Portosystemic Shunts in Dogs and Cats

What is a Portosystemic shunt?

The liver is a vital organ of the body. It functions as part of the digestive system, filtering toxins and by-products of digested food and drink. In a normal pet, blood flows from the intestines to the liver through a major blood vessel to be filtered. This major blood vessel is called the portal vein. Once filtered, blood returns to the heart to be redistributed to the rest of the body. During pregnancy, however, this works differently as the mother’s liver filters the toxins for her fetus. As a result, the portal vein of the fetus bypasses the liver via a shunt and returns straight to the heart. Usually, this shunt closes in the first few days after the puppy/kitten’s birth.

Portosystemic shunt (PSS) occurs in puppies and kittens where the shunt remains open, and blood from the digestive tract bypasses the liver without filtration of toxins. As the puppy/kitten no longer has its mother’s liver to process the toxins (eg. ammonia), this results in the accumulation of toxins in the bloodstream. This happens in about 1 in 500 dogs, occurring in mostly purebred dogs rather than mixed breeds. This disease has also been documented in purebred cats, mainly in Persians and Himalayans. There are two types of PSS – congenital and acquired. Most portosystemic shunts are congenital, but sometimes it can be acquired with liver disease/damage. Congenital PSS can be found in the liver (intrahepatic) or before the liver (extrahepatic). Intrahepatic shunts are found more commonly in large pure-breed dogs, and extrahepatic shunts usually occur in miniature- or toy-breed dogs.

Dog breeds with a higher risk of PSS include Yorkshire terrier, Maltese terrier, Silky terrier, miniature schnauzer, miniature and toy poodles, Bichon Frise, shih tzu, Havanese, Pekingese, German shepherd dog, golden retriever, Doberman pinscher, Labrador retriever, Irish setter, and Samoyed.

What are the symptoms of PSS?

The most common symptom of congenital PSS is poor weight gain and stunted growth. The patient may even be the runt of the litter. Other symptoms include vomiting, diarrhea, lethargy, unresponsiveness, seizures, disorientation, circling, dull coat and poor skin condition, increased thirst and urination. Often, after a meal, the patient may appear more disorientated than usual – pacing, or even head-pressing. The severity of symptoms depends on the location of the shunt and the amount of toxins in the body. In some cases, there can be no symptoms at all.

How is PSS diagnosed?

Symptoms and history of the patient, together with blood tests (including bile acids pre- and post-meal), urinalysis, and imaging tests. In Malaysia, the only imaging tests available are X-ray, CT scan, MRI, ultrasonography and fluoroscopy.

Treatment

Medical management using dietary adjustments, antibiotics, and lactulose can be sufficient in managing the condition well enough. Sometimes, diet change alone helps improve the dog or cat’s condition. Surgery, however, is an option if the shunt is extrahepatic and can be a successful cure for more dogs than cats.  

Surgery

PSS surgeries are well documented and most often recommended for congenital shunts that can be closed surgically. The location of the shunt is key to successful surgery. A PSS patient is often cured if the shunt is closed without any complications or if no further acquired shunts develop after closing the main shunt. Fluoroscopy-assisted assessment of the shunt before and after ligation is the current technique of choice as it allows visualization of the shunt (if more than 1) and also how the redirection of blood flows back into the liver after the shunt closure (see image below). Surgery remains a curative option for this disease and is recommended for cases that show a promising prognosis after a thorough diagnosis is made.

Fluoroscopy showing shunting (left) and correction of the shunt (right)*
*(Image credits to Professor Vicky Lipscomb of Royal Veterinary College, London)

PSS surgery is available at Kota Damansara Veterinary Centre. You may call to make an appointment to consult a surgeon there if necessary.