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.
Epidurography requires injecting iodinated contrast media into the epidural space. Injections are made either at the L7-S1
intervertebral space, between the sacrum and first coccygeal vertebra, or between coccygeal vertebrae. It is technically easier
to perform and has fewer side effects than myelography. Unfortunately, epidurograms can be difficult to interpret since it
is normal to see irregular filling as the neural structures and epidural fat displace contrast. A lack of contrast on the
ventral vertebral canal and compression of more than 50% of the vertebral canal are consistent with degenerative lumbosacral
stenosis (Figures 7 & 8).27,29 Make sure to perform myelography before epidurography if you plan to perform both procedures. Also obtain radiographs in
flexed, extended, and neutral positions to increase the likelihood of identifying a lesion.
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).