Hydrocephalus is a condition in which an abnormal amount of fluid accumulates within the cranial vault of the skull. In a young dog, hydrocephalus is associated with enlargement of the head, which becomes dome shaped, and an opening on the top of the skull, called a soft spot. The fluid accumulation in hydrocephalus arises from an excessive amount of cerebrospinal fluid due to overproduction of the fluid, obstruction of fluid flow, inadequate reabsorption of fluid, or a combination of these. When this condition is present at birth, it is usually due to a hereditary defect which is seen most often in small breeds, such as the Chihuahua, Pekingese, and Boston Terrier. Hydrocephalus can also be acquired secondarily to other brain injuries, most commonly brain infections, traumas, brain tumors and poisonings.
A dome-shaped skull is one of the major signs of hydrocephalus, and many breeders deliberately breed for this characteristic. Also, the soft spot, or hole, in the top of the skull, is seen in many of these same dogs, and this, too, is abnormal, although accepted by breeders of dogs such as Chihuahua and Pekingese as normal characteristic. As a result, hydrocephalus is on the increase in certain breeds of dogs today. Many of these dogs will never show clinical signs of hydrocephalus and can live out a normal life span. Unfortunately, this leads breeders to believe that the dome-shaped skull and soft spot are not abnormal or a serious hazard. The defect is being propagated by breeding, and such dogs are at risk of developing progressive signs of hydrocephalus during their lifetime. Such breeding practices should be stopped to prevent hereditary hydrocephalus.
Many cases of hydrocephalus show no obvious signs. Others show only the dome-shaped head and the soft spot. Still others progress to a point where some or all of the following signs may occur:
- Awkward gait
- Knuckling of the feet
- Loss of vision
- Excessive sleeping
Diagnosis is made by the history, clinical signs, and physical examination; it can be confirmed by x-rays in most cases. Treatment involves the use of diuretic drugs to remove the excess fluid. Corticosteroids are administered to reduces the swelling and inflammation. Surgical treatment involves draining of the excess fluid by inserting temporary or permanent drain tubes. The prognosis, even with treatment, is not good, and most cases are progressive once serious neurological symptoms occur.