What is ... ?: 

With hydrocephalus there is an abnormal build-up of cerebrospinal fluid (CSF) in cavities in the brain (the ventricles). This results in increased pressure on the brain, which causes the clinical signs seen with this condition.

Hydrocephalus can be congenital (i.e., the animal is born with the condition)  or acquired, in which case the condition is acquired later in life due to some disease process that blocks normal drainage of the CSF. The congenital form, discussed here, is seen most often in brachycephalic (dogs with a shortened head) and toy breeds.

How is ... inherited?: 

The mode of inheritance is unknown, but there is a predisposition to this condition in the breeds listed below.

What does ... 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 lack of thriftiness (smaller than littermates, slow to grow), a domed skull (which gradually becomes more pronounced), abnormal movement behaviour (e.g., 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, or they may lose their housetraining.
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 ... 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.

How is ... treated?: 

There are various drugs that may be used to decrease cerebrospinal fluid production. Treatment often needs to be repeated, although some dogs will stabilize by about 2 years of age. If no improvement is seen within a few weeks of beginning medical treatment, your veterinarian may suggest surgical implantation of a shunt to drain the CSF.
Affected dogs are susceptible to other medical problems and may have a poor tolerance to various drugs. Antiepileptic drugs may be used for control of seizures.

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.

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").

Breeding advice: 

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.



Ackerman, L. 1999. The Genetic Condition: A Guide to Health Problems in Purebred Dogs. pp 135-136. AAHA Press. Lakewood, Colorado.

Coates JR. Hydrodephalus. In: Côté E, ed. Clinical Veterinary Advisor Dogs and Cats. Missouri: Mosby Elsevier, 2007:534-535.

What breeds are affected by ... ?