Chiari malformations

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MRI of the brain of a 3 year old female Cavalier King Charles Spaniel with syringomyelia (asterisks) that first developed signs of pain at 1.7 years old.[1]

Chiari malformations are a rare genetic neurological disease of dogs[2].

Chiari malformations are complex developmental disorders involving the caudal brainstem, cerebellum and cranial cervical spinal cord, particularly the Cavalier King Charles Spaniel[3], Pekingese[4].

This condition can arise from occipital and foramen magnum dysplasia which leads to cerebellar herniation[5][6] or from odontoid process dysplasia leading to atlantoaxial subluxation[7].

Developmental anomalies within the cranium result in occipital bone hypoplasia leading to caudal fossa overcrowding, obstruction of CSF pathways and secondary hydrosyringomyelia[8].

Trauma superimposed on a pre-existing Chiari type 1 congenital abnormality may play a role in some clinical cases[9].

Clinical signs may include cervical pain, torticollis, spinal hyperesthesia, exercise intolerance, paresis in one or both thoracic limbs or tetraparesis, ataxia/hypermetria in thoracic or in all four limbs, bunny-hopping hindlimb gait, poor hopping responses, and proprioceptive deficits. Spinal reflexes may be exaggerated.

Variable lower motor neuron deficits, such as muscle atrophy, weakness, and decreased spinal reflexes, have been noted in several dogs, especially affecting the thoracic limb ipsilateral to the "scratched" side. Presumably, these signs of a cervicothoracic syndrome could be explained if the hydrosyringomyelic lesions extended to low cervical and cranial thoracic cord levels. Denervation of spinal epaxial muscles may lead to muscle atrophy and scoliosis[10] and, when cervical muscles are involved, torticollis.

Diagnosis usually requires radiographs and CT scans. Varying degrees of ventricular enlargement/hydrocephalus or hydrosyringomyelia may be present.

Medical treatment with furosemide and prednisolone may reduce intracranial pressure.

A cranioplasty is curative in most cases but technically difficult in many non-specialty clinics.


  1. C. Rusbridge
  2. Vite, Ch (2004) Developmental disorders. In: Braund's Clinical Neurology in Small Animals: Localization, Diagnosis and Treatment. IVIS, Ithaca, New York, USA
  3. Rusbridge C, Knowler SP. (2004) Inheritance of occipital bone hypoplasia (Chiara type I malformation) in Cavalier King Charles Spaniels. J Vet Intern Med 18:673-678
  4. Simoens P et al (1994) Morphometric analysis of the foramen magnum in Pekingese dogs. Am J Vet Res 55(1):34-39
  5. Cerda-Gonzalez S et al (2009) Morphology of the caudal fossa in Cavalier King Charles Spaniels. Vet Radiol Ultrasound 50(1):37-46
  6. van Herpen H & Voorhout G (1993) Occipital dysplasia in a Pomeranian dog. Tijdschr Diergeneeskd 118(10):327-328
  7. Zaki FA (1980) Odontoid process dysplasia in a dog. J Small Anim Pract 21(4):227-234
  8. Rusbridge C, Knowler SP. (2002) Syringohydromyelia secondary to occipital bone hypoplasia (Chiari malformation) in Cavalier King Charles Spaniels. In: Proceedings of ESVN 15th Annu Symposium
  9. Churcher RK, Child G. (2000) Chiari 1/syringomyelia complex in a King Charles Spaniel. Aust Vet J 78:92-95
  10. Child G, Higgins RJ, Cuddon PA. (1986) Acquired scoliosis associated with hydromyelia and syringomyelia in two dogs. J Am Vet Med Assoc 189:909-912