Neurological Signs and MRI Findings of Caudal Occipital Malformation Syndrome in Dogs

Abstract

Caudal occipital malformation syndrome (COMS) in dogs is a disorder similar to human Chiari type-1 malformation. With increased availability of magnetic resonance imaging (MRI), COMS has come to be recognized as an increasingly prevalent condition in dogs. We made a retrospective study of 30 dogs in which COMS was diagnosed by MRI in order to identify the clinical signs and neurological findings, and elucidate their relationship to the MRI results. The most frequent clinical signs and neurological findings were seizures, vestibular syndrome, and depressed postural reactions. MRI disclosed herniation of the cerebellum compatible with a Chiari type-1 malformation, attenuation or obliteration of the dorsal subarachnoid space at the cervicomedullary junction, and rostral displacement of the caudal cerebellum by the occipital bone. In some dogs, a "kinked" appearance of the caudal medulla, hydrocephalus or enlarged lateral ventricle, and syringohydromyelia were also noted. The clinical signs and neurological findings showed no correlation with the MRI results. In dogs, therefore, MRI is necessary for diagnosing COMS and leading to a plan for management and treatment of the syndrome.