Small Animal Radiology and Ultrasound: A Diagnostic Atlas and Text

674 Small Animal Radiolo g y and Ultrasono graphy
Block Vertebra. Block vertebra refers to the congenital fusion of two or more adjacent vertebrae
(Fig. 6-10). This anomaly usually has no pathologic significance, although a predisposition
to herniation of intervertebral discs adjacent to the block vertebra has been
suggested. 42-44 The dogs in those reports were chondrodystrophic, and therefore the relationship
between the disc prolapse and the block vertebra may have been fortuitous. This
abnormality usually results in a smooth bony union between adjacent vertebral bodies. The
disc space may be completely absent or a portion of a disc space may be identified.
Articular facets usually are still present; however, joint fusion may be observed. The intervertebral
foramen usually is malformed and may be absent. The block vertebra usually is
equivalent in length to the two fused vertebral bodies; however, abnormal angulation and
shortening of the vertebra may be observed. Fusion of vertebral bodies also may occur as a
result of trauma or infection such as diskospondylitis. If these lesions have healed completely,
differentiation of an acquired block vertebra from a congenital lesion may be
impossible.
Kyphosis, Lordosis, and Scoliosis. Kyphosis (dorsal arching), lordosis (ventral arching),
and scoliosis (lateral bowing) are observed rarely in dogs and cats. Hemivertebrae may
produce a kyphosis. Severe deformities of the vertebral bodies and articular facets may
produce a kyphosis, lordosis, or scoliosis. Severe kyphosis and scoliosis have been
reported in an Afghan Hound, a Fox Terrier, and a mixed breed dog. 44,45 The Afghan
Hound had an abnormal gait but no neurologic abnormalities. The Fox Terrier had
spinal cord compression.
Atlantoaxial Subluxation. Atlantoaxial luxations or subluxations may be of congenital
or traumatic etiology. 46-55 The condition is observed most commonly in small and toy
Fig. 6-9 A 6-year-old male French
Bulldog with an acute onset of leftsided
hemiplegia. The lateral thoracic
spinal radiograph revealed
hemivertebrae (small white arrow).
These are readily apparent when
compared with the more normal
vertebrae (large white arrow). These
findings were of no clinical significance.
The dog’s neurologic problem
was due to a cervical disc extrusion.
Diagnosis: Multiple hemivertebrae.
Fig. 6-10 A 7-year-old male Miniature Poodle with occasional back pain. The lateral radiograph
revealed absence of the intervertebral disc space between L5 and L6 (white numerals) as well as an
absence of the articular spaces of the dorsal components. The intervertebral disc space between L1 and
L2 (black numerals) was narrowed, the neural foramina diminished in size, and the spaces between the
articular components dorsally are closer together than normal. Diagnosis: Block vertebrae of L5-6 and
intervertebral disc extrusion at L1-2.