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

CASE SUMMARY A 10-year-old cat presented 5 days after a traumatic event with acute recumbency followed by some clinical improvement. The neuroanatomical localisation was the C1-C5 spinal cord segments. Initial survey radiographs, including lateral flexed views, showed no convincing abnormalities. Magnetic resonance imaging (MRI) revealed a marked focal intramedullary lesion at the level of the dens and suspected oedema extending over C2-C3 vertebrae, suggesting early syrinx formation. The cat made an initial excellent recovery on restricted exercise without medical treatment. The MRI changes largely resolved on follow-up MRI 4 weeks later yet recurred following a relapse 4 months later. At this stage, a post-traumatic syrinx had developed. Moreover, the suspected atlantoaxial instability was finally diagnosed on radiography with fully flexed lateral views. A hyperflexion injury causing tearing of the atlantoaxial ligaments was considered most likely given the lack of malformations or fractures. The cat made a full recovery on conservative management. RELEVANCE AND NOVEL INFORMATION This is the first report of sequential MRI findings in a cat with atlantoaxial instability. Moreover, post-traumatic syringomyelia formation following atlantoaxial injury has not been reported. Sequential MRI aids in the diagnosis of hyperflexion injury if survey radiographs fail to identify atlantoaxial instability.