What is hydrocephalus?
With hydrocephalus there is an abnormal build-up of cerebrospinal fluid (CSF) in cavities ( the ventricles) in the brain. The resulting increased pressure on the brain causes the clinical signs that occur with this condition.
Hydrocephalus can be primary (congenital ) - the animal is born with the condition, or secondary - the condition is acquired later in life due to some disease process that blocks normal drainage of the CSF. The primary form, discussed here, is seen most often in brachycephalic (dogs with a shortened head) and toy breeds.
How is hydrocephalus inherited?
The mode of inheritance is unknown, but there is a predisposition to this condition in the breeds listed below.
What breeds are affected by hydrocephalus?
Toy breeds - Cairn terrier, chihuahua, Maltese, Manchester terrier, pomeranian, toy poodle, Yorkshire terrier - and brachycephalic breeds - Boston terrier, English bulldog, Lhasa apso, Pekingese, Shih tzu
For many breeds and many disorders, the studies to determine the mode of inheritance or the frequency in the breed have not been carried out, or are inconclusive. We have listed breeds for which there is a consensus among those investigating in this field and among veterinary practitioners, that the condition is significant in this breed.
What does hydrocephalus mean to your dog & you?
Puppies with severe hydrocephalus often die at a very early age due to pressure from the increased fluid in the brain. In other less severely affected pups, the signs gradually become apparent over the first few months of life, and in some mild cases the condition is only diagnosed later in life.
The types of signs seen with this condition include unthriftiness (smaller than littermates, slow to grow), a domed skull (which gradually becomes more pronounced), abnormal movement behaviours (restlessness, aimless walking), problems with vision, and seizures. These pups are very slow to learn - it may be extremely difficult to housetrain them for example.
Generally the signs gradually worsen, although by 2 years of age they may stabilize. To minimize brain damage, the condition must be recognized and appropriate treatment begun early. However, affected animals will likely always be slow and have a limited ability to learn.
How is hydrocephalus diagnosed?
Hydrocephalus can be difficult to diagnose. Your veterinarian will consider the combination of physical, behavioural and neurological abnormalities in your dog. The diagnosis can be confirmed by MRI or CT scanning, or by ultrasonography in some cases.
For the veterinarian: Ultrasonography can be performed through an open fontanelle to confirm ventricular enlargement. An open fontanelle is not diagnostic per se of hydrocephalus, as it may occur in a normal healthy dog.
Some hydrocephalic dogs have a bilateral divergent strabismus ("setting sun sign").
How is hydrocephalus treated?
Corticosteroids are used, and then gradually tapered off, with the aim of lowering the amount of cerebrospinal fluid in the brain. Your veterinarian may also prescribe short-term diuretics with the same goal. Treatment often needs to be repeated, although some dogs will stabilize by about 2 years of age. Affected dogs are susceptible to other medical problems and may have a poor tolerance to various drugs.
Phenobarbital may be required in dogs that experience seizures.
A sophisticated procedure that may be of some benefit in severe cases of hydrocephalus is surgical placement of a permanent shunt to drain the fluid. Your veterinarian will refer you to a specialist if you wish to to consider this option.
Depending on the severity of the clinical signs, and recognizing the ongoing medical problems these dogs may face, your veterinarian will likely discuss with you humane euthanasia as another option for your pup.
Affected animals should not be bred. Even though little is known about the heritability of this condition, it is also preferable to avoid breeding dogs who are unaffected but have a familial history of hydrocephalus.