Spine – lumbosacral region and cauda equina syndrome

image of Spine – lumbosacral region and cauda equina syndrome
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Cauda equina syndrome in small animals is a commonly encountered and well described clinical entity. Large breed dogs are more often affected than small breed dogs or cats. The single most important cause of cauda equina syndrome is DLSS, and predominantly affects non-chondrodystrophic large breed dogs. Clinical signs in DLSS result from compression of the cauda equina, or of the nerve roots of the lumbosacral disc combined with disc herniation, as well as hypertrophic degenerative changes of the articular process joints, ligaments and vertebrae. This chapters looks at indications; radiography; normal anatomy; contrast studies; alternative imaging techniques and abnormal imaging findings.

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23.1 Lateral view of a 5-year-old German Shepherd Dog with DLSS. The sacrum is displaced ventrally, with its floor thickened by deposition of new bone. There is a thickened and elongated ‘roof’ (arrowheads) corresponding to the sacral lamina and ventral aspect of the L7–S1 articular process joints. The lumbosacral disc space is narrowed and irregular, and the dorsal part of the sacral endplate is angled slightly caudally and has a large rounded osteophyte protruding into the intervertebral foramen. The endplates and adjacent vertebral bodies appear sclerotic, with spondylotic changes ventrally and dorsally. The vertebral canal and lumbosacral intervertebral foramen are obscured by mineralized granular material; the vertebral canal at this level appears narrow. At L6–7, mineralization within the intervertebral foramen and ventral part of the vertebral canal is also present.
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23.2 (a) Lateral radiograph of the lumbosacral region of a normal 2-year-old mixed-breed dog and (b) the corresponding VD view. Parallel radiolucent lines between the sacrum and ilium represent sacroiliac joint cartilage, which persists throughout life (arrowed). The increased opacity ventral to the S1 vertebral body is normal, corresponding to the summation of sacral wings and iliac articular surfaces which taper ventrally and should not be misdiagnosed as a periosteal reaction. Note the normally fused sacral spines on the VD view. The lumbosacral disc space is narrower on the VD view than on the lateral view. This is normal because the disc space is not aligned with the primary beam on the VD view. To optimize visibility of the lumbosacral disc space and sacrum on the VD view, the X-ray beam should be angled about 15 degrees in a caudocranial direction so as to strike these structures perpendicularly. (c) Lateral lumbosacral radiograph of a normal 5-year-old Boxer. Superimposition of the L7 pedicles on the vertebral body results in a curvilinear opacity (arrowheads), and the vertebral notch appears as a focal lucency (arrowed), which should not be mistaken for pathology.
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23.3 Lateral lumbosacral stress radiographs of a normal dog after a cervical myelogram. Normal lumbosacral angle in (a) flexion and (b) extension. The dural sac does not change position, shape or diameter during flexion and extension.
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23.4 Cervical myelogram in a 9-year-old German Shepherd Dog presenting with clinical signs of cauda equina compression. (a) Thoracolumbar region. There is T12 to L3 spondylosis and moderate ventral extradural cord compression at the T13–L1 disc space with similar but milder pathology at the disc spaces cranial and caudal to this level. The thoracolumbar lesion was not apparent clinically. (b) Lumbosacral region. There are degenerative changes at the L6–7 and the L7–S1 disc spaces, including spondylosis with mild ventral dural sac compression at both sites.
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23.5 L6–7 lumbar myelogram in a cat with an intramedullary lymphoma at the lumbosacral intumescence. There is spillage of contrast medium into the epidural space as well as multiple small radiolucent filling defects caused by iatrogenic air injection. (a) Lateral view. (b) VD view. The thickened intumescence is outlined with white arrowheads.
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23.6 Lumbosacral disc herniation and DLSS in a 7-year-old Bernese Mountain Dog with right pelvic limb paresis. (a) Lateral plain film radiograph showing a narrowed intervertebral disc space, thickened and sclerotic endplates and mineralization overlying the intervertebral foramen (arrowed). (b) Lateral flexed view after cervical myelogram. Note the wide dural sac extending far into the sacrum. There is slight dorsal deviation but no compression visible of the dural end-sac. Note the small vacuum phenomenon dorsally in the disc space. (c) The lateral extended view shows pronounced ventral compression and ventrally displaced vacuum phenomenon. (d) Linear tomogram in extension of the same region. The highlighted area again shows the vacuum phenomenon (arrowhead) and the mineral opacity just ventral to the dorsally elevated dural end-sac (arrowed). (e) The VD view reveals the attenuation and deviation of the dural sac to the left side (the left side of the dog is on the right side of the figure).
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23.7 Flexion–extension myelogram in a dog with suspected lumbosacral compression with a false-positive result. (a) Lateral extended view. Forced extension of the pelvic limbs increased the pressure in the vertebral canal, leading to venous congestion and resulting in diffuse compression of the dural sac. True dynamic compressions are usually seen as focal lesions at the intervertebral disc space. (b) Lateral flexed view, which is normal.
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23.8 Non-diagnostic lumbosacral study in a dog with a short dural end-sac. (a) Cervical myelogram; the thin dural sac is positioned in the dorsal part of the vertebral canal and ends at the lumbosacral junction. (b) Same dog after a caudal intervertebral disc space epidurogram has been performed. There is a filling defect dorsally in the L7 area (arrowheads). At surgery, this was found to be a large fat pad, which did not compress the cauda equina.
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23.9 Lateral epidurogram in a dog with lumbosacral disc herniation. The hernia is seen as a filling defect in the ventral part of the vertebral canal over the intervertebral disc space (arrowed). Note the extradural contrast medium with leakage beyond the vertebral canal.
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23.10 Lateral lumbosacral view after discogram, in a dog with lumbosacral disc herniation. The entire area of the disc is opacified by contrast medium and there is leakage into the ventral part of the vertebral canal. The mushroom-shaped contrast medium has a well delineated dorsal border. This indicates that the annulus fibrosus has probably ruptured while the dorsal longitudinal ligament remains intact, implying a ‘contained’ disc herniation.
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23.11 MRI of a 3-year-old Labrador Retriever with a nerve root neoplasm at the lumbosacral level. (a) At the level of the intervertebral foramina of L7–S1, the T1W transverse pre-contrast image shows a space-occupying lesion within the vertebral canal on the right side of the midline (arrowhead). It has low signal intensity and displaces the normal nerve roots (arrowed) to the left. (b) After administration of gadolinium DTPA, the lesion shows pronounced contrast enhancement.
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23.12 CT study of the lumbosacral region of an 8-year-old male Labrador Retriever with left-sided lumbosacral foraminal stenosis. (a) Transverse view in a bone window at the level of the caudal endplate of L7, showing spondylosis along the left ventral aspect of the vertebra and extending dorsally into the left foramen. (b) Transverse view in a soft tissue window a few millimetres cranially from the previous image. The left foramen is filled with material of soft tissue attenuation. The right foramen is not visualized owing to slight obliquity. (c) Parasagittal reconstruction of the right intervertebral foramen in a soft tissue window, containing normal hypoattenuating perineural fat. (d) Parasagittal reconstruction of the left intervertebral foramen in a soft tissue window, containing soft tissue proliferation within the foramen, implying some degree of neural compression. Such findings may be clinically silent in older patients.
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23.14 Lateral lumbosacral radiograph of a dog with fractures of the cranial endplate and transverse processes of Cd1, with dorsal displacement of Cd1. The vertebral canal is totally disrupted. The spinous process of S3 is fractured and the associated lamina is ventrally displaced. Note the bony fragments ventral to Cd1 and Cd2. It was discovered during surgery that there was also avulsion of the cauda equina at the L6–7 level and haemorrhage in the vertebral canal.
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23.15 CT of a 3-year-old Shiba Inu with signs of nerve root impairment, 4 months after a motor vehicle accident. (a) Dorsal reconstruction of the lumbosacral area in a bone window. There are old fractures of the right cranial aspect of the sacrum, right iliac wing and iliosacral joint and right transverse process of L7, with cranial displacement of the fragments. (b) Transverse view in a bone window at the caudal aspect of L7. The sacral fracture fragment is wedged into the right lumbosacral intervertebral foramen, impinging on the nerve (not shown).
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23.16 Transverse CT of the sacrum in a bone window of a 6-year-old dog 17 days after a motor vehicle accident. There is a sagittal fracture of the left lateral aspect of the sacrum which could not be seen on referral films. The fracture edges are unsharp and rounded with early callus formation visible dorsally and ventrally to the fracture.
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23.17 VD view of the cranial pelvis of a 10-month-old Collie with an asymmetrical lumbosacral transitional vertebra. Note the axis deviation at the lumbosacral junction caused by broad fusion of the left transverse process of L7 with the ilium. Early left-sided coxarthrosis is present. The right transverse process of L7 is shorter and oriented less cranially than normal.
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23.18 (a) Lateral and (b) VD radiographs of the lumbosacral region of a 2.5-year-old male American Staffordshire Terrier with a symmetrical lumbarization of S1 and lumbosacral stenosis. (a) S1 is not fused to the rest of the sacral segment (arrowed) and has a very low lamina, indicative of congenital stenosis of the vertebral canal. Degenerative lumbosacral changes are present, as well as small and opacified lumbosacral intervertebral foramina. (b) S1 has broad, symmetrical wing-like transverse processes fused to the ilium. Note the separation of the S1 spinous process from those of S2 and S3 when compared with Figure 23.2b . Congenital lumbosacral and foraminal stenosis compounded by degenerative changes were later confirmed with MRI.
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23.19 VD lumbosacral radiograph of a 9-year-old female English Bulldog with spina bifida. Besides the breed-specific tail agenesis, there is lack of fusion of the dorsal spinous processes of the sacrum (arrowed).
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23.20 Sagittal MRI CBASS (completely balanced steady-state) sequence of the caudal lumbar spine of a 6-month-old male French Bulldog presented with paraparesis and urinary and faecal incontinence as a result of spina bifida and meningocele. In this high-resolution, fluid-sensitive sequence, cerebrospinal fluid and epidural fat are hyperintense, resulting in a myelographic effect. A large defect of the lamina of L7 continuous with the dorsal interarcuate space is seen. The dural sac extends in the direction of the defect. Linear structures of low signal intensity, possibly representing nerve roots, leave the vertebral canal through this defect. There is high signal intensity in the dorsal spinal cord at the level of L5 and L6, which could represent oedema.
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23.21 Sacral osteochondrosis in a 4-year-old German Shepherd Dog with lumbosacral pain. (a) On the lateral lumbosacral radiograph the intervertebral disc space at L7–S1 appears narrow and butterfly-like. The dorsal part of the sacral endplate is angled caudally and a large detached bone fragment can be seen in the vertebral canal. The L7 and sacral endplates as well as the adjacent vertebral bodies appear sclerotic. (b) On the VD view the cranial border of the sacrum appears irregular; the free fragment is to the left of midline (arrowed). Note also the bilateral spondylosis at the caudal endplate of L7. The (c) flexion and (d) extension views after cervical myelography revealed no clear compression. (e) Post-mortem sagittal section through the lumbosacral spine in another German Shepherd Dog with sacral osteochondrosis, showing the abnormal intervertebral disc, the defect in the dorsal part of the sacrum and the fragment (mainly cartilage) protruding into the vertebral canal.
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23.22 CT of a 5-year-old male Airedale Terrier with a history of chronic caudal lumbar pain and right pelvic limb muscle fasciculation. (a) Dorsal and (b) sagittal reconstructions of the lumbosacral region in a bone window. Gas (vacuum phenomenon) is present within a defect in the caudal vertebral body of L7 and the lumbosacral disc space, most likely the result of intravertebral disc herniation into the L7 vertebral body (Schmorl’s node). (Reproduced from with permission from )
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23.23 CT of the lumbosacral region of a 10-year-old large-breed dog, in a bone window. (a) Sagittal reconstruction showing collapse of the L7–S1 intervertebral disc space, which centrally has a hypoattenuating region, consistent with severe disc degeneration and vacuum phenomenon. Sclerosis of the facing endplates and spondylosis attest to the chronicity of the process. The arrow points to protruded disc material. (b) Transverse image at the lumbosacral disc space showing the gas attenuation.
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23.24 MRI study of the lumbosacral region of an 8-year-old mixed-breed dog with DLSS and pronounced lumbosacral pain and pudendal nerve dysfunction. (a) Sagittal T2W image showing decreased volume and signal intensity of the lumbosacral disc, which protrudes dorsally. Within the annulus is a vertically oriented hyperintense line indicative of annular rupture. Dorsal displacement of the cauda equina is limited by the redundant flaval ligament. Mild annular protrusion is also present at L6–7. (b) Transverse T2W image at the mid-L7 level. The L7 nerves (arrowed) are of normal size and signal intensity immediately cranial to their exit from the vertebral canal. (c) Transverse T2W image at the level of the lumbosacral disc, showing predominantly right-sided disc protrusion (arrowhead) displacing and compressing the S1 nerve root (arrowed). The patient underwent decompressive surgery, with rapid improvement of neurological status.
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23.25 Intervertebral disc disease and degenerative stenosis at L6–7 in a 5-year-old German Shepherd Dog. Radiologically, a narrowed intervertebral disc space is present, with sclerotic endplates and vertebral bodies as well as mild ventral spondylosis. At the level of L7–S1 moderate spondylotic changes can be seen. The (a) flexion and (b) extension myelogram studies reveal dynamic vertebral canal stenosis dorsally at the L6–7 level, caused by a thickened dorsal lamina of L7. (c) The VD view demonstrates marked lateral spondylosis bilaterally at the L6–7 disc space, with mild left lateral compression of the cauda equina at this level, as well as mild bilateral compression at the lumbosacral junction.
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23.26 Flexion–extension myelography in a dog with the dural end-sac ending at S1–2 and dynamic lumbosacral ‘instability’ and stenosis. (a) In flexion there is good alignment of L7 and S1 and no sign of compression of the dural end-sac. Note the slight spondylotic changes ventral to the caudal endplate of L7 and the cranial endplate of S1. The endplates are sclerotic and thickened. (b) In extension there is ventral subluxation of the sacrum with dorsoventral narrowing of the dural end-sac due to folding of a thickened flaval ligament. The instability is caused by gliding of the degenerated disc.
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23.27 MRI of multiple juxta-articular cysts at the lumbosacral area in a 6-year-old German Shepherd Dog. The clinical signs were thought to be caused by nerve root compression induced by the cysts at the L6–7 level. (a) The left parasagittal T2W image reveals a lesion with high signal intensity (fluid) in the right L6–7 intervertebral foramen. (b) T2W and (c) post-contrast T1W transverse images at the L6–7 level reveal bilateral juxta-articular cysts with a typical high signal intensity in T2W and corresponding low signal intensity in T1W sequences. The borders of the cysts showed only minimal contrast enhancement. (d) The dorsal fat-suppressed sequence (STIR) demonstrates the two large cysts at the L6–7 level and a small cyst on the right at the lumbosacral level, and is suggestive of a small cyst at L5–6 (right side).
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23.28 Transverse CT bone window images of the sacroiliac region. The left image is of a 10-year-old Cane Corso with no clinical signs. There is bilateral ossification of the sacroiliac ligaments, sclerosis of the adjacent sacral and iliac surfaces and ventral osteophyte production. The right image is of a normal 2-year-old Beagle at the same level, for comparison.
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23.29 Lumbosacral radiographs of a Labrador Retriever with acute discospondylitis. (a) On the lateral view there is mild soft tissue swelling ventral to the lumbosacral disc space. The vertebral endplates are lytic, bordered by sclerosis in the adjacent vertebral bodies. At the ventral border irregular periosteal reactions are present. The sacrum is displaced ventrally. (b) In addition to the lytic endplates, the VD view also shows an incidental incomplete lumbosacral transitional vertebra with an isolated spinous process and incomplete sacralization of the transverse processes of L7 (arrowheads).
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23.30 Lateral pelvis radiograph showing a retrograde urethrocystogram in a male mixed-breed dog with a caudal prostatic abscess and discospondylitis. The pelvic urethra is displaced ventrally by a large space-occupying abscess (arrowheads) in the pelvic canal. Note the narrowed lumbosacral intervertebral foramen and disc space with irregular adjacent vertebral endplates.
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23.31 Lumbar radiographs of an 8-year-old dog with a prostatic adenocarcinoma with metastasis to the lumbar vertebrae. (a) Composite of two lateral views showing irregular bony proliferation ventrally along the vertebral bodies from L2 to the sacrum. No soft tissue swelling or bone lysis can be seen. The intervertebral disc spaces are normal. (b) On the VD view the bony proliferation can be seen on both sides of the vertebrae, but to a lesser extent.
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23.32 Radiographs of the pelvic region of a 9-year-old mixed-breed dog with left-sided lameness and pain due to a left iliac wing chondrosarcoma. (a) Lateral view showing a relatively short L7 vertebra and extensive spondylosis at the L6–S1 disc spaces. The vertebral canal and intervertebral foramina are obscured by overlying bony reactions. (b) VD view showing the spondylosis also involving the lateral aspects of the L6–S1 disc spaces. Note the aggressive bone lesion in the left iliac wing and the mineralization of the soft tissues between the left L7–S1 intervertebral foramen and the iliac wing (arrowed). The neurological signs of unilateral pain and lameness were caused by compression of the nerve root lateral to the foramen (determined on post-mortem examination).
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