Magnetic Resonance Imaging of the Ligamentous Structures of the Occipitoatlantoaxial Region in the Dog

Abstract

Our objectives were to establish a magnetic resonance (MR) protocol for the examination of, and then describe, the normal ligaments and the supporting structures of the occipitoatlantoaxial region. This was done in 10 cadaver dogs. In addition, MR images of three patients with cervical pain localized to the occipitoatlantoaxial region are included to provide examples of ligamentous abnormalities. All ligaments were hypointense in all pulse sequences. The apical, dorsal atlantoaxial, and dorsal longitudinal vertebral ligaments were seen best in the sagittal T1W and PD-weighted images. The transverse ligament was best visualized in the transverse plane in all pulse sequences and appeared to be confluent with the dorsal longitudinal vertebral ligament dorsal to the dens in the sagittal plane. A 20° dorsal plane reconstructed image in 0.6-mm slice thickness was necessary to visualize the alar ligaments, which were visible in 9/10 dogs. The dorsal longitudinal vertebral ligament appeared continuous with the apical ligament and tectorial membrane. Abnormalities in clinically affected dogs included thickening of the alar ligaments, absence of transverse ligament and elongation, and irregularity of the apical ligament.

Traumatic spinal cord injury caused by suspected hyperflexion of the atlantoaxial joint in a 10-year-old cat

“…12 All ligaments were identified on MRI in dogs but not reported in cats. 12 In our cat, the apical and transverse ligament appeared intact, yet the alar ligament could not be convincingly identified.…”

“…12 All ligaments were identified on MRI in dogs but not reported in cats. 12 In our cat, the apical and transverse ligament appeared intact, yet the alar ligament could not be convincingly identified. A ligament abnormality such as a rupture or tear could not be convincingly identified in our cat, which might be influenced by the lack of specific sequences such as proton density.…”

“…Case studies in dogs with atlantoaxial instability do not report such a focal lesion with ring enhancement, nor post-traumatic syringomyelia as such. 9–12 One study found syringomyelia associated with atlantoaxial instability in two dogs, yet both were associated with enlarged ventricles and one was also associated with the caudal occipital malformation syndrome, suggesting the syrinx might be unrelated to the atlantoaxial instability. 9 Nonetheless, a review article stated that this phenomenon has not been described in veterinary literature, yet reported from the author’s own experience that over time disturbances in cerebrospinal fluid flow at the site of the spinal cord injury can result in the development of syringomyelia.…”

“…A ligament abnormality such as a rupture or tear could not be convincingly identified in our cat, which might be influenced by the lack of specific sequences such as proton density. 12 Owing to the risk of spinal cord injury, collection of cerebrospinal fluid from the cerebellomedullary cistern is contraindicated in cervical spinal instability, yet was performed in this cat as instability was initially not identified and to obtain a sample close to the lesion. The lack of deterioration following cerebellomedullary cistern sampling may support a tearing of the ligamentous structures over a rupture.…”

Computed tomography, magnetic resonance imaging and a novel surgical approach of atlanto-axial instability with incongruence in dogs

“…Irrespective of the aetiopathogenesis, AA instability causes acute and/or chronic spinal cord compression [1,2]. Secondary lesions typically develop in affected individuals including spinal cord compression, contusions or haemorrhage which can predispose to hydromyelia, focal or diffuse syringohydromyelia and gliosis [9,15,17,26]. The principal radiographic sign of AA subluxation is enlargement of the space between the tip of the spinous process of the axis and the dorsal arch of the atlas [26] on laterolateral radiography.…”