Small Animal Radiology and Ultrasound: A Diagnostic Atlas and Text

700 Small Animal Radiolo g y and Ultrasono graphy
FIG. 6-49 A 6-year-old male Labrador Retriever with
tail biting for 8 weeks. On the lateral view the lumbar
sinus venogram revealed the opacified sinuses from C3
to the lumbosacral junction. On the ventrodorsal view
the right dorsal lumbar sinus is obstructed at L7-S1
(small black arrow), and the left dorsal lumbar sinus is
blocked slightly caudal to this level (long black arrow).
Differential diagnoses include disc extrusion, hypertrophy
of dorsal longitudinal ligament, degenerative joint
disease with periarticular osteophytes encroaching
upon the spinal canal, and fibrous adhesions within the
spinal canal from unknown causes. Diagnosis: L7-S1
disc extrusion.
This examination was successful in 80% of the dogs in one study. 215 Although compression
of the cauda equina could be observed when the lumbosacral joint was flexed, the compression
was demonstrated most often when the lumbosacral joint was extended. Some
normal variation in the appearance of the dural sac was described. 215 The normal vertebral
sinus venogram shows the sinuses in the sacral and caudal lumbar area. When the
venogram is abnormal, the sinus may be displaced laterally or dorsally or both.
Occasionally the sinus will be blocked and there will be a lack of opacification (Fig. 6-49).
Epidurography may demonstrate the prolapsed disc as a filling defect along the floor of the
spinal canal. In an experimental study, epidurography was better than myelography or
venography but demonstrated an injected silicon mass in only 41% of the dogs. 217 Both
false-positive and false-negative results may occur. 218 CT and MRI will demonstrate the
soft-tissue mass and loss of the epidural fat. MRI is superior to the other techniques
because it demonstrates the neural structures more completely. 220
M E TA B O L I C D I S E A S E S
Metabolic disease may be reflected in the spine by overall loss of bone density and the
appearance of relatively sclerotic vertebral endplates. 222 This can be due to hyperparathyroidism
(either primary or secondary), hyperadrenocorticism, osteoporosis due to immobility,
multiple myeloma, or other causes. 223-229 The loss of bone mineral usually is not a
problem but rarely may predispose to spinal fracture (Fig. 6-50). The spine of apparently
normal older cats frequently appears osteopenic (Fig. 6-51). A metabolic disorder that
results in vertebral changes is mucopolysaccharidosis in the cat. This may cause osteopenia,
agenesis of the odontoid process, widening of the intervertebral disc spaces, and shortening
of the vertebral bodies. 230 A diet that is overly rich in vitamin A can produce
proliferative changes involving the arches and lateral bodies of the cervical vertebrae. 231
Lead poisoning has been reported to cause metaphyseal sclerosis of the vertebral bodies. 231
Osteopetrosis may affect the vertebral bodies as well as the appendicular skeleton.
Hypothyroidism, either congenital or juvenile onset, will result in delayed closure of
growth plates, shortened vertebral bodies, and may result in intervertebral protrusions. 232-235