Cranial thoracic disc protrusions in three German Shepherd dogs

Although intervertebral disc degeneration can occur at any level of the spine, cervical and thoraco-lumbar discs are more commonly affected. The presence of the inter-capital ligament between the rib heads results in an extremely low incidence of cranial thoracic intervertebral disc herniation. In this case series, the clinical, radiological, and surgical findings, as well as the post-operative outcome, in three German Shepherd dogs with T2–T3 disc protrusions is reported. These dogs had chronic progressive paraparesis and lumbar myelography and post-myelographic computerised tomography revealed ventrolateral, extra-dural spinal cord compressions over the T2–T3 intervertebral disc. All animals exhibited transient deterioration in their clinical signs and one developed unilateral Horner’s syndrome following T2–T3 hemi-dorsal laminectomy. Subsequently two of the dogs improved progressively and neurological dysfunction had completely resolved by 2 months. To the authors’ knowledge, this is the first case series describing T2–T3 disc protrusions in the dog.     

IMAGING FINDINGS IN DOGS WITH CAUDAL INTERVERTEBRAL DISC HERNIATION

The radiographic and magnetic resonance imaging (MRI) findings for four dogs with herniation of the Cd1–Cd2 intervertebral disc are described. All dogs were 7 years of age at the time of presentation, with one neutered male and three neutered females. Breeds included one Beagle, one Bassett hound, and two large, mixed breed dogs. All dogs had tail pain on manipulation, two had pain during defecation, and two maintained an abnormal tail position. Three dogs had radiographs in which mineralization within the disc space was apparent. Two of these dogs also had mineralization within the vertebral canal. Three dogs underwent MRI, which was characterized by varying degrees of disc herniation and nerve root compression at Cd1–Cd2. Mobility may be a factor predisposing to disc herniation in the cranial aspect of the caudal spine. We documented that caudal disc herniation does occur occasionally in dogs and that radiography and MRI may be used to identify this disease. Caudal intervertebral disc herniation should be considered as a differential for dogs with caudal vertebral pain, pain with tail manipulation, pain during defecation, or abnormal tail carriage.     

CLINICAL AND MAGNETIC RESONANCE IMAGING CHARACTERISTICS OF THORACOLUMBAR INTERVERTEBRAL DISK EXTRUSIONS AND PROTRUSIONS IN LARGE BREED DOGS

Treatment recommendations differ for dogs with intervertebral disk extrusion vs. intervertebral disk protrusion. The aim of this retrospective, cross‐sectional study was to determine whether clinical and magnetic resonance imaging (MRI) variables could be used to predict a diagnosis of thoracolumbar intervertebral disk extrusion or protrusion in dogs. Dogs were included if they were large breed dogs, had an MRI study of the thoracolumbar or lumbar vertebral column, had undergone spinal surgery, and had the type of intervertebral disk herniation (intervertebral disk extrusion or protrusion) clearly stated in surgical reports. A veterinary neurologist unaware of surgical findings reviewed MRI studies and recorded number, location, degree of degeneration and morphology of intervertebral disks, presence of nuclear clefts, disk space narrowing, extent, localization and lateralization of herniated disk material, degree of spinal cord compression, intraparenchymal intensity changes, spondylosis deformans, spinal cord swelling, spinal cord atrophy, vertebral endplate changes, and presence of extradural hemorrhage. Ninety‐five dogs were included in the sample. Multivariable statistical models indicated that longer duration of clinical signs (P = 0.01), midline instead of lateralized disk herniation (P = 0.007), and partial instead of complete disk degeneration (P = 0.01) were associated with a diagnosis of intervertebral disk protrusion. The presence of a single intervertebral herniation (P = 0.023) and dispersed intervertebral disk material not confined to the disk space (P = 0.06) made a diagnosis of intervertebral disk extrusion more likely. Findings from this study identified one clinical and four MRI variables that could potentially facilitate differentiating intervertebral disk extrusions from protrusions in dogs.     

MAGNETIC RESONANCE IMAGING OF ARTICULAR PROCESS JOINT GEOMETRY AND INTERVERTEBRAL DISK DEGENERATION IN THE CAUDAL LUMBAR SPINE (L5–S1) OF DOGS WITH CLINICAL SIGNS OF CAUDA EQUINA COMPRESSION

The geometry of the lumbosacral region has been suspected to play a role in the development of degenerative lumbosacral stenosis in the dog. In this study, 50 dogs (21 German Shepherd dogs and 29 dogs of other breeds) with clinical signs of cauda equina compression were studied by magnetic resonance (MR) imaging. The orientation of the articular process joints in the L5-S1 region and the angle difference between two adjacent motion segments were calculated. Intervertebral disc degeneration of the same region was identified and classified in four stages. A positive association between MR-imaging stage and articular process joint angle difference in the transverse plane was found in the two groups of animals. German Shepherd dogs and dogs of other breeds had different geometry of the lumbosacral region with different articular process joint angles in the transverse plane and statistically different stages of disc degeneration.     

MR-imaging of lumbosacral intervertebral disc degeneration in clinically sound German shepherd dogs compared to other breeds

German shepherd dogs are overrepresented in the group of dogs with cauda equina compression syndrome due to degenerative lumbosacral stenosis. A congenital predisposition for early degeneration of the lumbosacral intervertebral disc has been suspected. Our aims were to assess the morphologic appearance of the lumbosacral intervertebral disc and the lumbosacral junction in healthy German shepherd dogs compared to other breeds and to evaluate for an early onset of degenerative changes. The lumbosacral spine of 110 clinically sound German shepherd dogs and 47 healthy dogs of other large breeds was examined using magnetic resonance (MR) imaging. The degeneration of every intervertebral disc was graded using an established classification system. Signal intensity of the entire lumbosacral disc and the nucleus pulposus was determined independently. Lumbosacral malalignment was assessed according to a previously described method. The findings for the German shepherd dogs were compared to those of the other breeds. Although most dogs were younger than 18 months at the date of examination, significantly higher grades of degeneration were detected for the lumbosacral intervertebral disc of German shepherd dogs (P < 0.003). Degeneration of the lumbosacral intervertebral disc was independent from findings in the other lumbar discs. We conclude that the German shepherd dog has a predisposition for degenerative changes in the lumbosacral intervertebral disc.     

THORACOLUMBAR INTRADURAL DISC HERNIATION IN EIGHT DOGS: CLINICAL,LOW‐FIELD MAGNETIC RESONANCE IMAGING,AND COMPUTED TOMOGRAPHIC MYELOGRAPHY FINDINGS

Intradural disc herniation is a rarely reported cause of neurologic deficits in dogs and few published studies have described comparative imaging characteristics. The purpose of this retrospective cross sectional study was to describe clinical and imaging findings in a group of dogs with confirmed thoracolumbar intradural disc herniation. Included dogs were referred to one of four clinics, had acute mono/paraparesis or paraplegia, had low field magnetic resonance imaging (MRI) and/or computed tomographic myelography, and were diagnosed with thoracolumbar intradural disc herniation during surgery. Eight dogs met inclusion criteria. The prevalence of thoracolumbar intradural disc herniation amongst the total population of dogs that developed a thoracolumbar intervertebral disc herniation and that were treated with a surgical procedure was 0.5%. Five dogs were examined using low‐field MRI. Lesions that were suspected to be intervertebral disc herniations were observed; however, there were no specific findings indicating that the nucleus pulposus had penetrated into the subarachnoid space or into the spinal cord parenchyma. Thus, the dogs were misdiagnosed as having a conventional intervertebral disc herniation. An intradural extramedullary disc herniation (three cases) or intramedullary disc herniation (two cases) was confirmed during surgery. By using computed tomographic myelography (CTM) for the remaining three dogs, an intradural extramedullary mass surrounded by an accumulation of contrast medium was observed and confirmed during surgery. Findings from this small sample of eight dogs indicated that CTM may be more sensitive for diagnosing canine thoracolumbar intradural disc herniation than low‐field MRI.     

Facet joint geometry and intervertebral disk degeneration in the L5-S1 region of the vertebral column in German Shepherd dogs

OBJECTIVE: To evaluate the possible association between facet joint geometry and intervertebral disk degeneration in German Shepherd Dogs. ANIMALS: 25 German Shepherd Dogs and 11 control dogs of similar body weight and condition. PROCEDURE: Facet joint angles in the caudal portion of the lumbar region of the vertebral column (L5-S1) were measured by use of computed tomography, and the intervertebral discs were evaluated microscopically. The relationship between facet joint geometry and disk degeneration was evaluated by use of statistical methods. RESULTS: German Shepherd Dogs had significantly more facet joint tropism than control dogs, but an association with disk degeneration was not found. However, German Shepherd Dogs had a different facet joint conformation, with more sagittally oriented facet joints at L5-L6 and L6-L7 and a larger angle difference between the lumbar and lumbosacral facet joints, compared with control dogs. CONCLUSIONS AND CLINICAL RELEVANCE: A large difference between facet joint angles at L6-L7 and L7-S1 in German Shepherd Dogs may be associated with the frequent occurrence of lumbosacral disk degeneration in this breed.     

RADIOGRAPHIC LIVER SIZE IN PEKINGESE DOGS VERSUS OTHER DOG BREEDS

Differential diagnoses for canine liver disease are commonly based on radiographic estimates of liver size, however little has been published on breed variations. Aims of this study were to describe normal radiographic liver size in Pekingese dogs and to compare normal measurements for this breed with other dog breeds and Pekingese dogs with liver disease. Liver measurements were compared for clinically normal Pekingese (n = 61), normal non‐Pekingese brachycephalic (n = 45), normal nonbrachycephalic (n = 71), and Pekingese breed dogs with liver disease (n = 22). For each dog, body weight, liver length, T11 vertebral length, thoracic depth, and thoracic width were measured on right lateral and ventrodorsal abdominal radiographs. Liver volume was calculated using a formula and ratios of liver length/T11 vertebral length and liver volume/body weight ratio were determined. Normal Pekingese dogs had a significantly smaller liver volume/body weight ratio (16.73 ± 5.67, P < 0.05) than normal non‐Pekingese brachycephalic breed dogs (19.54 ± 5.03) and normal nonbrachycephalic breed dogs (18.72 ± 6.52). The liver length/T11 vertebral length ratio in normal Pekingese (4.64 ± 0.65) was significantly smaller than normal non‐Pekingese brachycephalic breed dogs (5.16 ± 0.74) and normal nonbrachycephalic breed dogs (5.40 ± 0.74). Ratios of liver volume/body weight and liver length/T11 vertebral length in normal Pekingese were significantly different from Pekingese with liver diseases (P < 0.05). Findings supported our hypothesis that Pekingese dogs have a smaller normal radiographic liver size than other breeds. We recommend using 4.64× the length of the T11 vertebra as a radiographic criterion for normal liver length in Pekingese dogs.     

Influence of intervertebral disc fenestration at the herniation site in association with hemilaminectomy on recurrence in chondrodystrophic dogs with thoracolumbar disc disease: a prospective MRI study

Objective— To describe the influence of fenestration at the disc herniation site on recurrence in thoracolumbar disc disease of chondrodystrophoid dogs.
Study Design— Prospective clinical study.
Animals— Chondrodystrophic dogs (n=19).
Methods— Dogs were divided into 2 groups: group 1 (9 dogs) had thoracolumbar disc extrusion (Hansen type I) treated by hemilaminectomy and concomitant fenestration of the affected intervertebral disc and group 2 (10 dogs) had hemilaminectomy without fenestration. All dogs had 3 magnetic resonance imaging (MRI) examinations: preoperatively, immediately postoperatively to assess removal of herniated disc material, and again 6 weeks after surgery.
Results— There were 13 male and 6 female dogs; mean age, 7.1 years. Thoracolumbar disc herniation was confirmed with MRI. Immediate post surgical MRI revealed that the herniated disc removal was complete in all but 1 dog and that fenestration did not lead to complete removal of nucleus pulposus within the intervertebral disc space. On the 3rd MRI examination, none of the group 1 dogs had further disc material herniation at the fenestrated site. Six of the 10 group 2 dogs had a recurrence of herniation leading to clinical signs in 3 dogs (pain in 2 dogs, paresis in 1 dog).
Conclusion— In thoracolumbar disc herniation, fenestration of the affected intervertebral disc space prevents further extrusion of disc material.
Clinical Relevance— Fenestration reduces the risk of early recurrence of disc herniation and associated postoperative complications.     

Evaluation of Fenestration for Treatment of Degenerative Disc Disease in the Caudal Cervical Region of Large Dogs

Seventeen large dogs (15 Doberman pinschers, one Labrador retriever, and one German short-haired pointer) with pain and gait abnormalities resulting from caudal cervical intervertebral disc degeneration were treated by disc fenestration. Four dogs recovered completely, two dogs appeared to have recovered but nerve root compression and pain returned 3 years later, five did not recover completely or did not improve, and six became progressively worse. In the dogs that recovered, preoperative myelograms showed that traction on or flexing the neck relieved the spinal cord compression. Such manipulation did not relieve slight persistent compression in the dogs that did not improve nor did it relieve severe compression by disc herniation or spinal canal stenosis in the dogs that became progressively worse. The return of nerve root compression after 3 years in two dogs was attributed to incomplete removal of dorsal anulus fibrosus. It was concluded that disc fenestration alone provided inadequate treatment of caudal cervical degenerative disc disease in large dogs.     

CERVICAL VERTEBRAL FUSION AND CONCURRENT INTERVERTEBRAL DISC EXTRUSION IN FOUR DOGS

Cervical vertebral fusion was noted radiographically in four dogs presented for signs of cervical spinal cord compression. Ventral extradural spinal cord compression was seen on myelography at intervertebral disc spaces adjacent to the fused vertebrae in two dogs and at a site removed in two dogs. At surgery, no intervertebral disc space was found in the area of fusion. No other instances of cervical vertebral fusion were identified in reviewing radiographs of 1225 other dogs with cervical intervertebral disc extrusion evaluated at our hospital. Clinical signs resolved in all dogs after surgical removal of extruded intervertebral disc material. Information from these four dogs suggest vertebral fusion may predispose adjacent discs to herniation.     

MAGNETIC RESONANCE IMAGING OF THE CERVICAL SPINE IN 27 DOGS

The cervical spine of 27 dogs with cervical pain or cervical myelopathy was evaluated using magnetic resonance imaging (MRI). Spin echo T1, T2, and post-contrast T1 weighted imaging sequences were obtained with a 0.5 Tesla magnet in 5 dogs and a 1.5 Tesla magnet in the remaining 22 dogs. MRI provided for visualization of the entire cervical spine including the vertebral bodies, intervertebral discs, vertebral canal, and spinal cord. Disorders noted included intervertebral disc degeneration and/or protrusion (12 dogs), intradural extramedullary mass lesions (3 dogs), intradural and extradural nerve root tumors (3 dogs), hydromyelia/syringomyelia (1 dog), intramedullary ring enhancing lesions (1 dog), extradural synovial cysts (1 dog), and extradural compressive lesions (3 dogs). The MRI findings were consistent with surgical findings in 18 dogs that underwent surgery. Magnetic resonance imaging provided a safe, useful non-invasive method of evaluating the cervical spinal cord.     

CONTRAST ENHANCEMENT OF EXTRADURAL COMPRESSIVE MATERIAL ON MAGNETIC RESONANCE IMAGING

Gadolinium‐enhancement of compressive extradural material is detected occasionally with magnetic resonance (MR) imaging in dogs. Our goal was to characterize contrast enhancement of extradural compressive material associated with intervertebral disc herniation, and to evaluate the association between enhancement and histopathologic findings and the onset of clinical signs. Ninety‐three dogs with a total of 99 lesions diagnosed as intervertebral disc herniation on MR imaging were assessed. Images were evaluated for lesion location, type of herniation, degree of compression, intramedullary T2‐weighted (T2W) intensities, and contrast enhancement. In 23 dogs, surgically removed compressive material was evaluated histopathologically for hemorrhage, inflammation, neovascularization, fibroplasia, fibrosis, mineralization, necrosis, and chronicity. Contrast enhancement of extradural compressive material, meninges, and both the compressive materials and meninges was present in 51.5%, 39.4%, and 17.2% of lesions, respectively. Extradural enhancement occurred more frequently in extrusions than protrusions (P=0.001). Meningeal enhancement and more severe neurologic deficits were significantly associated with a shorter duration of clinical signs (P=0.04 and 0.01, respectively). Intramedullary T2W hyperintensities, present with 44.4% of lesions, were associated with more severe neurologic deficits (P=0.001). Lesions with extradural enhancement were more often considered subacute to chronic in duration and more frequently associated with hemorrhage compared with nonenhancing material; however, no statistically significant association was established between contrast enhancement and histopathologic findings. Contrast enhancement of extradural compressive material and the meninges was found to be common with intervertebral disc herniation, and should not be interpreted as a specific sign of a mass lesion such as neoplasia.     

MRI FEATURES OF GASTROCNEMIUS MUSCULOTENDINOPATHY IN HERDING DOGS

Pelvic limb lameness that was localized clinically to the lateral gastrocnemius head was observed in dogs without history of trauma. The aim of this retrospective study was to describe magnetic resonance imaging (MRI) findings of this condition. Nine dogs were identified, eight Border Collies and one Australian Shepherd. They all had chronic pelvic limb lameness; no signs of joint effusion or instability were present. In MR images there was high signal intensity in the lateral head of the gastrocnemius muscle around the sesamoid bone in T2‐weighted, T2^*‐weighted, and STIR images and an iso‐ to mildly hyperintense signal in T1‐weighted images with marked contrast enhancement. The abnormal signal intensity most likely represents a myotendinous strain. The breed affiliation to Border Collies is striking, and a relation to biomechanical forces or motion pattern may be possible. Except for the dog with the most extensive lesion all dogs had an excellent outcome.     

INTRAVERTEBRAL DISC HERNIATION (SCHMORL'S NODE) IN FIVE DOGS

The herniation of intervertebral disc material into the vertebral body, known as Schmorl's nodes, is a well described disease process in man. Schmorl's nodes have not until now been described in the dog. This paper describes intravertebral disc herniation in the dog based on five patients taken from a retrospective study of dogs suspected of having cauda equina syndrome. The significance of intravertebral disc herniation in the dog at this time is that they indicate a disturbance in the vertebral endplate, they present definite radiographic signs, should be considered in patients with ostecohondrosis, and remain a possibls etiology for fibrocartilaginous emboli. Back pain is a common sign in people when Schmorl's nodes were the only pathologic findings. The common signs of palpatory pain in the lumbosacral region of the dogs in this report is noted but cannot be directly correlated at this time to the intravertebral disc herniation; however, it is suspected in two of the cases.     

Traumatic Intervertebral Disc Herniation with Paraplegia in a Black-Tailed Prairie Dog (Cynomys ludovicianus)

A 2-year-old castrated male black-tailed prairie dog (Cynomys ludovicianus) was presented 48 hours after peracute onset of rear limb paraplegia secondary to a traumatic incident. The prairie dog was nonambulatory in the rear legs with absent deep pain; hematuria and pollakiuria were also observed. Diagnostic imaging revealed intervertebral disc herniation with compression of the spinal cord at the L1-L2 disc spaces. Hemilaminectomy at the L1-L2 disc space was performed. After 48 hours, the prairie dog regained anal tone, and a deep pain response was noted. Azotemia developed during the course of hospitalization likely secondary to neuromuscular damage causing an obstruction in the lower urinary tract but resolved with supportive care. The prairie dog recovered complete use of its hind legs and had normal excretory function at a 3-month recheck. Practitioners should consider intervertebral disc herniation secondary to trauma as a differential diagnosis for neurologic deficits affecting the rear limbs of prairie dogs. Surgical management of intervertebral disc herniation is a viable treatment option in appropriate cases.     

A SACRAL LESION RESEMBLING OSTEOCHONDROSIS IN THE GERMAN SHEPHERD DOG

More than 30% (21 of 65) of German Shepherd dogs with clinical signs of cauda equina compression had radiographic and pathologic abnormalities compatible with osteochondrosis of the sacral endplate. Most of these dogs had a defect in the dorsal part of the sacral endplate and a detached bone fragment in the vertebral canal. Similar lesions were also found in growing and young adult dogs without clinical signs. The dogs with clinical signs of cauda equina compression also had severe degenerative disc disease with protrusion of the lumbosacral disc and compression of the cauda equina, suggesting that the signs of cauda equina compression more likely were related to the secondary degenerative changes (disc protrusions) rather than the primary disease. Clinically normal German Shepherds with sacral osteochondrosis usually were younger than 18 months, the dogs with cauda equina compression and sacral osteochondrosis older than 18 months (mean age 4.8 years). On the average, these dogs were two years younger as compared to dogs with cauda equina compression without sacral osteochondrosis. Male dogs are more often affected than females (5:1). There is a breed predisposition: in dogs other than German Shepherds, osteochondrosis of the sacral endplate seems to be extremely rare.     

COMPARISON BETWEEN NONCONTRAST COMPUTED TOMOGRAPHY AND MAGNETIC RESONANCE IMAGING FOR DETECTION AND CHARACTERIZATION OF THORACOLUMBAR MYELOPATHY CAUSED BY INTERVERTEBRAL DISK HERNIATION IN DOGS

Magnetic resonance imaging (MRI) and computed tomography (CT) are commonly used to evaluate dogs with thoracolumbar myelopathy; however, relative diagnostic sensitivities for these two modalities have not been previously reported. The purpose of this prospective study was to compare diagnostic sensitivity and observer agreement for MRI and CT in a group of dogs with thoracolumbar myelopathy due to surgically confirmed intervertebral disk herniation (IVDH). All included dogs had magnetic resonance (MR) imaging followed by noncontrast CT using standardized protocols. Three experienced observers interpreted each imaging study independently without knowledge of clinical or surgical findings. The operating surgeon was aware of MR findings but not CT findings at the time surgical findings were recorded. Forty‐four dogs met the inclusion criteria. The sensitivity of CT was 88.6% (79.5%–94.2%) and of MR was 98.5% (95% confidence interval, 94.1%–99.7%) for diagnosis of intervertebral disk herniation. Specificity was not calculated, as all dogs had IVDH at surgery. Magnetic resonance imaging was more accurate than CT for identifying the site of intervertebral disk herniation‐associated spinal cord compression and differentiating disk extrusion vs. protrusion. Computed tomography was less accurate for lesion localization in per acute cases, as well as for chondrodystrophic, female, older and smaller (<7 kg) dogs. Inter‐rater agreement was good for lesion lateralization for both MR and CT (κ = 0.687, 95% CI = 0.552, 0.822, P = 0.002, and κ = 0.692, 95% CI = 0.542, 0.842, P = 0.003). Findings from the current study indicated that MR imaging was more sensitive and accurate than noncontrast CT for diagnosis and characterization of thoracolumbar myelopathy due to IVDH in dogs.     

Functional outcome in dogs after surgical treatment of caudal lumbar intervertebral disk herniation.

Caudal lumbar disk herniations (i.e., third lumbar [L3] to seventh lumbar [L7] intervertebral spaces) represent approximately 15% of surgically treated thoracolumbar disk herniations in dogs. A retrospective case-control study was conducted to determine the postoperative outcome of this subset of dogs in the authors' neurosurgical practice. Medical records (1985 through 1996) were reviewed for dogs with caudal lumbar disk herniation confirmed at surgery. Thirty-six cases were identified. For each case, two dogs that underwent surgical treatment for upper motor neuron thoracolumbar disk herniation (tenth thoracic [T10] to L3 intervertebral spaces) were selected as controls. Probabilities of functional recovery for cases and controls were 81% and 85%, respectively (p value of 0.49). In dogs with caudal lumbar disk herniation, complete sensorimotor loss was the only significant predictor of functional recovery (p value of 0.005). Disk herniations that occur at the thoracolumbar junction and those that occur in the caudal lumbar region should not be considered to be different in terms of surgical treatment and postoperative outcome. The lower motor neuron signs that often accompany caudal lumbar disk herniation reflect the site of spinal cord injury and do not necessarily predict a poor prognosis.     

RESULTS OF MYELOGRAPHY IN SEVEN DOGS WITH MYELOMALACIA

Myelomalacia is a hemorrhagic infarction of the spinal cord that can occur as a sequel to acute spinal cord injury. Myelomalacia may be focal or diffuse; the diffuse form is typically associated with cranial migration of neurologic signs ("ascending syndrome") and is often fatal. In a retrospective study of seven affected dogs, diffuse myelomalacia was associated with intervertebral disc extrusion in five dogs, focal myelomalacia was associated with fibrocartilagenous embolus in one dog, and had no apparent cause in one dog. The myelographic signs included a variable degree of contrast medium infiltration into the spinal cord in six dogs (86%) and/or spinal cord swelling in six dogs (86%). In one dog with focal myelomalacia, the only myelographic sign was spinal cord swelling.