Facial changes related to brachycephaly in Cavalier King Charles Spaniels with Chiari‐like malformation associated pain and secondary syringomyelia

Abstract Background Recent studies including an innovative machine learning technique indicated Chiari‐like malformation (CM) is influenced by brachycephalic features. Objectives Morphometric analysis of facial anatomy and dysmorphia in CM‐associated pain (CM‐P) and syringomyelia (SM) in the Cavalier King Charles Spaniel (CKCS). Animals Sixty‐six client‐owned CKCS. Methods Retrospective study of anonymized T2W sagittal magnetic resonance imaging of 3 clinical groups: (1) 11 without central canal dilation (ccd) or SM (CM‐N), (2) 15 with CM‐P with no SM or <2 mm ccd (CM‐P), and (3) 40 with syrinx width ≥4 mm (SM‐S). Morphometric analysis assessed rostral skull flattening and position of the hard and soft palate relative to the cranial base in each clinical group and compared CKCS with and without SM‐S. Results Sixteen of 28 measured variables were associated to SM‐S compared to CM‐N and CM‐P. Of these 6 were common to both groups. Predictive variables determined by discriminant analysis were (1) the ratio of cranial height with cranial length (P < .001 between SM‐S and CM‐N) and (2) the distance between the cerebrum and the frontal bone (P < .001 between SM‐S and CM‐P). CM‐P had the lowest mean height of the maxillary area. Conclusions and Clinical Importance CKCS with CM‐P and SM‐S have cranial brachycephaly with osseous insufficiency in the skull with rostral flattening and increased proximity of the hard and soft palate to the cranial base. Changes are greatest with CM‐P. These findings have relevance for understanding disease pathogenesis and for selection of head conformation for breeding purposes.