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.
Shunts are more common in purebred dogs than mixed breeds. The breeds predisposed to congenital shunts include: miniature schnauzer, Yorkshire terrier, Irish wolfhound, cairn terrier, Maltese
, Australian cattle dog, golden retriever
, Labrador retriever, and Old English sheepdog.
It occurs more often in female dogs, and of the affected males, there is also an increased incidence of cryptorchidism, in which 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
Circling or pacing
Apparent staring into the corner
Pressing of the head against objects
Excess salivation (more common in cats)
Increased thirst and frequent urination (more likely in dogs)
Straining to urinate
Blood in the urine
Failure to grow and thrive
History and physical exam
Complete blood count (CBC)
Blood ammonia level
Abdominal radiographs (x-rays)
Portography (special dye study)
Transcolonic scintigraphy to monitor the pattern of blood flow
Abdominal exploratory surgery
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 dog with a shunt should never be used for breeding purposes.