Hydrocephalus, which literally means “water on the brain,” is a buildup of fluid inside the skull. This accumulation puts pressure on the brain, causing signs such as an enlarged, dome-shaped head, seizures, blindness, and behavioral changes. The condition is often congenital, meaning that is present before or at birth, and can occur in both dogs and cats. Small dogs are particularly susceptible. In mild cases, drugs can help treat signs, but severe cases often end in euthanasia, as surgery is costly.


With hydrocephalus, cerebrospinal fluid (CSF) accumulates inside the skull and the brain. The congenital form of hydrocephalus is called primary hydrocephalus. Secondary hydrocephalus is acquired later in life and is often associated with tumors, trauma, or inflammation, which may block the flow of CSF or alter the normal production or drainage of the fluid. Only the primary form will be discussed here.

Congenital hydrocephalus can be caused by a number of factors, including heredity, prenatal infection, exposure to drugs that cause birth defects, and trauma from a difficult birthing process. After birth, they experience fluid buildup, which exerts damaging pressure on the brain.

Symptoms and Identification

Affected animals will typically begin showing signs of head enlargement in the first weeks after birth. This is because the bones of the skull have not yet fused, making enlargement possible. Once the skull reaches its growth limit, the fluid continues to build, causing pressure on the brain and leading to neurological symptoms, which usually start around eight to twelve weeks.

Young animals with hydrocephalus are often the “runt” of the litter, being smaller in size than littermates and slower to learn. Approximately 75 percent of diagnosed canines were reportedly impossible to housebreak.

Other signs can include seizures, head pressing, eyes that gaze downward and outward (called ventrolateral strabismus), gait abnormalities and blindness. Some pets with hydrocephalus may show no clinical signs, or have signs that gradually worsen over time.

Diagnosis is often presumed, based on history and physical examination, without taking additional steps to confirm the condition. Severe cases, however, will become unmanageable well before then and require a definitive diagnosis via CT scan or MRI in order to determine the extent of fluid accumulation. If available, EEG, or electroencephalography, may help support the diagnosis of hydrocephalus. An ultrasound can also be helpful but may only be possible when the skull has not fused completely. Even when hydrocephalus is diagnosed, the underlying cause is often unknown.

Affected Breeds

Small dogs are predisposed to the condition, including Cairn Terriers, Chihuahuas, Maltese, Pomeranians, Toy Poodles, Yorkshire Terriers, Boston Terriers, English Bulldogs, Lhasa Apsos, Pekingese, Pugs, and Shih Tzus. Siamese cats may also be predisposed to the condition.


Definitive treatment involves a shunt that redirects CSF from the sensitive site surrounding the brain to a more benign location, such as the abdominal cavity, where it can be easily reabsorbed. Because the procedure is expensive, and requires a specialized brain surgeon, most canines never receive it.

Symptomatic treatment can include drug therapy to reduce seizure activity, corticosteroids to relieve brain swelling and inflammation, and diuretics to reduce the amount of fluid. However, most medical treatment only provides a temporary solution to the problem.

Unfortunately, euthanasia is the most common outcome for pets that suffer anything but the mildest signs of the disease.


All affected dogs should be removed from the breeding pool. Any animals with a family history of hydrocephalus should be considered carefully during breeding selection.

This article was reviewed by a Veterinarian.