Case of the month August 2006 Cavalier King Charles Spaniel, m, 3.5 y

Episodes of suddenly occurring onsets of forelimb and/or hind limb lameness. During episodes crying out of pain. Frequency of episodes increasing. Scratches his head. History Dog was referred to the Neurology division of the Vetsuisse Faculty Berne because of

Results of neurologic examination Manipulation of neck leads to withdrawal of right forelimb; biting into paw; similar reactions of hind limbs Paraesthesia Head scratching, episodes of agitation, then suddenly back to normal All reflexes normal Localisation Brainstem, medulla oblongata, cervical spine, inner ear

FSE T2 transverse dorsal right Level of middle ear right Normal for comparison dorsal Level of middle ear (M) MM MRI of head and neck

Plain dorsal right Level of middle ear MRI of head and neck right Contrast enhanced dorsal Level of middle ear FE 3D T1 transverse

T2 mid sagittal dorsal rostral MRI of head and neck C cerebellum, arrows: second cervical vertebra C

Findings ?

Both middle ears („bullae“) are filled with hyperintense material in T2 (arrows; compare with normal) and T1. Neither the material nor the epithelial lining of the bullae takes up contrast.

A small part of the cerebellum is herniated caudally to the dorsal border of the foramen magnum (arrow); the most cranial part of the spinal cord is incarcerated between the dens axis (D) and the dorsal foramen magnum. The spinal cord shows a severely widened and deformed central canal (arrowheads). D Findings

Summary Fluid filled middle ears on both sides without signs of acute middle ear inflammation. Cerebellar herniation caudally through the foramen magnum, incarceration of the most cranial spinal cord and severe hydrosyringomyelia (dilatation of the central canal) of the cervical spinal cord. Interpretation These findings are consistent with Chiari malformation type 1.

Arnold Chiari malformations are developmental disorders which are overrepresented in Cavalier King Charles Spaniels. They can be clinically silent or cause severe neurological deficits. Their main feature is the caudal displacement of the cerebellum, resulting in „crowding“ of the foramen magnum and disruption of normal cerebrospinal fluid (CSF)-flow leading to hydrosyringomyelia. Associated are increased intracranial pressure and malformation of the foramen magnum. Fluid filled middle ears are common findings in this breed, but not related to the Arnold Chiari malformation. Comment

For this condition a hereditary component is suspected, and dogs with that malformation should be excluded from breeding. MRI provides a safe and non-invasive method for in vivo diagnosis of this disorder. Further information on this condition is available on: Comment or contact