Hydrocephalus in Toy Breed Puppies

By Ryan Llera, BSc, DVM; Tammy Hunter, DVM; Ernest Ward, DVM

What is hydrocephalus?

Hydrocephalus (from a Greek word meaning “water on the brain”) is an excess of cerebrospinal fluid (CSF) that has leaked inside the skull, leading to brain swelling. CSF is the fluid that surrounds the brain and spinal cord, providing both nutrients and protection.

Build-up of CSF in the brain can occur if the flow or absorption of CSF is blocked, or if too much CSF is produced by the body. This build-up leads to increased pressure within the skull, which presses on the sensitive brain tissue. Increased intracranial pressure can lead to permanent, irreversible brain damage and death.

What causes hydrocephalus in dogs?

There are two main types of hydrocephalus in dogs: congenital (present at birth) and acquired.

Congenital hydrocephalus is a birth defect most often associated with a dome-shaped skull (sometimes referred to as “water head” or “apple head”), a large fontanelle (“soft spot”) on top of the skull, and eyes that appear to gaze downward (called the “setting sun sign”). Affected dogs may not have any obvious clinical signs, especially when they are very young. Clinical signs associated with congenital hydrocephalus include abnormal walking, changes in behavior, circling or falling over on one side, head pressing into the floor or against the wall, loss of vision, and failure to become house-trained or learn basic commands. It is important to note that not all puppies with large fontanelles will develop hydrocephalus.

Acquired hydrocephalus develops when the flow of CSF is blocked or altered by infection, tumor, or swelling. The most common cause of acquired hydrocephalus is a brain tumor. Clinical signs are similar to those of congenital hydrocephalus but can be challenging to separate from the underlying neurological disease.

Are certain breeds more likely to develop hydrocephalus?

Small, miniature, and toy breeds, as well as brachycephalic dogs (those with shorter faces), seem to be more affected. These breeds include the Boston terrier, Chihuahua, English bulldog, Manchester terrier, Pekingese, toy French poodle, Lhasa Apso, and Yorkshire terrier.

How is hydrocephalus diagnosed?

In young puppies, usually the only signs needed to make a presumptive diagnosis are a large fontanelle and clinical signs consistent with hydrocephalus. Ultrasound evaluation through the fontanelle can reveal dilated or enlarged brain ventricles (open areas in each half of the brain). CAT scans or MRIs can also be used to diagnose hydrocephalus. In cases of suspected acquired hydrocephalus, CT or MRI is necessary to make a definitive diagnosis. Electroencephalography (EEG), which involves connecting electrical sensors to the head in multiple locations, may also be used to help diagnose hydrocephalus.

How is hydrocephalus treated?

In the acute or early phases of hydrocephalus, treatment is directed toward reducing CSF production and inflammation by using corticosteroids (such as cortisone or prednisone). In more severe or chronic cases, anti-seizure medications may be needed, such as phenobarbital, zonisamide, potassium bromide, or levetiracetam. Drugs such as furosemide, acetazolamide, and omeprazole may benefit affected dogs by decreasing CSF amounts or lowering production of CSF fluid.

Surgery can be performed at some veterinary teaching or specialty hospitals to place a tube that runs from the open spaces in the brain to the abdomen (VP shunt). Success rates as high as 80% are reported in cases treated early. Considerable risks and potential complications are associated with this procedure, so be sure to thoroughly discuss the benefits and risks of shunts with your veterinarian.

For acquired hydrocephalus, therapy is focused on treating the underlying cause and may range from medications to surgery to radiation therapy.

Should dogs with congenital hydrocephalus be bred?

Dogs with congenital hydrocephalus should absolutely not be bred. Because congenital hydrocephalus is a birth defect, neither parent should be bred again.

What is the prognosis for dogs with hydrocephalus?

Hydrocephalus in dogs is a serious, often life-threatening condition. The predicted outcome for hydrocephalus depends on its duration and severity. Puppies with congenital hydrocephalus may do well following shunt placement if severe brain damage has not occurred. Dogs with acquired hydrocephalus have a poorer prognosis, due to the likelihood of an underlying tumor or infection, such as encephalitis (inflammation of the brain). Your veterinarian will discuss your pet’s prognosis and treatment options based on its individual condition.

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