Water on the Brain in Dogs

4 min read

Hydrocephalus in Dogs

Hydrocephalus is an expansion or abnormal dilation of the ventricular system due to an increased volume of spinal fluid. In this case, the ventricles that are affected are those connected with the spinal cord. The abnormal dilation may affect only on 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 ventricular system obstruction.

There are two types of hydrocephalus – obstructive and compensatory. Both compensatory and obstructive hydrocephalus can be congenital (present at birth) or acquired.

In the case of obstructive hydrocephalus, spinal fluid accumulates due to an obstruction along the normal circulatory pattern (noncommunicating hydrocephalus), or the fluid accumulates at the fluid resorption site near the meningeal arachnoid villi (communicating hydrocephalus). The meninges are composed of three membranous envelopes – the pia mater, which lies against the brain; the arachnoid, the middle layer; and the dura mater, the outer, thicker layer closest tot he skull – that surround the brain and spinal cord. Intracranial (within the skull) pressure may be high or normal. However, clinical signs may be noted when intracranial pressure is normal.

Congenital obstruction causes primary obstructive 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.

Acquired obstruction results in secondary obstructive hydrocephalus. It is caused by tumors, abscesses, and inflammatory diseases (including inflammation resulting from hemorrhage that has been caused by traumatic injuries or other causes of bleeding). The sites of obstruction include the interventricular foramina (channels that connect the paired lateral ventricles with the third ventricle at the midline of the brain), the mesencephalic aqueduct, or the lateral apertures of the fourth ventricle.

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. This is ventricular dilation incidental to the primary disease.

Overproduction of spinal fluid can also cause hydrocephalus. However, this is rare. A tumor in the eye may also cause water on the brain.

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.

Congenital hydrocephalus usually becomes apparent at a few weeks up to a year of age. Acute onset of signs can occur in dogs with previously undiagnosed congenital hydrocephalus. The exact cause of this uncertain. Acquired hydrocephalus can occur at any age.

Symptoms and Types

  • May be without symptoms
  • Wetting or soiling in the house
  • Sleepiness
  • Excess vocalization
  • Hyperexcitability
  • Blindness
  • Seizures
  • A large dome-shaped head (due to intracranial swelling)
  • Crossed-eyes
  • Gait abnormalities
  • Coma
  • Abnormal breathing
  • Animal may arch its head back and extend all four legs


  • Congenital
  • Genetics
  • Prenatal infection
  • Parainfluenza virus (dogs)
  • Exposure to teratogens (drugs that interfere with fetal development) in utero
  • Brain hemorrhage in newborn after difficult labor
  • Vitamin A deficiency
  • Acquired
  • Intracranial inflammatory diseases
  • Masses in the cranium


You will need to provide your veterinarian with a thorough and 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.

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