Diagnosis & Imaging
Lumbar puncture (spinal tap)
A lumbar puncture is a procedure to sample cerebrospinal fluid and measure its pressure from the lower back, used in evaluating hydrocephalus in selected situations.
In short: Lumbar puncture (spinal tap)
- It samples CSF and measures pressure via a needle in the lower back.
- It can assess CSF pressure and analyze the fluid.
- In NPH, removing fluid (tap test) can help predict shunt response.
- It is used selectively and may be unsafe in certain situations.
What it is
A lumbar puncture (spinal tap) is a procedure in which a thin needle is inserted into the lower back to sample cerebrospinal fluid and measure its pressure. It is used in evaluating hydrocephalus and related conditions in selected situations.
Understanding Lumbar puncture (spinal tap)
A lumbar puncture allows measurement of the CSF opening pressure and analysis of the fluid (for example, for infection or other findings). In normal pressure hydrocephalus (NPH), removing a larger volume of CSF (a lumbar tap test) and assessing whether symptoms — especially gait — improve can help predict whether a shunt will help. However, a lumbar puncture is not always appropriate: in obstructive hydrocephalus with raised pressure, removing fluid from the lower back can be dangerous, so imaging is typically reviewed first to ensure it is safe. The procedure is therefore used selectively, guided by the clinical situation.
Why it matters
Understanding lumbar puncture helps families see how CSF can be sampled and its pressure measured, and how, in NPH, removing fluid can help predict shunt response — while recognizing it is used selectively and is not safe in every situation.
Common questions
What is a lumbar puncture?
A procedure to sample CSF and measure pressure from the lower back.
How is it used in NPH?
A tap test removes fluid to see if symptoms improve, predicting shunt response.
Is it always safe?
No — it can be unsafe in obstructive hydrocephalus with raised pressure, so imaging is reviewed first.
Bottom line
A lumbar puncture samples CSF and measures pressure from the lower back, used selectively — including the tap test in NPH — and only when safe.
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