Abstract
Previous research in Cavalier King Charles Spaniels (CKCS) has found that Chiari-like malformation and syringomyelia (CM/SM) are associated with a volume mismatch between the caudal cranial fossa (CCF) and the brain parenchyma contained within. The objectives of this study were to i) compare cerebellar volume in CKCS (a “high risk’ group which frequently develops CM/SM), small breed dogs (medium risk – occasionally develop CM/SM), and Labradors (low risk – CM/SM not reported); ii) evaluate a possible association between increased cerebellar volume and CM/SM in CKCS; iii) investigate the relationship between increased cerebellar volume and crowding of the cerebellum in the caudal part of the CCF (i.e. the region of the foramen magnum). Volumes of three-dimensional, magnetic resonance imaging derived models of the CCF and cerebellum were obtained from 75 CKCS, 44 small breed dogs, and 31 Labradors. As SM is thought to be a late onset disease process, two subgroups were formed for comparison: 18 CKCS younger than 2 years with SM (CM/SM group) and 13 CKCS older than 5 years without SM (CM group). Relative cerebellar volume was defined as the volume of the cerebellum divided by the total volume of brain parenchyma. Our results show that the CKCS has a relatively larger cerebellum than small breed dogs and Labradors and provide evidence that increased cerebellar volume in CKCS is associated with crowding of cerebellum in the caudal part of the CCF. In CKCS there is an association between increased cerebellar volume and SM. These findings have implications for the understanding of the pathological mechanisms of CM/SM, and support the hypothesis that it is a multifactorial disease process governed by increased cerebellar volume and failure of the CCF to reach a commensurate size.
Highlights
Chiari-like Malformation (CM) and syringomyelia (SM) is a debilitating and painful disease complex in the Cavalier King Charles Spaniel dog breed (CKCS) which is regarded as a complex oligogenic trait of moderately high heritability [1,2,3,4]
No significant differences were detected between CKCS and other breed groups in Brainstem caudal cranial fossa (CCF) Percentage (CKCS 37.860.3% vs. Small breed dogs (SB) 37.360.8% [p = 1.000] and LD 35.860.6% [p = 0.062]), Brainstem Brain Percentage was significantly larger in CKCS than small breed dogs (CKCS 6.5560.1% vs. SB 5.9460.2% [p = 0.003] and LD 6.5660.2% [p = 1.000])
Our results show that in CKCS the Cerebellum is more crowded in the caudal CCF than in small breed dogs and Labradors, supporting the theory that CM is due to descent and herniation of the cerebellum through the foramen magnum
Summary
Chiari-like Malformation (CM) and syringomyelia (SM) is a debilitating and painful disease complex in the Cavalier King Charles Spaniel dog breed (CKCS) which is regarded as a complex oligogenic trait of moderately high heritability [1,2,3,4]. More than half of CKCS over 4 years of age have SM, fluid filled cavities within the spinal cord (syringes) [8]. CM/SM in the CKCS is commonly associated with pain, especially in the cervical region, and with various neurological dysfunctions such as scoliosis, limb paresis and ataxia [5,11]. Affected dogs might be hypersensitive to touch and often scratch an area on the shoulder, ear, neck or sternum, commonly only on one side of the body and without making skin contact (‘phantom scratching’) [11].
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