Occipital dysplasia is a congenital malformation of the foramen magnum causing failure of complete ossification of the supraoccipital bone. The bone is replaced by a membranous band of tissue. The foramen magnum is "keyhole shaped" and abnormally large. Occipital dysplasia does not typically result in compression of the cerebellum because the caudal fossa remains unchanged, but it does result in a decreased volume of the caudal fossa, resulting in syringohydromyelia.
The disorder affects small-breed dogs (Yorkshire Terrier, Cavalier King Charles Spaniel, Toy Poodle, Pomeranian, Pekingese, Chihuahua), a though there are reports in medium breed dogs, like Beagle and Cocker Spaniel. The diagnosis is made by clinical and radiographic findings. Signs include generalized ataxia and occasional neck scratching. Surgical removal of the tissue band have been effective in improvement of clinical signs related to ataxia and cerebellovestibular disease.
- A Practical Guide to Canine and Feline Neurology. edited by Curtis W. Dewey
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- Concurrent occipital hypoplasia, occipital dysplasia, syringohydromyelia, and hydrocephalus in a Yorkshire terrier. Can Vet J. 2010 Aug; 51(8): 904–908.