A case of foramen magnum syndrome caused by atlanto-occipital assimilation with intracanal fibrosis.

We describe a case of foramen magnum syndrome secondary to atlanto-occipital assimilation with spinal-cord compression caused by retro-odontoid fibrous pannus. Association of atlanto-occipital assimilation with the occurrence of severe neurological symptoms resulting from upper spinal cord compression remains rare in the literature. The embryonic process leading to this malformation is discussed. The anatomy and pathogenesis of this syndrome are described.