As SM progresses, the supraoccipial bone resorbs
In a November 2012 UK study by a team of veteran CM/SM researchers of 12 cavalier King Charles spaniels with Chiari-like malformation, they found that all of these conditions increased over time: syrinx width, height of the foramen magnum, length of cerebellar herniation, and caudal cranial fossa volume. The increase in the volume of the cranial fossa may be due to resorption of the supraoccipital bone as syringomyelia progresses. They conclude: "We hypothesise that active resorption of the supraoccipital bone occurs due to pressure from the cerebellum. These findings have important implications for our understanding of the pathogenesis and variable natural clinical progression of CM and syringomyelia in CKCS."
Details at http://bit.ly/10teTKs