Table 1.

Classification of dogs based on MRI evaluations and owner-reported clinical signs.

CM classification
CM normal	No cerebellar herniation or impaction (cerebellar uvula rostral to foramen magnum)
CM abnormal	CM abnormal 1: cerebellar impaction (cerebellar uvula on the line of the foramen magnum, no CSF present dorsal to the cervicomedullary junction) and non-rounded shape (e.g., flattened, pointed or indented by supraoccipital bone). CM abnormal 2: cerebellar herniation (cerebellar uvula caudal to the line of the foramen magnum, no CSF present dorsal to the cervicomedullary junction) and non-rounded shape (e.g., pointed or indented by supraoccipital bone). The line of the foramen magnum was defined as a straight line between the most ventral aspect of the supraoccipital bone and the most caudal aspect of the basioccipital bone on sagittal MR images (23).
SM classification
SM normal	No SM
SM abnormal	SM abnormal 1: symmetric (i.e. circular, round syrinx). SM abnormal 2: asymmetric (e.g., extending into a dorsal horn). Localization: cervical, thoracic, extensive (both cervical and thoracic, continuous), or multifocal (both cervical and thoracic, discontinuous). For extensive and multifocal localizations, the most severely affected location (cervical or thoracic) was noted (C:x–T:x) based on max. SHRs.
ORCS classification
Without ORCS	No ORCS
With ORCS	ORCS present

CM, Chiari-like malformation; CSF, cerebrospinal fluid; SM, syringomyelia; ORCS, owner-reported clinical signs; max. SCSAR, maximum syrinx cross-sectional area:spinal cord cross-sectional area ratio.