Chiari-like malformation and syringomyelia in Pomeranian dogs

This PhD thesis includes five studies resulting in six publications, each contributing to the understanding of Chiari-like malformation (CM) and syringomyelia (SM) in Pomeranian dogs, and by extension, in dogs in general. The first publication, Phenotypic characterization of Pomeranians with or without Chiari-like malformation and syringomyelia, describes owner-reported clinical signs and their association with CM/SM. Signs such as phantom scratching, vocalization, head shaking, spontaneous pain, air licking, and scratching or rubbing the head and ears were linked to these conditions. Signalment factors—age, body weight, country of origin, and having a pedigree—were also associated with CM and/or SM. These findings may help owners, breeders, and veterinarians identify at-risk dogs and recommend MRI for diagnosis. The second study, Longitudinal assessment of syringomyelia in Pomeranians, examined how SM progressed over time in affected dogs. A general trend of SM worsening or cavity enlargement was observed, which is important for future studies evaluating treatment efficacy, whether medical or surgical. The third study led to two publications: Craniocervical morphometry in Pomeranians Part I: Intra-observer, interobserver, and intermodality (CT vs. MRI) agreement and Part II: Associations with Chiari-like malformation and syringomyelia. These examined measurement consistency between observers and the anatomical differences linked to CM/SM. Observer agreement was higher for SM than for CM, particularly among experienced versus novice observers, highlighting the subjectivity in CM diagnosis. Morphometric differences, such as shorter clivus length and smaller caudal cranial fossa area, were significantly associated with SM. These anatomical traits enhance our understanding of the disorders’ pathophysiology. The fifth publication, CT-based and manual external skull measurements for Chiari-like malformation and syringomyelia in Pomeranians, compared CT-based morphometric features with manual external skull measurements using tape measures and calipers. A key finding was that a shorter mandible significantly increased the odds of a dog having SM. This is a clinically accessible tool to help identify at-risk dogs when combined with other signs and signalment data. However, it is emphasized that this should not replace MRI as the diagnostic gold standard. The final publication, CT- and MRI-based volumetry for Chiari-like malformation and syringomyelia in Pomeranians, explored volumetric differences in the skull and brain. Dogs with SM had smaller ventricular system and caudal cranial fossa volumes, and these could help predict SM status. Other volume differences—such as in the brain, skull, and cervical vertebral column—were also seen, but many were influenced by the dog’s overall body size. Dogs with SM tended to weigh less than unaffected dogs. No volumetric parameters were significantly associated with CM, reinforcing its classification as a complex, variably interpreted malformation. Together, the studies in this thesis have substantially advanced the knowledge of CM and SM in Pomeranians. They provide insight into clinical signs, disease progression, observer variability, and anatomical features associated with these disorders. Future research may build on these findings to improve diagnostic methods, evaluate treatments, identify genetic risk factors, and ultimately enhance welfare for affected dogs.