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Illustration depicting lumbar puncture (spinal tap) Spinal needles used in lumbar puncture Illustration depicting common positions for lumbar puncture procedure. The person is usually placed on their side (left more commonly than right). The patient bends the neck so the chin is close to the chest, hunches the back, and brings knees toward the ...
The CSF tap test, sometimes lumbar tap test or Miller Fisher Test, is a medical test that is used to decide whether shunting of cerebrospinal fluid (CSF) would be helpful in a patient with suspected normal pressure hydrocephalus (NPH).
Intracranial pressure (ICP) is the pressure exerted by fluids such as cerebrospinal fluid (CSF) inside the skull and on the brain tissue. ICP is measured in millimeters of mercury and at rest, is normally 7–15 mmHg for a supine adult. This equals to 9–20 cmH 2 O, which is a common scale used in lumbar punctures. [1]
Lumbar puncture is performed to measure the opening pressure, as well as to obtain cerebrospinal fluid (CSF) to exclude alternative diagnoses. If the opening pressure is increased, CSF may be removed for transient relief (see below). [8] The CSF is examined for abnormal cells, infections, antibody levels, the glucose level, and protein levels.
Given normal anatomy, the intracranial pressure will be reflected as a rapidly rising pressure measured from the lumbar needle, within 10–12 seconds. If there is a stenosis in the spine, there will be a damped, delayed response in the lumbar pressure, thus a positive Queckenstedt's maneuver.
Patients with CSF leaks have been noted to have very low or even negative opening pressures during lumbar puncture. However, patients with confirmed CSF leaks may also demonstrate completely normal opening pressures. In 18–46% of cases, the CSF pressure is measured within the normal range.
There are many cisterns in the brain with several large ones noted with their own name. At the base of the spinal cord is another subarachnoid cistern: the lumbar cistern which is the site for a lumbar puncture. Some major subarachnoid cisterns: Cisterna magna also called cerebellomedullary cistern - the largest of the subarachnoid cisterns.
A lumbar puncture is done by positioning the person, usually lying on the side, applying local anesthetic, and inserting a needle into the dural sac (a sac around the spinal cord) to collect cerebrospinal fluid (CSF). When this has been achieved, the "opening pressure" of the CSF is measured using a manometer.