Atlanto-occipital fusion and ataxia in the calf.

Atlanto-occipital fusion is a rare bony anomaly due to the failure of the developing arches of the first cervical vertebra to separate from the occiput. It may be associated with compressive myelopathy and must therefore be considered in the differential diagnosis of ataxia in the young animal. This report reviews the embryological development of the region and reports the findings in two cases of fusion in the calf.