Radiology of Lumbosacral Instability Syndrome
World Small Animal Veterinary Association World Congress Proceedings, 2003
Pim Wolvekamp, DVM, PhD, DECVDI
Division of Diagnostic Imaging, Faculty of Veterinary Medicine, Utrecht University
Utrecht, The Netherlands

"Radiographic procedures supplement the physical neurological examination and its interpretation, but must only be used to confirm a tentative physical or clinical diagnosis".

General technique and interpretation

Because most spinal lesions are minute in size and of low radiographic density, superior diagnostic films and exact positioning are required to possibly demonstrate these lesions. For spinal radiography, a combination of high-detail films and screens is used in small-sized cassettes (24 x 30 cm). The latter is important because segmental radiography of the spine reduces the negative effects of geometric unsharpness (as does a focal-film distance of at least 100 cm). A fine-line grid is necessary to prevent image-fogging by scattered radiation. Routine projections include lateral views with the animal in lateral recumbency, and ventrodorsal views with the animal in supine position. Additional projections may include spot films of localized abnormalities. During radiography the spinal column must be exactly parallel with the table surface, and the animal stretched as much as possible. In this way, lateral and ventrodorsal views without too much distortion are achieved that facilitate not only the interpretation of the relative width of the intervertebral foramina and disc spaces, but also the possible detection of calcified protruded disc material in the vertebral canal.

For radiographic procedures the animal must be sedated or anaesthetised. Only in this way, accurate positioning is possible, and motion artifacts due to resistance of an animal that is afraid and in pain are prevented. Accurate and systematic interpretation of survey (noncontrast) spinal radiographs will yield in many cases a positive diagnosis taking away the need for additional painstaking contrast examinations.

At first, the technical qualities of the radiographs are scrutinized, including attention for exposure, positioning, detail, and coding.

The next step includes inspection of the lumbosacral area, with attention for abnormal rotation and curving.

After this, the bony components of the lumbosacral area of the vertebral column are individually evaluated, including the surrounding soft tissue structures and intervertebral disc spaces.

At this point, special attention is given to the presence of disc calcification, narrowed disc space, malalignment and congenital deformities (transitional vertebrae) At last, an attempt is made to correlate the radiographic findings with the clinical findings.

Cauda Equina Syndrome

Cauda equina syndrome can be defined as sensory and/or motor nervous dysfunction resulting from compression, destruction or displacement of nerve roots or their accompanying vasculature in the region of the cauda equina. This includes the Sciatic nerve L6-7, the Pudendal nerve S1-3, the parasympathetic Pelvic nerve S1-2, and the Caudal nerve Cd1-5. Common descriptive synonyms for "cauda equina syndrome" are lumbosacral spondylopathy, lumbosacral instability, lumbar spinal stenosis, lumbosacral discospondylitis and lumbosacral spondylolisthesis.

Etiology of cauda equina syndrome

1.  degenerative changes:
protrusion of L-S disc
L-S malalignment
hypertrophy of dorsal annulus/ligament
hypertrophy of lig. flavum
arthrosis of true vertebral joints

2.  secondary changes:

Radiographic examination of dogs with "cauda equina syndrome"

Cauda equina syndrome of large-breed dogs is in most cases the result of chronic dynamic cord compression due to instability and secondary disc herniation and/or soft tissue changes. Because surgical intervention may be helpful in an early stage of the disease, radiographic examination has a critical role during the diagnostic work-up of these animals. Degeneration of the lumbosacral disc, chronic instability of the lumbosacral junction, or discospondylitis and neoplastic disease in the lumbosacral area resulting in compression of the cauda equina may produce radiographic changes on noncontrast radiographs. Next to this, additional contrast examinations of this area may be performed, including myelography, epidurography and/or discography. At academic centres, Ct- and MRI investigations may be available.


In most large breed dogs, the radiographic presentation of the cauda equina by the myelographic contrast lines does not follow the bony contours of the vertebral canal but instead terminates dorsally in a thin line. This makes diagnostic evaluation of abnormalities in the lumbosacral region impossible. In small-breed dogs and cats, the caudal contrast lines of the myelogram follow the bony contours of the spinal canal much more caudally, through the sacral region into the coccygeal vertebrae. In these animals, myelographic outlining of the cauda equina certainly allows for evaluation of the lumbosacral area.

Epidurography and Discography

Epidurography and discography are suitable radiographic contrast techniques that are used to investigate abnormalities in the lumbosacral area and lumbosacral disc in small animals with the clinical symptoms of cauda equina compression syndrome. Epidurography is especially of use in larger-breed dogs where the lumbar myelogram may terminate just at the lumbosacral transition or inside the first sacral segment. Discography is used to evaluate the integrity if the lumbosacral disc. For epidurography and discography the same contrast media as for myelography are used. In addition to noncontrast radiography and the regular contrast examinations a special radiographic procedure must be included, called dynamic radiography.

Dynamic Radiography of the Vertebral Column

Radiographic examination of the vertebral column of small animals may include noncontrast radiography, myelography, epidurography and discography, and CT- and MRI-investigations. In addition, dynamic stress radiography can be performed. Dynamic stress radiography includes:

1.  traction and compression during investigations of dogs with suspected disc herniation;

2.  hyperextension, hyperflexion and (bi)lateral flexion of the cervical region in dogs with "wobbler" syndrome;

3.  hyperextension and hyperflexion of the lumbosacral area in dogs with cauda equina syndrome.

Stress radiography is performed in combination with noncontrast radiography (cervical disc herniation, thoracolumbar subluxation), myelography ("wobbler" and cauda equina syndrome) and epidurography (cauda equina syndrome), and sometimes during repeated CT-investigations of the lumbosacral area.

During stress radiography abnormalities may become visible that are otherwise concealed during routine radiographic procedures, such as:

 collapse of intervertebral disc space

 vacuum phenomenon in degenerated disc space

 vertebral malalignment or instability

 cord compression due to soft tissue proliferation

 cord compression by thickened/arthrotic facets

 cord compression by "tipped" vertebral body

As a result, radiographic examination of animals suspected of cauda equina syndrome includes the following techniques:

1.  noncontrast radiography of the L-S junction: routine and dynamic

2.  dynamic myelography

3.  dynamic epidurography

4.  discography

5.  Ct-imaging, with two-dimensional reconstruction

6.  MRI-imaging

Radiographic changes during (dynamic) noncontrast radiography:

 lumbosacral malalignment or subluxation

 narrowing of L7-S1 disc space

 vacuum phenomenon in lumbosacral disc space

 bulging of (calcified) disc

 ventral and lateral spondylosis

 sclerosis of vertebral end-plates

 avulsed bony fragment from dorsocranial rim of S1 end-plate

 bone lysis due to discospondylitis

Radiographic changes during dynamic contrast radiography:

 ventral compression of cauda equina by hypertrophied or hyperplastic dorsal annulus fibrosis/dorsal ligament or by disc protrusion type II;

 dorsal compression of cauda equina by hypertrophied or hyperplastic ligamentum flavum

 compression of cauda equina by neoplastic mass

 leaking of contrast medium from nucleus of abnormal L-S disc during discography.

Speaker Information
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Pim Wolvekamp, DVM, PhD, DECVDI
Division of Diagnostic Imaging
Faculty of Veterinary Medicine, Utrecht University
Utrecht, The Netherlands

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