Accuracy, intermethod agreement, and inter-reviewer agreement for use of magnetic resonance imaging and myelography in small-breed dogs with naturally occurring first-time intervertebral disk extrusion

Outcome of the Use of Clinical Reasoning Alone in Dogs with Acute Thoracolumbar Myelopathy and/or Pain

Acute thoracolumbar myelopathy is a common neurological presentation in dogs. Although certain spinal conditions present with characteristic clinical pictures, managing such cases with clinical reasoning alone (i.e., without cross-sectional imaging) has never been explored. The aim of this study was to define the outcome of patients with suspected intervertebral disc extrusion (IVDE), ischaemic myelopathy (IM) or acute non-compressive nucleus pulposus extrusion (ANNPE) that were managed with clinical reasoning alone. The database of the Queen's Veterinary School Hospital (Cambridge) was searched for paraparetic or paraplegic dogs with suspected IVDE or IM/ANNPE that were initially managed medically without undergoing imaging. Clinical presentation and outcome were recorded. If cross-sectional imaging was subsequently performed, information about the final diagnosis was collected and compared with the initially suspected diagnosis. A total of 123 IVDE cases were collected: 81% had a successful outcome with no imaging performed; 16% had IVDE confirmed with imaging and successful outcome with surgery or medical management; and just 3% were found to have an alternative diagnosis or were euthanised without imaging. A total of 16 IM/ANNPE cases were collected: 94% had a successful outcome, and one dog was euthanised. Successful outcomes can be obtained by using clinical reasoning alone in most dogs with suspected IVDE or IM/ANNPE.

Residual volume of extruded disc material and residual spinal cord compression measured on postoperative MRI do not predict neurological outcomes in dogs following decompressive surgery for thoracolumbar intervertebral disc extrusion

Published studies on the validity of using quantitative MRI measures of pre- and postoperative spinal cord (SC) compression as prognostic indicators for dogs undergoing surgery for intervertebral disc extrusion (IVDE) are currently limited. The aim of this retrospective analytical study was to describe the volume of postoperative residual extradural material (VREM) and the ratio of the cross-sectional area (CSA) of maximum SC compression to the CSA of SC in a compression-free intervertebral space as MRI measures of preoperative and postoperative compression (residual spinal cord compression, RSCC), and to compare these measures between the neurological outcome in a group of dogs. Inclusion criteria were dogs that underwent surgery for thoracolumbar IVDE, were imaged pre- and immediately postoperatively by MRI, and had a neurological follow-up examination 2 to 5 weeks postoperatively. Two blinded observers independently performed measurements in pre- and postoperative MRI studies. Dogs were classified into positive outcome (PO) and negative outcome (NO) groups based on follow-up neurologic examination scores. Seventeen dogs were included (12 PO, 5 NO). Interobserver agreement for MRI measurements was good to excellent (ICCs: 0.76-0.97). The prevalence of residual extradural material in postoperative MRI studies was 100%. No significant differences in mean preoperative SC compression, mean RSCC, mean SC decompression, or VREM were found between outcome groups (P = .25; P = .28; P = .91, P = .98). In conclusion, neither postoperative VREM nor RSCC could predict successful neurological outcomes.

Outcomes in Dogs with Multiple Sites of Cervical Intervertebral Disc Disease Treated with Single Ventral Slot Decompression

In dogs with acute myelopathy but showing multiple sites of spinal compression from intervertebral disc disease (IVDD) on imaging, one approach is surgical decompression of the single acute disc extrusion while ignoring other previously extruded or protruded discs. However, little is known regarding the outcomes of this approach. This study described the outcomes and investigated prognostic factors in 40 dogs with multiple sites of cervical disc extrusion or protrusion on MRI who underwent ventral slot decompression for the single acute disc. The overall recovery rate was 97.5%. The median recovery time was seven days. The number of affected discs (including disc extrusion and protrusion) and the presence and number of the affected discs causing severe spinal compression did not influence the 30-day outcome. Compared with 23 dogs with single disc extrusion treated surgically, the recovery time and outcomes were similar between the two groups. The total number of affected discs was not associated with recovery time or outcomes. In conclusion, if an acute disc could be identified, ventral slot decompression targeting the single acute disc is a viable management approach for dogs with an acute presentation but diagnosed with multiple sites of spinal cord compression from IVDD.

ACVIM consensus statement on diagnosis and management of acute canine thoracolumbar intervertebral disc extrusion

Background

Thoracolumbar intervertebral disc extrusion (TL‐IVDE) is the most common cause of acute paraparesis and paraplegia in dogs; however, guidelines on management of the condition are lacking.

Objectives

To summarize the current literature as it relates to diagnosis and management of acute TL‐IVDE in dogs, and to formulate clinically relevant evidence‐based recommendations.

Animals

None.

Methods

A panel of 8 experts was convened to assess and summarize evidence from the peer‐reviewed literature in order to develop consensus clinical recommendations. Level of evidence available to support each recommendation was assessed and reported.

Results

The majority of available literature described observational studies. Most recommendations made by the panel were supported by a low or moderate level of evidence, and several areas of high need for further study were identified. These include better understanding of the ideal timing for surgical decompression, expected surgical vs medical outcomes for more mildly affected dogs, impact of durotomy on locomotor outcome and development of progressive myelomalacia, and refining of postoperative care, and genetic and preventative care studies.

Conclusions and Clinical Importance

Future efforts should build on current recommendations by conducting prospective studies and randomized controlled trials, where possible, to address identified gaps in knowledge and to develop cost effectiveness and number needed to treat studies supporting various aspects of diagnosis and treatment of TL‐IVDE.

Diagnosis and Treatment of a Spinal Intraosseous Keratinized Cyst of L1 in a Dog

An 8 yr old female spayed golden retriever presented for a 3 wk history of progressive pelvic limb ataxia. MRI revealed a well-circumscribed T2-weighted hyperintense, T1-weighted poorly contrast-enhancing extradural mass to the right of the spinal cord at the level of L1 causing severe spinal cord compression. A right-sided hemilaminectomy was performed to remove the mass, and histopathology revealed an intraosseous keratinized cyst. A complete neurologic recovery was made within 2 wk following the surgery. This case illustrates a rare diagnosis and the first case report describing MRI findings and favorable clinical outcome after surgical management of a spinal intraosseous keratinized cyst.

Identification of Characteristic Genes in Whole Blood of Intervertebral Disc Degeneration Patients by Weighted Gene Coexpression Network Analysis (WGCNA)

Intervertebral disc degeneration (IDD) is a major cause of lower back pain. However, to date, the molecular mechanism of the IDD remains unclear. Gene expression profiles and clinical traits were downloaded from the Gene Expression Omnibus (GEO) database. Firstly, weighted gene coexpression network analysis (WGCNA) was used to screen IDD-related genes. Moreover, least absolute shrinkage and selection operator (LASSO) logistic regression and support vector machine (SVM) algorithms were used to identify characteristic genes. Furthermore, we further investigated the immune landscape by the Cell-type Identification By Estimating Relative Subsets Of RNA Transcripts (CIBERSORT) algorithm and the correlations between key characteristic genes and infiltrating immune cells. Finally, a competing endogenous RNA (ceRNA) network was established to show the regulatory mechanisms of characteristic genes. A total of 2458 genes were identified by WGCNA, and 48 of them were disordered. After overlapping the genes obtained by LASSO and SVM-RFE algorithms, genes including LINC01347, ASAP1-IT1, lnc-SEPT7L-1, B3GNT8, CHRNB3, CLEC4F, LOC102724000, SERINC2, and LOC102723649 were identified as characteristic genes of IDD. Moreover, differential analysis further identified ASAP1-IT1 and SERINC2 as key characteristic genes. Furthermore, we found that the expression of both ASAP1-IT1 and SERINC2 was related to the proportions of T cells gamma delta and Neutrophils. Finally, a ceRNA network was established to show the regulatory mechanisms of ASAP1-IT1 and SERINC2. In conclusion, the present study identified ASAP1-IT1 and SERINC2 as the key characteristic genes of IDD through integrative bioinformatic analyses, which may contribute to the diagnosis and treatment of IDD.

A comparative study between high-definition volumetric imaging computed tomography and multi-slice computed tomography in the detection of acute thoraco-lumbar disc extrusions in dogs

Computed tomography (CT) is commonly used to image intervertebral disc extrusion (IVDE) in dogs. The current gold standard for CT imaging is the use of multi-slice CT (MS CT) units. Smaller high-definition volumetric imaging (HDVI) mobile CT has been marketed for veterinary practice. This unit is described as an advanced flat panel. The goal of this manuscript was to evaluate the ability of the HDVI CT in detecting IVDE without the need for CT myelography, compared with the detection of acute disc extrusions with a MS CT without the need for MS CT myelogram. Retrospective blinded analyses of 219 dogs presented for thoraco-lumbar IVDE that had a HDVI CT (n = 123) or MS CT (n = 96) were performed at a single referral hospital. A total of 123 cases had HDVI CT scans with surgically confirmed IVDE. The IVDE was identified in 88/123 (72%) dogs on pre-contrast HDVI CT. The remaining 35/128 (28%) cases required a HDVI CT myelogram to identify the IVDE. Ninety-six cases had MS CT scans with surgically confirmed IVDE. The IVDE was identified in 78/96 (81%) dogs on the pre-contrast MS CT. The remaining 18/96 (19%) cases had a MS CT myelogram to identify the IVDE. Multi-slice CT detected IVDE significantly more than HDVI CT (p = 0.032). This study showed that the ability of HDVI CT for detecting IVDE is lower than that of MS CT. The HDVI CT system may be useful in smaller referral practices, with a lower case load where space is limited.

Association of magnetic resonance assessed disc degeneration and late clinical recurrence in dogs treated surgically for thoracolumbar intervertebral disc extrusions

BACKGROUND

Radiographic signs of intervertebral disc mineralization are thought to indicate sites of future recurrence of disc extrusion (Hansen type I) but the relationship between evidence of disc degeneration on magnetic resonance imaging (MRI) and future disc extrusion with recurrence of clinical signs has not been examined.

OBJECTIVES

To examine the relationship between MRI-assessed degeneration of thoracolumbar intervertebral discs and late recurrence of clinical signs in dogs presented with acute thoracolumbar intervertebral disc extrusion and treated by hemilaminectomy alone.

ANIMALS

Ninety-two client-owned dogs presented to 2 referral hospitals between 2009 and 2014.

METHODS

Retrospective analysis of association between clinical signs consistent with recurrent thoracolumbar intervertebral disc extrusion and MRI evidence of disc degeneration in dogs undergoing hemilaminectomy for acute thoracolumbar intervertebral disc extrusion. Univariable and multivariable Cox regression analyses were used to explore associations between recurrence of clinical signs and several characteristics of T10-L3 discs at initial diagnosis.

RESULTS

Ninety-two cases were included, of which 42 (46%) were Dachshunds and median age was 5.3 years. Clinical signs recurred in 33/92 (36%) dogs. Finding a completely degenerate disc in the T10 to L3 region (in addition to the operated site) at the time of surgery was associated with a hazard ratio of 2.92 (95% confidence interval: 1.37-6.20) for recurrence of clinical signs.

CONCLUSIONS AND CLINICAL IMPORTANCE

Our results suggest that in cases of thoracolumbar intervertebral disc extrusion in dogs, recurrence of signs is likely if at least 1 completely degenerate disc in addition to the currently symptomatic disc is visible on MRI.

Short-term clinical outcomes of 220 dogs with thoraco-lumbar disc disease treated by mini-hemilaminectomy

Thoraco-lumbar intervertebral disc extrusion is a common condition seen in veterinary practice. Although there are different surgical techniques described for decompression, most of these techniques are based on the surgeon’s preference or experience rather than clinical research. Our objective was to determine the clinical outcomes, using return to ambulation and micturition, as well as complication rates, in a large cohort of dogs by using a mini-hemilaminectomy for decompression of the thoraco-lumbar spinal cord with Hansen type I thoraco-lumbar intervertebral disc extrusions (IVDE). A retrospective study was performed on dogs presented for acute thoraco-lumbar IVDE undergoing surgical decompression. In total, 252 spinal decompression surgeries were performed. The recovery rates for patients graded with a modified Frankel score (MFS) of 5 to 0 were 100%, 99%, 100%, 96%, 86% and 64%, respectively. The mean days to micturition across all the MFS 5–0 were 1.5 (standard deviation [SD] ± 0.7), 1.8 (SD ± 1), 4.3 (SD ± 1.7), 6.4 (SD ± 2.2), 9.3 (SD 3) and 11.9 (SD ± 2.2), respectively. The mean days to ambulation across all the groups 5–0 were 2 (SD ± 0.7), 2.6 (SD ± 1), 7.6 (SD ± 4.4), 10.1 (SD ± 2.5), 16.1 (SD ± 2.9) and 19.3 (SD ± 2.6), respectively. Postoperative complications were seen in 32 of the surgeries, with a complication rate of 13%. Minor complications accounted for 38% of all complications, and major complications constituted 62% of all complications. In total, 15 dogs died or were euthanised as a direct result of thoraco-lumbar disc extrusion or the surgical procedure, with a mortality rate of 6% across all groups. A mini-hemilaminectomy provides similar clinical outcomes described in the literature for other methods of spinal cord decompressive surgery, and it also provides patients with similar short-term outcomes to other described decompressive surgical techniques in the dog, which have been described in the literature.

Diagnostic Imaging in Intervertebral Disc Disease

Imaging is integral in the diagnosis of canine intervertebral disc disease (IVDD) and in differentiating subtypes of intervertebral disc herniation (IVDH). These include intervertebral disc extrusion (IVDE), intervertebral disc protrusion (IVDP) and more recently recognized forms such as acute non-compressive nucleus pulposus extrusion (ANNPE), hydrated nucleus pulposus extrusion (HNPE), and intradural/intramedullary intervertebral disc extrusion (IIVDE). Many imaging techniques have been described in dogs with roles for survey radiographs, myelography, computed tomography (CT), and magnetic resonance imaging (MRI). Given how common IVDH is in dogs, a thorough understanding of the indications and limitations for each imaging modality to aid in diagnosis, treatment planning and prognosis is essential to successful case management. While radiographs can provide useful information, especially for identifying intervertebral disc degeneration or calcification, there are notable limitations. Myelography addresses some of the constraints of survey radiographs but has largely been supplanted by cross-sectional imaging. Computed tomography with or without myelography and MRI is currently utilized most widely and have become the focus of most contemporary studies on this subject. Novel advanced imaging applications are being explored in dogs but are not yet routinely performed in clinical patients. The following review will provide a comprehensive overview on common imaging modalities reported to aid in the diagnosis of IVDH including IVDE, IVDP, ANNPE, HNPE, and IIVDE. The review focuses primarily on canine IVDH due to its frequency and vast literature as opposed to feline IVDH.

Classification of Intervertebral Disc Disease

Intervertebral disc disease (IVDD) has been recognized in dogs since the 1800s, when the first descriptions of extruded disc material within the vertebral canal were published. In the intervening time our understanding of intervertebral disc pathology in dogs and cats has increased dramatically, with many variations of IVDD described. Whilst the volume of literature and collective understanding of IVDD has expanded, there has also been scope for confusion as the definition of intervertebral disc disease, with its myriad different manifestations, becomes more complicated. A large volume of literature has aimed to combine the use of histopathology, diagnostic imaging and clinical findings to better understand the various ways in which IVDD can be classified. Much of this research has focused on the classification of mechanisms of intervertebral disc degeneration, centering around the differences between, and overlaps in, IVDD in chondrodystrophic and non-chondrodystrophic dog breeds. However, with the increasing availability of advanced imaging modalities allowing more accurate antemortem diagnosis, the concept of IVDD has expanded to include other clinical presentations that may not fit into traditional models of classification of IVDD. This review aims to provide an up to date overview of both historical and current systems of IVDD classification, highlighting the important findings and controversies underpinning them.

Proposta de sequenciamento das projeções mielográficas na identificação de compressão da medula espinhal em cães com doença do disco intervertebral cervical

RESUMO O objetivo deste trabalho foi verificar em quais projeções foi possível identificar compressão da medula espinhal em cães com doença do disco intervertebral (DDIV) cervical e propor um sequenciamento das projeções a ser realizado no exame mielográfico dessa região. Foram avaliadas quatro projeções mielográficas (lateral, ventrodorsal e oblíquas esquerda e direita) de 41 pacientes diagnosticados com DDIV cervical. Em 40 pacientes (97,5%), foi possível identificar compressão da medula espinhal na projeção lateral; em 22 (53,6%), nas oblíquas; e em 11 (26,8%), na ventrodorsal (P<0,05). Havia lateralização da compressão em 22 (53,6%) pacientes; 100% delas (n=22) foram detectadas pelas projeções oblíquas e 50% (n=11) pela ventrodorsal. Em 10 (24,4%) cães, foi observado mais que um local de compressão, tendo as projeções ventrodorsal e oblíquas auxiliado na definição do local de compressão em 50% e 70%, respectivamente. Pode-se concluir que todas as projeções mielográficas estudadas permitem identificar compressão na medula espinhal em cães com DDIV cervical, sendo a incidência lateral a que mais a revelou, seguida das oblíquas e da ventrodorsal, estabelecendo-se, assim, uma proposta de sequenciamento das projeções mielográficas a serem realizadas para essa região.

Agreement of surgeon's perception of the effectiveness of spinal cord decompression with findings on postoperative magnetic resonance imaging for dogs surgically treated for intervertebral disk extrusion

OBJECTIVE

To determine the accuracy of the surgeon's perception versus postoperative MRI findings in assessing the effectiveness of spinal cord decompression achieved in dogs surgically treated for intervertebral disk extrusion (IVDE) and whether postoperative MRI findings were more likely to be associated with various outcomes.

ANIMALS

68 dogs surgically treated for cervical or thoracolumbar IVDE.

PROCEDURES

Data on clinical, neurologic, pre- and postoperative MRI, and intraoperative findings as well as outcomes and recovery times (6-month follow-up period) were prospectively collected and compared between various groups.

RESULTS

54 (79%) dogs had thoracolumbar IVDE, and 14 (21%) had cervical IVDE. Median degree of spinal cord compression as assessed on transverse T2-weighted MRI images was 45.6% before surgery and 8.8% after surgery. The correlation between surgeons' perception (n = 3) and postoperative MRI findings for the degree of spinal cord decompression achieved was only fair (κ = 0.40). Unsatisfactory spinal cord decompression as assessed via postoperative MRI was associated with severity of preoperative neurologic grade and preoperative compression, thoracolumbar (vs cervical) IVDE, and ventral (vs ventrolateral or dorsolateral) circumferential distribution of extruded material. Satisfactory (vs unsatisfactory) decompression as assessed via MRI was associated with a lower postoperative neurologic grade, greater likelihood of a successful outcome, and lower mean recovery time.

CONCLUSIONS AND CLINICAL RELEVANCE

Results suggested that for dogs surgically treated for IVDE, the surgeon's perception of adequate spinal cord decompression may be less reliable than postoperative MRI findings. Postoperative MRI appeared particularly useful for dogs with a severe preoperative neurologic status, severe preoperative spinal cord compression, and thoracolumbar IVDE.

Association between anesthesia duration and outcome in dogs with surgically treated acute severe spinal cord injury caused by thoracolumbar intervertebral disk herniation

Background

Retrospective research recently identified a possible relationship between duration of surgery and outcome in severely affected dogs treated surgically for acute thoracolumbar intervertebral disk herniation (TL‐IVDH).

Hypothesis

That increased duration of surgery is associated with poorer outcome in dogs with absent pain perception treated surgically for TL‐IVDH.

Animals

Two hundred ninety‐seven paraplegic dogs with absent pain perception surgically treated for acute TL‐IVDH.

Methods

Retrospective cohort study. Medical records of 5 institutions were reviewed. Inclusion criteria were paraplegia with absence of pain perception, surgical treatment of TL‐IVDH, and 1‐year postoperative outcome (ambulatory: yes or no). Canine data, outcome, and surgery and total anesthesia duration were retrieved.

Results

In this study, 183/297 (61.6%) dogs were ambulatory within 1 year, 114 (38.4%) dogs failed to recover, including 74 dogs (24.9%) euthanized because of progressive myelomalacia. Median anesthesia duration in dogs that regained ambulation within 1 year of surgery (4.0 hours, interquartile range [IQR] 3.2‐5.1) was significantly shorter than those that did not (4.5 hours, IQR 3.7‐5.6, P = .01). Multivariable logistic regression demonstrated a significant negative association between both duration of surgery and total anesthesia time and ambulation at 1 year when controlling for body weight and number of disk spaces operated on.

Conclusions and Clinical Importance

Findings support a negative association between increased duration of anesthesia and outcome in this group of dogs. However, the retrospective nature of the data does not imply a causal relationship.

Clinical and Clinicopathological Features in Dogs with Uncomplicated Spontaneous Hyperadrenocorticism Diagnosed in Primary Care Practice (2013-2014)

The objective of this study was to report clinical and clinicopathological abnormalities in canine spontaneous hyperadrenocorticism (HAC) and assess the relationship between patient size and those findings. A questionnaire was made available to primary care veterinarians to gather information on cases diagnosed with canine spontaneous HAC. Inclusion criteria were an adrenocorticotropic stimulation test and/or low-dose dexamethasone suppression test consistent with HAC. Exclusion criteria included concurrent systemic diseases, any clinical sign (CS) not typically associated with HAC, a urinary corticoid:creatinine ratio within reference interval, administration of steroids during the 3 mo before diagnosis, treatment with any drug causing CSs of HAC, and ongoing treatment for canine spontaneous HAC. Sixty-two cases were identified. The prevalences of various CSs were similar to those historically reported. No association between the patient weight and CSs was identified. The platelet count was negatively correlated to the weight (P = .005, r² = 0.3). Alanine aminotransferase (P = .016, r² = 0.17) and alkaline phosphatase (P = .05, r² = 0.0014) activities were positively correlated to the CS ratio. In this group of dogs, CSs were not significantly different between dogs ≤20 kg and dogs >20 kg. The prevalences of various clinical findings appeared to be similar to those historically reported. Dogs with more CSs tended to have higher alanine aminotransferase and alkaline phosphatase activities.

Transcranial magnetic motor evoked potentials and magnetic resonance imaging findings in paraplegic dogs with recovery of motor function

Background

Transcranial magnetic motor evoked potentials (TMMEP) are associated with severity of clinical signs and magnetic resonance imaging (MRI) findings in dogs with spinal cord disease.

Hypothesis

That in initially paraplegic dogs with thoracolumbar intervertebral disc herniation (IVDH), MRI findings before surgery and TMMEPs obtained after decompressive surgery are associated with long‐term neurological status and correlate with each other.

Animals

Seventeen client‐owned paraplegic dogs with acute thoracolumbar IVDH.

Methods

Prospective observational study. TMMEPs were obtained from pelvic limbs and MRI (3T) of the spinal cord was performed at initial clinical presentation. Follow‐up studies were performed ≤ 2 days after reappearance of motor function and 3 months later. Ratios of compression length, intramedullary hyperintensities' length (T2‐weighted hyperintensity length ratio [T2WLR]), and lesion extension (T2‐weighted‐lesion extension ratio) in relation to the length of the 2nd lumbar vertebral body were calculated.

Results

TMMEPs could be elicited in 10/17 (59%) dogs at 1st and in 16/17 (94%) dogs at 2nd follow‐up. Comparison of TMMEPs of 1st and 2nd follow‐up showed significantly increased amplitudes (median from 0.19 to 0.45 mV) and decreased latencies (from 69.38 to 40.26 ms; P = .01 and .001, respectively). At 2nd follow‐up latencies were significantly associated with ambulatory status (P = .024). T2WLR obtained before surgery correlated with latencies at 2nd follow‐up (P = .04).

Conclusions

TMMEP reflect motor function recovery after severe spinal cord injury.

Investigation of parameters predicting the need for diagnostic imaging beyond computed tomography in the evaluation of dogs with thoracolumbar myelopathy: Retrospective evaluation of 555 dogs

Thoracolumbar myelopathy encompasses a number of disease processes such as intervertebral disc disease, discospondylitis, trauma, congenital malformations, neoplasia, and intramedullary spinal cord disease. Compressive disc herniations are most common in dogs and require imaging procedures such as myelography, computed tomography (CT), and/or magnetic resonance imaging (MRI) to determine the need and location for decompressive surgery. The purposes of this retrospective, cross-sectional study were to evaluate all dogs undergoing thoracolumbar CT imaging as the initial diagnostic step between 2010 and 2015 and determine whether any of the imaging characteristics could be used to predict the need for additional imaging in the form of myelography, CT myelography, and/or MRI. A total of 555 dogs were identified in this time frame which underwent CT imaging for myelopathy of the thoracolumbar region. Various parameters including age, gender, sexual status, breed, chronicity, site of lesion, time of study, and contrast administration were evaluated. Findings indicated that 7.6% of dogs needed additional imaging after CT. Dachshunds were less likely to need additional imaging (P = 0.0111) as were patients scanned during normal business hours (P = 0.0075). Increasing age of the patient increased the likelihood of additional imaging (P = 0.0107). Dogs which did not have additional imaging performed were 21.89 times more likely to require surgery than those which did have additional imaging (P < 0.0001). Findings supported the use of CT as a first-line imaging modality for dogs presenting with thoracolumbar myelopathy.

Magnetic resonance imaging versus computed tomography to plan hemilaminectomies in chondrodystrophic dogs with intervertebral disc extrusion

OBJECTIVE

To determine the influence of preoperative computed tomography (CT) versus magnetic resonance (MR) on hemilaminectomies planned to treat thoracolumbar (TL) intervertebral disc (IVD) extrusions in chondrodystrophic dogs.

STUDY DESIGN

Prospective clinical study.

SAMPLE POPULATION

Forty chondrodystrophic dogs with TL IVD extrusion and preoperative CT and MR studies.

METHODS

MR and CT images were randomized and reviewed by 4 observers masked to the dog's identity and corresponding imaging studies. Observers planned the location along the spine, side, and extent (number of articular facets to be removed) based on individual reviews of CT and MR studies. Intra-observer agreement was determined between overall surgical plan, location, side, and size of the hemilaminectomy planned on CT versus MR of the same dog.

RESULTS

Similar surgical plans were developed based on MR versus CT in 43.5%-66.6% of dogs, depending on the observer. Intra-observer agreement in location, side, and size of the planned hemilaminectomy based on CT versus MR ranged between 48.7%-66.6%, 87%-92%, and 51.2%-71.7% of dogs, respectively. Observers tended to plan larger laminectomy defects based on MR versus CT of the same dog.

CONCLUSION

Findings from this study indicated considerable differences in hemilaminectomies planned on preoperative MR versus CT imaging. Surgical location and size varied the most; the side of planned hemilaminectomies was most consistent between imaging modalities.

Evaluation of T2-weighted versus short-tau inversion recovery sagittal sequences in the identification and localization of canine intervertebral disc extrusion with low-field magnetic resonance imaging

Sagittal T2-weighted sequences (T2-SAG) are the foundation of spinal protocols when screening for the presence of intervertebral disc extrusion. We often utilize sagittal short-tau inversion recovery sequences (STIR-SAG) as an adjunctive screening series, and experience suggests that this combined approach provides superior detection rates. We hypothesized that STIR-SAG would provide higher sensitivity than T2-SAG in the identification and localization of intervertebral disc extrusion. We further hypothesized that the parallel evaluation of paired T2-SAG and STIR-SAG series would provide a higher sensitivity than could be achieved with either independent sagittal series when viewed in isolation. This retrospective diagnostic accuracy study blindly reviewed T2-SAG and STIR-SAG sequences from dogs (n = 110) with surgically confirmed intervertebral disc extrusion. A consensus between two radiologists found no significant difference in sensitivity between T2-SAG and STIR-SAG during the identification of intervertebral disc extrusion (T2-SAG: 92.7%, STIR-SAG: 94.5%, P = 0.752). Nevertheless, STIR-SAG accurately identified intervertebral disc extrusion in 66.7% of cases where the evaluation of T2-SAG in isolation had provided a false negative diagnosis. Additionally, one radiologist found that the parallel evaluation of paired T2-SAG and STIR-SAG series provided a significantly higher sensitivity than T2-SAG in isolation, during the identification of intervertebral disc extrusion (T2-SAG: 78.2%, paired T2-SAG, and STIR-SAG: 90.9%, P = 0.017). A similar nonsignificant trend was observed when the consensus of both radiologists was taken into consideration (T2-SAG: 92.7%, paired T2-SAG, and STIR-SAG = 97.3%, P = 0.392). We therefore conclude that STIR-SAG is capable of identifying intervertebral disc extrusion that is inconspicuous in T2-SAG, and that STIR-SAG should be considered a useful adjunctive sequence during preliminary sagittal screening for intervertebral disc extrusion in low-field magnetic resonance.

MRI-based relationships between spine pathology, intervertebral disc degeneration, and muscle fatty infiltration in chondrodystrophic and non-chondrodystrophic dogs

BACKGROUND CONTEXT

Human studies have revealed a link between muscle degeneration and low back pain, although the cause and effect of this relationship is not clear. Dogs provide a naturally developing model of intervertebral disc (IVD)-related low back pain that may provide insight into relationships between IVD and muscle degeneration.

PURPOSE

This study aimed to quantify, via magnetic resonance imaging (MRI), the magnitude and location of fatty infiltration in spine muscles of chondrodystrophic (CD) and non-chondrodystrophic (NCD) dogs suffering from both intervertebral disc herniation (IVDH) and non-disc-related spinal disorders, and relate this to intervertebral disc degeneration (IVDD).

STUDY DESIGN

This study used retrospective MRI-based analysis of IVDD and muscle fatty infiltration in CD and NCD dogs.

METHODS

A portion of this study was funded ($1,000) by the Pet Trust Fund, Ontario Veterinary College. Magnetic resonance imaging from 180 dogs were separated into four groups: (1) CD with IVDH; (2) CD with non-IVDH spinal pathology; (3) NCD with IVDH; (4) NCD with non-IVDH spinal pathology. For each dog at intervertebral levels T12-T13 to L6-L7, IVDD was subjectively graded and muscle-fat indices (MFIndices) were quantified for multifidus, erector spinae, and psoas muscle groups.

RESULTS

Intervertebral disc degeneration grade was higher (p<.0001) for CD compared with NCD dogs, and for dogs diagnosed with IVDH compared with dogs with non-IVDH pathology. Muscle-fat indices of multifidus and psoas were higher (p<.01), indicating greater fatty infiltration, for NCD compared with CD dogs, and for dogs with non-IVDH pathology compared with dogs with IVDH. Erector spinae demonstrated higher (p<.0001) MFIndices compared with multifidus and psoas; however, this level of fatty infiltration was not dependent upon breed or pathology.

CONCLUSIONS

Dog groups with higher average IVDD grades demonstrated less fatty infiltration within their multifidus and psoas muscles, compared with groups with lower IVDD grades. This finding was consistent across both CD and NCD breeds as well as across dogs presenting with IVDH and those presenting with a non-IVDH spinal pathology. Thus, the presence or severity of IVDD is not uniquely related to fatty infiltration in these muscles, but rather the presence, or possibly severity or chronicity, of general spine pathology is likely a better predictor of fatty infiltration.

Relationships between cerebrospinal fluid characteristics, injury severity, and functional outcome in dogs with and without intervertebral disk herniation

BACKGROUND

Cerebrospinal fluid (CSF) is commonly acquired in dogs with intervertebral disk herniation (IVDH) and is a common method to assess inflammatory responses following spinal cord injury (SCI).

OBJECTIVES

The purpose of the study was to describe relationships between cisternal CSF characteristics, behavioral measures of SCI, T2- weighted (T2W) hyperintensity on magnetic resonance imaging (MRI), and long-term outcome in dogs with IVDH. Diagnostic accuracy of CSF for differentiating IVDH from other myelopathies was also assessed.

METHODS

The retrospective case series included 727 dogs, 443 with thoracolumbar IVDH, 103 with cervical IVDH, and 181 with other spinal cord diseases. Signalment, initial neurologic function, ambulatory function at long-term follow-up, T2W MRI, and CSF variables were recorded for dogs with IVDH. Signalment, etiology, and CSF data were retrieved for dogs with other myelopathies. Associations between CSF predictors, diagnosis, and outcomes were assessed.

RESULTS

CSF total nucleated cell count (TNCC) increased with SCI severity (rho -0.256, P < .001) in dogs with IVDH, TNCC was significantly higher in the presence of T2W hyperintensity (P = .001) in dogs with thoracolumbar IVDH, but TNCC, RBC count, microprotein, and percent neutrophils decreased with increasing injury duration (rho -0.253, P < .001; rho -0.269, P < .001; rho -0.141, P = .004, and rho -0.356, P < .001, respectively). CSF characteristics were not accurate for differentiating IVDH from other spinal cord diseases.

CONCLUSIONS

In dogs with IVDH, CSF TNCC, RBC count, microprotein, and percent neutrophils are correlated with clinical aspects of SCI such as injury severity and duration, but cannot differentiate IVDH from other etiologies.

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.

Agreement between magnetic resonance imaging, myelography, and surgery for detecting recurrent, thoracolumbar intervertebral disc extrusion in dogs

OBJECTIVES

Although magnetic resonance imaging (MRI) is reported to be superior to myelography to determine the location and site of first time disc herniation, comparison of these diagnostic methods in cases of recurrent intervertebral disc disease (IVD) herniation after a first surgery has not been evaluated. The objective was to compare the diagnostic accuracy of MRI and myelography in a series of dogs undergoing repeat surgical decompression for recurrent IVD extrusion when compared to the gold standard of surgery.

METHODS

Ten dogs with recurrent IVD herniation underwent MRI and myelography followed by surgical decompression. Three observers reviewed the images to determine the site and side of the first surgery and the recurrent lesion. Agreement was determined by calculating a kappa (κ) score.

RESULTS

Substantial interobserver agreement was noted for recurrent lesion site using MRI and myelography (κ = 0.77 vs. 0.73) and when comparing MRI and myelography to the reported surgical site (κ = 0.73 vs. 0.67). Interobserver agreement was greater with MRI for circumferential location compared to myelography (κ = 0.76 vs. 0.43), similar to what was found when comparing to surgical side (κ = 0.82 vs. 0.49). The previous surgical site in this study had no effect on ability to identify the new lesion.

CLINICAL SIGNIFICANCE

Despite the limitations of MRI, there was greater agreement between observers using MRI for both the recurrent and first lesion.