Myelography and epidurography

Occasionally, contrast radiographic studies have been used to diagnose degenerative lumbosacral stenosis. Myelography requires injecting iodinated contrast agents into the subarachnoid space either at the cisterna magna or L5-L6 intervertebral space. In general, the dural sac ends between the L6 and S1 vertebrae in dogs.⁴ Large-breed dogs often have more cranial terminations than small-breed dogs.⁵ In some dogs, the dural sac extends into the sacrum, but the dural sac tends to lie more dorsally in the vertebral canal.¹⁴ As a result, ventral lesions may not be identified. Consequently, myelography generally is not helpful in diagnosing degenerative lumbosacral stenosis. Myelography does allow clinicians to evaluate the entire vertebral column for other lesions.

Figure 7: A lateral epidurogram of a dog. Iodinated contrast has been injected into the epidural space between the first and second coccygeal vertebra. Note the filling defect overlying the lumbosacral space consistent with intervertebral disk herniation; Figure 8: Another lateral epidurogram. Note the large filling defect overlying the lumbosacral intervertebral disk; Figure 9: Axial CT images at the level of the lumbosacral intervertebral disk space in a dog. The image on the right is a soft tissue window while the image on the left is a bone tissue window. Note the narrowing of the vertebral canal and lack of epidural fat (long white arrow), as well as ventral spondylosis deformans (short white arrows). The lack of epidural fat can be seen in the bottom right inset (black arrow).