That's according to a research sample of clinically affected, scanned cavaliers in the new research paper out from Clare Rusbridge et al. This is the same one Rod notes in an earlier thread about 76% of these dogs also had further syrinxes lower than the C5 vertebrae (and thus dogs with syrinxes are likely to be worse than a mini scan will show).
Abstract below, but this excerpt from the paper interested me as it suggests a hitherto unexpectedly large number of dogs with clinical signs of SM (all dogs in the study had clinical signs)-- one in four!!! -- have CM only -- which suggests people with such dogs really need to be treating it AS WITH SM, not attributing the problem to some other likely cause (something vets also need to recognise):
The median age of the dogs included in the study was 5 years (1.2–10.8 years). CM was present in all patients. None of the dogs showed compressive craniocervical pathology other than CM. There was no evidence of SM on MRI in 12/49 (25%) dogs. In all dogs with MRI evidence of SM (37/49; 75%), SM was present within the C1–C4 region (Figs. 2 and 3). Of those dogs with SM within C1– C4 region, 76% (28/37) also had SM within the C5–T1 and/ or T2–L2 regions, but only 49% (18/37) had SM within the L3–L7 region.Abstract
Chiari-like malformation (CM) and syringomyelia (SM) is an important disease complex in the Cavalier King Charles Spaniel (CKCS) but data about the anatomical distribution of SM along the spinal cord are lacking in veterinary medicine. The objective of this study was to define the anatomic distribution of SM in CKCS clinically affected by CM/SM. Magnetic resonance imaging (MRI) of the brain and the entire spinal cord of 49 dogs was performed and different morphological parameters compared.
Syrinx formation was present in the C1–C4 region and in other parts of the spinal cord. The maximal dorsoventral syrinx size can occur in any region of the spinal cord and the total syrinx size was positively correlated with age. Seventy-six per cent of CKCS with a cranial cervical syrinx also have a syrinx affect- ing more caudal spinal cord regions. MRI restricted to the cervical region may underestimate the extent of SM and the severity of the disease process in the majority of dogs.