Objective measurements of the atlantoaxial joint on radiographs performed without flexion can increase the confidence of diagnosis of atlantoaxial instability in toy breed dogs

Clinical presentation, imaging characteristics, and short-term outcome of eight cats presented with suspected traumatic atlantoaxial hyperflexion

Traumatic atlantoaxial hyperflexion is considered rare in cats, and only a few case reports have been published. There are other conditions that can result in a peracute onset of neurological signs localized to the cervical spinal cord segments, including acute noncompressive nucleus pulposus extrusion, ischemic myelopathy, or vertebral fractures. Appropriate treatment for these conditions can only be initiated after an accurate diagnosis has been obtained. The aim of this observational, retrospective, single-center, descriptive case series study was to describe the clinical presentation, imaging characteristics, and short-term outcome of eight cats presented with suspected traumatic atlantoaxial hyperflexion. Young male healthy domestic shorthair cats were overrepresented (7/8) and typically presented with a peracute, nonprogressive, nonpainful, nonlateralizing C1-C5 myelopathy (tetraplegia or nonambulatory tetraparesis) following a road traffic accident or head trauma. All MRI studies demonstrated a solitary, focal, ill-defined intramedullary lesion immediately dorsal to the dens of the axis, affecting both grey and white matter. All cats were treated medically. In 50% of the cats, the neurological grade improved at discharge or short-term follow-up, 25% of the cats recovered completely, one cat was static at short-term follow-up, and one cat was euthanized due to persistent forebrain signs and lack of neurological improvement.

Craniocervical Morphometry in Pomeranians-Part II: Associations with Chiari-like Malformation and Syringomyelia

BACKGROUND

The aim of Part II of this two-part study is to describe and analyze the association of various aspects and measurements related to the morphometry of the skull and craniocervical region to CM/SM status of Pomeranians, by means of computed tomography (CT) and magnetic resonance imaging (MRI).

METHODS

Prospectively, Pomeranians were included that underwent both CT and MRI studies of the head and cervicothoracic vertebral column. For those cases where qualitative classifications differed between observers, the experienced observer re-evaluated the studies and decided on a final classification that was used for further analysis. For quantitative measurements, the means of the observers' measurements were used for analysis.

RESULTS

Among statistically significant differences in measurements, we found that dogs with SM had a significantly shorter clivus length based on both MRI (p = 0.01) and CT measurements (p = 0.01), and a significantly smaller caudal cranial fossa area based on both MRI (p = 0.02) and CT measurements (p = 0.02).

CONCLUSIONS

Significant morphometrical differences were identified between dogs with or without CM/SM. The findings in this study add to those already described in other breeds and provide further insight into factors that may play a role in the pathogenesis of CM/SM in Pomeranians.

Craniocervical Morphometry in Pomeranians-Part I: Intra-Observer, Interobserver, and Intermodality (CT vs. MRI) Agreement

BACKGROUND

Currently, there are no diagnostic imaging-based studies that have focused specifically on the craniocervical morphology of Pomeranian dogs in relation to Chiari-like malformation and syringomyelia (CM/SM). The aims of Part I of this two-part study are to assess the intra-observer, interobserver, and intermodality reliability and agreement for various aspects of the craniocervical morphology of Pomeranians with and without CM/SM.

METHODS

Prospectively, Pomeranians were included that underwent both CT and MRI studies of the head and cervicothoracic vertebral column. Two observers (experienced and novice) independently performed CM and SM classifications, qualitative assessments, and quantitative measurements. The experienced observer performed these assessments twice. A third observer (experienced) performed CM and SM normal or abnormal classifications.

RESULTS

Ninety-nine (99) dogs were included. Interobserver reliability was influenced by observer experience level. For the experienced versus novice observers, substantial interobserver agreement was found for classification of SM as normal or abnormal (Cohen's kappa = 0.63), while interobserver agreement was fair for classification of SM as normal or abnormal (Cohen's kappa = 0.31). Interobserver, intra-observer, and intermodality reliability were variable for different measurements and assessments, and best overall for the CT-based measurements.

CONCLUSIONS

Interobserver reliability and agreement results should be taken into account in the evaluation of results of future studies as well as the evaluation of imaging studies of Pomeranians presented clinically.

Three-dimensional kinematics of the craniocervical junction of Cavalier King Charles Spaniels compared to Chihuahuas and Labrador retrievers

Our knowledge about the underlying pathomechanisms of craniocervical junction abnormalities (CCJA) in dogs mostly derives from measurements based on tomographic imaging. These images are static and the positioning of the dogs' head does not reflect the physiological in vivo position of the craniocervical junction (CCJ). Aberrant motion patterns and ranges of motion (ROM) in sound individuals of CCJA predisposed breeds may be a pathogenetic trigger. To further extend our limited knowledge of physiological motion of the CCJ, this prospective, comparative study investigates the in vivo motion patterns and ROM of the CCJ in walk and trot in sound Cavalier King Charles Spaniels and Chihuahuas. The Labrador retriever is used as a reference breed without predisposition for CCJA. This is the first detailed description of CCJ movement of trotting dogs. Biplanar fluoroscopy images, recorded in walking and trotting dogs, were matched to a virtual reconstruction of the skull and cranial cervical spine utilising Scientific Rotoscoping. Kinematic data reveal the same motion patterns among all breeds and gaits with individual temporal and spatial differences in each dog. A stride cycle-dependent lateral rotation of the cranial cervical spine and axial rotation of the atlantoaxial joint in trot in dogs is described for the first time. The ROM of the atlantoaxial and atlantooccipital joints in walk and trot were not statistically significantly greater in the CCJA-predisposed breeds CKCS and Chihuahua. ROM values of all translational and rotational degrees of freedom were larger in walk than trot, although this is only statistically significant for the atlantoaxial joint. Until proven otherwise, a more species-specific than breed-specific general motion pattern of the CCJ in walking and trotting, clinically sound dogs must be assumed. Species-specific anatomic properties of the CCJ seem to supersede breed-specific anatomical differences in clinically sound dogs.

Novel transforaminal approach allows surgical decompression of an atlantoaxial band in dogs: a cadaveric study and clinical cases

OBJECTIVES

To describe a novel transforaminal approach for surgical excision of the atlantoaxial (AA) band and examine its feasibility, safety, and mechanical advantages in an ex vivo study and clinical cases.

SAMPLES

26 canine cadavers and 2 canine patients with AA bands.

PROCEDURES

The transforaminal approach via the first intervertebral foramen was designed to avoid damaging the dorsal AA ligament (DAAL) and dorsal laminas to maintain joint stability. The cadaveric study started on December 2020 and lasted 3 months. The ligamentum flavum (LF) was removed using a novel approach; then, gross examination was conducted to verify the potential damage to the spinal cord and associated structures and the adequacy of LF removal. Subsequently, the ex vivo tension test of the DAAL was conducted to establish whether the approach induced mechanical damage to the ligaments. Finally, 2 dogs diagnosed with an AA band were surgically treated with the transforaminal approach.

RESULTS

In the cadaveric study, postsurgical evaluation verified the subtotal removal of LF without damage to the dura mater. There were no significant differences in the mechanical properties of the DAAL, including the ultimate strength (P = .645) and displacement (P = .855), between the surgical and intact groups during the ex vivo tension test. In clinical cases, clinical signs and neurologic grades improved until the final follow-up.

CLINICAL RELEVANCE

The described surgical procedure using a transforaminal approach appears to sufficiently permit the removal of an AA band while reducing damage to the DAAL and spinal cord. Our study highlights the feasibility of the transforaminal approach.

Accuracy of a patient-specific 3D-printed drill guide for placement of bicortical screws in atlantoaxial ventral stabilization in dogs

Atlantoaxial instability (AAI) in dogs refers to abnormal motion at the C1–C2 articulation due to congenital or developmental anomalies. Surgical treatment options for AAI include dorsal and ventral stabilization techniques. Ventral stabilization techniques commonly utilize transarticular and vertebral body screws or pins. However, accurate screw insertion into the vertebrae of C1 and C2 is difficult because of the narrow safety corridors. This study included 10 mixed dogs, 1 Pomeranian, and 1 Shih-Tzu cadaver. All dogs weighed <10 kg. Each specimen was scanned using computed tomography (CT) from the head to the 7th cervical vertebrae. This study used 12 bone models and 6 patient-specific drill guides. Bone models were made using CT images and drill guides were created through a CAD (computer-aided design) program. A total of six cortical screws were used for each specimen. Two screws were placed at each of the C1, C2 cranial, and C2 caudal positions. Postoperative CT images of the cervical region were obtained. The degree of cortex breaching and angle and bicortical status of each screw was evaluated. The number of screws that did not penetrate the vertebral canal was higher in the guided group (33/36, 92%) than in the control group (20/36, 56%) (P = 0.003). The screw angles were more similar to the reference angle compared to the control group. The number of bicortically applied screws in the control group was 28/36 (78%) compared to 34/36 (94%) in the guided group. Differences between the preoperative plan and the length of the applied screw at the C1 and C2 caudal positions were determined by comparing the screw lengths in the guide group. The study results demonstrated that the use of a patient-specific 3D-printed drill guide for AAI ventral stabilization can improve the accuracy of the surgery. The use of rehearsal using bone models and a drilling guide may improve screw insertion accuracy.

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.

Morphometric Magnetic Resonance Imaging Evaluation of Cervical Spinal Canal and Cord in Normal Small-Breed Dogs

Cervical spinal disease is one of the most common neurological disorders in small-breed dogs. Magnetic resonance imaging (MRI) is a common test for dogs with cervical spinal diseases. However, there is no information on cervical spinal canal and cord using MRI in normal small-breed dogs. Therefore, this study aimed to perform analyses to establish morphologic MRI reference ranges of the cervical spinal canal and cord in normal small-breed dogs. Cervical MRI examinations were taken in 20 client-owned small dogs. The height, width, and cross-sectional area (CSA) of the spinal canal and cord were measured on sagittal and transverse T2-weighted images at each vertebral body level and each intervertebral disk level from C1-C2 to C7 (a total of 12 levels). The height ratio, the width ratio, and the CSA ratio were calculated. The height, width, and CSA of the spinal canal and cord increased as the dog's weight increased (p < 0.01), except for that at C1-C2. However, there was no correlation between the body weight and height ratio and the width ratio and CSA ratio at all levels, except for that at C1-C2. Also, there was a negative correlation between the body weight and CSA ratio at C1-C2. There were no statistical differences for the CSA of the spinal canal, the CSA of the spinal cord, and the CSA ratio between nearby levels, except for that at C1-C2. There was no statistical difference between measurements at each same level of the sagittal and transverse images. The results of this study may provide basic and morphometric information for diagnosing and researching cervical spinal diseases in small-breed dogs.

Three-Dimensional Kinematic Motion of the Craniocervical Junction of Chihuahuas and Labrador Retrievers

All vertebrate species have a distinct morphology and movement pattern, which reflect the adaption of the animal to its habitat. Yet, our knowledge of motion patterns of the craniocervical junction of dogs is very limited. The aim of this prospective study is to perform a detailed analysis and description of three-dimensional craniocervical motion during locomotion in clinically sound Chihuahuas and Labrador retrievers. This study presents the first in vivo recorded motions of the craniocervical junction of clinically sound Chihuahuas (n = 8) and clinically sound Labrador retrievers (n = 3) using biplanar fluoroscopy. Scientific rotoscoping was used to reconstruct three-dimensional kinematics during locomotion. The same basic motion patterns were found in Chihuahuas and Labrador retrievers during walking. Sagittal, lateral, and axial rotation could be observed in both the atlantoaxial and the atlantooccipital joints during head motion and locomotion. Lateral and axial rotation occurred as a coupled motion pattern. The amplitudes of axial and lateral rotation of the total upper cervical motion and the atlantoaxial joint were higher in Labrador retrievers than in Chihuahuas. The range of motion (ROM) maxima were 20°, 26°, and 24° in the sagittal, lateral, and axial planes, respectively, of the atlantoaxial joint. ROM maxima of 30°, 16°, and 18° in the sagittal, lateral, and axial planes, respectively, were found at the atlantooccipital joint. The average absolute sagittal rotation of the atlas was slightly higher in Chihuahuas (between 9.1 ± 6.8° and 18.7 ± 9.9°) as compared with that of Labrador retrievers (between 5.7 ± 4.6° and 14.5 ± 2.6°), which corresponds to the more acute angle of the atlas in Chihuahuas. Individual differences for example, varying in amplitude or time of occurrence are reported.

Verminous myelopathy secondary to aberrant Dirofilaria immitis migrans was detected in the cervical subarachnoid space of four dogs using MRI and CT

Aberrant Dirofilaria immitis migrans is a rare cause of neurologic signs in dogs, however, published studies describing the computed tomographic (CT) and magnetic resonance imaging (MRI) characteristics of this problem are currently lacking. The objective of this retrospective case series study was to describe the clinical and imaging findings for four adult dogs with verminous myelopathy due to aberrant Dirofilaria immitis migrans within the cervical subarachnoid space. All dogs were toy breeds, were heartworm antigen positive, had neurologic signs (ranging from cervical hyperesthesia to tetraparesis), and similar MRI findings. In two patients additionally imaged with CT, findings were variable. On MRI, each dog had a single large, dorsal- to laterally located, intradural-extramedullary, fusiform mass with characteristic stippled, mixed T2-weighted and T1-weighted signal intensity, hypo-to-iso T1-weighted signal intensity, and spinal cord compression. Nematodes were identified as serpentine or circular subarachnoid structures with low T2-weighted and T1-weighted signal in the sagittal and transverse image planes, respectively. CT (n = 2 dogs) demonstrated focal regions of mildly enhancing intradural-extramedullary spinal cord compression in 1 dog. Dorsal laminectomy and durotomy were performed in two dogs at C3-C4. A C4-5 hemilaminectomy with durotomy and dural biopsy was performed in one dog. Extraction of live, immature adult, female D. immitis worms was performed in three dogs. Operated dogs had complete post-surgical resolution of clinical signs. One dog was euthanized without surgery; necropsy revealed an adult heartworm in the spinal subarachnoid space at C2. Findings indicated that cervical spinal subarachnoid D. immitis aberrant migration should be considered as a differential diagnosis for dogs with this combination of clinical and CT/MRI imaging findings, and that the prognosis may be good with early detection and surgical removal.

Flexed radiographic angles for determination of atlantoaxial instability in dogs

OBJECTIVE

To determine a flexed position for radiographic diagnosis of atlantoaxial instability (AAI) and to identify radiographic measurement cutoffs to differentiate affected dogs from neurologically healthy toy breeds.

STUDY DESIGN

Retrospective case series and prospective case controls.

ANIMALS

Thirty-nine client-owned toy breed dogs in which AAI had been diagnosed and 20 neurologically healthy client-owned toy breed dogs.

METHODS

Medical records from three institutions were retrospectively reviewed to identify dogs affected with AAI. Flexed lateral images were reviewed, and measurements were obtained by using anatomic landmarks. Radiography was performed with control dogs to obtain the same measurements.

RESULTS

Flexed lateral radiographs of thirty dogs affected with AAI were found to be positioned at a mean of 51° flexion. When flexed lateral radiographs were evaluated with a cutoff value for atlas to axis angle (AAA) >10°, evaluation of all breeds represented revealed a 90% sensitivity and 90% specificity. When this cutoff was evaluated in Yorkshire terriers, Chihuahuas, and mixes of these breeds, the sensitivity was 92%, and the specificity was 92%. When the control sample was positioned at 51° ± 10°, only two of the dogs were within the AAA cutoff value of >10°. There was no difference between the measurements obtained by using the flexed lateral view (mean = 50.9°) and the exaggerated flexed lateral view (mean = 38.9°) in the control sample.

CONCLUSION

This study established objective measurements for the positioning and diagnosis of AAI on flexed lateral radiographs in toy breed dogs.

CLINICAL SIGNIFICANCE

Atlantoaxial instability can be objectively diagnosed in sedated or anesthetized toy breed dogs when applying 51° flexion to cervical radiographs.