Developmental anomalies within the cranium result in occipital bone hypoplasia leading to caudal fossa overcrowding, obstruction of CSF pathways and secondary hydrosyringomyelia.
Trauma superimposed on a pre-existing Chiari type 1 congenital abnormality may play a role in some clinical cases.
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 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.
- C. Rusbridge
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