Page 367 - Atlas of Small Animal CT and MRI

Intervertebral disk disease and other degenerative disorders 357

Cauda equina and lumbosacral disorders MR imaging features are similar to those seen with CT.
Static and dynamic lumbosacral abnormalities that Nerve roots of the cauda equina are T1 and T2 hypoin­
cause cauda equina syndrome include intervertebral tense relative to surrounding epidural fat and are therefore
disk protrusion, lumbosacral subluxation, vertebral well visualized on both sequences in the normal dog.
canal stenosis, proliferation of soft tissues within or Vertebral canal and intervertebral foraminal T1 and T2
adjacent to the vertebral canal, and spondylotic new intensity is reduced when epidural fat is displaced because
bone encroachment on the intervertebral foramina. of intervertebral disk extrusion/protrusion, stenosis, or
20
Large‐breed male dogs are most commonly affected, subluxation. In addition to standard sequences, a 3D vol­
and German Shepherd Dogs are highly overrepre­ ume acquisition (e.g. T1 + C SPGR) of the lumbosacral
sented. 20–22 The lumbosacral angle of inclination, junction provides thinly collimated images that can pro­
decreased lumbosacral joint mobility, articular process vide more in‐plane anatomical detail and be reformatted
joint angle, and the presence of transitional vertebrae in other planes. Neuritis is sometimes detected because
and sacral endplate osteochondrosis have all been postu­ of enlargement and increased contrast enhancement
lated as inciting anatomical factors. Dogs with cauda compared to the contralateral spinal nerve. A dorsal plane,
equina syndrome are more likely to have a more sagit­ STIR, or fat‐suppressed contrast‐enhanced T1 sequence
tally oriented articular facet angle, a greater difference in generally provides an excellent symmetrical view of the
caudal lumbar and sacral spine angle, and asymmetry of caudal lumbar spinal cord, the cauda equina, and associ­
the facet articulations. 23,24 The caudal lumbar and sacral ated spinal nerves when performed with thin collimation
vertebral canal transverse areas, normalized to vertebral (≤ 2 mm) (Figures 3.5.13, 3.5.14).
body sagittal diameter or transverse vertebral body area,
have also been shown to be significantly smaller in dogs other degenerative disorders of the spine
with cauda equina syndrome as compared to clinically Articular facet osteoarthrosis
normal dogs. CT examinations acquired in hindlimb
25
flexion and extension have been used to assess dynamic Osteoarthrosis of the articular facets can occur as a
changes in vertebral canal diameter and intervertebral progressive geriatric disorder or as the sequela of an
foraminal area in dogs with lumbosacral disease. 25–28 The underlying disorder, such as cervical spondylomyelop­
L7–S1 intervertebral foraminal area is significantly athy or trauma. General features of osteoarthrosis
smaller on extended limb images, suggesting that posi­ include periarticular new bone formation, subchondral
tional imaging studies may be useful for diagnosis of bone sclerosis, enthesopathy, and synovial hypertro­
dynamic foraminal nerve entrapment. 27 phy. This proliferation can result in dorsolateral spinal
Imaging features of the lumbosacral region of dogs cord compression. CT and MR features of degenerative
with cauda equina syndrome are highly variable. Although joint disease are addressed in Chapter 6.5.
there seems to be excellent agreement between CT and Spondylosis deformans
MR for detection of intervertebral disk protrusion or
extrusion, dural sac position, quantity of epidural fat, and Spondylosis deformans is characterized by progressive
spinal nerve root swelling, the correlation of these features new bone formation that bridges adjacent vertebral bod­
with surgical findings is only moderate. 22 ies and is usually distributed on the ventral and lateral
CT examinations should include thinly collimated surfaces of the affected vertebrae. Although spondylosis
transverse images through the caudal lumbar and sacral deformans is generally considered clinically insignificant,
region acquired at an angle perpendicular to the verte­ encroachment of lateralized new bone on intervertebral
bral canal. CT features associated with cauda equina foramina can result in nerve root entrapment with subse­
syndrome include lumbar spine (LS) subluxation, quent clinical signs. Distribution is most common in the
intervertebral disk degeneration and extrusion, spondy­ thoracic and lumbar spine and at the lumbosacral junc­
losis, reduction of vertebral canal transverse area (pri­ tion. 29–31 A study assessing the relationship of spondylosis
marily due to reduced canal height) at the level of the and intervertebral disk disease (IVDD) found a weak
LS junction, and loss of distinction of nerve roots at the positive association in dogs with type II IVDD but no
LS junction due to diminished epidural fat. Extruded correlation in dogs with type I IVDD. 32
intervertebral disk material can migrate into the caudal CT features of spondylosis deformans include hyper­
lumbar and LS intervertebral foramina causing nerve attenuating new bone formation contiguous with the
root compression and resulting lateralized clinical signs. ventral margins of affected vertebrae. New bone may be
Extruded disk material is hyperattenuating and displaces incompletely or completely bridging depending on
the relatively low attenuating epidural fat in the vertebral the stage of progression and will often have delinea­
canal and intervertebral foramina. ted cortical and medullary components. Associated
357