Small Animal Radiology and Ultrasound: A Diagnostic Atlas and Text

C H A P T E R S I X
The Spine
SURVEY RADIOGRAPHIC TECHNIQUES
Radiography of the spine requires precise positioning; therefore the patient should be anesthetized.
However, when fracture, dislocation, or diskospondylitis is suspected, dorsoventral
and lateral survey radiographs may be attempted without anesthesia. In these
situations, some degree of malpositioning may be tolerated because the expected lesions
usually are not subtle.
Because the x-ray beam diverges, there will be geometric distortion of the disc spaces
that are farther away from the central x-ray beam. This change is more apparent when large
films are used, because there is greater divergence at the edge of the radiation field. Using
smaller cassettes and centering over the area of interest is important, especially when evaluation
of disc space width is a primary concern. It is less important when surveying the
spine for a site of infection, such as diskospondylitis, or when evaluating the spine for possible
fractures.
C E RV I C A L S P I N E
Radiography of the cervical spine requires careful positioning. For a true lateral view, the
animal’s nose should be slightly elevated and the mandibles should be supported so that
they are positioned parallel to the film. Because the midcervical area tends to sag toward
the film when the animal is in lateral recumbency, a radiolucent material (i.e., roll cotton
or foam sponge) must be put under the neck at the level of C4 to C7. Similar material
should be placed between the forelimbs and beneath the sternum to prevent rotation. The
position of the neck should be neutral (i.e., the position it naturally assumes when the animal
is anesthetized).
The ventrodorsal view should be taken when the cervical vertebrae are aligned with the
thoracic vertebrae. The body should be in perfect ventrodorsal alignment with no tilting to
either side. When radiographing the cranial cervical vertebrae for the dorsoventral view, a
vertical x-ray beam perpendicular to the table top is used. When radiographing the caudal
cervical vertebrae, the x-ray beam should be angled from caudoventral to craniodorsal in
order to project the intervertebral disc spaces properly. 1 Muscle spasm may prevent proper
positioning; however, diazepam, administered intravenously at a dosage of 0.25 mg/kg, will
usually relieve the muscle spasm.
An oblique lateral view of the cervical spine sometimes is useful. For this radiographic
view, the patient is positioned midway between the ventrodorsal and lateral views, with the
skull and spine in a straight line. This may be accomplished by elevating the sternum and
skull by the means of a wedge-shaped foam sponge. The neural foramina of the “up” side,
the left neural foramen on a right recumbent oblique view, will be superimposed over the
vertebral bodies and will not be readily apparent.
T H O R AC I C, T H O R AC O LU M B A R, LU M B A R, A N D S AC R O C O C C YG E A L
S P I N E S
Lateral radiographs of the thoracic, thoracolumbar, lumbar, and sacral spine require external
patient support. Because the torso tends to rotate, the ventral-most aspect of the chest
becomes closer to the table and film than does the dorsal portion of the chest. To prevent
this, a radiolucent material should be placed under the sternum to bring it up to the level
of the thoracic vertebrae. In addition, the abdomen should be supported by placing lucent
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