puncture
The suboccipital approach is technically more challenging and involves entering the cerebellomedullary cistern.
Indications for the procedure:
- Comparative study of cerebrospinal fluid characteristics (comparing CSF from the spinal canal and the cistern).
- Performing pneumoencephalography.
- Administration of medications directly into the CSF space.
The insertion point is located strictly along the midline. To find it, measure the exact midpoint of the distance between the external occipital protuberance (protuberantia occipitalis externa) and the spinous process of the second cervical vertebra (axis).
Technique of suboccipital puncture
The procedure requires a strict sequence of steps, as the needle passes in close proximity to vital structures of the brainstem.
- The needle is slowly advanced inward until physical contact is made with the lower part of the occipital bone.
- After hitting the bone, the needle is slightly withdrawn, and its hub (cannula) is elevated upward.
- The tip of the needle gently slides along the surface of the occipital bone, heading toward the atlanto-occipital membrane (membrana atlantooccipitalis).
- The surgeon feels the moment of piercing the dense membrane and the dura mater (DM) as a characteristic "give" or "pop" — this occurs due to a sharp drop in tissue resistance.
- The stylet is removed from the lumen. The appearance of CSF drops is a reliable sign that the needle tip has successfully entered the cistern.
Briefly: answers to topical questions
What are the indications for a lumbar puncture?
Indications for a lumbar puncture include CSF analysis and reduction of intracranial pressure. The procedure is indicated for:
- Suspected meningitis (the gold standard for diagnosis).
- Suspected encephalitis (with altered mental status, depressed level of consciousness, seizure activity, focal deficits, and meningeal signs).
- Suspected neuroborreliosis involving the central nervous system.
Which tissue layers does the needle sequentially pass through during a lumbar puncture?
When performing a puncture, the needle sequentially passes through soft tissues, ligaments, and the meninges of the spinal cord. The layers pierced include:
- Skin.
- Lumbar fascia.
- Supraspinous ligament (lig. supraspinale).
- Interspinous ligament (ligg. interspinalia).
- Yellow ligament (ligg. flava).
- Dura mater.
At what spinal level does the spinal cord terminate in an adult?
In an adult, the spinal cord terminates at the level of the first or second lumbar vertebra, approximately opposite the intervertebral disc between L1 and L2. Below this level, spinal cord substance is absent.
What are the absolute contraindications for a lumbar puncture?
Absolute contraindications for a lumbar puncture include:
- Progressive cerebral edema.
- Herniation syndrome associated with the risk of cerebellar tonsillar herniation through the foramen magnum.
- Increased bleeding tendency or hemorrhagic diathesis, as this may lead to a traumatic tap («bloody tap») and distort the diagnostic picture.
For a suboccipital puncture, remember the landmarks: "Protuberance — Axis — Membrane". Look for the midpoint between the occipital protuberance and the axis to puncture the atlanto-occipital membrane.
Class and exam questions
How to precisely determine the location for a lumbar puncture?
A horizontal line must be drawn through the highest points of the iliac crests (crista iliaca)—this will indicate the L3–L4 interspace.
What does the feeling of a "give" mean during a cisternal puncture?
It occurs at the moment the needle pierces the atlanto-occipital membrane and dura mater due to a sharp drop in tissue resistance.
Why is it necessary to slightly withdraw the needle after hitting the occipital bone?
This is necessary to elevate the needle hub and allow its tip to slide along the bone directly to the membrana atlantooccipitalis.
What else to study on this topic
- Characteristics of CSF analysis from different parts of the CNS
- Technique and significance of pneumoencephalography
- Specifics of specialized long needles with stylets
- Mechanisms of intracranial pressure reduction during CSF drainage
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