Scientific programme: neurology. in: proceedings of the 49th british equine veterinary association congress, 2010 - birmingham

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Neurology
Sponsored by University of Liverpool 16.20–16.40
‘How to’ interpret equine cervical radiographs
and other imaging modalities
Richard J. Piercy
Royal Veterinary College, London, UK.
Plain radiography of the cervical vertebrae can be used to assess lesions occur between, rather than within, the vertebrae (Hahn et the likelihood of cervical stenotic myelopathy in horses with spinal al. 2008). Particularly high quality radiographs are usually required ataxia (Moore et al. 1994), but accurate assessment requires a for such measurements, but analysis suggests that this approach precise lateral radiograph (Rush 1998), ensuring that the ventral may be helpful in differentiating CSM from other conditions (Van prominences of the transverse processes are perfectly overlying Biervliet 2007). Further comparison of both methods in a large each other. Radiographic obliquity results in indistinct margins of group of horses is needed based on a gold standard diagnosis the ventral aspect of the vertebral canal and results in erroneous established at post mortem examination, since myelography is values for objective measurements. A thorough understanding of problematic (see discussion below), although available post the 3 dimensional anatomy of the cervical vertebrae aids in mortem material may be skewed towards severely affected horses, interpretation (Withers et al. 2009).
since these animals may more often be subjected to euthanasia.
Cervical radiographs should be evaluated subjectively and Plain radiography is often considered sufficient to make a objectively. Subjective interpretation is based on examining for presumptive diagnosis of cervical compression without the need presence of 5 characteristic malformations of the cervical vertebrae for further tests. In countries where EPM or other conflicting that include (1) flare of the caudal epiphysis of the vertebral body; differential diagnoses are possibilities, many clinicians favour (2) abnormal ossification of the articular processes; (3) myelography for diagnosis. Unfortunately, for most inter-vertebral subluxation/misalignment between adjacent vertebrae; (4) extension sites, myelography results in a high number of false positive and of the vertebral caudal dorsal lamina and (5) osteoarthritis of the false negative results (van Biervliet et al. 2004). Myelography articular processes. Estimating the significance of lesions identified remains, however, a prerequisite if surgical intervention is through subjective interpretation can be hard and is based on the considered a viable option on the basis of severity of signs and clinician’s experience and interpreting the balance of probability. For the owner’s wishes and expectations. This is because plain example, osteoarthritis of (especially the caudal) vertebral articular standing radiography does not definitively pinpoint the actual site processes is recognised commonly in normal horses (Whitwell and of the compressive lesion(s) (Moore et al. 1994). Note that neck Dyson 1987). Hence recognition of characteristic vertebral flexion and extension while under anaesthesia are contraindicatedif there is evidence of compression on the initial neutral views.
malformations is considered supportive in diagnosis at best Ventrodorsal projections may be attempted in small or young (Papageorges et al. 1987). Oblique radiographs are helpful in certain animals, especially in the cranial neck and may demonstrate an circumstances (Withers et al. 2009).
assymetric compressive lesion that might otherwise account for Objective assessment of vertebral canal diameter is more some false negative diagnoses in larger horses.
accurate than subjective evaluation of vertebral malformation foridentifying young horses affected by CSM but may lead to false References
negative diagnoses in older horses (Levine et al. 2007). Both inter- Hahn, C.N., Handel, I., Green, S.L., Bronsvoort, M.B. and Mayhew, I.G. (2008) and intra-vertebral measurements are used. The sensitivity and Assessment of the utility of using intra- and intervertebral minimum sagittal specificity of the intra-vertebral sagittal ratio method is diameter ratios in the diagnosis of cervical vertebral malformation in horses. Vet. approximately 90% for vertebral sites between the third and Radiol. Ultrasound 49, 1-6.
seventh cervical vertebrae (Moore et al. 1994). In most normal Levine, J.M., Adam, E., MacKay, R.J., Walker, M.A., Frederick, J.D. and Cohen, N.D.
(2007) Confirmed and presumptive cervical vertebral compressive myelopathy in horses, the sagittal ratio exceeds 52% from the third to sixth older horses: a retrospective study (1992-2004). J. vet. intern. Med. 21, 812-819.
cervical vertebrae and 56% at the seventh cervical vertebrae in Moore, B.R., Reed, S.M., Biller, D.S., Kohn, C.W. and Weisbrode, S.E. (1994) Assessment horses greater than 320 kg. The positive predictive value of such of vertebral canal diameter and bony malformations of the cervical part of the
spine in horses with cervical stenotic myelopathy. Am. J. vet. Res. 55, 5-13.
measurements is probably higher and the negative predictive value Papageorges, M., Gavin, P.R., Sande, R.D., Barbee, D.D. and Grant, B.D. (1987) lower, in ataxic horses from countries where conflicting diagnoses Radiographic and myelographic examination of the cervical vertebral column in (such as EPM) are not routinely encountered (i.e. false positives are 306 ataxic horses. Vet. Radiol. 28, 53.
less likely, but false negatives are more likely because the underlying Rush, B.R. (1998) Spinal radiography and myelography. In: Current Techniques in Equine Surgery and Lameness, 2nd edn., Eds: N.A. White and J.N. Moore, W.B.
prevalence of CSM in ataxic horses is higher). Similarly, the positive and negative predictive values of objective cervical radiography Van Biervliet, J. (2007) An evidence-based approach to clinical questions in the practice measurements in the absence of ataxia (for example during of equine neurology. Vet. Clin. N. Am.: Equine Pract. 23, 317-328.
prepurchase radiography) have not been evaluated, but false van Biervliet, J., Scrivani, P.V., Divers, T.J., Erb, H.N., de Lahunta, A. and Nixon, A. (2004) Evaluation of decision criteria for detection of spinal cord compression based on positives are likely to be more, and false negatives, less common, cervical myelography in horses: 38 cases (1981-2001). Equine vet. J. 36, 14-20.
since the prevalence of CSM in this population will be much lower. Whitwell, K.E. and Dyson, S. (1987) Interpreting radiographs. 8: Equine cervical Some clinicians advocate use of ratiometric measurements that vertebrae. Equine vet. J. 19, 8-14.
take into account the distance between adjacent vertebrae (inter- Withers, J.M., Voute, L.C., Hammond, G. and Lischer, C.J. (2009) Radiographic anatomy of the articular process joints of the caudal cervical vertebrae in the vertebral ratios) based on the rationale that most compressive horse on lateral and oblique projections. Equine vet. J. 41, 895-902.
Proceedings of the 49th British Equine Veterinary Association Congress 2010 - Birmingham, United Kingdom Thurs H5 v2_Layout 1 17/08/2010 16:00 Page 53 Reprinted in IVIS with the permission of BEVA Thursday 9th September 2010
16.40–16.50
‘How to’ inject cervical vertebral facets, using ultrasound
guidance
Richard Hepburn
The Willesley Equine Clinic, B&W Equine Group, Byams Farm, Willesley, Tetbury, Gloucestershire GL8 8QU, UK.
A thorough understanding of cervical vertebral anatomy and the needle entry will vary greatly with head position. The probe should ultrasonographic appearance of the cervical vertebral facet joints be placed inside a sterile glove or probe cover that has been filled is essential before attempting facet injections. This author with a small amount of acoustic gel. The horse’s head is then held recommends Berg et al. (2003), which has excellent images in a neutral position. An image of the affected joint is obtained, showing the location and appearance of the cervical facets. with the joint space positioned centrally within the scan image.
Cervical facet joints are formed from the caudal articular The depth of the joint should be noted (typically about 4–5 cm).
process of the cranial vertebra and the cranial process of the The probe is then held in a fixed position, and a 12.5 cm 18 gauge caudal vertebra. The joint is the most dorso-lateral point of the spinal needle is inserted approximately 1 cm dorsal to the probe, vertebra, being approximately 4–6 cm dorsal to the palpable with its long axis parallel to the long access of the probe, at a transverse processes, and sits at an angle of approximately 30–40° downward angle that will cause the needle to cross the centre of the ultrasound image at the depth of the facet joint. The needle Imaging the facet joints for injection is most effectively is then advanced towards and into the joint and is seen as a performed using a micro-convex or phased array probe (6–10 hyperechoic line on the ultrasound screen. Repositioning can be MHz, 4–8 cm depth), as the small footprint facilitates easy needle required and can initially be confusing (Fig 2).
placement (Fig 1).
With the standard image right is dorsal and left is ventral.
A 10 cm square area dorsal to the transverse process of the The skin acts as a pivot: to move the tip of the needle dorsally, affected vertebra should be clipped with a No. 40 blade. A the hub should be moved ventrally and vice versa. Alternatively, standardised approach to the ultrasound image aids interpretation a biopsy guide can be attached to the probe and the biopsy line - this author always positions the probe reference dorsal, with the on the ultrasound machine positioned so it transects the joint; screen reference to the right, and holds the probe in a transverse however, if the horse moves excessively during needle placement orientation. The probe is placed 8–10 cm dorsal to the palpable the biopsy guide can prevent easy repositioning. Both techniques transverse process, angled slightly downwards and then moved are equally accurate, with 89% injections being either intra- ventrally until the joint margins are imaged. If vertebral body is articular or intracapsular (Nielsen et al. 2003).
imaged the probe should be moved cranially or caudally to image The needle will typically enter the joint margin easily, if not facet neck and then joint. Angling the probe in a slight cranial raising the head can open the joint space. No attempt should be direction can aid identification of the joint space. The facet joint made to advance the needle deeper as dural puncture could margins are seen as 2 crescent shaped hyperechoic contours which occur. Synovial fluid will occasionally flow spontaneously or can cast acoustic shadows, separated by an anechoic joint space. It is be aspirated. Injection should be easy and if resistance is felt the often possible to image deeper into the joint space. A reasonable needle should be rotated or withdrawn 1–2 mm as the tip may degree of variation in ultrasonographic appearance occurs be embedded in articular cartilage. Injection should be directly between horses and between individual facet joints. Small visualised as hyperechoic sparkling within the joint space. Whilst osteophytes can often be imaged, as can some lipping of the joint communication between the left and right facets of a given margins. Significant changes include proliferation of bone dorsally, articulation can occur, they should essentially be treated as multiple osteophytes and widening of the joint space. separate joints and injected individually. This author uses either Prior to injection the horse should be sedated (0.01 mg/kg triamcinolone acetate when injecting 2 facet joints (16 mg max bwt detomidine and 0.01 mg/kg bwt butorphanol) and per horse - 8 mg/joint), or methyl-prednisolone acetate when pretreated with a NSAID (1 mg/kg bwt flunixin meglumine) to limit muscular discomfort from the procedure. The clipped area The reader should be aware that an alternative technique over the affected joint should then be prepared aseptically. The exists, where the ventral margin of the facet is injected, with the use of local anaesthetic is typically unrewarding as the location of needle positioned ventral to the probe, with the joint space Proceedings of the 49th British Equine Veterinary Association Congress 2010 - Birmingham, United Kingdom

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