Myelography in Horses (Equis) | Vetlexicon
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Myelography

ISSN 2398-2977


Introduction

  • Structures in the vertebral canal can be outlined with contrast medium.

Uses

  • To confirm the nature, extent and site of the cervical vertebral malformation Spine: cervical vertebral malformation (CVM) Spine: deformity (cf normal Spine: cervical normal flexed - myelogramSpine: cervical normal neutral - myelogram).
  • To confirm a diagnosis of spinal cord compression due to soft tissue changes.
  • To assess spinal cord compression associated with trauma Spine: fracture.
  • To differentiate normal cervical static stenosis at C5-6/C6-7 evident radiographically from cases associated with intramedullary lesions.

Advantages

  • Diagnosis not possible with other diagnostic modalities.

Disadvantages

  • Requires general anesthesia for complete assessment.
  • Infrequent side-effects include focal seizures, generalized seizures, peripheral neuropathy, blindness, increase in neurologic grade/ataxia, stiffness or neck pain, and non-specific hyperthermia.

Do not use technique unless the results would alter the management of the case.

  • Standing technique does not permit flexed, extended and ventrodorsal views.

Alternative techniques

Time required

Preparation

Procedure

  • Depending on number of views taken: 30-45 min.

Decision taking

Criteria for choosing test

  • Compression of >50% of the dorsal dye column considered significant but false positive and false negative results still occur Spine: cervical malformation C2-C3 - flexed contrast radiograph.
  • Minimum flexed dural diameter measurements definitive.
  • Loss of ventral dye column on flexion of the neck is normal.

Requirements

Personnel

Veterinarian expertise

  • Operator must be able to perform atlanto-occipital (AO) and/or lumbo-sacral (LS) CSF taps on recumbent horses and be familiar with assessment of cervical radiographs.

Anesthetist expertise

Other involvement

  • Personnel familiar with the flexion and extension necessary to achieve appropriate images will help to facilitate an efficient procedure.

Materials required

Minimum equipment

  • Anesthesia equipment Anesthesia: general - overview.
  • X-ray machine capable of 125 kV for caudal cervical spine.
  • Parallel grid.
  • 35 x 43 cm cassettes.

Ideal equipment

  • A specialized, non-radiopaque table that can be radiographed through makes image capture efficient, as the receiving plate can be easily moved under the horse and table.

Minimum consumables

  • 15 cm 18-gauge spinal needle.
  • 7.5 cm 18-gauge spinal needle.
  • Water-soluble, non-ionic contrast agents such as iohexol, iopamidol, metrizamide.

Iohexol is associated with fewer side-effects than metrizamide and achieves similar radiographic results.

Preparation

Pre-medication

  • Intravenous catheter placement (jugular vein, ideally on the side of horse that will be uppermost during the procedure).

Dietary preparation

  • Routine fasting per anesthesia protocol.

Site preparation

  • Clip and sterilely prepare the AO site for injection.

Restraint

Technique

Approach

Step 1 - Position the horse

  • Position in right lateral recumbency.
  • Elevate head and neck elevated to ~25° on an inclined board.
  • Head placed at right angle to neck.

Core procedure

Step 1 - Preparation

  • Clip and sterile preparation of atlanto-occipital injection site and lumbosacral site.

Step 2 - Check cerebrospinal fluid 

  • Puncture lumbosacral subarachnoid space with 15 cm 18-gauge spinal needle CSF: collection.
  • Allow 10-30 ml of CSF to drip out.
  • Examine CSF for gross and microscopic evidence of inflammation.

Cancel procedure if evidence of inflammation found.

Step 3 - Insert second needle 

  • Insert second needle into the atlanto-occipital subarachnoid space CSF: collection.

Step 4 - Inject contrast medium 

  • Slowly inject 30-50 ml of the contrast medium into the atlanto-occipital subarachnoid space while CSF is allowed to flow from the lumbosacral needle.
  • Leave head elevated for 3-5 min.

Note

  • A one needle procedure through the AO site is also commonly performed which avoids the need for a LS egress, however, CSF pressure increases will transiently occur

Exit

Step 1 - Radiography 

  • Radiograph cervical vertebrae in neutral, flexed and extended positions.
  • Ventrodorsal views may be helpful.

Aftercare

Immediate Aftercare

Monitoring

  • Monitor for side effects such as focal seizures, generalized seizures, peripheral neuropathy, blindness, increase in neurologic grade/ataxia, stiffness or neck pain, and nonspecific hyperthermia

General Care

Analgesia

Wound protection

  • A protective wrap is generally unnecessary and infrequently placed.
  • CSF extravasation post-injection is uncommon in horses.

Potential complications

  • Worsening ataxia/neurologic grade, pyrexia, neck pain/stiffness.

Outcomes

Complications

  • Pyrexia.
  • Fever.
  • Hyperesthesia, neck muscle fasciculations and exacerbation of neurologic signs.
  • Prolonged anesthetic recovery.

Reasons for treatment failure

  • Failure to enter the AO space.
  • Equipment failure.
  • Non-diagnostic images.

Prognosis

  • Depends on the result of the examination.

Further Reading

Publications

Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Gough S L, Anderson J D C & Dixon J J (2020) Computed tomographic cervical myelography in horses: Technique and findings in 51 clinical cases. J Vet Intern Med 34 (4), 2142-2151 PubMed.
  • Estell K, Spriet M, Phillips K L et al (2018) Current dorsal myelographic column and dural diameter reduction rules do not apply at the cervicothoracic junction in horses. Vet Radiol Ultrasound 59 (6), 662-666 PubMed.
  • Mullen K R, Furness M C, Johnson A L et al (2015) Adverse reactions in horses that underwent general anesthesia and cervical myelography. J Vet Intern Med 29 (3), 954-60 PubMed.
  • Levine J M, Scrivani P V, Divers T J et al (2010) Multicenter case-control study of signalment, diagnostic features, and outcome associated with cervical vertebral malformation-malarticulation in horses. JAVMA 237 (7), 812-22 PubMed.
  • van Biervliet J et al (2004) Evaluation of decision criteria for detection of spinal cord compression based on cervical myelography in horses: 38 cases (1981-2001). Equine Vet J 36 (1), 14-20 PubMed.
  • Widmer W R et al (1998) A prospective clinical trial comparing metrizamide and iohexol for equine myelography​. Vet Radiol Ultrasound 39 (2), 106-109 PubMed.
  • Tomizawa N et al (1994) Relationships between radiography of cervical vertebrae and histopathology of the cervical cord in wobbling 19 foals. J Vet Med Sci 56 (2), 27-233 PubMed.