Hydrocephalus, also commonly referred to as "water on the brain" is an uncommon condition in which cerebrospinal fluid (CSF) accumulates inside the skull outside the brain. Dogs and cats typically acquire the defect that leads to this condition while in utero but are not subject to the fluid accumulation until after birth. Consequently, hydrocephalic animals are born normal but eventually, when the increased fluid pressure builds, it exerts damaging pressure on the brain.
This congenital form of hydrocephalus is called primary hydrocephalus. Secondary hydrocephalus is acquired later in life and tends to be related to trauma, infections or other processes that may alter the normal production and/or drainage of CSF. Only the primary form of the disease will be discussed here.
Hydrocephalic dogs are usually affected by an inherited problem in the CSF-producing ventricles of the brain or in those anatomical regions responsible for CSF drainage. Cats, however, are more likely to suffer these problems in-utero as a result of feline distemper virus infection or maternal exposure to certain drugs (such as griseofulvin).
The mode of inheritance of this disease in dogs is not known.
Symptoms and Identification
Affected animals will most typically begin to show signs of head enlargement in the weeks after birth. This is because the bones of the skull have not yet fused and enlargement is still possible. Once the skull has reached its limit, however, the fluid continues to build and a build-up of pressure inside the skull leads to neurological symptoms, usually beginning at around 8 to 12 weeks.
Seizures, head-pressing, a characteristic position of the eyes (down and sometimes outwards), blindness, or sometimes (as happens most commonly in milder cases) difficulty in training--especially in house training. Over 75% of these dogs have been reported to have housebreaking difficulty.
Milder cases will have symptoms that tend to reach a plateau at about age 1 or 2 and may lead near-normal lives but severe cases will become unmanageably affected well before then.
Diagnosis is often reached presumptively. In other words, the condition is mild enough that no steps are taken to definitively determine the cause of the abnormal signs. In more severe cases where worryingly progressive signs are in evidence, however, a definitive diagnosis via CT scan or MRI is required to determine the extent of the fluid accumulation. Ultrasound examination can be helpful here as well, but it's considered much inferior to CT or MRI in this regard.
Dogs with dome-shaped heads are by far most predisposed. That includes most every toy breed and brachycephalic (short-nosed) breed but also some terriers (the Manchester and Cairn Terriers, in particular).
Of the toys, the Chihuahua, Maltese, Pomeranian, Toy Poodle and Yorkshire Terrier are especially affected.
Of the brachycephalics, the Boston Terrier, English Bulldog, French Bulldog, Lhasa Apso, Pekingese, Pug and Shih Tzu may be overrepresented.
Most canine patients are never definitively treated due to the expense and specialized nature of hydrocephalus treatment. Unfortunately, euthanasia is the most common outcome for those who suffer anything but the mildest symptoms of hydrocephalus.
Symptomatic treatment, however, can include drug therapy to reduce seizure activity and/or corticosteroids to relieve inflammation of the brain. Omeprazole may also be employed. This is an antacid drug that somehow also woks to reduce CSF fluid pressure on the brain.
Definitive treatment involves a highly specialized procedure in which a shunt is placed to redirect CSF from the sensitive site surrounding the brain to a more benign location where it can be easily reabsorbed (such as the abdominal cavity). Expect to employ a neurologist or surgeon for this delicate procedure.
Sadly, the cost of treating hydrocephalus definitively is so precipitously high that few elect to undertake it. $5,000 to $10,000 for shunt placement is to be expected. Palliative drug therapy, however, is affordably inexpensive at around $30 to $50, on average, due to the small size of affected dogs and the generic nature of the drugs most commonly used.
All affected dogs should be removed from the breeding pool. Any family history of hydrocephalus should also invite scrutiny when it comes time to breeding selection for all affected breeds.
Ackerman, L. 1999. The Genetic Condition: A Guide to Health Problems in Purebred Dogs. pp 135-136. AAHA Press. Lakewood, Colorado.