Cerebrospinal fluid is fluid found in the subarachnoid space, surrounding the brain and spinal cord. The subarachnoid space is the area between the tough outermost membrane layer (called the dura mater) and the softer innermost layer (the pia mater) that covers the brain and spinal column.

The fluid resembles serum, and its purpose is to maintain equal pressure within the brain and spinal cord. A cerebrospinal fluid (CSF) tap is the collection of this fluid for diagnostic purposes.

What Does A Cerebrospinal Fluid Tap Reveal?

Veterinarians collect a sample of this fluid to diagnose brain or spinal cord disease. It is typically performed to diagnose the cause of abnormal neurological signs such as seizures, altered mental status, and other abnormalities. It is often performed after advanced imaging techniques, such as computed tomography (CT scan) and magnetic resonance imaging (MRI) uncovers some abnormality in the central nervous system. Abnormalities may include inflammation, viral or bacterial infection, bleeding, or suspected tumors.

A cerebrospinal fluid tap may also be performed to deliver pain-relieving medication prior to a surgical procedure. It may also be performed to inject dye in the spinal column to detect and abnormal position of the spinal cord. After the dye is injected, radiographs (x-rays) are taken, which is referred to as a myelogram.

How Is a Cerebrospinal Fluid Tap Performed?

There are two different types of spinal taps: a cisternal tap and a lumbar tap.

To perform a cisternal tap, the back top of the neck is shaved and sterilized. A spinal needle is inserted at the base of the skull, and into the spinal column, penetrating the dura mater and arachnoid membranes to the subarachnoid space. A syringe is attached to the spinal needle to draw out the fluid. The fluid can also be allowed to drip into a collection tube.

A lumbar tap (also called lumbar puncture) is performed in the lower back of a patient. The area is shaved and sterilized, and a spinal needle is inserted. A syringe is attached to the needle and fluid is withdrawn or the fluid is allowed to drip into a collection tube.

Is a Cerebrospinal Fluid Tap Painful?

Because the procedure is performed under general anesthesia, no pain is involved. There may be some pain and discomfort following the procedure. As with people, the pain experienced will vary among individual animals.

Is Sedation or Anesthesia Required?

General anesthesia is necessary to perform the procedure. General anesthesia will induce unconsciousness, complete control of pain and muscle relaxation. Pets undergoing this procedure often receive a pre-anesthetic sedative-analgesic drug to encourage relaxation followed by a brief intravenous anesthetic to allow placement of a breathing tube in the windpipe, and subsequently inhalation (gas) anesthesia in oxygen during the actual procedure.