Syringomyelia is the development of one or more fluid-filled cavities within the spinal cord. Hydromyelia is the accumulation of fluid within an enlarged central canal of the spinal cord. Since it is often difficult to differentiate between syringomyelia and hydromyelia, the term syringohydromyelia was created and is often used.
Syringohydromyelia causes progressive ataxia (loss of muscle coordination), paresis partial motor paralysis), scoliosis (curvature of the spine), and spinal pain as a possible end result. Causes can include trauma, neoplasiation) inflammatory conditions, and developmental malformations. The most common is Chiari I malformation, which exists when there is an underdeveloped occipital bone that induces overcrowding of the caudal fossa. This condition interferes with the circulation of spinal fluid and can result in hydrocephalus and/or syringohydromyelia of the cervical spinal segments.
Syringohydromyelia associated with Chiari I malformation is most common in small-breed dogs, especially Cavalier King Charles Spaniels and any age dog can be affected. Signs consist of ataxia and tetraparesis (muscular weakness in all four limbs), neck pain, and persistent scratching at the base of the head or shoulder. Radiography and myelography exams are usually normal but an MRI can identify the cavitation in the spinal cord and any caudal fossa malformations that exist. Treatment is directed at the underlying cause whenever possible. Symptoms may improve by administering corticosteroids (prednisone at 1 mg/kg, sid). Surgery to decompress the caudal fossa also can be helpful for Chiari I malformations.