Cerebral Spinal Fluid Collection - (Spinal Tap)

Cerebral Spinal Fluid Collection

Alternative Names

Cisternal puncture; collecting a spinal fluid specimen; lumbar puncture; spinal tap; ventricular puncture

Why is the Test Performed?

This test is performed to measure pressures within the cerebrospinal fluid and to collect cerebral spinal fluid for testing. Cerebral spinal fluid collection can be a diagnostic test for many neurologic disorders, particularly infections and brain/spinal cord damage.

How The Test is Performed

Lumbar puncture (spinal tap) is the most common means of collecting a specimen of cerebral spinal fluid. You are positioned on your side with your knees curled up to your abdomen and your chin tucked in to your chest. (Occasionally this procedure is performed with the person sitting bent forward). The skin is scrubbed, and a local anesthetic is injected over the lower spine. The spinal needle is inserted, usually between the 3rd and 4th lumbar vertebrae. Once the needle is properly positioned in the subarachnoid space, pressures can be measured and fluid can be collected for testing. After the sample is collected, the needle is removed, the area is cleaned, and a bandage is applied. You will be asked to remain flat, or nearly flat, for 6 to 8 hours after the test. Lumbar puncture with fluid collection may also be part of other procedures, particularly a myelogram ( X-ray or CT scan after dye has been inserted into the cerebral spinal fluid).
Alternative methods of obtaining cerebral spinal fluid are rarely used, but may be indicated if there is a problem such as lumbar deformity or infection, which would make lumbar puncture impossible or unreliable. Cisternal puncture involves insertion of a needle below the occipital bone (back of the skull). It can be hazardous because the needle is inserted close to the brain stem. Ventricular puncture is even more rare, but may be indicated when sampling of cerebral spinal fluid is necessary in people with possible impending brain herniation. It is usually performed in the operating room. A hole is drilled in the skull and a needle is inserted directly into the lateral ventricle of the brain.

How The Test Will Feel

The position may be uncomfortable, but it is imperative that you remain in the curled position to avoid moving the needle and possibly injuring the spinal cord.
The scrub will feel cold and wet. The anesthetic will sting or burn when first injected. There will be a hard pressure sensation when the needle is inserted, and there is usually some brief pain when the needle goes through the meninges. This pain should stop in a few seconds. Overall, discomfort is minimal to moderate. The entire procedure usually takes about 30 minutes but may take longer. The actual pressure measurements and fluid collection only takes a few minutes.

How To Prepare for the Test

You must sign a consent form. You must be prepared to remain in the hospital for at least the 6 to 8 hours that you must remain flat.

Normal Values

Pressure: 50 to 180 mm H20
Appearance: clear, colorless
CSF total protein: 15 to 45 mg/100 ml
Gamma globulin: 3 to 12% of the total protein
CSF glucose: 50 to 80 mg/100 ml (or approximately 2/3 of serum glucose level)
CSF cell count: 0 to 5 WBC's, no RBC's
chloride: 110 to 125 mEq per liter
Note: mg/ml = milligrams per milliliter; mEq/L = milliequivalent per liter

Special Considerations

This test should not be performed on people in which increased intracranial pressure is suspected.

What Abnormal Results Mean

• Pressure, increased: increased intracranial pressure (pressure within the skull) from trauma or infection
   
• Pressure, decreased: obstruction to the flow of cerebral spinal fluid above the puncture site (spinal cord tumor), shock, fainting, diabetic coma
   
• Appearance

• cloudy: infection, white blood cells in the cerebral spinal fluid, protein in the cerebral spinal fluid, microorganisms
   
• bloody or reddish colored: bleeding within the brain or subarachnoid space, spinal cord obstruction, traumatic lumbar puncture (first specimen bloody, rest clear)
   
• brown, orange, yellow color: elevated protein in the cerebral spinal fluid, old (greater than 3 days) blood in the cerebral spinal fluid
   
• Protein, increased: blood in the cerebral spinal fluid, diabetes mellitus, polyneuritis, tumors, trauma
   
• Protein, decreased: rapid cerebral spinal fluid production
   
• Gamma globulin, increased: demyelinating disease (e.g. {ms} multiple sclerosis), neurosyphilis, Guillain-Barre syndrome
   
• Glucose, increased: systemic hyperglycemia (elevated blood sugar)
   
• Glucose, decreased: systemic hypoglycemia ( low blood sugar), bacterial or fungal infection (such as meningitis), mumps, old subarachnoid hemorrhage
   
• WBC, increased: active meningitis, acute infection, beginning of a chronic illness, tumor, abscess, brain infarction (stroke), demyelinating disease (such as {ms} )
   
• RBC: bleeding into the spinal fluid, traumatic lumbar puncture

Note: Chloride and other chemical tests help to differentiate disorders that affect the nerves (such as poliomyelitis) from meningeal disorders (meningitis, tuberculosis).
Additional conditions under which the test may be performed:

• anthrax
• arteriovenous malformation (cerebral)
• chronic inflammatory polyneuropathy
• dementia due to metabolic causes
• encephalitis
• epilepsy
• febrile seizure (children)
• generalized tonic-clonic seizure
• hydrocephalus
• inhalation anthrax
• normal pressure hydrocephalus (NPH)
• pituitary tumor
• Reye's syndrome

What the Risks Are

• Risks of lumbar puncture include:
  • hypersensitivity (allergic) reaction to the anesthetic
  • discomfort during the test
  • headache after the test
  • bleeding into the spinal canal
• brain herniation (if performed on a person with increased intracranial pressure), and resulting in brain damage and/or death
• damage to the spinal cord (particularly if the person moves during the test)
• Cisternal puncture or ventricular puncture carry additional risk of damage to the brainstem or brain tissue and risk of bleeding within the brain; resulting in incapacitation or death.

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