Small Animal Radiology and Ultrasound: A Diagnostic Atlas and Text

686 Small Animal Radiolo g y and Ultrasono graphy
Fig. 6-26 A 6-year-old male mixed
breed dog with acute paraparesis and
pain over the thoracolumbar spine.
The lateral radiograph revealed narrowing
of the disc space as compared
with those spaces immediately cranial
and caudal to this site. There
appears to be a decreased space
between the articular facets at T12-
13 when compared with those adjacent
to it. Increased density is
present in the area of the neural
foramen at this site. Diagnosis:
Acute intervertebral disc prolapse at
T12-13.
Fig. 6-27 A 7-year-old male mixed
breed dog with right forelimb lameness.
The dog would hold the limb
off the ground at rest. The left
recumbent lateral oblique view of a
cervical myelogram revealed
increased density in the neural foramen
at C3-4 (open black arrow). This
was best appreciated when compared
with the other neural foramina.
Diagnosis: Intraforaminal
intervertebral disc extrusion at C3-4.
Fig. 6-28 A 7-year-old female
mixed breed dog with neck pain. The
lateral cervical myelogram revealed a
small ventral extradural mass at C5-
6 and a larger mass at C6-7 (black
arrow). Because only one contrast
column is seen, there is indication
that the mass is on the midline.
Diagnosis: Intervertebral disc protrusion
at C5-6 and C6-7.
survey radiograph, or surgery is anticipated, documentation of the site of prolapsed disc
material is required and a myelogram is indicated. Myelography can determine the site of
the disc prolapse accurately in 97% of the patients. 119
Myelographically, the disc prolapse will produce signs of an extradural mass. If there is
spinal cord swelling or hemorrhage associated with the disc prolapse, there may be myelographic
signs of an intramedullary lesion. The disc material may be located on the ventral
midline of the spinal canal, displacing the contrast column dorsally in a single line over the
mass (Figs. 6-28 and 6-29). Infrequently, the disc material will be tightly constrained on the
midline and a double-line sign may be seen. 25,27 If the disc material is ventral and slightly
off the midline of the spinal canal, the myelogram also will show a double-line sign (Fig.
6-30). In some cases, the disc material will extrude into a completely lateral position within