Hydrocephalus means water on the brain. The brain and spinal cord are normally surrounded and supported by a cushion of fluid that serves to protect the delicate tissue from injury. It also delivers nutrients and hormones to the brain and carries toxins away. Cerebrospinal Fluid (CSF) is constantly produced, absorbed, and drained through the circulatory system at an equalized rate. In hydrocephalic animals, there is blockage at some point in the system causing abnormal fluid accumulation inside the skull and eventually increased pressures on the brain itself. This can result in brain damage and learning disabilities, blindness, seizures, coma, and ultimately death if not resolved. Hydrocephalus can occur as a result of trauma, tumor formation, or infection; but most often it is congenital or the result of maternal exposure to certain drugs and viral infections. Toy breeds with dome-shaped heads have an increased risk for developing congenital hydrocephalus.
When an animal is first born, the bones of the skull are not yet fused together. They are soft and flexible and will accommodate a significant amount of excess CSF. A hydrocephalic puppy or kitten may have an enlarged dome-shaped head with a soft spot called an open-fontanel, an altered gait, and seem disinterested or mentally dull. The eyes may be pushed downward or outward in the eye sockets, and they may be partially or completely blind. As the skull hardens and the bones fuse together, the fluid pressures will increase and symptoms will increase in severity. Seizures are common, and the untreated hydrocephalus will eventually become life-threatening.
When congenital hydrocephalus is suspected, brain imaging by MRI or CT scan may be performed to confirm the condition. An ultrasound can be performed if there is an open fontanel where the skull bones have not yet fused together. X-rays are usually not very helpful. Blood chemistry profiles are used to assess whether the animal has concurrent metabolic disease such as kidney and liver dysfunction.
Medications can be started to provide temporary improvement in swelling and symptoms. Diuretics like furosemide (Lasix) can help draw fluid away from the brain but can also cause dehydration and electrolyte loss. Corticosteroids like prednisone can reduce swelling but should not be used long term due to side effects. For unknown reasons, an antacid called omeprazole (Prilosec) can reduce CSF production by as much as 25% and may be used in combination with steroids or diuretics to control fluid pressure on the brain. Diarrhea and constipation may result from long-term use. Patients with mild symptoms can sometimes be managed with medications; however, severe hydrocephalus will require surgery.
Surgery for hydrocephalus is performed by a surgical specialist after a consultation with a neurologist. The procedure does not correct the physical obstruction in the normal CSF drainage pathways. Instead, it involves placing a shunt – a drain tube – between the one of the ventricles, or chambers in the brain where the cerebrospinal fluid is produced, and the abdomen. (The shunt can alternatively drain to the heart.) This allows the excess fluid to drain away from the skull and relieves pressure on the brain. The fluid is then re-absorbed into the circulatory system and excreted by the kidneys. For larger animals, the shunt may have to be replaced as the pet grows in size.
Complications after surgery include infection around the shunt (<10%) or occlusion in the tubing; in either case, the shunt must be removed. Also, the amount of drainage may not be adequate, and a second shunt may be needed. The pet may require drug therapy in addition to the surgery.
Overall, the prognosis for congenital hydrocephalus is guarded at best. The severity of symptoms is directly related to the expected outcome; therefore, the disease should be treated aggressively. Symptoms are not likely to improve without treatment; they are usually progressive. Survivors of hydrocephalus should not be allowed to breed and reproduce, as their offspring will inherit the defect.