A portosystemic shunt is an abnormal communication between blood vessels, which causes blood to bypass the liver. The portal vein is a major vessel in the body which enters the liver and allows toxic components of the blood to be detoxified by the liver. When a shunt is present, the portal vein, or one of its related veins, is inappropriately connected to another vein which creates blood flow around the liver.

The most common type of shunt is a single congenital shunt. This means that the animal is born with the problem. Acquired shunts may occur secondary to liver disease.

Congenital shunts occur in both dogs and cats. Most animals start showing signs by six months of age. However, shunts have been diagnosed in adults as old as 10 years.

There is an increased risk of shunts in Persian and Himalayan cats, but most affected cats are mixed breeds. Male cats seem to be over-represented in this population. Of the affected males, there is also an increased incidence of cryptorchidism (one or both testicles remain undescended).

The impact of a portosystemic shunt on your pet can present itself in a variety of ways. The most common clinical signs are a result of elevated toxin levels in the blood secondary to failure of removal by the liver. One of the important toxins is ammonia, which causes abnormalities of the central nervous system.

What to Watch For

Lack of appetite

Lethargy

Weakness

Disorientation

Stumbling

Circling or pacing

Apparent staring into the corner

Pressing of the head against objects

Seizures

Blindness

Behavioral changes

Excess salivation (more common in cats)

Vomiting

Diarrhea

Increased thirst and frequent urination (more likely in dogs)

Straining to urinate

Blood in the urine

Failure to grow and thrive

Weight loss

Diagnosis

History and physical exam

Complete blood count (CBC)

Biochemical profile

Urinalysis

Bile acids

Blood ammonia level

Clotting tests

Abdominal radiographs (x-rays)

Abdominal ultrasound

Portography (special dye study)

Transcolonic scintigraphy to monitor the pattern of blood flow

Abdominal exploratory surgery

Treatment

Surgical ligation (closure) of the shunt is the treatment of choice. However, animals must be medically stabilized prior to surgery.

IV fluid therapy restores hydration deficits and corrects electrolyte imbalances.

Lactulose decreases absorption of intestinal toxins such as ammonia by altering intestinal pH.

Antibiotics alter intestinal bacteria such that ammonia production is decreased.

Feeding a protein restricted diet since protein in the diet can precipitate neurologic abnormalities.

In animals with vomiting and diarrhea, gastric protectants help reduce acidity of the gastrointestinal tract and may alleviate some of the symptoms.

Anti-convulsant drugs may be necessary in animals with seizures that are not responsive to the aforementioned medical treatments.

Home Care and Prevention

Give all medications as prescribed by your veterinarian. Feed only the prescribed diet. Monitor your pet for recurrence or worsening of the original clinical signs that alerted you to a problem.

As this is a congenital disorder, there are no known preventative measures for your individual pet. However, any cat or cat with a shunt should never be used for breeding purposes.