Page 230 - Adams and Stashak's Lameness in Horses, 7th Edition

196 Chapter 3

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B

A

Figure 3.6. (A and B) Lateromedial (LM) projections of the distal material consistent with a communication between the draining tract
limb after injection of iodinated contrast material into an externally and the bursa. Image (B) shows a well‐defined filling defect outlined by
draining tract. Image (A) shows filling of the navicular bursa with contrast contrast material representing a wood foreign body (black arrows).

sagittal ratio methods for diagnosing cervical vertebral
malformations. It was concluded that a sagittal diameter
ratio of less than or equal to 48% at any intra‐ or
intervertebral site from C2 to C7 represents cervical ver­
tebral malformation. Hughes et al. examined intra‐
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and inter‐observer agreement of cervical vertebral
sagittal diameter ratios and found that intra‐observer
repeatability was moderate and that significant inter‐
observer variation was seen, as such acceptable agree­
ment was rarely achieved for any observer pair.
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Considering the above discussion, the practitioner
should be aware of the inevitable false‐positive results
because some horses may have a narrow vertebral site
and not necessarily represent a spinal cord compressive
lesion, as well as being cognizant of the subjective nature
of such measurements and their interpretation.
Myelography with nonionic, water‐soluble contrast
material has proven to be an acceptable and safe diag­
Figure 3.7. Lateral survey radiograph of the caudal cervical nostic procedure in the horse. 8,33,36,44 Iohexol and iopa­
spine, showing moderate enlargement and irregular bony prolifera­ midol are nonionic contrast agents that have relatively
tion (arrow heads) around the articular facets of C6–C7, with few side effects. 33,37,61 With the horse under general anes­
narrowing of the intervertebral foramen (arrow). There is also mild thesia and in the lateral recumbent position, its head is
enlargement of the articular facets at C5–C6.
elevated, and approximately 40–50 mL iopamidol 300,
or 370 mg iodine/mL or iohexol 300, or 350 mg iodine/
mL is injected into the subarachnoid space at the cis­
the intervertebral sagittal ratio as a way to evaluate sur­ terna magna. 8,36 Iohexol may produce slightly less of an
vey radiographs for cervical vertebral malformation. inflammatory reaction than iopamidol, but both con­
This technique represents the ratio of the minimal dis­ trast agents are relatively safe for myelography in the
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tance taken from the most cranial aspect of the vertebral horse. The higher concentration contrast material pro­
body to the most caudal aspect of the vertebral arch of vides better contrast in large horses.
the vertebra located cranially and the maximal sagittal Lateral cervical radiographs centered over the cra­
diameter of the vertebral body. A study by Hahn et al. nial, mid‐cervical, and caudal cervical regions are made
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in 2008 compared the utility of the intra‐ and intervertebral with the spine in a neutral position. A flexed lateral