Influence of the Vertek aiming device on the surgical accuracy of computer-assisted drilling of the equine distal sesamoid bone-An experimental cadaveric study.

OBJECTIVE: To determine the effect of the Vertek aiming device (VAD) on the surgical accuracy of navigated drilling of the distal sesamoid bone (DSB). STUDY DESIGN: Experimental cadaveric study. SAMPLE POPULATION: A total of 30 paired equine cadaveric limbs from 15 horses. METHODS: Each specimen was placed in a purpose-built frame (PBF). Preoperative cone beam computed tomography (CBCT) images were acquired with an imaging unit coupled with a surgical navigation system. In the DSB of each specimen, a 4.5 mm glide hole and a 3.2 mm thread hole were drilled under navigation guidance, to simulate drilling for the repair of a mid-sagittal DSB fracture. In the VAD group navigated drilling was assisted by using the VAD. In the free-hand drilling group navigated drilling was performed without the VAD. Pre-and postoperative CBCT scans were merged and surgical accuracy aberrations (SAA) between the planned drill corridor and the created bone tunnel were measured. Descriptive statistics and repeated-measures analyses of variance (rep.-meas. ANOVA) were performed to compare SAA measurements between the study groups. RESULTS: The SAA measurements ranged from 0 to 2.9 mm in the free-hand group and from 0 to 2.8 mm in the VAD group. The median overall SAA was lower in the VAD group than in the free-hand navigated group (0.6 mm ± [0.5-0.7] vs. 0.8 mm ± [0.7-1], rep.-meas. ANOVA p = .007). CONCLUSION: The additional use of the VAD in the described set-up for navigated drilling significantly improved surgical accuracy. CLINICAL SIGNIFICANCE: The combined use of the VAD and PBF may help improve surgical accuracy in navigated lag screw repair of DSB fractures.

Determination of cutoff values on computed tomography and magnetic resonance images for the diagnosis of atlantoaxial instability in small-breed dogs.

OBJECTIVE: To determine cutoff values for the diagnosis of atlantoaxial instability (AAI) based on cross-sectional imaging in small-breed dogs. STUDY DESIGN: Retrospective multicenter study. SAMPLE POPULATION: Client-owned dogs (n = 123) and 28 cadavers. METHODS: Dogs were assigned to three groups: a control group, a "potentially unstable" group, and an AAI-affected group, according to imaging findings and clinical signs. The ventral compression index (VCI), cranial translation ratio (CTR), C1-C2 overlap, C1-C2 angle, atlantoaxial distance, basion-dens interval, dens-to-axis length ratio (DALR), power ratio, and clivus canal angles were measured on CT or T2-weighted magnetic resonance (MR) images. Receiver operating characteristic (ROC) analysis was performed to define cutoff values in flexed (≥25°) and extended (<25°) head positions. RESULTS: Cutoff values for the VCI of ≥0.16 in extended and ≥0.2 in flexed head positions were diagnostic for AAI (sensitivity of 100% and 100%, specificity of 94.54% and 96.67%, respectively). Cutoff values for the other measurements were defined with a lower sensitivity (75%-96%) and specificity (70%-97%). A combination of the measurements did not increase the sensitivity and specificity compared with the VCI as single measurement. CONCLUSION: Cutoff values for several imaging measurements were established with good sensitivity and specificity. The VCI, defined as the ratio between the ventral and dorsal atlantodental interval, had the highest sensitivity and specificity in both head positions. CLINICAL SIGNIFICANCE: The use of defined cutoff values allows an objective diagnosis of AAI in small-breed dogs. The decision for surgical intervention, however, should remain based on a combination of clinical and imaging findings.

Bronchioalveolar carcinoma in an adult alpaca (Vicugna pacos).

BACKGROUND: This report describes a case of a bronchiolar adenocarcinoma in a 6-year old alpaca mare. For the first time in an alpaca, neoplasia was classified by histopathology as a lepidic-predominant bronchiolar adenocarcinoma. CASE PRESENTATION: The mare was referred to the Clinic for Ruminants after a 6-week period of forced breathing and weight loss. The clinical examination included complete blood count, blood chemistry, ultrasound, radiographs and a CT-scan of the thorax. A bilateral pneumothorax and several, structures within the lung parenchyma were diagnosed. Differential diagnosis included neoplasia, tuberculosis and fungal granulomas. The owner requested euthanasia due to the mare's ongoing deterioration. At postmortem examination, the granulomatous changes in the lungs were histopathologically classified as lepidic dominant bronchiolar adenocarcinoma. CONCLUSIONS: Neoplastic diseases are more often seen in South American camelids compared to other farm animal species. The use of a CT scan was helpful in classifying the lung lesions and give a clear prognosis.

Polymelia in a chimeric Simmental calf: nociceptive withdrawal reflex, anaesthetic and analgesic management, anatomic and genetic analysis.

BACKGROUND: Polymelia is a congenital defect characterized by one or more supernumerary legs. The genetics and aetiology of this condition in cattle have not yet been thoroughly investigated even though several case reports do exist. The model of the nociceptive withdrawal reflex (NWR) has been characterized in several species to study spinal nociceptive processing. It is a polysynaptic spinal reflex that can be elicited by noxious electrical stimulation and recorded by electromyography. Thorough nociceptive examination and preventive analgesic management has not yet been an aspect in the perioperative management of polymelia cases. CASE PRESENTATION: A 4-month-old female Simmental calf was presented with notomelia. The animal was in good health and showed no neurologic deficiencies. Preoperatively, computed tomography was performed to gain more detailed anatomical information. To evaluate the sensitivity of the accessory limb, NWR testing was performed and revealed a connection of the afferent reflex pathway of the accessory limb to the efferent of the normal limb. The accessory limb was surgically removed under general anaesthesia. Intensive care included multimodal pain therapy adapted to the pain intensity scored during regular pain assessment. A gross anatomical dissection as well as a genetic analysis of the accessory limb were performed postoperatively. The calf was identified as a chimera. CONCLUSION: This calf was successfully relieved of its accessory limb. Chimerism has not been described in the congenital defect polymelia. As the accessory limb was pain sensitive and a common nociceptive reflex pathway was identified, thorough perioperative pain management was performed with the intention to prevent chronic neuropathic pain development.

Metabolic profiling of listeria rhombencephalitis in small ruminants by 1 H high-resolution magic angle spinning NMR spectroscopy.

Listeria rhombencephalitis is caused by infection with Listeria monocytogenes and is associated with a high mortality rate in humans and ruminants. Little is known about the metabolic changes associated with neurolisteriosis in particular and infectious central nervous system (CNS) diseases in general. The purpose of our study was to investigate the metabolic changes associated with listeria rhombencephalitis in small ruminants (goats and sheep) as a model for inflammatory CNS disease by 1 H high-resolution magic angle spinning nuclear magnetic resonance (1 H HR-MAS NMR) spectroscopy of brain biopsies obtained from the brainstem and thalamus. Statistical analysis revealed distinct differences in the metabolic profile of brainstem biopsies, the primary location of listeria rhombencephalitis with moderate or severe inflammatory changes. N-Acetylaspartate (NAA), N-acetylaspartylglutamate, choline, myo-inositol and scyllo-inositol were decreased, and glycine, phosphocholine, taurine and lactate were increased, in the diseased group (n = 13) in comparison with the control group (n = 12). In the thalamus, which showed no or only mild inflammatory changes in the majority of animals, no statistically significant metabolic changes were observed. However, trends for metabolic alterations were partly the same as those found in the brainstem, including NAA, choline and lactate. This may be an indicator of metabolic changes occurring in the early stages of the disease. Therefore, further research with a larger number of animals is needed to evaluate the presence of subtle metabolic changes associated with mild inflammatory changes in the thalamus. In conclusion, 1 H HR-MAS NMR investigation of listeria rhombencephalitis identified brain metabolite changes, offering new insights into the disease pathophysiology.

Direct determination of phosphate sugars in biological material by (1)H high-resolution magic-angle-spinning NMR spectroscopy.

The study aim was to unambiguously assign nucleotide sugars, mainly UDP-X that are known to be important in glycosylation processes as sugar donors, and glucose-phosphates that are important intermediate metabolites for storage and transfer of energy directly in spectra of intact cells, as well as in skeletal muscle biopsies by (1)H high-resolution magic-angle-spinning (HR-MAS) NMR. The results demonstrate that sugar phosphates can be determined quickly and non-destructively in cells and biopsies by HR-MAS, which may prove valuable considering the importance of phosphate sugars in cell metabolism for nucleic acid synthesis. As proof of principle, an example of phosphate-sugar reaction and degradation kinetics after unfreezing the sample is shown for a cardiac muscle, suggesting the possibility to follow by HR-MAS NMR some metabolic pathways. Graphical abstract Glucose-phosphate sugars (Glc-1P and Glc-6P) detected in muscle by 1H HR-MAS NMR.

MAGNETIC RESONANCE IMAGING FINDINGS IN SMALL RUMINANTS WITH BRAIN DISEASE.

Brain disease is an important cause of neurologic deficits in small ruminants, however few MRI features have been described. The aim of this retrospective, case series study was to describe MRI characteristics in a group of small ruminants with confirmed brain disease. A total of nine small ruminants (six sheep and three goats) met inclusion criteria. All had neurologic disorders localized to the brain and histopathologic confirmation. In animals with toxic-metabolic diseases, there were bilaterally symmetric MRI lesions affecting either the gray matter (one animal with polioencephalomalacia) or the white matter (two animals with enterotoxemia). In animals with suppurative inflammation, asymmetric focal brainstem lesions were present (two animals with listeric encephalitis), or lesions typical of an intra-axial (one animal) or dural abscess (one animal), respectively. No MRI lesions were detected in one animal with suspected viral cerebellitis and one animal with parasitic migration tracts. No neoplastic or vascular lesions were identified in this case series. Findings from the current study supported the use of MRI for diagnosing brain diseases in small ruminants.

A transmandibular lateral transsphenoidal navigated surgical approach to access a pituitary macroadenoma in a warmblood mare.

A 16-year-old warmblood mare was referred with a progressive history of behavioral changes and left-sided blindness. Following neuroanatomical localization to the forebrain, magnetic resonance imaging of the head revealed a well-delineated, 4.5 cm in diameter, round pituitary mass causing marked compression of the midbrain and optic chiasm. Euthanasia was recommended but declined by the owners. Veterinary specialists and a human neurosurgeon collaboratively prepared for surgical case management. A novel navigated transmandibular lateral transsphenoidal approach was developed to access the region of the sella turcica and practiced on cadaver specimens. The horse was anesthetized and placed in sternal recumbency with the head above the heart line. Using a cone beam computed tomography (CBCT)-coupled navigation system, a navigated pin traversing the vertical ramus of the mandible and the lateral pterygoid muscle was placed in a direct trajectory to the predetermined osteotomy site of the basisphenoid bone. A safe corridor to the osteotomy site was established using sequential tubular dilators bypassing the guttural pouch, internal and external carotid arteries. Despite the use of microsurgical techniques, visualization of critical structures was limited by the long and narrow working channel. Whilst partial resection of the mass was achieved, iatrogenic trauma to the normal brain parenchyma was identified by intraoperative imaging. With consent of the owner the mare was euthanized under the same general anesthesia. Post-mortem magnetic resonance imaging and gross anatomical examination confirmed partial removal of a pituitary adenoma, but also iatrogenic damage to the surrounding brain parenchyma, including the thalamus.

An anatomical study of the subarachnoid space surrounding the trigeminal ganglion in horses-in preparation for a controlled glycerol rhizotomy in equids.

Introduction: Equine trigeminal-mediated headshaking is a painful neuropathic disorder comparable to trigeminal neuralgia in humans. The selective destruction of pain fibers within the trigeminal ganglion, called rhizotomy, is the surgical treatment of choice for idiopathic trigeminal neuralgia refractory to medical treatment in humans. The human trigeminal ganglion is enclosed by a dural recess called the Meckel's or trigeminal cave, in which the ganglion is surrounded by a cerebrospinal fluid (CSF)-filled subarachnoid space. During glycerol rhizotomy, glycerol is percutaneously injected in this CSF-filled space. Until now, information about the anatomy of the dural recess and the subarachnoid space surrounding the trigeminal ganglion is lacking in horses. The aim of this study was to explore if a CSF-filled subarachnoid space around the trigeminal ganglion exists in horses. Materials and methods: Six equine cadaver heads were investigated for CSF accumulation around the ganglion with a 3 Tesla MRI. After anatomical dissection to expose the trigeminal root, a polymer-based radiopaque contrast agent was injected through the porus trigeminus into the subarachnoid space (cisternography). The exact delineation and the volume of the contrast agent accumulation were determined on subsequent micro-computed tomographic scans and segmentation. Finally, the distribution of the contrast agent within the subarachnoid space was examined histologically in three specimens. Results: In all 12 specimens included in this study, the trigeminal ganglion was surrounded by a subarachnoid space forming a trigeminal cistern. The mean volume of the trigeminal cave in this study was 0.31 mL (±SD: 0.11 mL). Distribution of the contrast agent along the peripheral nerves (i.e., ophthalmic, maxillary and/or mandibular nerve) was observed in 7 out of 12 specimens. Discussion/conclusion: A subarachnoid space surrounding the trigeminal ganglion exists in the horse and could be targeted for glycerol rhizotomy in horses suffering from trigeminal-mediated headshaking. However, the clinical relevance of contrast agent distribution along the peripheral nerves remains to be assessed.

Clinical Evaluation of a New Surgical Augmentation Technique for Transarticular Atlantoaxial Fixation for Treatment of Atlantoaxial Instability.

The feasibility of a newly developed augmentation of ventral fixation technique for surgical stabilization of atlantoaxial instability was clinically evaluated in a cohort of eleven dogs, and long-term clinical outcomes were retrospectively analyzed. The new technique combines wire/suture fixation through a transverse hole in the axis anchored by two screws placed in the alae atlantis or at the cranial end of plates used to bridge the atlantoaxial joint ventrally. A previous biomechanical study demonstrated good stability of this technique during shear loading, comparable to the stability achieved with other standard techniques. Ten dogs improved clinically after surgery and returned to a normal life within 3-6 months of surgery. One dog developed aphonia, dysphagia, and died of aspiration pneumonia three days after surgery. The augmentation of conventional ventral atlantoaxial fixation with the transverse bony corridor of the proximal axis body may be a valuable way to enhance stabilization of the atlantoaxial joint.

Accuracy of end-on fluoroscopy in predicting implant position in relation to the vertebral canal in dogs.

Objective: To evaluate the accuracy of end-on fluoroscopy in predicting implant position in relation to the vertebral canal in the canine thoracolumbar vertebral column. Study design: In vitro imaging and anatomic study. Animals: Canine cadaveric thoracolumbar vertebral columns (n = 5). Methods: Smooth Steinmann pins were inserted bicortically into the thoracolumbar vertebral columns between T10 and L7 using recommended insertion angles. Penetration of the spinal canal was not strictly avoided. After pin placement, end-on fluoroscopy images were obtained of each pin. Pin position was subsequently assessed by four evaluators and determined to either being out of the vertebral canal or in, with the latter being additionally divided into partially or completely penetrating the canal. To assess potential differences in modalities, fluoroscopy images were gray-scale inverted and evaluated again later by the same four individuals. Correct identification of pin position in relationship to the vertebral canal was assessed for both fluoroscopy images. Anatomic preparation of the spines was used for verification of pin position in relation to the spinal canal. Some data from this study were compared with historical data on accuracy using orthogonal radiography and computed tomography (CT). Results: Overall sensitivity and specificity of F to detect vertebral canal penetration was 98.8 % (95% confidence interval (CI), 96.0-99.6) and 98.0% (95% CI, 77.0-99.9), respectively. For Fi, sensitivity and specificity were 97.0% (95% CI, 91.5-99.0) and 98.5% (95% CI, 81.5-99.9) respectively. F exceeded Fi for the sensitivity of detecting pin penetration into the vertebral canal (p = 0.039) but specificities were not different (p = 0.585). When comparing to historical data, the overall accuracy of end-on fluoroscopy (F) and inverted fluoroscopy (Fi) was statistical better than conventional radiographic assessment (p < 0.001). Conclusion: End-on fluoroscopy is a highly accurate method for the assessment of pin position in relationship to the thoracolumbar spinal canal in cadaveric dogs. Clinical significance: End-on fluoroscopy, with or without inversion, is accurate in identifying vertebral canal violation by bicortically placed Steinmann pins. When CT is not available, end-on fluoroscopy might be a valuable imaging modality to determine pin position in the canine vertebral column.

Accuracy and Safety of Neuronavigation for Minimally Invasive Stabilization in the Thoracolumbar Spine Using Polyaxial Screws-Rod: A Canine Cadaveric Proof of Concept.

OBJECTIVES: The main aim of this study was to evaluate the feasibility of minimally invasive stabilization with polyaxial screws-rod using neuronavigation and to assess accuracy and safety of percutaneous drilling of screw corridors using neuronavigation in thoracolumbar spine and compare it between an experienced and a novice surgeon. STUDY DESIGN: Feasibility of minimally invasive polyaxial screws-rod fixation using neuronavigation was first performed in the thoracolumbar spine of two dogs. Accuracy and safety of drilling screw corridors percutaneously by two surgeons from T8 to L7 in a large breed dog using neuronavigation were established by comparing entry and exit points coordinates deviations on multiplanar reconstructions between preoperative and postoperative datasets and using a vertebral cortical breach grading scheme. RESULTS: Feasibility of minimally invasive stabilization was demonstrated. For the experienced surgeon, safety was 100% and mean (standard deviation) entry point deviations were 0.3 mm (0.8 mm) lateral, 1.3 mm (0.8 mm) ventral and 0.7 mm (1.8 mm) caudal. The exit points deviations were 0.8 mm (1.9 mm) lateral, 0.02 mm (0.9 mm) dorsal and 0.7 mm (2.0 mm) caudal. Significant difference in accuracy between surgeons was found in the thoracic region but not in the lumbar region. Accuracy and safety improvement are noted for the thoracic region when procedures were repeated by the novice. CONCLUSION: This proof of concept demonstrates that using neuronavigation, minimally invasive stabilization with polyaxial screws-rod is feasible and safe in a large breed dog model.

Evaluation of Paraspinal Musculature in Small Breed Dogs with and without Atlantoaxial Instability Using Computed Tomography.

OBJECTIVE: The aim of this study was to evaluate differences in paraspinal musculature between dogs with and without atlantoaxial instability (AAI) using computed tomography scans. STUDY DESIGN: Retrospective multicentre study evaluating transverse reconstructed computed tomography scans of 83 small breed dogs (34 with and 49 without AAI) for the cross-sectional paraspinal musculature area at three levels (Occiput/C1, mid-C1, mid-C2). Ratio of moments, dorsal-to-ventral muscle-area ratios (d-v-ratio) and ratios of the dorsal and ventral musculature to C2 height (d-C2-ratio and v-C2-ratio) were evaluated for differences between groups using multivariate analysis of variance (p < 0.05) taking the head-neck position into account. RESULTS: Dogs with AAI showed a significantly lower d-v-ratio at levels 2 and 3, d-C2-ratio at level 2 and ratio of moments at all levels. When head-neck positions were analysed separately, ratio of moments was significantly lower in affected dogs at level 1 and 2. Also lower was d-C2-ratio at level 2, but only in flexed positioning. The head-neck position had a significant influence on ratio of moments and d-v-ratio at all three levels and on d-C2-ratio at level 1. CONCLUSION: Significant changes in muscle area were observed only for the hypaxial muscles at the C1 level, indicating a limited role of muscular adaption in AAI patients. Our results confirm an altered ratio of moments in dogs with AAI. The head-neck position has a significant impact and should be taken into account when evaluating spinal musculature.

Sampling Method Affects HR-MAS NMR Spectra of Healthy Caprine Brain Biopsies.

The metabolic profiling of tissue biopsies using high-resolution-magic angle spinning (HR-MAS) 1H nuclear magnetic resonance (NMR) spectroscopy may be influenced by experimental factors such as the sampling method. Therefore, we compared the effects of two different sampling methods on the metabolome of brain tissue obtained from the brainstem and thalamus of healthy goats by 1H HR-MAS NMR spectroscopy-in vivo-harvested biopsy by a minimally invasive stereotactic approach compared with postmortem-harvested sample by dissection with a scalpel. Lactate and creatine were elevated, and choline-containing compounds were altered in the postmortem compared to the in vivo-harvested samples, demonstrating rapid changes most likely due to sample ischemia. In addition, in the brainstem samples acetate and inositols, and in the thalamus samples Æ´-aminobutyric acid, were relatively increased postmortem, demonstrating regional differences in tissue degradation. In conclusion, in vivo-harvested brain biopsies show different metabolic alterations compared to postmortem-harvested samples, reflecting less tissue degradation. Sampling method and brain region should be taken into account in the analysis of metabolic profiles. To be as close as possible to the actual situation in the living individual, it is desirable to use brain samples obtained by stereotactic biopsy whenever possible.

Influence of the Head Neck Position on Imaging Measurements Used to Assess the Craniovertebral Junction in Small Breed Dogs: A Cadaveric Study.

OBJECTIVE: The study aimed to determine the influence of head neck position on imaging measurements used to assess the craniovertebral junction (CVJ) and to recommend the most appropriate position for the evaluation of the CVJ. STUDY DESIGN: A cross-sectional sample of adult dogs' cadavers was subjected to a computed tomography scan of the cranium and the cranial cervical region in three standardized head positions. Imaging measurements often used to assess the CVJ were measured. The influence of the head neck position, breed, weight and gender on imaging measurements was tested using repeated measures analysis of variance. RESULTS: Twenty-eight cadavers of small breed dogs were enrolled in the study. All cadavers examined had occipital dysplasia. All transarticular imaging measurements were dependent on the head neck position. In addition, the breed, weight and gender had an influence on several measurements. CONCLUSION: We recommend a standardized head neck position of 50 degrees flexion if quantitative imaging measurements of the CVJ are used to diagnose pathologies in this region. Future studies should focus on the definition of cut-off values for quantitative imaging measurements of the CVJ to differentiate between healthy and diseased small breed dogs. Regarding atlantoaxial instability, a combination of six parameters (C1-C2 angle, C1-C2 overlap, atlantoaxial distance, dens-to-axis length ratio, ventral compression index and clivus canal angle) is promising for its diagnosis.

Accuracy and Safety of Image-Guided Freehand Pin Placement in Canine Cadaveric Vertebrae.

OBJECTIVE: The aim of this study was to validate an imaging technique for evaluation of spinal surgery accuracy and to establish accuracy and safety of freehand technique in the thoracolumbar spine of large breed dogs. STUDY DESIGN: After thoracolumbar spine computed tomography (CT), 26 drilling corridors were planned then drilled to receive 3.2 mm positive profile pins using a freehand technique. After pin removal, CT was repeated. All entry points, exit points and angles of the preoperative planned trajectories were compared with postoperative ones using an image registration and fusion technique by three observers. Corridor coordinates for entry and exit points were evaluated in three dimensions and angles were measured in one plane. Intraclass correlation coefficient (ICC) was used to establish the imaging technique reliability and descriptive statistics were used to report on the freehand technique accuracy. Safety was evaluated using a vertebral cortical breach grading scheme. RESULTS: Intraclass correlation coefficient for the entry points, exit points and angle were 0.79, 0.96 and 0.92 respectively. Mean deviations for the entry points, exit points and angle were 3.1 mm, 6.3 mm and 7.6 degrees respectively. Maximum deviations were 6.3 mm, 11.0 mm and 16.4 degrees. Most deviations were lateral and caudal. All corridors were judged as safe. CONCLUSION: The imaging technique reliability was good to excellent to study spinal surgery accuracy. Implant deviations should be anticipated when planning stabilization surgery in large breed dogs using the freehand-guided technique.

Morphometric and functional study of the canine atlantoaxial joint.

The atlantoaxial joint can be affected by instability, in most cases a congenital pathology in young small breed dogs. Causes of atlantoaxial instability (AAI) are variable but are usually attributed to a lack of ligamentous support. The purpose of the present study was to specify the role of the ligamentous structures in the stabilisation of the atlantoaxial joint and to find possible adaptations of the ligaments' internal structure to their specific function. Five Beagle cadavers were included in this study. Each dog was subjected to a computed tomography (CT) and a magnetic resonance imaging (MRI) examination of the upper cervical region. This region was then dissected and the ligamentous structures stabilising the atlantoaxial joint were measured and removed for histological analysis. A ligament to dens ratio (LDR) was established in order to provide a basis for comparison with the measurements taken in other dog breeds. MRI and gross anatomical measurements were very similar, confirming the validity of the results. MRI thus seems reliable for evaluating the ligamentous structures of the canine occipitoatlantoaxial region. The movement exerting the greatest stress on the atlantoaxial ligaments and inducing the greatest distension of the alar ligaments was a head flexion combined with a rotation. A clear adaptation of the ligamentous shape and internal structure to their specific function was observed. Histologically, alar ligaments consisted of wavy collagen fibres and a high proportion of elastic fibres, providing them with a remarkable elasticity compared to the transverse ligament structure which was much more rigid.

Correlative Magnetic Resonance Imaging and Histopathology in Small Ruminant Listeria Rhombencephalitis.

Background: Listeria rhombencephalitis, infection of the brainstem with Listeria monocytogenes, occurs mainly in humans and farmed ruminants and is associated with high fatality rates. Small ruminants (goats and sheep) are a large animal model due to neuropathological similarities. The purpose of this study was to define magnetic resonance imaging (MRI) features of listeria rhombencephalitis in naturally infected small ruminants and correlate them with histopathology. Secondly, the purpose of this study was to compare the results with MRI findings reported in humans. Methods: Twenty small ruminants (13 sheep and 7 goats) with listeria rhombencephalitis were prospectively enrolled and underwent in vivo MRI of the brain, including T2-weighted, fluid attenuation inversion recovery, and T1-weighted sequences pre- and post-contrast administration and postmortem histopathology. In MRI, lesions were characterized by location, extent, border definition, signal intensity, and contrast enhancement. In histopathology, the location, cell type, severity, and chronicity of inflammatory infiltrates and signs of vascular damage were recorded. In addition, histopathologic slides were matched to MRIs, and histopathologic and MRI features were compared. Results: Asymmetric T2-hyperintense lesions in the brainstem were observed in all animals and corresponded to the location and pattern of inflammatory infiltrates in histopathology. Contrast enhancement in the brainstem was observed in 10 animals and was associated with vessel wall damage and perivascular fibrin accumulation in 8 of 10 animals. MRI underestimated the extension into rostral brain parts and the involvement of trigeminal ganglia and meninges. Conclusion: Asymmetric T2-hyperintense lesions in the brainstem with or without contrast enhancement can be established as criteria for the diagnosis of listeria rhombencephalitis in small ruminants. Brainstem lesions were similar to human listeria rhombencephalitis in terms of signal intensity and location. Different from humans, contrast enhancement was a rare finding, and abscessation was not observed.

Craniovertebral Junction Anomalies in Small Breed Dogs with Atlantoaxial Instability: A Multicentre Case-Control Study.

OBJECTIVE: The main purpose of this study was to define criteria to systemically describe craniovertebral junction (CVJ) anomalies and to report the prevalence of CVJ anomalies in small breed dogs with and without atlantoaxial instability (AAI). MATERIALS AND METHODS: Retrospective multicentre matched case-control study evaluating magnetic resonance imaging and computed tomographic images of small breed dogs with and without AAI for the presence of CVJ anomalies. RESULTS: One hundred and twenty-two dogs were enrolled (61 with and 61 without AAI). Only dogs with AAI had dens axis anomalies such as separation (n = 20) or a short-rounded conformation (n = 35). Patients with AAI were more likely to have atlantooccipital overlapping based on transection of McRae's line by the dorsal arch of the atlas (odds ratio [OR] = 5.62, p < 0.01), a transection of Wackenheim's clivus line (OR = 41.62, p < 0.01) and rostral indentation of the occipital bone (OR = 2.79, p < 0.05). Patients with AAI were less likely to have a larger clivus canal angle (OR = 0.94, p < 0.01) and larger occipital bone lengths (OR = 0.89, p < 0.05). CLINICAL SIGNIFICANCE: Small breed dogs with AAI are more likely to have other CVJ anomalies such as atlantooccipital overlapping or dens anomalies. The grade of brachycephaly does not differ between patients with and without AAI. Certain objective criteria from human literature were found useful for the assessment of both AAI and atlantooccipital overlapping such as McRae's line, Wackenheim's clivus line, and clivus canal angle. The classification criteria used can help to evaluate CVJ anomalies in a more systematic way.