(“Water on the Brain”)
The brain and spinal cord are bathed in cerebrospinal fluid (the fluid that is tapped and analyzed when one has a “spinal tap”). This fluid is created in special chambers in the brain called “ventricles.” It circulates and is ultimately reabsorbed. In hydrocephalus, there is too much fluid, either because of a drainage problem or an over-production problem. When the problem is congenital, the skull is still soft enough to expand somewhat (leading to a dome-shaped head) but it does not take long for the skull bones to harden. Because the skull cannot expand with increased contents, the result is compression of the brain by the extra fluid.
HOW DO ANIMALS GET HYDROCEPHALUS?
Most animals with hydrocephalus are puppies with congenital anomalies leading to hydrocephalus (they are not born with hydrocephalus but they are born with the anatomical problems that quickly lead to hydrocephalus). The most commonly affected breeds are those with a natural tendency towards the domed-head: Chihuahua, Pomeranian, Yorkshire terrier, English bulldog, Lhasa apso, Pug, Pekingese, Boston terrier, Maltese, toy poodle, and Cairn terrier).
What happens to these puppies is that parts of the brain called the “rostral colliculi” fuse together causing a narrowing of the aqueducts that carry the cerebrospinal fluid. In the cat, more common causes of narrowing of the aqueducts include maternal exposure to the drug griseofulvin (used to treat the ringworm fungus), or maternal exposure to the feline distemper virus during pregnancy. Inflammatory conditions in the brain can also cause swelling that narrows the aqueducts.
WHEN TO SUSPECT HYDROCEPHALUS
When a puppy or kitten is 8-12 weeks old, symptoms are usually evident. The skull looks especially round and there is an open fontanelle (“skull soft spot”) on the top of the head. The pet may show what is called the “setting sun” sign which means the eyes are directed downwards (and possibly outwards). The animal may suffer from seizures (less than 20% of affected puppies), blindness, pressing the head into corners, or extreme difficulty in house-training (over 75%).
The drawing shows a puppy with the "setting sun sign." Note the irises are positioned low, like
CONFIRMING THE CONDITION
Post-mortem radiograph of a hydrocephalic puppy.
Radiographs of the skull will show thin skull bones but to truly confirm the condition imaging of the brain is needed. This can be done by using ultrasound through the open fontanelle or CT or MRI.
Temporary relief of the increased fluid pressure can be achieved with medication. Diuretics can be used to decrease fluid production in the brain but one must be careful about causing the patient to become dehydrated. Electrolyte imbalances are also possible. Corticosteroids such as prednisone can relieve swelling in the brain and are also helpful. Oddly, the antacid omeprazole- has been shown to decrease cerebrospinal fluid production by 26% though we do not know how this occurs.
For a more permanent resolution, a shunt must be surgically placed. A shunt is a small tube that is surgically implanted in one of the brain’s ventricles. It siphons excess fluid away and drains it to another area of the body where it is harmless (such as the abdominal cavity). As the animal grows, “shunt revisions” are required to re-fit the shunt. If there is evidence of infection in the central nervous system, a shunt cannot be placed. This is because the placement of a foreign body (i.e. the shunt itself) will provide a shelter for the infection and the infection will never clear. The infection must be resolved before shunt placement.
Complications of the shunt include: infection (4-10% of all shunts placed in humans get infected), over-drainage, under-drainage/obstruction of the tubing. The shunt can drain to either the abdominal cavity or heart. Fewer complications (as well as easier placement) are associated with shunts that go to the abdomen. Overall, success rate for the ventriculoperitoneal shunt is felt to be approximately 80%.
Shunt placement is a specialized procedure. Expect to see either a surgery specialist or neurologist for this procedure.
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Last revised: 10/9/2014