Causes of Hydrocephalus
Canine hydrocephalus is almost always congenital, which means that the condition is present at birth. Accordingly, it is most commonly diagnosed in puppies. Hydrocephalus occasionally occurs in adult animals, but that is uncommon in domestic dogs. Several different classification schemes are used to characterize hydrocephalus in veterinary medicine. One distinguishes between two general types of the disorder: communicating hydrocephalus and non-communicating hydrocephalus. Communicating hydrocephalus is where the animal’s brain is not able to absorb a normal amount of cerebrospinal fluid (CSF) from the network of brain chambers known as the cerebral ventricular system. Cerebral “venetricles” are individual chambers inside the brain through which CSF normally flows. In dogs with communicating hydrocephalus, there is no physical obstruction of the free movement of CSF through and between the ventricles. There either is overproduction of cerebrospinal fluid (although this is not particularly common in dogs), or there is some defect in or damage to the dog’s brain that prevents it from absorbing CSF properly. Communicating hydrocephalus is usually congenital. However, it also can be acquired during a dog’s lifetime as a result of trauma, inflammation, brain hemorrhage, infection, dietary Vitamin A deficiency or brain tumors. In another classification scheme, this is referred to as compensatory hydrocephalus, because excess CSF fills the ventricular spaces, which may or not be enlarged due to damage, development or another disease process.
Unlike communicating hydrocephalus, non-communicating hydrocephalus does involve some blockage of the normal flow of cerebrospinal fluid through the cerebral ventricular system. This usually is a congenital physical obstruction that is present at birth. It can be caused by exposure of the mother during her pregnancy to drugs, chemicals or other toxins that cause birth defects in puppies; these are called “teratogenic” substances. Certain infections by bacteria, viruses (especially parainfluenza virus) or other microorganisms during pregnancy can also lead to congenital hydrocephalus in one or more puppies in a litter. Although not as common, obstructive hydrocephalus can also be acquired secondary to traumatic injuries, hemorrhage (bleeding) inside the brain, brain abscesses and/or cancer.
While hydrocephalus can be either congenital or acquired by something that happens within a dog’s brain after it is born, the effects of the condition are largely the same. The symptoms of hydrocephalus principally are due to physical compression of blood vessels inside of the brain (the cerebral vasculature), which is caused by excess intracranial pressure from the abnormal build-up of cerebrospinal fluid in the ventricles. This pressure on the blood vessels compromises blood flow and decreases the delivery of oxygen and other nutrients to brain tissues. The effects of hydrocephalus are also attributable to physical damage to nerve cells, called “neurons.” This happens as a result of the enlarged, fluid-filled ventricles compressing the neurons against other structures and against the bones of the skull.
One way to reduce the chances of congenital hydrocephalus is to prevent the bitch from being exposed during her pregnancy to toxic drugs, chemicals, viruses, bacteria or other infectious microorganisms that may cause teratogenic birth defects in her puppies. Obviously, head trauma should be avoided. Dogs diagnosed with hydrocephalus should not be bred. Otherwise, there are no reported ways to prevent the development of hydrocephalus in domestic dogs.
Intracranial pressure, which is the pressure inside of the skull, can be dangerously increased in dogs with hydrocephalus. In many cases, even with medical treatment, hydrocephalus will leave residual neurological symptoms in affected dogs. These residual signs typically indicate irreversible brain damage.