Overview of Canine Portosystemic Shunt (PSS, Hepatic Shunt)
A portosystemic shunt, commonly abbreviated and referred to as PSS, hepatic shunt or liver shunt, is an abnormal communication between blood vessels, which causes blood to bypass the liver that can occur in dogs. 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 dog or other 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
Diagnosis of Portosystemic Shunt (PSS) in Dogs
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
Treatment for Portosystemic Shunt (PSS) in Dogs
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 of Liver Shunts in Dogs
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.
Information In-depth for Portosystemic Shunt in Dogs
A congenital portosystemic shunt is a condition that exists when your pet is born. This is a serious disorder because the liver does not receive adequate blood flow, and therefore does not grow normally. Most animals with shunts have livers that are smaller than normal. Because of the inadequate blood flow and improper growth, the liver does not function properly.
The liver is an enormously important organ that has many functions. The most notable abnormalities that result from a shunt are those affecting:
The central nervous system (CNS). The neurologic disorders are collectively referred to as hepatic encephalopathy and can range from lethargy and dullness to seizures, blindness, and erratic behavior.
The gastrointestinal system. The most common gastrointestinal signs are anorexia, vomiting and diarrhea.
The urinary tract. The most frequently documented urinary signs are straining to urinate and blood in the urine. The urinary problems are a result of ammonium biurate bladder stones that occur secondary to liver dysfunction. Some pets also drink more and urinate more than normal. Your pet may show many of these signs or only a few.
Although the CNS problems are the most common, some pets show only urinary tract or gastrointestinal signs. Some animals may show a failure to grow normally as the only obvious abnormality. Because the clinical signs can be quite varied, there are a number of other conditions that can cause similar signs, including:
Infectious diseases. Distemper is a common viral illness of young dogs. Infections with protozoal organisms such as Toxoplasma and Neospora can occur in dogs . All of these diseases may cause abnormalities of the CNS and gastrointestinal tract, causing signs similar those seen in patients with portosystemic shunts.
Toxicities. Ingestion of, or exposure to, certain toxins may produce multiple neurologic abnormalities that can mimic the signs seen with hepatic encephalopathy. Toxins may include ethylene glycol (antifreeze), lead, flea products (organophosphates) and prescription medications. These animals often present with vomiting and/or diarrhea as well.
Hydrocephalus. This is a congenital brain defect that may cause seizures or abnormal behavior in young animals.
Epilepsy. This is a seizure disorder most commonly seen in dogs, with no known cause.
Hypoglycemia. Low blood sugar will often cause weakness and seizures, if severe. Young animals are prone to developing hypoglycemia if they are not eating normally.
Urea cycle enzyme deficiency. This is a rare metabolic disorder in which the animal is missing an enzyme necessary for normal ammonia processing. Build-up of ammonia causes encephalopathy, but the patient does not have a shunt.
Hepatic microvascular dysplasia. This disorder has only been described in dogs. It is another congenital disorder that causes abnormal liver function and can therefore cause many of the same signs that are seen with shunts. This is not a surgically correctable disorder.
Urinary tract infections. Bladder infections or inflammation will cause blood in the urine and straining to urinate. A simple urinary disorder would not cause the other clinical signs often seen in patients with shunts.
Gastroenteritis. There are multiple causes of vomiting and diarrhea. Although some pets with hepatic shunts will show only gastrointestinal signs, this is less common.