Findings
- From C4-5 to C6-C7, the articular processes are variably enlarged, sclerotic and irregularly-marginated. This is considered severe at C5-C6 and C6-C7, and mild to moderate at C4-5.
- Superimposed over the C5-C6 and C6-C7 articular process joints in the periphery, there are small rounded Lucent areas (arrowheads).
- On the below projection, the left articular process joint space is near-completely collapsed along its dorsal margin (arrow heads).
The inter- and intravertebral sagittal ratios are listed as follows (normal is greater than 48.5%):
C2-C3: 85% C3: 58%
C3-C4: 81% C4: 57%
C4-C5: 70% C5: 61%
C5-C6: 80 % C6: 60%
C6-C7: 82% C7: 66%
Conclusions
- Multifocal, various degrees of C4-C7 vertebral articular facet osteoarthrosis, worse at C5-C6 and C6-C7. Given the age and signalment of the patient, cervical vertebral stenotic myelopathy is considered most likely.
- The associated multifocal small articular process joints lucencies likely represent degenerative bone cysts.
Ultrasound
- Bilaterally, the C3-C6 articular process joints are variably irregularly marginated, most severe at C5-C6.
Post-mortem CT
- Variable degree of osteophytosis is identified and characterized as follows:
- C7-T1: mild bilateral (right>left)
- C6-C7: severe bilateral
- C5-C6: moderate to severe bilateral
- C4-C5: moderate bilateral
- C3-C4: mild bilateral
A little bit more…
- Cervical stenotic myelopathy (CSM) is due to malformation of the cervical vertebrae, resulting in stenosis of the vertebral canal and compression of the spinal cord
- Mostly affects larger fast growing horses.
- Presentation of clinical signs may be acute or progressive.
- Two forms:
- Dynamic compression: occurs primarily at C3-C4 and C4-C5. Usually developmental and seen in horses 8-18 months of age. Affects male and lightbreed/warmblood horses more commonly.
- Static compression: seen predominately in the caudal cervical region at C5–C6 and C6–C7 and mostly a sequela of osteoarthrosis. Seen in older horse ~1-4 yrs old.
- The following radiographic features may support a diagnosis of CSM:
- Subluxation of adjacent vertebrae
- Flaring of the caudal physis of the vertebral body (ski-slope appearance, yellow circle)
- Abnormal ossification of the vertebra
- Caudal extension of the dorsal laminae (blue arrows)
- Osteoarthrosis
- Myelography is the preferred method to screen for spinal cord compression.
- Careful: lateral radiographic projections are useful only in detecting dorsoventral compression.
- Various measurements have been proposed. All should be used with caution.
- Intra and Intervertebral Sagittal Diameter Ratios (Hahn et al.):
- Intravertebral sagittal ratio: a / d
- Intervertebral ratio: b / e or c / e
- A ratio <48.5% at any site for both intra- or Intervertebral measurements is best indicator of spinal cord compression. False positives and negatives are possible.
- Differential diagnoses for ataxias localizing to the cervical region: equine protozoal myeloencephalitis, trauma, equine degenerative myeloencephalopathy, and equine herpesvirus 1 myeloencephalopathy.
- Prognosis and response to therapy dependent on the age of the horse and the severity/duration of neurologic signs. Athletic performance is guarded.
References
- Berg, L. C., et al. “Ultrasonography of the equine cervical region: a descriptive study in eight horses.” Equine veterinary journal 35.7 (2003): 647-655.
- Hahn, Caroline N., et al. “Assessment of the utility of using intra‐and intervertebral minimum sagittal diameter ratios in the diagnosis of cervical vertebral malformation in horses.” Veterinary radiology & ultrasound 49.1 (2008): 1-6.
- Rush, Bonnie R., and J. Grady. “Cervical stenotic myelopathy.” Compendium Equine (2008): 430-437.
- Janes, J. G., et al. “Comparison of magnetic resonance imaging with standing cervical radiographs for evaluation of vertebral canal stenosis in equine cervical stenotic myelopathy.” Equine veterinary journal 46.6 (2014): 681-686.
- Moore, Bonnie Rush, et al. “Assessment of vertebral canal diameter and bony malformations of the cervical part of the spine in horses with cervical stenotic myelopathy.” American journal of veterinary research 55.1 (1994): 5-13.
- Woodie, Brett, Amy L. Johnson, and Barrie Grant. “Cervical vertebral stenotic myelopathy.” Veterinary Clinics of North America: Equine Practice 38.2 (2022): 225-248.
- Janes, J. G., et al. “Cervical vertebral lesions in equine stenotic myelopathy.” Veterinary pathology 52.5 (2015): 919-927.
