Small Animal Radiology and Ultrasound: A Diagnostic Atlas and Text

Chapter Six The Spine 683
rarely encroaches upon the spinal cord or on the nerve root. Thus spondylosis almost never
has clinical ramifications except for pain in “nearly” bridged vertebrae. In rare cases the
amount of spondylosis may become extensive. Bridging spondylosis involving four or more
contiguous vertebrae has been termed diffuse spinal idiopathic hyperostosis (DISH) (Fig. 6-
21). Close scrutiny of these animals will reveal stiffness in some individuals. Spondylosis
may be seen at necropsy in dogs as young as 6 months of age but is usually a disease of older
large-breed dogs. 103 The ossification may start from one vertebra and grow toward the
other, may start on both and meet in the middle, may start in the middle and progress in
both directions, or may have any combination of these variations. Spondylosis may result in
complete spinal fusion. Some mechanical interference with normal activity may result, but
in most cases the bony lesion does not produce clinical signs. Narrowing of the intervertebral
disc space may occur secondary to spondylosis, but in most cases the disc is not
prolapsed. Spondylosis may also occur secondary to chronic disc prolapse. The distinction
between these two conditions usually is based on the amount of spondylosis that is present.
If only one disc space is affected and there is no evidence of spondylosis at other sites, then
the lesion most likely is primary disc degeneration with secondary spondylosis. If there is
extensive spondylosis with only one narrowed disc space, then the lesion most likely is
primarily spondylosis deformans with secondary disc degeneration. If clinical signs are
present, a myelogram is needed to document or rule out disc prolapse.
Degenerative Joint Disease. Arthritis of the articular facets of the spine may be seen. This
may result in the production of periarticular osteophytes with irregularity of the articular
facets and loss of the normal joint space (Figs. 6-22 and 6-23). The clinical significance of this
radiographic change is unknown but may be a source of “back pain” if severe. On rare occasions
the osteophytes may become so large that they impinge upon the spinal cord or nerve
roots. Another rare problem is the development of synovial cysts arising from the chronically
inflamed joint capsules. These cysts may develop in the extradural space and ultimately
impinge upon the spinal cord. Myelographic findings usually indicate a dorsal, single, or bilateral
extradural mass. 104 Lesions with a stalk may be found anywhere in the extradural space. 105
Fig. 6-20 A 12-year-old male
mixed breed dog with occasional
vomiting. A and B, Lateral radiographs
revealed moderate bony
bridging at several intervertebral
spaces. These sites are not considered
to be active sites of disease.
Diagnosis: Spondylosis.
A
B