Disk Herniation In Dogs Research Articles

Randomized Controlled Trial of Durotomy as an Adjunct to Routine Decompressive Surgery for Dogs With Severe Acute Spinal Cord Injury.

Although many interventions for acute spinal cord injury (SCI) appear promising in experimental models, translation directly from experimental animals to human patients is a large step that can be problematic. Acute SCI occurs frequently in companion dogs and may provide a model to ease translation. Recently, incision of the dura has been highlighted in both research animals and human patients as a means of reducing intraspinal pressure, with a view to improving perfusion of the injured tissue and enhancing functional recovery. Observational clinical data in humans and dogs support the notion that it may also improve functional outcome. Here, we report the results of a multi-center randomized controlled trial of durotomy as an adjunct to traditional decompressive surgery for treatment of severe thoracolumbar SCI caused by acute intervertebral disc herniation in dogs. Sample-size calculation was based on the proportion of dogs recovering ambulation improving from an expected 55% in the traditional surgery group to 70% in the durotomy group. Over a 3.5-year period, we enrolled 140 dogs, of which 128 had appropriate duration of follow-up. Overall, 65 (51%) dogs recovered ambulation. Recovery in the traditional decompression group was 35 of 62 (56%) dogs, and in the durotomy group 30 of 66 (45%) dogs, associated with an odds ratio of 0.643 (95% confidence interval: 0.320-1.292) and z-score of -1.24. This z-score indicates trial futility to reach the target 15% improvement over traditional surgery, and the trial was terminated at this stage. We conclude that durotomy is ineffective in improving functional outcome for severe acute thoracolumbar SCI in dogs. In the future, these data can be compared with similar data from clinical trials on duraplasty in human patients and will aid in determining the predictive validity of the "companion dog model" of acute SCI.

Video telescope operating monitor-assisted surgery is equivalent to conventional surgery in treatment of cervical intervertebral disc herniation in dogs.

To compare the use of the video telescope operating monitor (VITOM) and use of a conventional unassisted surgical method for treatment of cervical intervertebral disc herniation in dogs. 39 dogs with cervical intervertebral disc disease. Prospective study. Dogs were prospectively nonrandomly assigned to either the VITOM (n = 19) or conventional surgery (20) group depending on VITOM system availability. Signalment and preoperative neurologic status were recorded for all dogs. Preoperative and postoperative CT myelography was performed to compare intervertebral space location, spinal cord dimensions at the decompression level, ventral slot dimensions, and residual disc material. Surgical complications and postoperative neurologic outcomes were recorded. Data were compared between the 2 groups using fixed-effects or mixed-effects models to consider double reading of CT myelography images. No significant differences were noted between the 2 groups regarding the decompression ratio (P = .85), vertebral length body ratio (P = .13), ventral slot width ratio (P = .39), residual disc material (P = .30), and sinus bleeding (P = .12). No significant differences were found between the 2 groups regarding postoperative neurologic grade (P = .17). VITOM-assisted ventral slot decompression is equivalent to conventional surgery in treatment of cervical intervertebral disc herniation in dogs. The use of VITOM remains a good alternative to the conventional surgical method.

Somatosensory evoked potentials of the tibial nerve during the surgical decompression of thoracolumbar intervertebral disk herniation in dogs.

This study aimed to identify the impact on spinal cord integrity and determine the electrophysiological safety level during surgery for thoracolumbar intervertebral disk herniation in dogs. A total of 52 dogs diagnosed with thoracolumbar intervertebral disk herniation were enrolled. The tibial nerve somatosensory evoked potential elicited on the scalp by stimulation of the tibial nerve was recorded before and during hemilaminectomy. Both the amplitude and latency of the somatosensory evoked potential were periodically registered, and the percentage changes from the pre-operative control values (amplitude rate and latency rate) were calculated. When the multifidus muscles were retracted after removal from the spinous processes and vertebrae, the somatosensory evoked potential amplitude rate decreased in all dogs, while the latency rate increased in 33 dogs examined. The amplitude rate remained unchanged during the halting procedure, loosening retraction, and hemilaminectomy. After removing the disc material from the spinal canal, the amplitude rate was increased. The somatosensory evoked potential latency increased when the multifidus muscles were retracted and shortened after multifidus muscles closure in four cases. The outcome of all cases showed improvement in clinical signs 7 days after operation. Spinal cord conduction is impaired by retraction of the multifidus muscles and improved by removal of disk materials. Maintaining intraoperative SEP amplitudes above 50% of control may help avoid additional spinal cord injury during surgery. Since we have no case that worsened after the surgery, however, further studies are necessary to confirm this proposal.

A 50-step walking test for analysis of recovery after decompressive surgery for thoracolumbar disc herniation in dogs.

BackgroundDespite its importance, there is no agreed definition of recovery of ambulation in dogs with spinal cord injury.ObjectivesTo validate a new walking test in dogs recovering from thoracolumbar spinal cord injury.AnimalsTwo hundred twenty‐four dogs weighing <20 kg: 120 normally ambulatory dogs, plus 104 dogs undergoing decompressive surgery for acute thoracolumbar intervertebral disc herniation.MethodsProspective cohort studies. The distance each freely‐ambulatory dog walked during 50 step cycles was regressed on ulna length. For each postsurgical dog, we recorded when the calculated 50‐step distance was completed without falling, or their inability to complete this distance by 4 months or more after surgery. Bayesian analysis compared outcomes for presurgical neurologic categories; association of recovery with several preoperative variables was explored using logistic and time‐to‐event regression.ResultsFor control dogs, 50‐step distance (m) = 1.384 × ulnar length (cm) + 2.773. In postsurgical dogs, the 50‐step test provided decisive evidence that deep pain‐negative dogs were less likely to recover ambulation than dogs with intact pain perception (12/29 recovered vs 71/75; Bayes factor [BF] = 5.9 × 106) and, if they did recover, it took much longer (median 91 days vs median 14 days; BF = 1.5 × 103). Exploratory analysis suggested that presurgical neurologic status (subhazard ratio [SHR] = 0.022; P < .001) and duration of presurgical anesthesia (SHR = 0.740; P = .04) were associated with rapidity of recovery.Conclusions and Clinical ImportanceThis straightforward 50‐step walking test provides robust data on ambulatory recovery well‐suited to large scale pragmatic trials on treatment of thoracolumbar spinal cord injury in dogs.

Randomized clinical trial comparing outcomes after fentanyl or ketamine-dexmedetomidine analgesia in thoracolumbar spinal surgery in dogs.

BackgroundOpioids are widely used for perioperative pain control in dogs undergoing spinal surgery, but alternatives may be required because data suggest that opioids exacerbate inflammation in the injured spinal cord and veterinary access to opioids may become more restricted in the future.ObjectivesTo compare recovery of ambulation and other functions between spinal cord‐injured dogs receiving peri‐operative fentanyl and those receiving a ketamine‐dexmedetomidine combination.AnimalsA total of 102 client‐owned dogs undergoing decompressive surgery for thoracolumbar intervertebral disc herniation.MethodsRandomized clinical trial. Dogs were randomized 1:1 to fentanyl or a ketamine‐dexmedetomidine combination for intra and postoperative analgesia. Primary outcome was time to recovery of ambulation; secondary outcomes were the postoperative Colorado Acute Pain Scale, the short‐form Glasgow Composite Measure Pain Scale, time to recovery of voluntary urination and time to unassisted eating.ResultsNo difference was found in time to recovery of ambulation between groups (adjusted sub‐hazard ratio, 0.83; 95% confidence interval [CI], 0.55‐1.24; P = .36) or in pain scores (Colorado: χ 2 = 14.74; P = .32; Glasgow: χ 2 = 6.61; P = .76). Differences in time to recovery of eating and urination were small but favored ketamine‐dexmedetomidine (adjusted odds ratios, 3.31; 95% CI, 1.53‐7.16; P = .002 and 2.43; 95% CI, 1.00‐5.96; P = .05, respectively).Conclusions and Clinical ImportanceThere was no evidence that, at the doses used, fentanyl impaired ambulatory outcome after surgery for thoracolumbar intervertebral disc herniation in dogs. Pain control appeared similar between groups. Secondary outcomes suggested minor benefits associated with ketamine‐dexmedetomidine. The ketamine‐dexmedetomidine combination appears to be a reasonable alternative to peri‐operative opioids.

Clinical Trial Design-A Review-With Emphasis on Acute Intervertebral Disc Herniation.

There is a clear need for new methods of treatment of acute disc herniation in dogs, most obviously to address the permanent loss of function that can arise because of the associated spinal cord injury. Clinical trials form the optimal method to introduce new therapies into everyday clinical practice because they are a reliable source of unbiased evidence of effectiveness. Although many designs are available, parallel cohort trials are most widely applicable to acute disc herniation in dogs. In this review another key trial design decision—that between pragmatic and explanatory approaches—is highlighted and used as a theme to illustrate the close relationship between trial objective and design. Acute disc herniation, and acute spinal cord injury, is common in dogs and there is a multitude of candidate interventions that could be trialed. Most current obstacles to large-scale clinical trials in dogs can be overcome by collaboration and cooperation amongst interested veterinarians.

Extended durotomy to treat severe spinal cord injury after acute thoracolumbar disc herniation in dogs.

To report recovery of ambulation of dogs treated with extended thoracolumbar durotomy for severe spinal cord injury caused by intervertebral disc herniation. Descriptive cohort. Twenty-six consecutive paraplegic dogs presented with loss of deep pain sensation after acute thoracolumbar intervertebral disc herniation. Each dog underwent routine diagnostic assessment and surgery for removal of extradural herniated intervertebral disc, followed by a four-vertebral body length durotomy centered on the herniated disc. Each dog was followed up until it was able to walk 10 steps without assistance or until 6 months after surgery. Sixteen of 26 dogs recovered to walk unaided (all but one also recovered fecal and urinary continence), and six dogs did not; four dogs were lost to follow-up. One dog was euthanized because of signs consistent with progressive myelomalacia. There was no evidence of detrimental effects of durotomy within the period of study. Using Bayesian analysis, we found a point estimate of successful outcome of 71% with 95% credible interval from 52% to 87%. Extended durotomy seemed to improve the outcome of dogs in our case series without increase in morbidity. Extended durotomy appears safe and may improve the outcome of dogs with severe thoracolumbar mixed contusion and compressive injuries associated with acute intervertebral disc extrusion.

Relationship of preoperative neurologic score with intervals to regaining micturition and ambulation following surgical treatment of thoracolumbar disk herniation in dogs.

OBJECTIVE To estimate the times required for dogs to regain micturition and ambulation following surgical treatment for thoracolumbar Hansen type I intervertebral disk extrusion (IVDE) and determine whether these variables were associated with preoperative modified Frankel score (MFS). DESIGN Retrospective case series with nested cohort study. ANIMALS 54 dogs weighing < 20 kg (44 lb) that were surgically treated for Hansen type I IVDE at a referral hospital between January and December 2015. PROCEDURES Medical records and CT and MRI data were reviewed. Information was collected regarding dog signalment, type and duration of clinical signs, preoperative MFS, degree of spinal cord compression, type of medical and surgical treatment provided, and intervals from surgery to regaining micturition and ambulation (outcomes). Collected data were evaluated for correlations with outcomes. RESULTS Mean ± SD interval from surgery to regaining micturition was 4.1 ± 4.4 days, and mean interval from surgery to regaining ambulation was 13.8 ± 25.1 days. These intervals differed significantly. Significant negative correlations with MFS were identified for interval to regaining micturition (r = -0.63) and interval to regaining ambulation (r = -0.64). No other correlations with outcome were identified. CONCLUSIONS AND CLINICAL RELEVANCE The amount of time required for dogs to regain micturition and ambulation following surgery for thoracolumbar IVDE was correlated with preoperative severity of clinical signs, as reflected by preoperative MFSs. This information should be useful for pre- and postoperative decision-making and setting of expectations for owners of and clinicians treating affected dogs.

Re-opening the window on fenestration as a treatment for acute thoracolumbar intervertebral disc herniation in dogs.

Acute thoracolumbar intervertebral disc herniation in dogs is a common cause of "back" pain, pelvic limb paresis or paralysis and incontinence. Treatment of this condition has long been a source of controversy, especially since the introduction of surgical interventions in the 1950s. Unfortunately, formal clinical trials to compare efficacy of conservative and surgical interventions have never been carried out and the current lack of clinical equipoise on this subject now precludes such a trial on ethical grounds. In this article we re-examine and discuss earlier published data on recovery associated with the various therapies, focusing on evidence suggesting that decompressive surgery and fenestration may be equally efficacious.

Recurrence of disk herniation following percutaneous laser disk ablation in dogs with a history of thoracolumbar intervertebral disk herniation: 303 cases (1994-2011).

OBJECTIVE To determine rate of recurrence of disk herniation in dogs that underwent percutaneous laser disk ablation (PLDA) because of a previous episode of suspected or confirmed thoracolumbar intervertebral disk herniation (IVDH). DESIGN Retrospective case series. ANIMALS 303 dogs that underwent PLDA and for which a minimum of 3 years of follow-up information was available (n = 294) or for which recurrence was documented within 3 years after the procedure (9). PROCEDURES Information on signalment, previous episodes of IVDH, specifics of the PLDA procedure, and recurrence was obtained from the medical records. Owners were contacted to complete a questionnaire regarding outcome and recurrence. RESULTS 60 of the 303 (19.8%) dogs had an episode of suspected or confirmed IVDH after undergoing PLDA, but only 11 of the 303 (3.6%) dogs had a recurrence of IVDH confirmed by means of CT or MRI and hemilaminectomy. Recurrence rate following PLDA was not significantly different between dogs that had been treated medically for previous episodes of IVDH and dogs that had been treated surgically. Overall, 270 of 286 (94.4%) owners reported that their dog was the same (109 [38.1%]) or improved (161 [56.3%]) immediately after PLDA, and 265 (92.7%) owners rated their satisfaction with the procedure as ≥ 9 on a scale from 1 (completely dissatisfied) to 10 (completely satisfied). CONCLUSIONS AND CLINICAL RELEVANCE Results suggested that PLDA was a relatively safe, minimally invasive procedure associated with a low rate of recurrence of disk herniation when performed in dogs with a history of previous episodes of suspected or confirmed IVDH.

Urinary 3-hydroxypropyl mercapturic acid (3-HPMA) concentrations in dogs with acute spinal cord injury due to intervertebral disc herniation

The aim of this study was to investigate urinary 3-hydroxypropyl mercapturic acid (3-HPMA), a metabolite of acrolein, as a novel biomarker in acute spinal cord injury (ASCI) due to intervertebral disc herniation in dogs. Urine from 10 client-owned dogs with ASCI collected at presentation and 10 control dogs was analyzed for 3-HPMA. The median urinary 3-HPMA concentration in ASCI dogs was significantly higher than in control dogs, but was not correlated with the severity of ASCI. The median urinary 3-HPMA concentration in intact dogs was higher than in neutered dogs. Higher urinary 3-HPMA concentrations in dogs after ASCI support a role for acrolein, a cytotoxic by-product of lipid peroxidation, in canine ASCI. Urinary 3-HPMA could be used as a biomarker in future clinical trials to measure the effect of therapeutic intervention of reducing acrolein after ASCI.

Practice patterns in the management of acute intervertebral disc herniation in dogs.

Acute intervertebral disc herniation is commonly managed by veterinary neurologists and surgeons. Anecdote suggests that patterns of management vary considerably and there is controversy surrounding many aspects of treatment. The goal of this study was to document patterns in management of acute spinal cord injury caused by acute intervertebral disc herniation among these two groups to aid in future discussions on best practices. A survey querying diagnostic, medical and surgical practices for dogs with acute intervertebral disc herniation was distributed to diplomates on the databases of the American College of Veterinary Surgeons and the American College of Veterinary Internal Medicine (Neurology). Responses were received from 314 board-certified veterinary surgeons and neurologists. Both groups handled timing of decompression, surgical approach, and most postoperative recommendations in a similar fashion. Case volume differed between groups, with 77% of neurologists and 18% of surgeons managing ê50 cases of acute intervertebral disc herniation per year. MRI was used most frequently as a diagnostic tool by neurologists (75%), while CT was used most commonly by surgeons (58%). Corticosteroids were routinely administered as a neuroprotective strategy by 34% of surgeons and 11% of neurologists. Disc fenestration was performed "always" or "most of the time" by 69% of neurologists and 36% of surgeons. Understanding the common practices in the management of canine acute intervertebral disc herniation can provide a springboard for future discussions regarding the best practices in diagnosing and treating this disease.

The accuracy of the patellar reflex for localization of the site of a single level thoracolumbar disc herniation in dogs

The patellar reflex was used in this study to determine the site of thoracolumbar spinal cord dysfunction (T3-L3 or L4-L6) as a result of disc herniation. The results of neurological examinations were compared with the findings of CT myelography. This study was conducted on 21 dogs, selected from a total of 26 dogs confirmed to have a single thoracolumbar lesion. Results revealed that the accuracy of the patellar reflex for lesion localization was 71.4%. The accuracy of the patellar reflex (normal or hyperreflexic) for lesion localization in the T3-L3 segment in 15 dogs was 100%, while the accuracy of the depressed patellar reflex for lesion localization in the L4-L6 segment in 6 dogs was 0%. The accuracy of the patellar reflex for detection of laterality of a thoracolumbar lesion was low (33.33%). The results suggest that the patellar reflex was not reliable for neurolocalization of thoracolumbar spinal cord lesions in dogs. This could be related to the fact that the depressed reflex did not always refer to a lesion in the L4-L6 spinal cord segment. Moreover, the patellar reflex was not reliable in detecting the laterality of thoracolumbar lesions.

Evaluation of the accuracy of neurologic data, survey radiographic results, or both for localization of the site of thoracolumbar intervertebral disk herniation in dogs

To determine the accuracy of neurologic data, survey radiographic results, or both for localization of the site of thoracolumbar intervertebral disk herniation in dogs. 338 dogs with surgically confirmed intervertebral disk herniation from disk spaces T10-11 to L6-7. Medical records and archived survey radiographs were reviewed for each case. Data were analyzed with multivariable logistic regression models. Three models were fit to develop subsets of the data consisting of survey radiographic data, neurologic examination data, and a combination of survey radiographic and neurologic examination data. The resulting models were validated by evaluating predictive performance against a validation subset of the data. Models incorporating survey radiographic data and a combination of survey radiographic and neurologic data had similar predictive ability and performed better than the model based solely on neurologic data but resulted in substantial errors in predictions. A combination of neurologic examination data as recorded in the medical records and radiographic data did not enhance predictive performance of multivariable logistic regression models over models limited to radiographic data. Neurologic and radiographic findings should not be used to completely exclude areas in an abnormal spinal cord region from further evaluation with advanced imaging.

Computed tomographic and histological findings of Hansen type I intervertebral disc herniation in dogs

To evaluate whether non-contrast-enhanced computed tomography (CT) as a stand-alone imaging modality can be used to define the Hansen type I intervertebral disc herniation (IVDH) lesion and also whether the Hounsfield unit (HU) value of herniated disc is relevant to clinical duration and to histopathological chronicity of extruded disc material. Information from a series of CT studies performed on 45 dogs with a presumptive diagnosis of Hansen type I IVDH was used. Clinical duration of IVDH was estimated based on time from onset of signs per owner communication to time of surgical intervention. Hansen type I IVDH was confirmed at surgery. Retrieved herniated disc was histologically examined. The HU values were analyzed to correlate the clinical duration and histopathological chronicity of the disc lesion. Non-contrast-enhanced CT provided sufficient diagnostic information to plan surgery in 42 of 45 dogs (93%). The value of the HU was significantly higher in clinically chronic cases (n = 12) compared to peracute cases (n = 11) (p <0.05). The HU values were significantly correlated with clinical duration (r = 0.482, p = 0.0008) and histopathological chronicity of the herniated disc (r = 0.408, p = 0.0056). Consistent with the previous reports, the use of non-contrast-enhanced CT alone was sufficient for the diagnosis and surgical planning in most patients with Hansen type I IVDH in the thoracolumbar spine. In addition, the present study suggested that HU values on CT images may be useful in the evaluation of disease chronicity of IVDH.

RELIABILITY OF T2-WEIGHTED SAGITTAL MAGNETIC RESONANCE IMAGES FOR DETERMINING THE LOCATION OF COMPRESSIVE DISk HERNIATION IN DOGS

Magnetic resonance imaging is used commonly to diagnose intervertebral disk herniation in dogs. It is common to locate areas of suspected compression on sagittal T2-weighted (T2-W) images and then obtain limited transverse images in these areas to reduce the acquisition time (a step-by-step approach). Our objective was to assess the frequency of correct localization of spinal cord compression due to disk herniation using only the sagittal images. The results from isolated readings of the sagittal T2-W images alone or combined with a single-shot fast spin echo (SSFSE) slab in 118 dogs were compared with a gold standard, based on a consensual reading of all images available, including complete transverse images across the entire spinal segments under study. The sites of compression were localized correctly from the sagittal images in 89.8% of dogs. If only the most significant lesions were accounted for, the percentage increased up to 95.2%. In 54.9% of the readings with incorrect localization, the actual compressive site was immediately adjacent to the one suspected from review of the sagittal images. The frequency of correct localization was higher in the cervical region, and was increased by examination of the SSFSE slab. The most common cause of disagreement was the presence of multiple degenerate bulging disks. Based on these results we recommend obtaining transverse images across the entire segment when multiple bulging disks are present. It is also recommended to obtain transverse images across the spaces immediately adjacent to the suspected site of herniation from review of the sagittal images.

Comparison of the effect of single-site and multiple-site disk fenestration on the rate of recurrence of thoracolumbar intervertebral disk herniation in dogs

To prospectively assess whether multiple-site disk fenestration decreases the incidence of recurrent thoracolumbar intervertebral disk herniation (IVDH), compared with single-site disk fenestration, in small-breed dogs treated for IVDH. Randomized controlled clinical trial. 207 client-owned dogs. Dogs undergoing decompressive surgery of the spinal cord because of thoracolumbar IVDH between 2001 and 2004 were randomly assigned to receive single-site disk fenestration at the level of surgical decompression (n = 103) or multiple-site disk fenestration of all disks from T11 through L4 (104). Follow-up consisted of complete reevaluation of patients, telephone surveys, and further surgery if signs indicative of recurrence occurred. 189 dogs were available for long-term follow-up: 95 dogs in the single-site disk fenestration group and 94 in the multiple-site disk fenestration group. Twenty-four dogs developed 28 confirmed episodes of recurrent thoracolumbar IVDH. The rate for first-time recurrence was 12.7% (24/189). First-time recurrence rates for single-and multiple-site disk fenestration groups were 17.89% (17/95) and 7.45% (7/94), respectively. Dogs undergoing single-site disk fenestration were significantly more likely to have recurrent thoracolumbar IVDH than were dogs undergoing multiple-site disk fenestration. Disk mineralization at the time of first surgery was associated with recurrence, and 87.5% (21/24) of recurrences occurred at a disk space adjacent to or 1 disk away from the initial lesion. Regardless of disk fenestration group, 22 of 24 (91.7%) recurrences occurred at a nonfenestrated disk space. Multiple-site disk fenestration decreased the rate of recurrent IVDH in small-breed dogs, compared with the use of single-site disk fenestration.

Naturally Occurring Disk Herniation in Dogs: An Opportunity for Pre-Clinical Spinal Cord Injury Research

Traumatic spinal cord injuries represent a significant source of morbidity in humans. Despite decades of research using experimental models of spinal cord injury to identify candidate therapeutics, there has been only limited progress toward translating beneficial findings to human spinal cord injury. Thoracolumbar intervertebral disk herniation is a naturally occurring disease that affects dogs and results in compressive/contusive spinal cord injury. Here we discuss aspects of this disease that are analogous to human spinal cord injury, including injury mechanisms, pathology, and metrics for determining outcomes. We address both the strengths and weaknesses of conducting pre-clinical research in these dogs, and include a review of studies that have utilized these animals to assess efficacy of candidate therapeutics. Finally, we consider a two-species approach to pre-clinical data acquisition, beginning with a reproducible model of spinal cord injury in the rodent as a tool for discovery with validation in pet dogs with intervertebral disk herniation.

Comparison of the diagnosis of intervertebral disc herniation in dogs by CT before and after contrast enhancement of the subarachnoid space

Eleven miniature dachshunds with a herniated intervertebral disc were examined by CT, first before and then after contrast enhancement of the subarachnoid space. The images were classified into three grades...

THE RELATIVE SENSITIVITY OF COMPUTED TOMOGRAPHY AND MYELOGRAPHY FOR IDENTIFICATION OF THORACOLUMBAR INTERVERTEBRAL DISK HERNIATIONS IN DOGS

We compared the relative sensitivity of computed tomography (CT) and myelography for identification of disk herniation in dogs. Criteria for patient selection included presurgical CT, myelography, or both and surgical or necropsy confirmation of disk herniation between the T3 and L6 vertebral articulations. Imaging findings were described as positive or inconclusive. Adverse events such as hypotension, cardiac arrhythmias, seizures, death, and lower urinary tract infection were compared between imaging groups. One hundred and eighty-two dogs met the inclusion criteria, with 116 dogs having myelography performed as the initial diagnostic imaging modality and 66 dogs having CT performed as the initial modality. The relative sensitivity for locating the site of disk herniation was 83.6% when myelography was the first test performed and 81.8% when CT was the first test performed. CT was more sensitive than myelography at detecting lesions in chronically affected dogs (P = 0.025). Myelography was more sensitive than CT at detecting lesions in smaller dogs (< 5 kg; P = 0.004). Dogs that received both imaging modalities were significantly more likely to die or be euthanized compared with myelography alone (P < 0.001). Both myelography and CT are reasonable diagnostic imaging modalities for locating the site of disk herniation. CT should be considered especially in heavier, more chronically affected dogs. The major limitations of this study include lack of randomization to imaging modality and the use of surgical exploration or necropsy as the gold standard.