Occipital fibrous dysplasia tonsillar herniation and cervical syringomyelia.

A small posterior fossa volume has been thought to lead to hind brain herniation. The resultant obstruction to the CSF pathways at the level of the foraman magnum has been implicated in the development and subsequent progression of syringomyelia. This report highlights the gradual development of a small posterior fossa due to fibrous dysplasia of the occipital bone with consequent tonsillar herniation resulting in syringomyelia.