Hydrocephalus is also referred to as water on the brain.  The ventricles that are next to the spinal cord are expanded due to an excess of spinal fluid.  It may involve both sides of the brain or only one side of the brain.  It may involve the entire ventricle system, or only part of it next to an obstruction.  The ventricle system is a system of hollow structures in the brain and spinal cord that spinal fluid flows through.

There are two types of hydrocephalus:  obstructive and compensatory.  Both of these can be present at birth or acquired.

In obstructive hydrocephalus, there is an obstruction in the ventricles blocking the movement of the spinal fluid.  This is called noncommunicating hydrocephalus.  Communicating hydrocephalus is when the fluid accumulates at the fluid resorption site near the meningeal arachnoid villi.  The meningeal is composed of three membranous envelopes — the pia mater against the brain, the aracnoid, in the middle, and the dura mater, the outer layer against the skull.  Sometimes intracranial pressure is normal and sometimes it is high.  Clinical signs can be present when the intracranial pressure is normal.

Congential obstruction usually causes primary obstructive hydrocephalus.  The most common site of the problem is the mesencephalic aqueduct.  Prenatal infections may narrow the aqueduct with subsequent hydrocelphalus.  This really messes up the architecture of the brain.

Acquired obstruction results in secondary obstructive hydrocephalus.  It is caused by such things as tumors, abscesses, and inflammatory diseases such as hemorrhage by traumatic injuries or other causes of bleeding.  The sites of obstruction can include the intreventricular foramina, the mesencephalic aqueduct, or the lateral apertures of the fourth ventricle.

With compensatory hydrocephalus, spinal fluid fills the space where the brain architecture has been messed up and is missing or was destroyed.  Intracranial pressure is a normal result.  This is ventricular dilation that happens incidental to the primary problem.

Dogs with congenital hydrocephalus are usually diagnosed when a few weeks to a year old.  Sometimes the dog will not have any symptoms and then will rapidly display a variety of symptoms.  The cause of this is unknown.

Symptoms of hydrocephalus include:  wetting or soiling in the house, sleepiness, excess vocalization, hyperexcitability, blindness, seizures, a large dome-shaped head, crossed eyes, gait abnormalities, coma, abnormal breathing, and arching his head back and extending all four legs.

Causes of hydrocephalus include congenital, genetics, prenatal infection, parainfluenza virus, exposure to drugs that interfere with fetal development in utero, brain hemorrhage in newborn after difficult labor, vitamin A deficiency, acquired, intracranial inflammatory diseases, and masses in the cranium.

Your veterinarian will perform a complete blood panel and urinalysis in order to rule out or confirm trauma, infection, or cancer.  He will x-ray the skull and top of the spine in the dog to view the ventricles.  If available, a CT scan or an MRI might be performed.  The veterinarian may also do a spinal tap with an analysis of the fluid or an EEG.

The dog who has hydrocephalus will probably require hospitalization if he needs surgery or is showing severe symptoms.  Dogs with mild hydrocephalus may be managed at home and live a good life with medication or other treatment.