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

Cervical Intervertebral Disk to Vertebral Body Ratios of Different Dog Breeds Based on Sagittal Magnetic Resonance Imaging.

To establish sagittal area and length reference values and ratios between apparently normal canine cervical vertebrae and intervertebral disks using magnetic resonance imaging. Retrospective evaluation of cervical vertebral column magnetic resonance imaging studies of 44 dogs representing 5 different breeds (Labrador Retriever, = 10; French Bulldog, = 10; Great Dane, = 9; Chihuahua, = 10; Dachshund, = 5). Mid-sagittal measurements of vertebral body and disk areas were obtained from C3 through C7 vertebrae and C2/C3 through C6/C7 intervertebral disks. Disk to vertebra area ratios were calculated and compared among dog breeds. Additionally, sagittal vertebral body and disk length measurements were obtained and disk to vertebra length ratios calculated. Inter and intra observer variability was assessed. There were significant differences for disk to vertebral body area and length ratios between evaluated dog breeds and cervical vertebral locations ( < 0.001). Mean area ratio of Chihuahuas was significantly larger than all other breeds, while results from Dachshunds were only significantly different than Chihuahuas and Labrador Retrievers. Mean area ratios were statistically different between the cranial and caudal cervical vertebral locations. Regarding length ratios, results from Chihuahuas were significantly different than all breeds except Dachshunds. Mean length ratios were statistically different between all cervical locations, except C2/C3 compared to C3/C4. Intra- and interobserver variability was very good to excellent. There are significant differences in area and length ratios between dog breeds. Differences also exist in area and length ratios between the cranial and caudal cervical vertebral column. These differences may play a role in the development of vertebral column diseases including intervertebral disk disease

Listeria Brainstem Encephalitis in Small Ruminants: Correlation of Magnetic Resonance Imaging and Histopathology.

Listeria Brainstem Encephalitis in Small Ruminants: Correlation of Magnetic Resonance Imaging and Histopathology Christina Stahl1, Anna Oevermann2, Daniela Gorgas1 1Clinical Radiology, Department of Clinical Veterinary Medicine, Vetsuisse-Faculty, University of Bern, Switzerland 2Neurocenter, Department of Clinical Research and Veterinary Public Health, Vetsuisse-Faculty, University of Bern, Switzerland Abstract Brainstem encephalitis is an intriguing form of Listeria monocytogenes central nervous system (CNS) infection in humans and ruminants and has a high fatality rate. However, intra vitam diagnosis remains difficult in both species (1, 2). We performed MRI of affected small ruminants, in which Listeria brainstem encephalitis is a common CNS disease, and correlated MRI features with histopathology in order to define MRI criteria for the diagnosis of listeria brainstem encephalitis. Fifteen small ruminants (nine sheep, six goats) with listeriosis underwent MRI examination of the brain using a 0.3 T system (five animals) and 1.0 T system (ten animals) including T2w, FLAIR and T1w sequences pre and post Gadolinium administration. Listeria brainstem encephalitis was confirmed by histopathology, and histopathological changes were correlated to MRI features. On MRI, lesions were best visualized in T2-weighted sequences. In all animals they were characterized by asymmetric increased signal intensity in the rhombencephalon in T2w and FLAIR sequences. The lesions showed a variable pattern and distribution, ranging from patchy with ill defined borders to diffusely affecting the entire cross-sectional area of the brainstem. Few animals had lesions in the diencephalon (three animals), whilst histopathologically detectable lesions commonly extended to the diencephalon and involved cranial nerve roots (twelve animals). The lesions were iso- to mildly hypointens in T1w sequence. Mild to moderate patchy or ring-like contrast uptake was observed in the rhombencephalon of five animals (one sheep, four goats), which showed vascular damage and perivascular fibrin accumulation on light microscopy. In the brainstem, the asymmetric T2-hyperintense lesions observed by MRI correlated well with the inflammatory infiltrates observed in histopathology (3). However, lesions in the diencephalon, cranial nerves and meninges of rostral brain areas were rarely detected by MRI, indicating that MRI underestimates involvement of the rostral brain and brain associated structures. Contrary to reported human cases of neurolisteriosis (4), contrast uptake was an inconsistent finding occurring in the rhombencephalon of only five animals. References 1. Armstrong RW, Fung PC. Brainstem encephalitis (rhombencephalitis) due to Listeria monocytogenes: case report and review. Clin Infect Dis. 1993;16(5):689-702. Review. 2. Oevermann A, Botteron C, Seuberlich T, Nicolier A, Friess M, Doherr MG, et al. Neuropathological survey of fallen stock: active surveillance reveals high prevalence of encephalitic listeriosis in small ruminants. Vet Microbiol. 2008 Aug 25;130(3-4):320-9. 3. Antal EA, Loberg EM, Dietrichs E, Maehlen J. Neuropathological findings in 9 cases of listeria monocytogenes brain stem encephalitis. Brain Pathol. 2005;15(3):187-91. 4. Reynaud L, Graf M, Gentile I, Cerini R, Ciampi R, Noce S, et al. A rare case of brainstem encephalitis by Listeria monocytogenes with isolated mesencephalic localization. Case report and review. Diagn Microbiol Infect Dis. 2007;58(1):121-3

Slit ventricle syndrome and subdural haemorrhage due to suspected overshunting in a dog with hydrocephalus internus

A 1.5-year-old Chihuahua was presented with clinical signs consistent with multifocal localisation. MRI revealed hydrocephalus internus. Following placement of a ventriculoperitoneal (VP) shunt with a low-pressure valve, improvement was noted. Clinical signs returned one month later. A second MRI revealed subdural haematoma, meningeal reaction and slit-like ventricles, and was interpreted as overshunting. Saline solution was injected in the ventricles via the shunt, which was then ligated. Clinical improvement was noted, followed again by relapse three months later. A third MRI revealed recurrence of hydrocephalus internus. The VP shunt was reconnected and, additionally, the valve was positioned and fixed in a vertical position. A disconnection of the valve occurred two weeks later, and the owners elected euthanasia. Complications following VP shunting in this case reveal many similarities to those described in overshunting in people and should be considered as a possible complication

Biomechanical properties of the atlantoaxial joint with naturally-occurring instability in a toy breed dog. A comparative descriptive cadaveric study

The biomechanical properties of the atlanto-axial joint in a young Yorkshire Terrier dog with spontaneous atlantoaxial instability were compared to those of another young toy breed dog with a healthy atlantoaxial joint. The range-of-motion was increased in flexion and lateral bending in the unstable joint. In addition, lateral bending led to torsion and dorsal dislocation of the axis within the atlas. On gross examination, the dens ligaments were absent and a longitudinal tear of the tectorial membrane was observed. These findings suggest that both ventral and lateral flexion may lead to severe spinal cord compression, and that the tectorial membrane may play a protective role in some cases of atlantoaxial instability

Use of contrast-enhanced fluid-attenuated inversion recovery sequence to detect brain lesions in dogs and cats.

BACKGROUND The diagnostic value of a contrast-enhanced T2-weighted FLAIR sequence (ceFLAIR) in brain imaging is unclear. HYPOTHESIS/OBJECTIVES That the number of brain lesions detected with ceFLAIR would be no greater than the sum of lesions detected with nFLAIR and ceT1W sequence. ANIMALS One hundred and twenty-nine animals (108 dogs and 21 cats) undergoing magnetic resonance imaging (MRI) of the head between July 2010 and October 2011 were included in the study. METHODS A transverse ceFLAIR was added to a standard brain MRI protocol. Presence and number of lesions were determined based on all available MRI sequences by 3 examiners in consensus and lesion visibility was evaluated for nFLAIR, ceFLAIR, and ceT1W sequences. RESULTS Eighty-three lesions (58 intra-axial and 25 extra-axial) were identified in 51 patients. Five lesions were detected with nFLAIR alone, 2 with ceT1W alone, and 1 with ceFLAIR alone. Significantly higher numbers of lesions were detected using ceFLAIR than nFLAIR (76 versus 67 lesions; P = 0.04), in particular for lesions also detected with ceT1W images (53 versus 40; P =.01). There was no significant difference between the number of lesions detected with combined nFLAIR and ceT1W sequences compared to those detected with ceFLAIR (82 versus 76; P =.25). CONCLUSION AND CLINICAL IMPORTANCE Use of ceFLAIR as a complementary sequence to nFLAIR and ceT1W sequences did not improve the detection of brain lesions and cannot be recommended as part of a routine brain MRI protocol in dogs and cats with suspected brain lesions