Small Animal Radiology and Ultrasound: A Diagnostic Atlas and Text

Chapter Six The Spine 701
FIG. 6-50 A 9-year-old female mixed breed dog with polyuria and polydipsia for 3 months and acute
back pain. The lateral radiograph of the thoracolumbar spine revealed a decrease in length of both
the body and arch components of T11, as well as a generalized osteopenia. Differential diagnoses for
the osteopenia include hyperadrenocorticism, primary or secondary hyperparathyroidism, and
nutritional deficiencies. Diagnosis: Pathologic impaction fracture of T11 due to primary hyperparathyroidism.
FIG. 6-51 A 10-year-old male domestic short-haired cat with hematuria. The spine revealed diffuse
osteopenia. Although many differential diagnoses should be considered, the most common is senile
osteopenia of unknown etiology. Diagnosis: Senile osteopenia.
Chronic vitamin A intoxication, usually associated with diets limited to liver, has been
documented to cause spondylosis and ankylosing spondylosis. 236
T R AU M A
Fractures. Spinal trauma may cause fractures or soft-tissue injuries. Minimal trauma may
result in fractures of abnormal vertebrae (e.g., those affected by tumor or other pathologic
process). 237 The most frequent site of injury in cats is the sacral spine, while in dogs the
lumbar spine is affected slightly more frequently than the sacral and thoracic spine. 238
Fractures most frequently occur through the vertebral body. Injury to more than one vertebra,
especially adjacent vertebral segments, is not uncommon, particularly in the lumbosacral
area. It is difficult to determine the extent of the spinal cord injury based solely on
the radiographic appearance of the fracture, because the nature of the fracture and the level
at which it occurs influence the neurologic signs. As a general rule, displacement of the
fragments more than one-half the diameter of the spinal canal is indicative of a severe
spinal cord injury. One categorization of spinal fractures is by the type of force that caused
the fracture (impaction, avulsion, shearing, bursting, or rotation); another method classifies
the fractures according to the manner in which the force is applied (rotation, hyperflexion,
or hyperextension). The factors that are most important for treatment decisions
are the displacement and stability of the fracture fragments.
The most common cause of impaction, or compression, fractures is trauma. This usually
results in a shortened vertebral body with the pedicles and laminae unaffected (Fig. 6-52).
Comparison with adjacent vertebral bodies is helpful in recognizing a compression fracture,
because the alteration in trabecular pattern that accompanies the fracture may be subtle.
Some systemic diseases (primary or secondary hyperparathyroidism, hyperadrenocorticism),
infection, and neoplasia may weaken the bony structures of the vertebrae and predispose
them to compression fractures. This usually results in compression of both the vertebral body
and the more dorsal structures (pedicles and laminae) (see Fig. 6-50).
Avulsion and shearing fractures commonly are seen as a result of trauma. A straight
shearing force may cause fracture through the entire vertebra (Figs. 6-53 and 6-54).