College of Veterinary Medicine

Small Animal DX & Therapeutic Techniques

Collection of Cerebral Spinal Fluid 


csf_needle.JPG (14296 bytes) Spinal needles for use in small animals are available in 20 to 22 gauge and 1- 1/2 to 3- 1/2 inches in length. All spinal needles have a stylet.
Look at the tip of the needle. The bevel of the needle is shorter than the bevel of a hypodermic needle. Spinal fluid is obtained from the subarachnoid space which is a shallow space. If you use a needle with a long bevel, part of the opening into the lumen of the needle may be outside the subarchnoid space.
csf_landmarks.JPG (14400 bytes)

First method: The site of CSF collection from the cisterna magna (a) is between the occipital crest (b) and the most prominent points of the wings of the atlas (c). Although some textbooks recommend insertion of the needle at the halfway point between these two landmarks, I find one tends to be just anterior to the cisterna at the halfway point. Instead, I divide this distance into thirds and make the puncture 2/3 of the way back from the occipital crest.

 

Second method: Instead of the above mentioned landmarks, use your fingertips to trace the wings of the atlas to their most anterior margins. Palpate the occipital crest to define the midline. The cisterna is located on the midline, at the level of the anterior aspect of the wings of the atlas.
csf_head.jpg (22600 bytes) The animal should be placed in lateral recumbency with the nose flexed and ears pulled ventrally. The dorsum should be close to the edge of the table.

csf_collect.JPG (17670 bytes)

The puncture site is clipped of hair and aseptically prepared for the procedure. The person performing the procedure is wearing sterile gloves. The puncture is made on the midline. The needle is advanced slowly and carefully, removing the stylet at intervals to check for the presence of spinal fluid in the needle. If you are unsure if there is fluid in the needle, wipe the stylet across your sterile glove and look for a streak of fluid. If the needle is dry, replace the stylet and continue to slowly advance the needle. If the needle hits bone, and fluid has not been obtained, angle the needle cranial or caudel (which direction depends upon initial point of needle entry) and try to "walk" the needle off the bone into the cisterna. If you are unsure whether to "walk" cranial or caudel, remove the needle, revaluate landmarks and try again. If you obtain blood, let a few drops flow. If the fluid remains heavily bloody, remove the needle. You entered a lateral venous sinus. Try again. If the fluid becomes clear, collect it for analysis.

Although a manometer can be applied to the needle to measure the opening pressure of CSF, I find that application of the manometer often results in loss of the puncture. Therefore I do not routinely measure CSF pressures. You can collect CSF using a small (3ml) syringe or by gravity into a sterile container. If you use a syringe to collect CSF, do not attach the syringe to the hub of the needle. Rather use the syringe to aspirate drops of CSF that form in the hub of the spinal needle. Continue to hold the hub of the spinal needle as spinal fluid is collected so the tip of the needle is not dislodged from the subarachnoid space. Compression of the jugular veins will increase the rate of flow of CSF. The sample for cytology and fluid analysis is placed into an EDTA tube. Samples for bacterial or viral culture are not anticoagulated.

Last Edited: Jan 28, 2009 4:15 PM   

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