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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]
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 test involves removing 30–50 ml of CSF through a lumbar puncture, after which motor and cognitive function is clinically reassessed. [1] The name "Fisher test" is after C. Miller Fisher , a Canadian neurologist working in Boston, Massachusetts, who described the test.
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.
Image of patient receiving lumbar puncture (LP). Cerebrospinal fluid (CSF) obtained from an LP can be tested to aid in the diagnosis of NPH. The Miller Fisher test involves a high-volume lumbar puncture (LP) with removal of 30–50 ml of CSF. Gait and cognitive function are typically tested just before and within 2–3 hours after the LP to ...
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.
Quincke's puncture" is a somewhat outdated eponym for lumbar puncture, [4] [5] used for the examination of the cerebrospinal fluid in numerous diseases such as meningitis and multiple sclerosis. In 1893 he described what is now known as idiopathic intracranial hypertension, which he labeled "serous meningitis". [6]