Cerebrospinal Fluid Collection and Examination

What is cerebrospinal fluid (CSF)?

Cerebrospinal fluid (CSF) is a clear, colorless body fluid found in the brain and spinal cord. A major function of CSF is to provide a cushion for the brain and spinal cord.

When is collection of CSF required?

CSF is usually collected when the pet shows clinical signs, such as seizures, incoordination, circling behavior, and neck or back pain, when no obvious cause (such as recent trauma) is known.

How is CSF collected?

CSF can be collected from two different sites: the cerebellomedullary cistern, located at the back of the head and the lumbar cistern, located at the lower part of the spinal column, near the pelvis. CSF collection requires a general anesthetic.

Your veterinarian will choose one of the two collection sites, based on the clinical signs your pet exhibits. The sample site is shaved and the skin is thoroughly disinfected. A small amount of CSF (about ½ teaspoon in total) is withdrawn into a sterile collection tube, using a special spinal needle.

Are there any risks associated with CSF collection?

Yes, some risks include those associated with any general anesthetic. It is important that your pet’s general health is evaluated prior to anesthesia by a series of screening tests. These tests include a complete blood count (CBC), a serum biochemistry profile, and a urinalysis (see handouts "Complete Blood Count", "Serum Biochemistry", and "Urinalysis" for more information on these tests).

Other risks are specific to CSF collection and include the risk of trauma to the spinal cord from the spinal needle, the possibility of brain herniation if the pet has increased pressure in the central nervous system, and the possibility of introducing bacteria through the collection site. These specific risks are minimized by careful attention to technique and a thorough evaluation of your pet prior to undertaking this procedure.

How is the CSF sample assessed?

A CSF sample must be processed within 30 to 60 minutes of collection, or the cells will deteriorate. Therefore, your veterinarian may refer your pet to a facility that is capable of immediately processing the sample. The veterinary pathologist will evaluate the sample for a total nucleated cell (white blood cell) count, a red blood cell count, a total protein determination, and a concentration of cells in the sample.

What can CSF evaluation tell us?

The evaluation of CSF frequently does not provide a specific diagnosis but often provides evidence to support the most likely diagnosis when additional factors are considered, such as the animals’ breed, age, and clinical signs.

Occasionally, a specific diagnosis can be reached. For example, bacteria or fungal organisms may be detected along with increased numbers of inflammatory cells, leading to a diagnosis of bacterial or fungal infection (e.g., meningitis or encephalitis). Sometimes, neoplastic (cancerous) cells may be found, indicating an underlying tumor in the brain or spinal cord.

Can any further evaluation of a CSF sample be done?

Yes, if the CSF protein content is markedly increased, further testing can include protein electrophoresis (see handout "Serum Protein Electrophoresis"). Electrophoresis will indicate what type of protein is involved in the increase, which will suggest its most likely cause.

If bacteria are identified within a CSF sample, or if large numbers of poorly preserved inflammatory cells are found, then a bacterial culture may be suggested. Occasionally, a sample may be evaluated for the presence of specific antibodies against infectious agents such as Toxoplasma or Ehrlichia.