Cerda-Gonzalez S, Olby NJ, Griffith EH.
BACKGROUND: Dorsal compressive lesions at the atlantoaxial junction (ie, AA bands) occur in dogs with Chiari-like malformations (CMs), but their clinical relevance is unclear. OBJECTIVE: Investigate the influence of AA bands on clinical status and syringomyelia (SM) in mature cavalier King Charles spaniels (CKCS). ANIMALS: Thirty-six CKCS, 5-12 years of age, including 20 dogs with neuropathic pain. METHODS: Dogs were examined and assigned a neurologic grade. Magnetic resonance imaging (MRI) of the craniocervical junction was performed with the craniocervical junction extended and flexed (ie, normal standing position). Imaging studies were assessed for the presence of an AA band, CM, SM or some combination of these findings. Band and SM severity were quantified using an objective compression index and ordinal grading scale, respectively. RESULTS: Of 36 CKCS imaged, 34 had CM. Atlantoaxial bands were present in 31 dogs and were more prominent in extended than flexed positions. Syringomyelia was found in 26 dogs, 23 of which also had AA bands. Bands were associated with both the presence (P = .0031) and severity (P = .008) of clinical signs and SM (P = .0147, P = .0311, respectively). Higher compression indices were associated with more severe SM (P = .0137). CONCLUSIONS: Prevalence of AA bands in older CKCS is high. Positioning of dogs in extension during MRI enhances the sensitivity of the study for detecting this important abnormality. There were significant associations among AA bands, clinical signs, and SM in dogs with CM; additional work is needed to understand whether or not this relationship is causal.