The term hydrocephalus is derived from the Greek words "hydro" meaning water and "cephalus" meaning head. As its name implies, it is a condition in which the primary characteristic is excessive accumulation of fluid in the brain. Although hydrocephalus was once known as "water on the brain", the "water" is actually cerebrospinal fluid (CSF) - a clear fluid surrounding the brain and spinal cord. The excessive accumulation of CSF results in an abnormal dilation of the spaces in the brain called ventricles. This dilation causes potentially harmful pressure on the tissues of the brain.
Normally CSF flows through the ventricles, exits into closed spaces that serve as reservoirs at the base of the brain, bathes the surfaces of the brain and spinal cord and then is absorbed into the bloodstream.
CSF has three important life-sustaining functions: 1) to keep the brain tissue buoyant, acting as a cushion or "shock absorber", 2) to act as the vehicle for delivering nutrients to the brain and removing waste, and 3) to flow between the cranium and spine to compensate for changes in intracranial blood volume (the amount of blood in the brain).
The balance between production and absorption of CSF is critically important. Ideally, the fluid is almost completely absorbed into the bloodstream as it circulates. However, there are circumstances which can prevent or disturb the production or absorption of CSF, or which will inhibit its normal flow. When this balance is disturbed, hydrocephalus is the result.
Hydrocephalus can be primary (congenital or inherited) when the pup is born with the condition, or secondary when the condition is acquired later in life due to another condition such as mass lesions (tumors and abscess), and inflammatory disease.
The mode of inheritance is unknown but toy breeds especially cairn terrier, Chihuahua, Maltese, Manchester terrier, Pomeranian, toy poodles, Yorkshire terrier and brachycephalic breeds like Boston terrier, English bulldog, Lhasa apso, Pekinese and Shih tzu are most affected. Dogs with primary hydrocephalus will begin to show symptoms anytime from a few weeks after birth to about one year.
The signs of hydrocephalus include behavioral abnormalities, excessive sleepiness, vocalization, hyperexcitability, blindness and seizures. With congenital hydrocephalus, the head may appear large and dome-shaped with open fontanelles.
The diagnosis of hydrocephalus is generally determined with a Cat Scan or MRI although an ultra sound of the brain through an open fontanelle may reveal the condition. A spinal tap, bile acid tests and a measurement of intracranial pressure may also be required.
Drug therapy is used to reduce CSF production with corticosteroids such as prednisone. Diuretics may also be used with the same goal. Anti-convulsant medication may be required to treat seizures. Surgery may be considered in severe cases of hydrocephalus to place a permanent shunt to drain the fluid. Surgery is also considered when a brain tumor or other mass lesion is the cause of the hydrocephalus.
The expected prognosis varies depending on the cause and severity of the disease. A good prognosis is expected in dogs with mild congenital form as they may only need occasional medical treatment. A guarded prognosis is indicated for dogs with severe or progressive disease.
Berendt, M, Clinical
Neurology in Small Animals-Localization, Diagnosis and Treatment
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Last Updated August 2009