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

LocalisationBrainstem, 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

?

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: http://www.ivis.org/advances/Vite/braund16/chapter.asp?LA=1

Comment

or contact martin.konar@kkh.unibe.ch