Hydrocephalus is an expansion or abnormal dilation of the ventricular system due to an increased volume of spinal fluid. The ventricles that are affected are those connected with the spinal cord. The abnormal dilation may affect only one side of the brain, or both sides. It may involve the entire ventricular system (a set of hollow structures in the brain continuous with the central canal of the spinal cord), or only elements next to a site of the obstructed ventricular system. The body may form too much fluid or, as occurs in most cases, the fluid that is produced cannot drain from the central nervous system as it normally does. The ventricles become swollen, and the increased pressure damages and/or prevents development of brain tissue.
Hydrocephalus can occur as a congenital condition (present at birth) as well as a result of trauma of the brain. Congenital hydrocephalus usually becomes apparent at a few weeks up to a year of age.
There are two types of hydrocephalus – obstructive and compensatory.
In the case of obstructive hydrocephalus, spinal fluid accumulates due to an obstruction along the normal circulatory pattern (non-communicating hydrocephalus), or the fluid accumulates at the fluid resorption site near the meningeal arachnoid villi (communicating hydrocephalus).
The most common site of obstruction is at the level of the mesencephalic (middle brain) aqueduct. Prenatal (before birth) infections may cause aqueductal stenosis(narrowing) with subsequent hydrocephalus. This may result in considerable disruption of the architecture of the brain, or it may be caused by tumors, abscesses, and inflammatory diseases (including inflammation resulting from hemorrhage that has been caused by traumatic injuries or other causes of bleeding.
With compensatory hydrocephalus, spinal fluid fills the space where the nervous system’s functional parts have been destroyed and/or failed to develop. Intracranial (within the brain) pressure is a normal result.
The congenital form of hydrocephalus is
more likely to occur in small and brachycephalic dogs: bulldogs, Chihuahuas, Maltese, Pomeranians, Toy Poodles, Yorkshire Terriers, Lhasa Apsos, Cairn Terriers, Boston Terriers, Pugs, and Pekingese. It is an inherited disease in Yorkshire terriers. Additionally, there is a high incidence of normal adult Beagles that are found to have enlarged ventricular systems and yet are clinically without symptoms. Acquired hydrocephalus can occur in all breeds.
Symptoms and Types
• May be without symptoms
• Wetting or soiling in the house
• Excess vocalization
• A large dome-shaped head
• Gait abnormalities
• Abnormal breathing
• Animal may arch its head back and extend all four legs
• Prenatal infection
• Parainfluenza virus
• Exposure to teratogens (drugs that interfere with fetal development) in utero
• Brain hemorrhage in newborn after difficult labor
• Vitamin A deficiency
• Intracranial inflammatory diseases
• Masses in the cranium
The hydrocephalic dog typically has a very limited life span. Severity differs, but only very few dogs with this condition will live over two years of age.
You will need to provide your veterinarian with a detailed history of your dog’s health, including any information you have about its birth and parentage, the onset of symptoms, and any possible incidents, including minor falls, that might have preceded this condition. Your veterinarian will perform a complete physical exam on your dog, with a complete blood profile, chemical blood profile, complete blood count, an electrolyte panel, and a urinalysis, in order to effectively rule out or confirm evidence of trauma, infection, or cancer.
Diagnostic imaging is essential. Skull radiographs may help to diagnose congenital hydrocephalus, but computed tomography (CT) and magnetic resonance imaging (MRI) are best for visualization, enabling your veterinarian to come to a definitive diagnosis.
Other diagnostic tests that can assist in the diagnosis of hydrocephalus are a spinal tap, with a laboratory analysis of the fluid, and an electroencephalogram (EEG) for measuring the brain’s electrical activity.
Most cases go untreated. Veterinary neurologists can be consulted and occasionally the excess fluid can be drained. With surgery or medical treatment, however, the dog will rarely live a normal life. Treatment is often unsuccessful and expensive.
All affected dogs should be removed from the breeding program. Any animals with a family history of hydrocephalus should be considered carefully during breeding selection.