Benjamin D. Young

Magnetic Resonance Imaging in Dogs with Neurologic Impairment Due to Acute Thoracic and Lumbar Intervertebral Disk Herniation

BACKGROUND Magnetic resonance imaging (MRI) is a correlate to physical examination in various myelopathies and a predictor of functional outcome. OBJECTIVES To describe associations among MRI features, neurological dysfunction before MRI, and functional outcome in dogs with disk herniation. ANIMALS One hundred and fifty-nine dogs with acute thoracolumbar disk herniation. METHODS Retrospective case series. Signalment, initial neurological function as assessed by a modified Frankel score (MFS), and ambulatory outcome at hospital discharge and >3 months (long-term) follow-up were recorded from medical records and telephone interview of owners. Associations were estimated between these parameters and MRI signal and morphometric data. RESULTS Dogs with intramedullary T2W hyperintensity had more severe pre-MRI MFS (median 2, range 0-4) and lower ambulatory proportion at long-term follow-up (0.76) than those dogs lacking hyperintensity (median MFS 3, range 0-5; ambulatory proportion, 0.93) (P=.001 and .013, respectively). Each unit of T2W length ratio was associated with a 1.9 times lower odds of long-term ambulation when adjusted for pre-MRI MFS (95% confidence interval 1.0-3.52, P=.05). Dogs with a compressive length ratio >1.31 (which was the median ratio within this population) had more severe pre-MRI MFS (median 3, range 0-5) compared with those with ratios < or =1.31 (median MFS 3, range 0-4; P=.006). CONCLUSIONS AND CLINICAL IMPORTANCE MRI features were associated with initial injury severity in dogs with thoracolumbar disk herniation. Based on results of this study, the T2W length ratio and presence of T2W intramedullary hyperintensity appear to be predictive of long-term ambulatory status.

Magnetic resonance imaging for the differentiation of neoplastic, inflammatory, and cerebrovascular brain disease in dogs

BACKGROUND The reliability and validity of magnetic resonance imaging (MRI) for detecting neoplastic, inflammatory, and cerebrovascular brain lesions in dogs are unknown. OBJECTIVES To estimate sensitivity, specificity, and inter-rater agreement of MRI for classifying histologically confirmed neoplastic, inflammatory, and cerebrovascular brain disease in dogs. ANIMALS One hundred and twenty-one client-owned dogs diagnosed with brain disease (n = 77) or idiopathic epilepsy (n = 44). METHODS Retrospective, multi-institutional case series; 3 investigators analyzed MR images for the presence of a brain lesion with and without knowledge of case clinical data. Investigators recorded most likely etiologic category (neoplastic, inflammatory, cerebrovascular) and most likely specific disease for all brain lesions. Sensitivity, specificity, and inter-rater agreement were calculated to estimate diagnostic performance. RESULTS MRI was 94.4% sensitive (95% confidence interval [CI] = 88.7, 97.4) and 95.5% specific (95% CI = 89.9, 98.1) for detecting a brain lesion with similarly high performance for classifying neoplastic and inflammatory disease, but was only 38.9% sensitive for classifying cerebrovascular disease (95% CI = 16.1, 67.0). In general, high specificity but not sensitivity was retained for MR diagnosis of specific brain diseases. Inter-rater agreement was very good for overall detection of structural brain lesions (κ = 0.895, 95% CI = 0.792, 0.998, P < .001) and neoplastic lesions, but was only fair for cerebrovascular lesions (κ = 0.299, 95% CI = 0, 0.761, P = .21). CONCLUSIONS AND CLINICAL IMPORTANCE MRI is sensitive and specific for identifying brain lesions and classifying disease as inflammatory or neoplastic in dogs. Cerebrovascular disease in general and specific inflammatory, neoplastic, and cerebrovascular brain diseases were frequently misclassified.

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.

Evaluation of standard magnetic resonance characteristics used to differentiate neoplastic, inflammatory, and vascular brain lesions in dogs.

Magnetic resonance (MR) imaging characteristics are commonly used to help predict intracranial disease categories in dogs, however, few large studies have objectively evaluated these characteristics. The purpose of this retrospective study was to evaluate MR characteristics that have been used to differentiate neoplastic, inflammatory, and vascular intracranial diseases in a large, multi-institutional population of dogs. Medical records from three veterinary teaching hospitals were searched over a 6-year period for dogs that had diagnostic quality brain MR scans and histologically confirmed intracranial disease. Three examiners who were unaware of histologic diagnosis independently evaluated 19 MR lesion characteristics totaling 57 possible responses. A total of 75 dogs with histologically confirmed intracranial disease were included in analyses: 51 with neoplasia, 18 with inflammatory disease, and six with cerebrovascular disease. Only strong contrast enhancement was more common in neoplasia than other disease categories. A multivariable statistical model suggested that extra-axial origin, T2-FLAIR mixed intensity, and defined lesion margins were also predictive of neoplasia. Meningeal enhancement, irregular lesion shape, and multifocal location distinguished inflammatory diseases from the other disease categories. No MR characteristics distinguished vascular lesions and these appeared most similar to neoplasia. These results differed from a previous report describing seven MR characteristics that were predictive of neoplasia in dogs and cats. Findings from the current study indicated that the high performance of MR for diagnosing canine intracranial diseases might be due to evaluator recognition of combinations of MR characteristics vs. relying on any one MR characteristic alone.

Thoracic and lumbar spinal cord diffusion tensor imaging in dogs.

To analyze four clinically applicable diffusion tensor imaging (DTI) protocols (two each in the transverse and sagittal planes) in the normal dog.

Accuracy of Conventional Radiography and Computed Tomography in Predicting Implant Position in Relation to the Vertebral Canal in Dogs

Objective: To compare the accuracy of radiography and computed tomography (CT) in predicting implant position in relation to the vertebral canal in the cervical and thoracolumbar vertebral column. Study Design: In vitro imaging and anatomic study. Animals: Medium-sized canine cadaver vertebral columns (n=12). Methods: Steinmann pins were inserted into cervical and thoracolumbar vertebrae based on established landmarks but without predetermination of vertebral canal violation. Radiographs and CT images were obtained and evaluated by 6 individuals. A random subset of pins was evaluated for ability to distinguish left from right pins on radiographs. The ability to correctly identify vertebral canal penetration for all pins was assessed both on radiographs and CT. Spines were then anatomically prepared and visual examination of pin penetration into the canal served as the gold standard. Results: Left/right accuracy was 93.1%. Overall sensitivity of radiographs and CT to detect vertebral canal penetration by an implant were significantly different and estimated as 50.7% and 93.4%, respectively (P<.0001). Sensitivity was significantly higher for complete versus partial penetration and for radiologists compared with nonradiologists for both imaging modalities. Overall specificity of radiographs and CT to detect vertebral canal penetration was 82.9% and 86.4%, respectively (P=.049). Conclusions: CT was superior to radiographic assessment and is the recommended imaging modality to assess penetration into the vertebral canal. Clinical Relevance: CT is significantly more accurate in identifying vertebral canal violation by Steinmann pins and should be performed postoperatively to assess implant position.OBJECTIVE To compare the accuracy of radiography and computed tomography (CT) in predicting implant position in relation to the vertebral canal in the cervical and thoracolumbar vertebral column. STUDY DESIGN In vitro imaging and anatomic study. ANIMALS Medium-sized canine cadaver vertebral columns (n=12). METHODS Steinmann pins were inserted into cervical and thoracolumbar vertebrae based on established landmarks but without predetermination of vertebral canal violation. Radiographs and CT images were obtained and evaluated by 6 individuals. A random subset of pins was evaluated for ability to distinguish left from right pins on radiographs. The ability to correctly identify vertebral canal penetration for all pins was assessed both on radiographs and CT. Spines were then anatomically prepared and visual examination of pin penetration into the canal served as the gold standard. RESULTS Left/right accuracy was 93.1%. Overall sensitivity of radiographs and CT to detect vertebral canal penetration by an implant were significantly different and estimated as 50.7% and 93.4%, respectively (P<.0001). Sensitivity was significantly higher for complete versus partial penetration and for radiologists compared with nonradiologists for both imaging modalities. Overall specificity of radiographs and CT to detect vertebral canal penetration was 82.9% and 86.4%, respectively (P=.049). CONCLUSIONS CT was superior to radiographic assessment and is the recommended imaging modality to assess penetration into the vertebral canal. CLINICAL RELEVANCE CT is significantly more accurate in identifying vertebral canal violation by Steinmann pins and should be performed postoperatively to assess implant position.

Quantitative magnetic resonance imaging in a naturally occurring canine model of spinal cord injury.

Study design:Retrospective cohort study.Objectives:To analyze magnetic resonance imaging (MRI) evaluator agreement in dogs with spinal cord injury (SCI) caused by intervertebral disk herniation (IVDH) using semiautomated and manual lesion segmentation and to analyze the associations between MRI and functional outcome.Setting:United States of America.Methods:T2-weighted MRIs from dogs with SCI resulting from thoracolumbar IVDH were identified from a database. Evaluators categorized MRIs on the basis of the presence or absence of a T2-hyperintense spinal cord lesion in axial and sagittal images. A semiautomated segmentation algorithm was developed and used to estimate the lesion volume. Agreement between evaluators and between semiautomated and manual segmentation was analyzed. The relationships of qualitative and quantitative MRIs with behavioral functional outcome were analyzed.Results:Axial images more commonly depicted lesions compared with sagittal images. Lesions in axial images had more consistent associations with functional outcome compared with sagittal images. There was imperfect qualitative agreement, and lesion volume estimation was imprecise. However, there was improved precision using semiautomated segmentation compared with manual segmentation.Conclusion:Lesion volume estimation in dogs with naturally occurring SCI caused by IVDH is challenging, and axial images have important advantages compared with sagittal images. The semiautomated segmentation algorithm described herein shows promise but may require further refinement.

Broadly Reactive Pan-Paramyxovirus Reverse Transcription Polymerase Chain Reaction and Sequence Analysis for the Detection of Canine Distemper Virus in a Case of Canine Meningoencephalitis of Unknown Etiology

Despite the immunologic protection associated with routine vaccination protocols, Canine distemper virus (CDV) remains an important pathogen of dogs. Antemortem diagnosis of systemic CDV infection may be made by reverse transcription polymerase chain reaction (RT-PCR) and/or immunohistochemical testing for CDV antigen; central nervous system infection often requires postmortem confirmation via histopathology and immunohistochemistry. An 8-month-old intact male French Bulldog previously vaccinated for CDV presented with multifocal neurologic signs. Based on clinical and postmortem findings, the dogs disease was categorized as a meningoencephalitis of unknown etiology. Broadly reactive, pan-paramyxovirus RT-PCR using consensus-degenerate hybrid oligonucleotide primers, combined with sequence analysis, identified CDV amplicons in the dogs brain. Immunohistochemistry confirmed the presence of CDV antigens, and a specific CDV RT-PCR based on the phosphoprotein gene identified a wild-type versus vaccinal virus strain. This case illustrates the utility of broadly reactive PCR and sequence analysis for the identification of pathogens in diseases with unknown etiology.

Necrotizing Meningoencephalitis in Atypical Dog Breeds: A Case Series and Literature Review

Background Canine necrotizing meningoencephalitis (NME) is a fatal, noninfectious inflammatory disease of unknown etiology. NME has been reported only in a small number of dog breeds, which has led to the presumption that it is a breed‐restricted disorder. Hypothesis/Objectives Our objective was to describe histopathologically confirmed NME in dog breeds in which the condition has not been reported previously and to provide preliminary evidence that NME affects a wider spectrum of dog breeds than previously reported. Animals Four dogs with NME. Methods Archives from 3 institutions and from 1 authors (BS) collection were reviewed to identify histopathologically confirmed cases of NME in breeds in which the disease has not been reported previously. Age, sex, breed, survival from onset of clinical signs, and histopathologic findings were evaluated. Results Necrotizing meningoencephalitis was identified in 4 small dog breeds (Papillon, Shih Tzu, Coton de Tulear, and Brussels Griffon). Median age at clinical evaluation was 2.5 years. Histopathologic abnormalities included 2 or more of the following: lymphoplasmacytic or histiocytic meningoencephalitis or encephalitis, moderate‐to‐severe cerebrocortical necrosis, variable involvement of other anatomic locations within the brain (cerebellum, brainstem), and absence of detectable infectious agents. Conclusions and Clinical Importance Until now, NME has only been described in 5 small dog breeds. We document an additional 4 small breeds previously not shown to develop NME. Our cases further illustrate that NME is not a breed‐restricted disorder and should be considered in the differential diagnosis for dogs with signalment and clinical signs consistent with inflammatory brain disease.

MRI CHARACTERISTICS OF CEREBRAL MICROBLEEDS IN FOUR DOGS

Cerebral microbleeds in people are small foci of hemosiderin-containing macrophages in normal brain parenchyma. They are the remnant of previous hemorrhage and occur with greater frequency in older individuals. Our purpose was to describe the magnetic resonance (MR) appearance of cerebral microbleeds in four dogs. These lesions appeared as round, hypointense foci measuring ≤4 mm on T2*-gradient-recalled echo images. They were less conspicuous or absent on T2-weighting, being iso- or hypointense, and uniformly invisible on T1-weighted images. No contrast enhancement was seen in any of the cerebral microbleeds. Necropsy-derived histopathologic analysis of one brain confirmed these lesions to be chronic cerebrocortical infarcts containing hemosiderin. The MR changes seen in dogs were analogous to what has been described in people and will be helpful in distinguishing cerebral microbleeds from other brain lesions.