Hydromyelia is a congenital dilation of the spinal cord central canal. In man this may be due to congenital malformations such as Dandy-Walker syndrome and Chiari malformations or may be acquired as result of infection, trauma or neoplasia. In dogs hydromyelia may be accidentally diagnosed during routine cisterna magna myelography. Hydromyelia, and its possible cause, may be confirmed by means of computed tomography or magnetic resonance imaging.3 The signs of the disease may be short term or may be progressive over several weeks to years due to ongoing destruction of the spinal cord, but in some mild cases there may be no obvious clinical signs.

The brain and spinal cord develop as a groove that folds over to become the neural tube. Layers of tissue that come from this tube normally become the brain and spinal cord and their covering tissues, including part of the spine and the meninges. Sometimes the neural tube does not develop normally, which may affect the brain, spinal cord, and meninges. In the most severe form of neural tube defect, the brain tissue may fail to develop. Tthis defect is fatal. Another type of defect results when the neural tube fails to close completely and remains an open channel. In its mildest form, an open channel defect may affect only bone; for example, in spina bifida occulta (which means hidden spine split in two), the bony spine fails to close, but the spinal cord and meninges are unaffected.

When the spinal cord is involved,the tissue protrudes from the spinal cord and the condition is called myelocele. A myelocystocele is a closed neural tube defect composed of extreme enlargement of the central canal (hydromyelia) that produces a fluid-filled sac covered by meninges (a meningocele) and normal skin that protrudes between the hard outermost layer of spinal cord (dura mater) and the spinal processes. It is most commonly located at the end of the neural tube, where it is trumpet shaped and is referred to as terminal myelocystocele. The signs of myelocystocele may vary depending on the location of the affected area. Pain may be apparent in the spine, head and neck. The dog may be unable to coordinate muscle activity when attempting to walk, and may drag the limbs due to weakness or partial paralysis of the fore-limbs, the hind-limbs or all limbs.



  1. Listing of Inherited Disorders in Animals (University of Sidney)
  2. Roger E. Stevenson. Human Malformations and Related Anomalies
  3. Kirberger RM, Jacobson LS, Davies JV, Engela J. Hydromyelia in the dog. 1: Vet Radiol Ultrasound. 1997 Jan-Feb;38(1):30-8
  4. Carlos Ayala, Brad Spellberg. Pathophysiology for the Boards and Wards (illustration)