Cerebrospinal taps are also performed as a component of contrast myelography.

Transcription

1 Flrence JUVET Resident in internal medicine University Veterinary Hspital, UCD Belfield DUBLIN 4 flrence.juvet@ucd.ie Hw t d a CSF tap? Definitin: CSF is an ultrafiltrate f plasma that is prduced predminantly by the chrids plexi within the ventricular system. CSF flws caudally thrugh the ventricular system t the central canal f the spinal crd tward the cauda equina. Indicatins Neurlgical signs that are referable t the CNS. Cerebrspinal fluid cllectin is helpful in evaluating any rganic brain r spinal crd disease. It helps t differentiate inflammatry, immune-mediated, degenerative, haemrrhagic, and neplastic frms f parenchymal disease. It is cnsidered when there is a recent histry f central nervus system (CNS) signs, and when neurlgic deficits are discvered upn physical examinatin. It is frequently perfrmed after advanced imaging (cmputed tmgraphy, magnetic resnance imaging) techniques demnstrate abnrmalities in the CNS. Cerebrspinal taps are als perfrmed as a cmpnent f cntrast myelgraphy. NB: CNS disease des nt cnsistently cause alteratins in CSF; abnrmalities depend n the lcatin and extent f the CNS lesin. Parenchymal, extradural and nn exfliative lesins may cause minimal (prtein elevatin) r n change in the CSF. Preparatin: General anaesthesia is required fr this prcedure. A spinal needle with a stylet is used fr the spinal tap. In small dgs and cats, a 22-gauge, 1"- 2" needle is used. In large dgs, a 20-gauge, 1"-3" needle is used. The CSF is allwed t drip directly int the cllectin tube (EDTA and plain). Psitining: 1. Cisternal tap - The animal is placed in lateral recumbency, with the head flexed ventrally t almst 90-degrees s that the atlant-ccipital space is pened. The ears are pulled frward t tense the skin n the back f the neck. The nse is held parallel t the table. A sandbag may be used under the head t keep the spine at a cnsistent distance frm

2 the surface f the table. A large rectangle shuld be clipped includindg the ccipital prtuberance the base f the ears and up t C 3 caudally and prepped surgically. 2. Lumbar tap - The animal is placed in lateral recumbency with the hind legs pulled in a cranial directin. This pens the interarcual space between the lumbar vertebrae. The animal must be immbilized with the entire spine in a straight psitin. A large rectangle ver the lumbar spine shuld be clipped and prepped surgically. Technique: Fr the ccipital tap: 1. The external ccipital prtuberance and the rstral wings f the atlas are palpated. Using the index finger, the depressin between these three structures is lcated. The needle will be inserted at this depressin. 2. The spinal needle with stylet in place is inserted thrugh the skin, subcutis and muscles f the neck. Bth the dura mater and arachnid membranes are penetrated with the needle. A slight ppping sensatin may be detected when the needle enters the subarachnid space. 3. The stylet is withdrawn with the advancement f the needle thrugh the membranes s that the presence f fluid can be detected. If n fluid is seen, the stylet is replaced befre the needle is advanced further. 4. The fluid is cllected by allwing the fluid t drip int the cllectin tube. 5. The needle is then smthly withdrawn and a swab is applied fr 1 min.

3 Prcedure fr the Lumbar Tap 1. The drsal spinus prcesses f the lumbar vertebrae are lcated, with attentin fcused n the L4-5 and L5-6 intervertebral spaces. 2. The spinal needle is inserted thrugh the skin, subcutis and musculature ver the spine and int the space immediately cranial t the drsal spinus prcess f the lumbar vertebra. Sample handling: CSF is submitted fr analysis, cytlgy (EDTA tube) and micrbilgic culturing (plain tube) and sme serlgies (i.e Distemper, Txplasma, Nespra in dgs and Txplasma in cats). Analysis f CSF requires the use f a cytspin centrifuge because the cellular cmpnent is very small. Prcessing f the sample must als be dne quickly (within 20 t 60 minutes), as the CSF cntains very little prtein, cells degrade when allwed t sit ver night r during mailing. The sample may be fixed using 2 drps f 10% buffered frmalin per ml f CSF if the sample can nt be delivered immediately t the lab. Hwever nt every lab is equipped fr cytlgical evaluatin f fixed CSF. Anther technique t retard cellular degeneratin is the additin f 20% albumin (2 drps). Prtein and enzyme cncentratins are relatively stable and submissin using rutine methds is usually sufficient fr accurate determinatins. Nrmal CSF is cmpletely clear and clurless. The sample may appear turbid with infectin r marked inflammatin and white bld cell (WBC) cunts > 500/ml. The clur may be pink t red with red bld cell (RBC) cunts > 6000/ml, and this is mst ften secndary t recent haemrrhage r haemrrhagic cnditins. A yellw clur (xanthchrmia) may be imparted t the fluid frm episdes f prir haemrrhage. Nrmal WBC cunts are < 8 frm the cisterna magna and < 12 frm the lumbar cisterna. All nrmal cells are mnnuclear in cell type.

4 Red bld cell cunts - Nrmal CSF cntains n red bld cells. With iatrgenic haemrrhage, ne WBC is expected fr every 500 RBCs. RBC cunts higher than this indicate pathlgic haemrrhaging. The presence f crenated RBCs r erythrphagcytsis is evidence f prir haemrrhage. Prtein levels - In nrmal CSF prtein levels are usually < 25 mg/dl in the dg and < 20 mg/dl in the cat when cllected frm the cisterna magna, and < 40 mg/dl when cllected frm the lumbar cistern. Prtein is elevated in any cnditin that causes breakdwn f the bld-brain barrier (e.g. inflammatin, infectin) r necrsis within the CNS (e.g. neplasia). Elevated CSF prtein withut cncurrent elevatins in cell cunts may be seen with feline pliencephalmyelitis, feline ischemic encephalpathy, canine degenerative myelpathy, and certain brain and spinal crd tumurs. With iatrgenic haemrrhage, it is imprtant t nte that the presence f 1000 RBCs will increase the CSF prtein level by 1 mg/dl. Antibdy titers - Titers t certain infectius diseases may be measured in CSF. Examples include canine distemper, txplasmsis and nesprsis. Culture and sensitivity testing - These tests are indicated with any CSF sample that has an elevated cell cunt, particularly if neutrphils predminate. Culturing may be attempted fr aerbic bacteria, anaerbic bacteria (and fungi). A high number f false-negative results ccur with bth bacterial and fungal infectins f the CNS. Cmplicatins: CSF cllectin requires a general anaesthesia and is assciated with uncmmn but serius risks: 1. Haemrrhage 2. Cerebellar herniatin (signs: nystagmus, change in papillary size, changes in respiratin pattern and reflex abnrmalities. 3. Respiratry arrest 4. Spinal crd puncture NB: CSF analysis shuld be perfrmed prir t inject radipaque cntrast medium fr a myelgraphy as these can lead t exacerbatin f the clinical signs when meningitis is present.

5 Suggested readings: BSAVA Manual f Canine and Feline Neurlgy BSAVA Manual f Canine and Feline Clinical Pathlgy