Editorial Type: Case Reports
 | 
Online Publication Date: 01 Jul 2004

Asymmetrical, Transitional, Lumbosacral Vertebral Segments in Six Dogs: A Characteristic Spinal Syndrome

Dr.med.vet., Diplomate ECVN,
Dr.med., and
DVM, Vet.med.Dr.
Article Category: Other
Page Range: 338 – 344
DOI: 10.5326/0400338
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Clinical findings in six dogs with asymmetrical, transitional, lumbosacral vertebral segments are reported. All dogs exhibited low back pain and varying degrees of asymmetrical cauda equina dysfunction. Results of myelography, epidurography, and magnetic resonance imaging (MRI) indicated a unilateral disk protrusion in all dogs. In the dogs with MRIs, focal degenerative alterations in the vertebral end plates and adjacent body of the vertebra were detected. All dogs were treated with a dorsal laminectomy or hemilaminectomy. Results following surgery were good or excellent in all six dogs.

Introduction

At the junction of the major divisions of the vertebral column, a single vertebra (vertebral segment) may assume characteristics typical of either division. The anomalous vertebra has been referred to as a “transitional segment.”1 While first thought to have no clinical importance, transitional lumbosacral vertebral anomalies have recently been implicated as a cause of cauda equina syndrome in the dog.2–4 The first description of premature degeneration and subsequent weakening of the lumbosacral disk in anomalous, transitional, lumbosacral vertebrae occurred in humans in 1933.5 Although the anomalous segment can often be identified with plain radiography in dogs, extension-flexion myelography, diskography, or epidurography is needed to further clarify the presence of the vertebral canal stenosis.16–9 Magnetic resonance imaging (MRI) has also proven to be extremely useful for imaging this area.10–12

Not all anomalous vertebral segments are asymmetrical; however, asymmetrical vertebrae have transverse processes that vary in size and shape, thereby markedly altering the sacroiliac attachments. Usually the lumbosacral transitional segment is the first sacral vertebra.4 Previously little attention was directed toward the specific influence that these asymmetrical segments had on the clinical presentation of cauda equina syndrome. It is the purpose of this report to describe the neurological, imaging, and intraoperative findings in six dogs with asymmetrical, transitional, lumbosacral vertebral segments.

Materials and Methods

Six dogs with clinical signs of cauda equina syndrome associated with abnormal, transitional, lumbosacral vertebrae that were referred to the Veterinary Hospital at the University of Zurich between November 2000 and March 2002 were included in this study.

Each dog had survey radiography performed of the entire spine in both lateral and ventrodorsal projections. The dogs were premedicated with medetomidinea (0.1 mg/kg intravenously [IV]) and butorphanolb (0.2 mg/kg IV), induced with propofolc (4 mg/kg IV), and maintained under general anesthesia with isofluraned in oxygen. Myelography was performed in three dogs following cisternal puncture using iotrolanee at a dosage of 150 mg/kg. Because the dural sac ended cranial to the lumbosacral junction, epidurography using the same contrast agent was performed in one dog (case no. 6) through a sacrococcygeal injection site. The amount of contrast agent used in this last dog was 3 g.

Magnetic resonance imaging of the lumbosacral junction was performed in three dogs using a 1.5 Tesla scannerf with a spine array coil. The MRIs were obtained with the dogs under general anesthesia and positioned in dorsal recumbency with the pelvic limbs in slight caudal extension. Standard fast spin echo sequences were used for all MRIs. Sagittal T2-weighted images (TR [repetition time] 3720 to 4000 ms, TE [echo time] 108 to 123 ms, field of view [FOV] 300 to 320 mm, slice thickness 2 mm, 2 to 3 acquisitions) and sagittal T1-weighted images (TR 550 to 672, TE 12 to 15, FOV 240 to 320 mm, slice thickness 2 mm, 1 to 4 acquisitions) were obtained in all animals. Dorsal plane images were obtained as T1-weighted (TR 400 to 621, TE 14 to 24, FOV 300 to 320 mm, slice thickness 2 mm, 2 to 3 acquisitions) in all dogs. Axial images were obtained in planes parallel to the intervertebral disk space and were T2-weighted in all cases (TR 4000 to 6360, TE 110 to 120, FOV 180 to 220 mm, slice thickness 2 mm, 3 to 4 acquisitions).

Surgery was performed in all dogs to decompress the cauda equina. The intraoperative findings were correlated with the findings of the diagnostic imaging procedures. All dogs were rechecked 3 weeks after surgery and were followed for 6 to 24 months by telephone contact with the owners. An excellent postoperative outcome was defined as complete resolution of clinical signs after surgery. A good outcome was defined as resolution of clinical signs while at rest, but residual or recurring episodes of pain during periods of intense activity, such as jumping. A poor outcome was defined as no improvement in clinical signs after surgery.

Results

Clinical Data

There were five males and one female dog included in the study. The mean age of the dogs was 4.3 years (range, 2 to 7 years). Breeds affected included four German shepherd dogs and two border collies.

At presentation, the dogs showed one or more of the following signs: low back pain (based on history and physical examination), lameness or root signature of one hind limb, and tail paresis. Neurological deficits varied in the dogs [see Table]. All dogs had received nonsteroidal or steroidal anti-inflammatory drugs for various times prior to presentation. Clinical signs had improved in some dogs during administration of these medications, but signs recurred after cessation of the drugs in every case.

Survey Radiography

The appearance of the transitional lumbosacral vertebral segment was similar in all dogs. On the ventrodorsal view, marked asymmetry in the pelvic attachment of the anomalous segment was found. The transitional vertebra was characterized by a large, flat process on one side that appeared to be solidly fused with the ilium, and a thin, lumbar-like transverse process on the contralateral side. The thin lateral process had no ilial attachment [Figure 1]. On the lateral radiograph, angulation of the floor of the vertebral canal of the anomalous segment was found, when compared to the last normal lumbar vertebra. The presence of an additional radiolucent disk space representing failure of the normal union between the first and second sacral (S1–S2) segments was an additional finding in the anomalous segment. The asymmetry of the lateral processes was not visible on the lateral view. All dogs had evidence of degenerative changes at the junction between the last lumbar vertebra and the anomalous segment, such as end-plate sclerosis, narrowing of the disk space, and presence of reactive bony osteophytes (i.e., spondylosis deformans).

Myelography and Epidurography

Both techniques identified elevation of the contrast column from a ventrally located extradural mass on the floor of the vertebral canal in the area of the lumbosacral disk. The mass-effect caused a compression of the dural sac against the roof of the sacrum that was more evident when the pelvic limbs were placed in extension [Figure 2]. Laterality of the extradural mass could not be determined on the lateral views. On the ventrodorsal view, the dural sac was displaced toward the side with the broader ilial attachment [Figure 3].

Magnetic Resonance Imaging

Degeneration of the intervertebral disk at the lumbosacral level was identified in all three dogs that underwent MRI. This degeneration was best seen on T2-weighted images in the sagittal plane and appeared as loss of signal intensity in the nucleus pulposus. Disk protrusion at this segment was more prominent on one side in all the dogs. The protrusion caused a loss of epidural fat and deviation of the cauda equina dorsally on both the sagittal T1-weighted and T2-weighted images.

On the transverse T2-weighted images, there was unilateral narrowing of the vertebral canal or the intervertebral foramen from a disk protrusion at the lumbosacral junction. This narrowing affected either S1 or the seventh lumbar (L7) vertebral body. Hypointense annular tissue attenuated the amount of epidural fat in the intervertebral foramen [Figure 4].

In dorsal plane T1-weighted images, focal alterations of the anomalous segment and sacral end plates were identified [Figure 5]. The focal alterations were more prominent on one side and consisted of an area of low signal intensity on T1-weighted images (compared to the intensity of an unaffected body of the vertebra and normal annular tissue). On T2-weighted sagittal images, the intensity of this altered area was similar to that of the normal, adjacent end plate. This focal alteration indicated sclerosis of the end plate and adjacent bone. In all three dogs, the sclerosis was present on the same side as the disk protrusion and opposite to the side with the broadest attachment to the ilium. The end plates were normal toward the side with the broadest fusion with the ilium in all three dogs.

Surgery and Outcomes

Surgery was performed in all dogs. With each dog in ventral recumbency and the lumbosacral joint in flexion, an approach was made to the dorsal laminae of L7, the transitional vertebral segment, and the sacrum. In three dogs, a standard dorsal laminectomy was performed, removing the caudal half of the dorsal lamina of the body of L7 and most of the lamina of the transitional segment. In the three dogs that had MRIs, a hemilaminectomy was performed over the site of compression. The extent of the hemilaminectomy was from the base of the dorsal process of L7 to the capsule of the facet joint of the transitional segment. Complete facetectomy was not performed in order to preserve stability. The interarcuate ligament was only partially removed over the exposed region.

During surgery, a unilateral disk protrusion opposite the large pelvic attachment was confirmed in the three dogs that had myelography and epidurography, as well as the three dogs that had MRIs. In all the dogs, the side of protrusion correlated well with the clinical signs. After retraction of the nerve roots, the annulus was visualized and excised, sparing the venous sinuses. In two dogs, an annulectomy at the site of protrusion was performed using a no. 11 scalpel bladeg and bone rongeurs. Two other dogs had a ruptured annulus, and pieces of the annular ring were removed from the spinal canal. Protrusion of the nucleus pulposus was not noted in these latter dogs. In all dogs, the L7 and S1 nerve roots were mobilized with gentle retraction to prevent adhesions in the intervertebral foramen, and a free autogenous fat graft was placed in the laminectomy defect. The soft tissues were apposed in layers by using synthetic absorbable suture materialh in a simple interrupted pattern. The skin was closed with nonabsorbable suture materiali using a simple interrupted pattern.

Follow-up times ranged from 6 to 24 months. Five of the dogs were still alive at the time of manuscript submission. Case no. 4 died 6 months after surgery from an unrelated cause. Outcomes were good (n=4) or excellent (n=2) in all animals [see Table].

Discussion

The most important finding in this report was the presence of a unilateral disk protrusion in dogs with asymmetrical, transitional, lumbosacral vertebral segments. The disk protrusion always occurred on the opposite side from the broadest fusion of the vertebra with the ilium. Asymmetrical lesions were suggested in the clinical presentation of all six dogs based on neurological examination, and in all cases, asymmetry was confirmed by myelography or MRI and during surgery. Asymmetrical disk protrusions have also been reported in dogs with degenerative lumbosacral stenosis, and they do not occur exclusively in dogs with transitional vertebral anomalies.713 However, the findings of this report showed that asymmetrical clinical and radiological lesions are typical for the condition described here.

Abnormal lumbosacral motion leads to compensatory skeletal changes, including sclerosis of the lumbosacral end plate, osteophyte development on the articular facets, hypertrophy of the interarcuate ligament and articular facet joint capsule, and bulging of the dorsal annulus.14 Most of these abnormalities were detected to varying degrees in the dogs in this series, but focal sclerosis of the end plates and adjacent body of the vertebra was the most consistent similarity in the dogs evaluated with MRI. Recently, the presence of a transitional vertebra was found to be useful in the prediction of painful disk degeneration in humans with low back pain.15 The cause of the disk degeneration is not thoroughly understood. Recent publications in people suggest that it may develop as a result of inflammatory alterations within the disk matrix. In disk specimens that were harvested during diskectomy, high levels of interleukin-6 and interleukin-8 were detected, and it was hypothesized that the high level of proinflammatory mediators may have indicated the existence of a specific inflammatory form of disk degeneration.16

Conversely, other investigators are of the opinion that sclerotic abnormalities precede disk degeneration.17 The nucleus, as an avascular structure, is highly dependent on fluid transfer through the microsystem of the end plates of the vertebral body. Important in the process of disk degeneration is the disturbance of this fluid transfer as the end plate is transformed into a sclerotic barrier. This derangement in fluid transfer results in narrowing of the intervertebral space and a dry, immobile nucleus pulposus.17 Simultaneously, parallelization of fibers in the annulus fibrosus decreases torque resistance and predisposes the disk to rupture and bulging.17

Dogs with transitional lumbosacral vertebral segments may have asymmetrical mobility at the lumbosacral junction. Based on the findings in the study reported here, degenerative changes were isolated to the side with the shortest or narrowest sacroiliac attachment. The opposite side, with the broadest attachment to the ilium, may have been more rigid, thereby providing more protection against degenerative processes.

In a published report of dogs with degenerative lumbosacral stenosis alone, the average age at presentation was 7 years.12 Although not statistically proven in the present report, dogs with asymmetrical, transitional, lumbosacral vertebral segments developed clinical signs earlier than dogs with degenerative lumbosacral stenosis. This finding supports the assertion of Morgan, who noted that transitional lumbosacral vertebrae predisposed dogs to early disk degeneration, low back pain, and signs of cauda equina syndrome.3 One possible explanation for the earlier occurrence of cauda equina syndrome in dogs with transitional lumbosacral vertebrae may be increased stress on the side that is poorly attached to the ilium.

Similar to reports on degenerative lumbosacral stenosis, the German shepherd dog was overrepresented in the study reported here. German shepherd dogs were affected in 44% of the cases in a large radiographic study of transitional lumbosacral vertebrae, and the anomaly was suspected to be inherited in this breed.4

In the dogs of the present report, outcomes 6 to 24 months after surgery were good to excellent. Although Daniellson, et al., reported on 12 dogs with transitional lumbosacral vertebral segments within a population of 161 dogs affected with degenerative lumbosacral stenosis, the specific postoperative outcomes for this subpopulation of dogs were not provided.18 Based on the limited number of dogs in the present study, postoperative results were comparable to the good outcomes reported for dogs with only degenerative lumbosacral stenosis.1819

Conclusion

Lateralized disk herniation on the side of the abnormal sacroiliac attachment was a typical finding in dogs with asymmetrical, transitional, lumbosacral vertebral segments. Diagnosis was achieved with conventional myelography and epidurography, although MRI provided better characterization of the cauda equina compression and the underlying degenerative alterations. Magnetic resonance imaging also allowed for a more limited surgical approach to decompress the nerve roots of the cauda equina. Short-term outcomes (<24 months) after surgery in this report were good to excellent and were comparable to outcomes for dogs with degenerative lumbosacral stenosis.

a

Domitor; Dr. E. Gräub AG, Bern, Switzerland

b

Temgesic; Essex AG, Luzern, Switzerland

c

Propofol-Lipuro 1%; Braun Medical AG, Emmenbruecke, Switzerland

d

Isofluran; Baxter AG, Volketswil, Switzerland

e

Isovist-240; Schering, Baar, Switzerland

f

Symphony, Siemens Medical Systems, Erlangen, Germany

g

Swann Morton Ltd., Sheffield, England

h

Ethicon PDS II 3-0; Johnson and Johnson, Belgium

i

Supramid 3-0; Braun Surgical GmbH, Tuttlingen, Germany

Table Clinical Data on Six Dogs With Asymmetrical, Transitional, Lumbosacral Vertebral Segments
Table
Figure 1—. A ventrodorsal radiograph of the lumbosacral region of a dog (case no. 3) with an asymmetrical, transitional, lumbosacral vertebral anomaly. The lateral, broader process on the right side results in a larger sacral attachment, while there is no sacral attachment to the smaller, “lumbar-like” process on the left side. Separation of the sacral spinous process is evident. In addition, the ilium is angled toward the right, causing the tip of the iliac crest to be positioned further cranially than the right one. Rotation around the longitudinal axis causes the width of the iliac wings to be unequal in thickness and the size of the obturator foramina to be different on both sides. Note that the caudal aspect of the sacroiliac joint is positioned further caudally on the left side.Figure 1—. A ventrodorsal radiograph of the lumbosacral region of a dog (case no. 3) with an asymmetrical, transitional, lumbosacral vertebral anomaly. The lateral, broader process on the right side results in a larger sacral attachment, while there is no sacral attachment to the smaller, “lumbar-like” process on the left side. Separation of the sacral spinous process is evident. In addition, the ilium is angled toward the right, causing the tip of the iliac crest to be positioned further cranially than the right one. Rotation around the longitudinal axis causes the width of the iliac wings to be unequal in thickness and the size of the obturator foramina to be different on both sides. Note that the caudal aspect of the sacroiliac joint is positioned further caudally on the left side.Figure 1—. A ventrodorsal radiograph of the lumbosacral region of a dog (case no. 3) with an asymmetrical, transitional, lumbosacral vertebral anomaly. The lateral, broader process on the right side results in a larger sacral attachment, while there is no sacral attachment to the smaller, “lumbar-like” process on the left side. Separation of the sacral spinous process is evident. In addition, the ilium is angled toward the right, causing the tip of the iliac crest to be positioned further cranially than the right one. Rotation around the longitudinal axis causes the width of the iliac wings to be unequal in thickness and the size of the obturator foramina to be different on both sides. Note that the caudal aspect of the sacroiliac joint is positioned further caudally on the left side.
Figure 1 — A ventrodorsal radiograph of the lumbosacral region of a dog (case no. 3) with an asymmetrical, transitional, lumbosacral vertebral anomaly. The lateral, broader process on the right side results in a larger sacral attachment, while there is no sacral attachment to the smaller, “lumbar-like” process on the left side. Separation of the sacral spinous process is evident. In addition, the ilium is angled toward the right, causing the tip of the iliac crest to be positioned further cranially than the right one. Rotation around the longitudinal axis causes the width of the iliac wings to be unequal in thickness and the size of the obturator foramina to be different on both sides. Note that the caudal aspect of the sacroiliac joint is positioned further caudally on the left side.

Citation: Journal of the American Animal Hospital Association 40, 4; 10.5326/0400338

Figure 2—. A lateral radiograph made during a myelogram of the lumbosacral region of case no. 1, showing collapse of the contrast column from a ventrally located extradural mass-effect. The compression of the dural sac is more evident with the pelvic limbs placed in extension, which results in pooling of the contrast agent in the most caudal part of the dural sac.Figure 2—. A lateral radiograph made during a myelogram of the lumbosacral region of case no. 1, showing collapse of the contrast column from a ventrally located extradural mass-effect. The compression of the dural sac is more evident with the pelvic limbs placed in extension, which results in pooling of the contrast agent in the most caudal part of the dural sac.Figure 2—. A lateral radiograph made during a myelogram of the lumbosacral region of case no. 1, showing collapse of the contrast column from a ventrally located extradural mass-effect. The compression of the dural sac is more evident with the pelvic limbs placed in extension, which results in pooling of the contrast agent in the most caudal part of the dural sac.
Figure 2 — A lateral radiograph made during a myelogram of the lumbosacral region of case no. 1, showing collapse of the contrast column from a ventrally located extradural mass-effect. The compression of the dural sac is more evident with the pelvic limbs placed in extension, which results in pooling of the contrast agent in the most caudal part of the dural sac.

Citation: Journal of the American Animal Hospital Association 40, 4; 10.5326/0400338

Figure 3—. A ventrodorsal radiograph made during a myelogram of the lumbosacral region of case no. 1, showing collapse and right displacement of the contrast column. Caudal pooling of the contrast agent is evident when the limbs are placed in extension because of complete compression of the dural sac.Figure 3—. A ventrodorsal radiograph made during a myelogram of the lumbosacral region of case no. 1, showing collapse and right displacement of the contrast column. Caudal pooling of the contrast agent is evident when the limbs are placed in extension because of complete compression of the dural sac.Figure 3—. A ventrodorsal radiograph made during a myelogram of the lumbosacral region of case no. 1, showing collapse and right displacement of the contrast column. Caudal pooling of the contrast agent is evident when the limbs are placed in extension because of complete compression of the dural sac.
Figure 3 — A ventrodorsal radiograph made during a myelogram of the lumbosacral region of case no. 1, showing collapse and right displacement of the contrast column. Caudal pooling of the contrast agent is evident when the limbs are placed in extension because of complete compression of the dural sac.

Citation: Journal of the American Animal Hospital Association 40, 4; 10.5326/0400338

Figure 4—. A transverse, T2-weighted magnetic resonance image at the level of the lumbosacral disk in case no. 5, demonstrating mediolateral to intraforaminal disk herniation on the left (black arrowhead). The left recess and foramen are obliterated, and the dural sac is displaced slightly to the right. Note the normal appearance of the contralateral intervertebral foramen (gray arrowhead).Figure 4—. A transverse, T2-weighted magnetic resonance image at the level of the lumbosacral disk in case no. 5, demonstrating mediolateral to intraforaminal disk herniation on the left (black arrowhead). The left recess and foramen are obliterated, and the dural sac is displaced slightly to the right. Note the normal appearance of the contralateral intervertebral foramen (gray arrowhead).Figure 4—. A transverse, T2-weighted magnetic resonance image at the level of the lumbosacral disk in case no. 5, demonstrating mediolateral to intraforaminal disk herniation on the left (black arrowhead). The left recess and foramen are obliterated, and the dural sac is displaced slightly to the right. Note the normal appearance of the contralateral intervertebral foramen (gray arrowhead).
Figure 4 — A transverse, T2-weighted magnetic resonance image at the level of the lumbosacral disk in case no. 5, demonstrating mediolateral to intraforaminal disk herniation on the left (black arrowhead). The left recess and foramen are obliterated, and the dural sac is displaced slightly to the right. Note the normal appearance of the contralateral intervertebral foramen (gray arrowhead).

Citation: Journal of the American Animal Hospital Association 40, 4; 10.5326/0400338

Figure 5—. A dorsal plane, T1-weighted magnetic resonance image of the lumbar spine of case no. 5, demonstrating focal alterations of the end plate and adjacent vertebral body at the lumbosacral junction. The anomalous vertebra is broadly attached to the ilium on the right side (RA). The low signal alterations (dark areas) at the end plates and adjacent bone are limited to the left half of the vertebral bodies.Figure 5—. A dorsal plane, T1-weighted magnetic resonance image of the lumbar spine of case no. 5, demonstrating focal alterations of the end plate and adjacent vertebral body at the lumbosacral junction. The anomalous vertebra is broadly attached to the ilium on the right side (RA). The low signal alterations (dark areas) at the end plates and adjacent bone are limited to the left half of the vertebral bodies.Figure 5—. A dorsal plane, T1-weighted magnetic resonance image of the lumbar spine of case no. 5, demonstrating focal alterations of the end plate and adjacent vertebral body at the lumbosacral junction. The anomalous vertebra is broadly attached to the ilium on the right side (RA). The low signal alterations (dark areas) at the end plates and adjacent bone are limited to the left half of the vertebral bodies.
Figure 5 — A dorsal plane, T1-weighted magnetic resonance image of the lumbar spine of case no. 5, demonstrating focal alterations of the end plate and adjacent vertebral body at the lumbosacral junction. The anomalous vertebra is broadly attached to the ilium on the right side (RA). The low signal alterations (dark areas) at the end plates and adjacent bone are limited to the left half of the vertebral bodies.

Citation: Journal of the American Animal Hospital Association 40, 4; 10.5326/0400338

References

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    Bailey CS, Morgan JP. Congenital spinal malformations. Vet Clin North Am Small Anim Pract 1992;22:985–1015.
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    Morgan JP. Congenital anomalies of the vertebral column of the dog: a study of the incidence and significance based on a radiographic and morphologic study. Am J Vet Radiol Soc 1968;18:76–79.
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    Morgan JP, Bahr A, Franti CE, et al. Lumbosacral transitional vertebrae as a predisposing cause of cauda equina syndrome in German shepherd dogs: 161 cases. J Am Vet Med Assoc 1993;20:1877–1882.
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    Morgan JP. Transitional lumbosacral vertebral anomaly in the dog: a radiographic study. J Small Anim Pract 1999;40:167–172.
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    Schmorl G, Junghanns H. The Human Spine in Health and Disease. 2nd American ed. New York: Grune & Stratton, 1971:54–57.
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    Hathcock JT, Pechman RD, Dillon AR, et al. Comparison of three radiographic contrast procedures in the evaluation of the canine lumbosacral canal. Vet Radiol 1988;29:4–15.
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    Lang J. Flexion-extension myelography of the canine cauda equina. Vet Radiol 1988;29:242–257.
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    Sisson AF, LeCouteur RA, Ingram TJ, et al. Diagnosis of cauda equina abnormalities by using electromyography, discography, and epidurography in dogs. J Vet Intern Med 1992;6:253.
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    Barthez PY, Morgan JP, Lipsitz D. Discography and epidurography for evaluation of the lumbosacral junction in dogs with cauda equina syndrome. Vet Radiol Ultrasound 1994;152–157.
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    Chambers JN, Selcer BA, Sullivan SA. Diagnosis of a lateralized lumbosacral disk herniation with magnetic resonance imaging. J Am Anim Hosp Assoc 1997;33:296–299.
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    Ramirez O, Thrall DE. A review of the imaging techniques for cauda equina syndrome. Vet Radiol Ultrasound 1998;39:283–296.
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    De Risio L, Thomas WB, Sharp NJH. Degenerative lumbosacral stenosis. Vet Clin North Am Small Anim Pract 2000;30:111–132.
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    Mayhew PD, Kapatkin AS, Wortman JA, et al. Association of cauda equina compression on magnetic resonance images and clinical signs in dogs with degenerative lumbosacral stenosis. J Am Anim Hosp Assoc 2002;38:555–562.
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    Wheeler SJ, Sharp NJH. Lumbosacral disease. In: Small Animal Spinal Disorders: Diagnosis and Surgery. St. Louis: Mosby Wolf, 1994:122–134.
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    Weishaupt D, Zanetti M, Hodler J, et al. Painful lumbar disk derangement: relevance of endplate abnormalities at MR imaging. Radiology 2001;218:420–427.
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    Burke J, Watson RGW, Mc Cormack, et al. The heterogenous nature of degenerative lumbar intervertebral disc disease. Eur Spine J 1999;8:S1.
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    Gosh P. The Biology of Intervertebral Discs. Vol. 1, 2. Boca Raton: CRC Press, 1989.
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    Daniellson F, Sjostrom L. Surgical treatment of degenerative lumbosacral stenosis in dogs. Vet Surg 1999;28:91–98.
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Copyright: Copyright 2004 by The American Animal Hospital Association 2004
<bold> <italic toggle="yes">Figure 1</italic> </bold> —
Figure 1 —

A ventrodorsal radiograph of the lumbosacral region of a dog (case no. 3) with an asymmetrical, transitional, lumbosacral vertebral anomaly. The lateral, broader process on the right side results in a larger sacral attachment, while there is no sacral attachment to the smaller, “lumbar-like” process on the left side. Separation of the sacral spinous process is evident. In addition, the ilium is angled toward the right, causing the tip of the iliac crest to be positioned further cranially than the right one. Rotation around the longitudinal axis causes the width of the iliac wings to be unequal in thickness and the size of the obturator foramina to be different on both sides. Note that the caudal aspect of the sacroiliac joint is positioned further caudally on the left side.

<bold> <italic toggle="yes">Figure 2</italic> </bold> —
Figure 2 —

A lateral radiograph made during a myelogram of the lumbosacral region of case no. 1, showing collapse of the contrast column from a ventrally located extradural mass-effect. The compression of the dural sac is more evident with the pelvic limbs placed in extension, which results in pooling of the contrast agent in the most caudal part of the dural sac.

<bold> <italic toggle="yes">Figure 3</italic> </bold> —
Figure 3 —

A ventrodorsal radiograph made during a myelogram of the lumbosacral region of case no. 1, showing collapse and right displacement of the contrast column. Caudal pooling of the contrast agent is evident when the limbs are placed in extension because of complete compression of the dural sac.

<bold> <italic toggle="yes">Figure 4</italic> </bold> —
Figure 4 —

A transverse, T2-weighted magnetic resonance image at the level of the lumbosacral disk in case no. 5, demonstrating mediolateral to intraforaminal disk herniation on the left (black arrowhead). The left recess and foramen are obliterated, and the dural sac is displaced slightly to the right. Note the normal appearance of the contralateral intervertebral foramen (gray arrowhead).

<bold> <italic toggle="yes">Figure 5</italic> </bold> —
Figure 5 —

A dorsal plane, T1-weighted magnetic resonance image of the lumbar spine of case no. 5, demonstrating focal alterations of the end plate and adjacent vertebral body at the lumbosacral junction. The anomalous vertebra is broadly attached to the ilium on the right side (RA). The low signal alterations (dark areas) at the end plates and adjacent bone are limited to the left half of the vertebral bodies.

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