Syringomyelia Awareness: What is Chiari Malformation?

A Chiari Malformation (CM) occurs at the craniocervical junction. This is where the skull and the top of the spine meet. At the bottom of the skull, there is a large hole called the foramen magnum. The foramen magnum allows the brainstem to exit the skull and become the spinal cord. When the lower lobe of the brain, the cerebellum, is displaced to the level of the foramen magnum (mild CM) or through the foramen magnum (severe CM) there is overcrowding in the foramen magnum. This causes obstruction of the normal flow of CSF from the brain down to the spinal cord. Many dogs with CM develop syringomyelia (SM). Syringomyelia is a condition where cavities, or holes, called a syrinx, develop within the spinal cord.

The spinal cord is made up of grey and white matter. Using a computer network as an analogy, the grey matter can be thought of as the actual computer, whereas the white matter represents the network cables connecting the computers together.

In a study by Dr. Clare Rusbridge et al, they found that pain is related to syrinx width and symmetry. Dogs with a wider, asymmetrical syrinx are more likely to experience pain, and dogs with a small, narrow syrinx may be asymptomatic.

Ventral Horn Damage – Syrinxes that damage the ventral horn, may result in neurological deficits such as decreased spinal reflexes, muscle atrophy and limb weakness.

Dorsal Horn Damage – Syrinxes that damage the dorsal horn of the grey matter are most likely to cause persistent pain. Dr. Clare Rusbridge also found that the larger the width of the syrinx, the more likely it was that the dog would exhibit pain and scratching behaviour.

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  1. Hi Felissa. Just want note, this article is written by Karen Kennedy a Canadian Radiologist. She has written a few articles regarding MRI imaging.

  2. Karen's article , although excellent was written a few years ago and research has moved understanding of the condition on. Basically it is a mis-match between the skull which is too small and the brain which is too large…. The BVA/KC leaflet that was given out at Crufts Dog show last years and also refers to the screening scheme for breeders (all breeds) can be found at

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