Iris Van Soens DVM, PhD, Dipl. ECVN

Cerebrospinal fluid (CSF) analysis is a highly sensitive but poorly specific test for the detection of neurological disease. CSF is a clear, colorless, nearly acellular, protein poor ultrafiltrate of plasma.

Cerebrospinal fluid collection

Cerebrospinal fluid collection occurs in lateral recumbency from the atlantooccipital (AO) site or the caudal lumbar spinal arachnoid space (SAS) at L6-L7 under general anesthesia.¹ As CSF predominantly runs rostrocaudally, collection caudal to a suspected lesion is preferred.² Maximally, 1 mL of CSF per 5 kg of body weight should be collected.³ The collection site is clipped and aseptically prepared. Sterile surgical gloves, a spinal needle (22G, 38mm) or small gauge short sterile hypodermic needle (21G, 16mm or 23G, 25mm) and sterile plain collection and EDTA (polymerase chain reaction testing) tubes are required (video 97.1). 

Atlantooccipital collection

The skull and cervical vertebra are placed at the edge of the table. An area from the occipital protuberance to the end of the dorsal arch of C2 is prepared. The neck is fully flexed with the sagittal plane of the muzzle parallel to the table. The anatomical landmarks are the occipital protuberance, the most prominent parts of the atlas wings, and the dorsal arch of C2. The needle is inserted on the horizontal midline between the atlas wings, half of the way between the occipital protuberance and the most prominent part of the dorsal arch of C2. The needle is directed towards the chin and inserted perpendicular to the skin. The needle is slowly advanced, and resistance may be felt just before the needle pierces through the meninges. In cats this resistance may not be felt; we, therefore, recommend removing the needle’s stylette once inserted through the skin. When the needle enters the cistern, fluid appears in the needle hub (video 97.1). If blood is seen, the needle is withdrawn and the procedure is repeated after patient repositioning and reassessing landmarks. If bone is encountered, the needle is slightly withdrawn and repositioned caudally or cranially.

Lumbar spinal arachnoid space collection

The appropriate feline intervertebral space for CSF collection is L6-L7.¹ An area is prepared from L5 to S2 in the midline. A spinal needle with stylette is introduced just caudal to the spinal process of L7 and advanced at a 45° angle to the skin; the needle must be kept parallel to the table and on the midline. If the needle hits bone, its direction is slightly cranially or caudally. When the needle enters the spinal canal, a slight tail and/or pelvic limb twitch might be appreciated due to irritation of the nerve roots or cauda equina. In most cases, the needle is inserted until it touches the ventral part of the canal. At this moment, the stylette is removed and fluid appears in the needle hub. If fluid is not appreciated, the needle is slightly withdrawn to encourage CSF flow.

Sample handling

CSF contains very low protein and lipid concentrations; if sample processing is delayed more than one hour, cellular changes, such as nuclear pyknosis, lysis, and membrane disintegration, occur.^4,5 If analysis is delayed, protein concentration can be increased by adding autologous fresh or frozen serum or plasma (11% by the volume or 3 drops per 0.25 mL),⁵ fetal calf serum (20% of the volume), or a hetastarch at a ratio of 1/1.⁴

References

1. Skerritt G (editor). King’s Applied Anatomy of the Central Nervous Sytem of Domestic Mammals 2^nd edition. Wiley Blackwell, 2018.

2. Thomson CE, Kornegay JN, Stevens JB. Analysis of cerebrospinal fluid form the cerebellomedullary and lumbar cisterns of dogs with focal neurologic disease: 145 cases (1985-1987). J Am Vet Med Assoc 196:1841-1844, 1990.

3. Carmichael N. Nervous system. In Davidson M, Else R, Lumsden J (editors). Manual of small animal clinical pathology. British Small Animal Veterinary Association. 235-240, 1998.

4. Fry MM, Vernau W, Kass PH, Vernau KM. Effects of time, initial composition, and stabilizing agents on the results of canine cerebrospinal fluid analysis. Vet Clin Pathol 35:72-77, 2006.

5. Bienzle D, McDonnell JJ, Stanton JB. Analysis of cerebrospinal fluid from dogs and cats after 24 and 48 hours of storage. J Am Vet Med Assoc 216:1761-1764, 2000.