LIVER SHUNT IN DOGS

A portosystemic shunt (PSS), commonly called a liver shunt is an abnormal blood vessel connection that allows blood from the gastrointestinal tract to bypass the liver and enter the general circulation without proper filtration.

The liver normally processes nutrients and helps remove or neutralize many substances absorbed from the gastrointestinal tract before they enter systemic circulation.

The liver is necessary for maintaining a healthy metabolism. When a PSS exists, toxins are left circulating in the blood, affecting several systems but primarily the central nervous system and gastrointestinal system.

A PSS can occur at any age but is most commonly diagnosed in younger animals and smaller breed animals. If untreated, a PSS may result in chronic disease, neurologic dysfunction and failure to thrive. Early diagnosis is critical to prevent further damage.

Causes and Types

Liver shunts can be divided into two categories: congenital and acquired. Congenital liver shunts occur when the fetus develops improperly formed vascular tissue, resulting in blood being diverted past the liver rather than being properly filtered.

This type of liver shunt is by far the most common and is frequently identified in breeds of dogs like Yorkies, Maltese, Shih-Tzus and miniature schnauzers.

Acquired liver shunts develop at a later age because of previous liver disease or increased portal vein pressures that have developed secondary to some prior insult.

Acquired shunts develop when increased pressure in the portal circulation causes abnormal blood vessels to form or enlarge, allowing blood to bypass the liver. While less frequent, acquired shunts are generally associated with older dogs that suffer from chronic liver disease.

Symptoms

Early Signs

• Poor growth
• Reduced appetite or picky eating
• Vomiting after meals
• Diarrhea or soft stools
• Lethargy

Neurological Signs

• Disorientation or confusion
• Head pressing against walls
• Staggering or unsteady walking
• Seizures in severe cases
• Sudden behavior changes after eating

Risks and Complications

Untreated liver shunts will result in very serious and progressive consequences. The accumulation of toxins in the dog’s circulation leads to hepatic encephalopathy, which impacts a dog’s brain function.

The symptoms of dogs with untreated liver shunts are progressive and may include severe neurological problems, poor liver development and an inability to metabolize food components.

In the most extreme situations, seizures, coma and life threatening metabolic disorders can develop. Growth retardation is another common problem for puppies due to their bodies being unable to digest or use nutrients.

Diagnosis

A diagnosis is typically based on an accumulation of clinical signs and additional diagnostic testing.

Common diagnostic testing

• Blood test results indicating altered liver function
• Elevated bile acids postprandially
• Hypouricemia
• Ultrasound of the abdomen to visualize liver anatomy and vascular Blood flow
• CT angiography (CTA) to precisely identify the abnormal shunting vessels
• Portography in complex cases

Treatment

Treatment is dependent upon the degree of the condition, the age of the dog and the location of the shunt.

Medical Management

Medical management is the first line of treatment; however, its primary purpose is to stabilize the dog before surgery or treat a milder case of the condition. Its focus is to decrease the amount of toxin that builds up within the body by decreasing the level of ammonia produced in the body.

Common approaches include:

• A low protein diet
• Dietary supplements to lower ammonia levels
• Administration of antibiotics to reduce bacterial populations in the gastrointestinal tract
• Lactulose to enhance the removal of toxins from the intestines

Although Medical Therapy will provide temporary relief from the symptoms associated with this condition, it will not repair the defect that exists with the Shunt.

Surgical Treatments

Surgery is considered to be an effective means of treating shunts that have been present since birth. Surgery provides the ability to correct the defect in the abnormal blood vessel and direct blood flow back through the Liver.

There are many forms of surgical treatments available. A few of them include ameroid constrictors or cellophane banding. Each method allows for gradual closure of the shunt, thereby minimizing risks associated with the abrupt cessation of blood flow.

Post-Treatment Care

Following surgical treatment, owners are required to monitor their dog’s recovery closely as well as manage their diet properly to promote a healthy functioning liver.

• Regular blood test follow ups
• Properly managed diets that support liver health
• Slow return to full normal activity
• Evaluation of possible neurologic signs

While many dogs improve significantly post surgically (especially if treated at an early age), it is also common for some dogs to have residual issues.

Prevention

It may not be possible to completely prevent congenital liver shunts; however, by implementing reasonable and prudent breeding practices, you can help lower your chances.

• Breeding should not occur in any animal with previously diagnosed genetic liver shunt defects.
• High risk breed animals should be screened early for potential liver shunts.
• Frequent veterinary visits should be scheduled for poorly growing puppies.
• If your puppy has exhibited any evidence of neurologic or gastrointestinal disease, schedule a prompt appointment with a veterinarian.