Differences in Epidural Pathology between Cervical and Thoracolumbar Intervertebral Disk Extrusions in Dogs

Morphometric Evaluation of Thoracolumbar Spinal Canal and Cord by Magnetic Resonance Imaging in Normal Small-Breed Dogs

Thoracolumbar intervertebral disc disease (IVDD) is the most common cause of spinal injury in dogs. MRI has been considered the gold standard for neurologic diagnosis, but studies focusing on the thoracolumbar spinal canal and spinal cord using MRI in small-breed dogs are limited. Therefore, this study aimed to establish an MRI reference range for the spinal cord and canal measurements (height, width, cord-to-canal ratio of height, width, cross-sectional area (CSA)) of each intervertebral disc level from T11 to L5 (total of seven levels) on transverse T2-weighted images in normal small-breed dogs. We hypothesized that the spinal cord and spinal canal measurements might vary according to the body weight and age. The width and height of the spinal cord and canal increased as the body weight increased at all levels (p < 0.05). The cord-to-canal ratio of the width showed a negative correlation to the body weight at all levels. The cord-to-canal ratio of the height did not show any correlation to the body weight at all levels. All measurements (height, width, cord-to-canal ratio of height, width, CSA) did not show any statistical correlation between the groups subdivided by age. These measurements could serve as a morphometric baseline for thoracolumbar spinal diseases and clinical research in small-breed dogs.

Clinical, magnetic resonance imaging, surgical features and comparison of surgically treated intervertebral disc extrusion in French bulldogs

Intervertebral disc (IVD) extrusion (IVDE) is the most reported neurological condition in French bulldogs (FBD). The aim of this study was to retrospectively evaluate neurological grade, magnetic resonance imaging (MRI), surgical findings and short-term recovery in surgically treated FBD diagnosed with IVDE referred to a single institution between January 2020 and March 2022 and to compare cervical and thoracolumbar IVDE. Data was gathered from medical records and analysed via Fischer's Exact-Test and Kruskal Wallis-tests. Statistical significance was assumed when p < 0.05. Thirty-nine FBD were diagnosed with IVDE. Cervical IVDE (C-IVDE) was diagnosed in 11/39 cases; the C3-C4 IVD space was the most commonly affected site (5/11). Thoracolumbar IVDE (TL-IVDE) was diagnosed in 28 cases; the L3-L4 IVD space was the most commonly affected site (7/28). At admission, C-IVDE was significantly associated with less severe neurological grade (grade 1-2) compared to TL-IVDE (grade 2-5) (p < 0.001). The extruded IVD material (EIVDM) was hypointense in T2w images in 11/11C-IVDE vs. 2/28TL-IVDE, and hypointense in T1w images in 10/11C-IVDE vs. 1/28TL-IVDE. The EIVDM was hyperintense in T2w images in 0/11C-IVDE vs. 26/28TL-IVDE and iso-to-hypointense in T1w images in 1/11C-IVDE vs. 27/28TL-IVDE (p < 0,001). The EIVDM extended over ≥2 IVD spaces in 0/11C-IVDE vs. 19/28TL-IVDE (p < 0,001). 10/11C-IVDE underwent single ventral slot, 1/11C-IVDE underwent unilateral cervical hemilaminectomy. All TL-IVDE underwent unilateral hemilaminectomy and 19/28TL-IVDE underwent unilateral hemilaminectomy over ≥2 IVD spaces (p < 0,001). Haemorrhagic EIVDM was noticed intraoperatively in 1/11C-IVDE vs. 28/28TL-IVDE (p < 0,001). Spinal cord compression was mild in 2/11C-IVDE and 3/28TL-IVDE; moderate in 9/11C-IVDE and 16/28TL-IVDE; severe in 0/11C-IVDE and 8/28TL-IVDE. There was no spinal cord compression in 1/28TL-IVDE with foraminal IVDE. There was no statistical difference between spinal cord compression and IVDE location (p = 0.112). The mean time to improvement was 1.1 day in C-IVDE (range 1-2 days). 90.1% of C-IVDE improved within the first 24 h. The mean time to improvement was 2.1 days in TL-IVDE (range from 1 day to 4 days). All dogs that did not improve (5/39) were grade 5 TL-IVDEs at presentation. In FBD, TL-IVDE tended to cause higher grade of neurological dysfunction, tended to result in compression of neural structures over multiple IVD spaces and required more extensive surgical treatment than C-IVDE.

Case report: Clinical and pathological findings in a canine patient with intervertebral disk extrusion resembling progressive myelomalacia

A 4-year-old female spayed dog presented to the emergency department for non-ambulatory tetraparesis, which progressed to tetraplegia. Computed tomography (CT) confirmed cervical intervertebral disk extrusion at C5-6 extending to C6-7, and an emergency ventral slot was performed. After the procedure, the patient was placed on mechanical ventilation due to respiratory failure. Repeat assessment upon weaning her ventilatory support suggested the patient's neurological status had declined. Based on her deterioration and suspicion of progressive myelomalacia on magnetic resonance imaging (MRI), she was euthanized. Post-mortem histopathology of the spinal cord supported the presence of progressive myelomalacia. To the author's knowledge, this is the first case report describing a progressive myelomalacia in a canine patient with cervical intervertebral disk extrusion.

Recurrence rate of intervertebral disc disease in surgically treated French Bulldogs: a retrospective study (2009-2019)

BACKGROUND

Intervertebral disc disease (IVDD) is a common diagnosis and well-investigated pathological condition in French Bulldogs with neurological deficiencies. However there is currently only one recently published retrospective descriptive study looking for recurrence rates of IVDD in French Bulldogs. Medical reports of French Bulldogs with a first episode of IVDD and surgical treatment were evaluated and reviewed for clinical signs of recurrence. Risk factors for Total-Recurrence, Cervical- and Thoracolumbar-Recurrence were evaluated by means of logistic regression models. The aim of this study was to assess frequency and risk factors associated with the recurrence of IVDD in French Bulldogs.

RESULTS

One hundred twenty-seven French Bulldogs with a first episode of IVDD and surgical treatment were evaluated. 52.7% (67/127) of these patients showed signs of recurrence. The recurrence rate in the cervical spine was slightly lower (47%) compared to the thoracolumbar spine (56.6%). A significant association with recurrence could be found for the factor age: French Bulldogs with a first episode of IVDD ≤ 3 years seem to be prone for Total-Recurrence (P = 0.002) and Cervical-Recurrence (with ORs ranging from 0.02 to 0.03 for patients older than 3 years). 50% of the recurrences (median) occurred within the first 12 month after the first episode of IVDD.

CONCLUSIONS

Recurrence of IVDD can be expected in more than half of French Bulldogs affected by IVDD. Especially young French Bulldogs are prone for recurrence in cervical spine. Almost every fourth patient with IVDD suffers from a recurrence within 12 months. Future dog owners should be informed about the risk of IVDD and the early onset of recurrences in French Bulldogs.

The spinal cord-to-vertebral canal area ratio measured with computed tomography is lower in the thoracolumbar than the cervical region in French Bulldogs

OBJECTIVE

To compare spinal cord-to-vertebral canal area ratios measured with CT between the cervical and thoracolumbar regions in French Bulldogs.

ANIMALS

37 French Bulldogs presented to a referral hospital between 2016 and 2019.

PROCEDURES

The study was conducted as a retrospective observational study. Exclusion criteria were evidence of vertebral malformations or spinal cord compression at the sites where measurements were obtained and the presence of cervicothoracic or thoracolumbar transitional vertebrae or neurologic deficits. CT images were reviewed, and measurements were performed by 2 investigators. Measurements of the spinal cord and vertebral canal were made at the level of or immediately cranial to the midbodies of C5 and L1.

RESULTS

A 2-tailed, paired t test indicated that the mean spinal cord-to-vertebral canal area ratio differed significantly (P < .01) between C5 (0.726) and L1 (0.605). The ratio was lower in the thoracolumbar region, suggesting that the vertebral canal was relatively larger in this region.

CLINICAL RELEVANCE

The epidural space did not appear to be larger in the cervical than in the thoracolumbar region in this population of French Bulldogs, contrary to previous reports. The reason for the more severe deficits observed with thoracolumbar disk extrusion in this breed remains to be characterized.

Clinical reasoning in canine cervical hyperaesthesia: which presenting features are important?

BACKGROUND

To evaluate whether clinical features from the history, presentation, physical and neurological examination of dogs with cervical hyperaesthesia are statistically predictive of the underlying diagnosis.

METHODS

Two hundred and ninety-eight dogs presenting with cervical hyperaesthesia between January 2010 and October 2018 were investigated. Only neurologically normal dogs with cervical hyperaesthesia on examination were included, while those with concurrent neurological deficits including gait abnormalities and proprioceptive deficits were excluded. Univariate analysis of clinical variables was performed, and those associated with each diagnosis were retained for multivariable binary logistic regression models.

RESULTS

Ninety-five per cent of cervical hyperaesthesia presentations were represented by eight conditions that included steroid-responsive meningitis arteritis (SRMA; n=100), intervertebral disc extrusion (n=78), syringomyelia (SM; n=51), intervertebral disc protrusion (n=30), neoplasia (n=8), cervical spondylomyelopathy (n=7), immune-mediated polyarthritis (n=5) and meningoencephalomyelitis of unknown aetiology (n=5). Younger age (P=0.003), pyrexia (P=0.003) and haematology abnormalities (P=0.03) comprising leucocytosis, neutrophilia or monocytosis were associated with a diagnosis of SRMA.

CONCLUSIONS

Easy-to-recognise clinical features can be used to identify the most likely differential diagnosis in neurologically normal dogs with cervical hyperaesthesia, which may aid the decision making of veterinary surgeons evaluating dogs with this presentation.

Calcification of extruded intervertebral discs in dachshunds: a radiographic, computed tomographic and histopathological study of 25 cases

Background

Three Nordic countries have national breeding programs to reduce the frequency of intervertebral disc disease in dachshunds. The programs include a radiographic examination of the vertebral column and dachshunds with more than four calcified discs visible on radiographs (CDVR) are discouraged from use in breeding. However, disc extrusion is also diagnosed in dachshunds without CDVR. The utility of the breeding programs is therefore questioned.

Results

A prospective study of 25 dachshunds surgically treated for disc extrusion was conducted. For all the dogs, preoperative radiographs were evaluated for detectable disc calcifications and preoperative computed tomography (CT) scans were evaluated for presence of calcified material in the vertebral canal. Postoperatively, extruded disc material was examined for degeneration and calcification by histology. Diagnostic imaging and histology were done independently. Radiographically visible calcification was identified in 17 (68.0%) of 25 extruded discs. Calcification was seen in the disc space for all these 17 discs, and for eight of the 17, there was also calcified material visible in the vertebral canal. Extruded material from all the 25 discs was found to be calcified, both by CT and histopathology.

Conclusions

In dachshunds with acute disc extrusion, radiographically visible calcification will frequently be found in the affected disc space, but not all affected disc spaces contain radiographically visible calcification. Using histopathology as the gold standard, a sensitivity of 0.3 (8/25) for radiography and 1.0 (25/25) for CT was found for detecting calcified disc material in the vertebral canal. Further, a sensitivity of 0.7 (17/25) was found for radiography for detecting remaining calcified material in the disc space. Thus, extruded disc material should be considered to be calcified, even in the absence of radiographically visible calcification.

Comparison of surgical and conservative treatment of hydrated nucleus pulposus extrusion in dogs

Background

Whether compressive cervical myelopathy caused by hydrated nucleus pulposus extrusion (HNPE) in dogs should be treated surgically or conservatively has been debated. Only 1 recent study has contradicted the former predominant reports of surgical treatment for HNPE.

Hypothesis and method

Single center retrospective study to compare the outcome of client‐owned dogs with HNPE after decompressive surgery or conservative treatment.

Animals

Thirty‐six dogs diagnosed with HNPE confirmed by magnetic resonance imaging (MRI).

Results

Eighteen of 36 dogs underwent surgery whereas 18 dogs were managed conservatively including cage rest and physiotherapy. The most common affected intervertebral disc space was C4‐5. In 3 dogs, HNPE was diagnosed at the level of T13‐L1. Median time to regain ambulation was 6.6 days (range, 0‐28 days) after surgery and 5.9 days (range, 0‐15 days) with conservative management (P = .37).

Only the length of a potential intramedullary lesion in cervical HNPE detected by MRI had an influence on the prognosis to gain ambulatory status in a time period of ≤9 days (P = .0035) and on short‐term survival (P = .0011).

Conclusions and clinical importance

Conservative management of HNPE in the cervical as well as in the thoracolumbar region represents a reasonable alternative to surgery, showing similar favorable outcome.