What is a portosystemic shunt?

A portosystemic shunt (PSS), also known as a liver shunt, occurs when an abnormal vessel forms causing blood to shunt, or bypass, the liver. Normally, blood from the intestines and digestive tract enter through the portal vein where it is carried to the liver and detoxified.

However, in cases where a shunt occurs, this excess blood bypasses the liver through the shunt vessel and enters straight back into the main blood supply, where it is pumped around the body.

This means that, not only can the liver not detoxify the blood, but it is also deprived of the various nutrients it needs to develop which stunts growth and can cause abnormal behaviour, seizures and urinary tract disorders.

What causes a liver shunt?

Portosystemic shunts fall into two different categories:

  • Congenital shunts, that occurs from a birth defect. This is the most common cause of portosystemic shunts
  • Acquired shunts, which develop later in life and most commonly occur in older cats and dogs with liver cirrhosis.

What are the symptoms of a portosystemic shunt in
cats and dogs?

The most common symptoms include but are not limited to:

  • Poor weight gain
  • Poor muscle development
  • Abnormal behaviours including:
    • Disorientation
    • Walking in circles
    • Staring into space
    • Head pressing


Less common symptoms include:

  • Excessive urination
  • Excessive thirst
  • Vomiting
  • Diarrhoea
  • Blindness
  • Bladder infections
  • Kidney stones


Similarly, pets suffering from a liver shunt are likely to take longer to recover from general anaesthetics, while those born with PSS are also likely to be smaller than average.


vet assessing a cat


How is the condition diagnosed?

As with many conditions, if you think your pet may be suffering from a PSS, you should contact your vet as soon as possible. First, your veterinary professional is likely to conduct a full physical examination to rule out any other underlying causes or pre-existing conditions. They are then likely to undertake a range of tests for diagnosis such as blood tests and urinalysis to look for any abnormalities.

However, as a shunt cannot be diagnosed by a blood test alone, advanced imagery such as an ultrasound, MRI and CT scans along with X-rays, or exploratory surgery will be needed to make an accurate diagnosis.


How is a portosystemic shunt treated?

There is a range of ways to treat PSS and treatment depends on the specific case and the symptoms that your cat or dog is presenting. Cases are usually treated medically first to prepare your pet for surgery.

Medical management

Typically, when it comes to PSS, medical management is undertaken first to ensure that your pet can withstand surgery and general anaesthetic, as pets suffering from the condition take longer to recover. Therefore, treatment usually includes antibiotics to decrease toxin production and lactulose to decrease the production of ammonia.

Similarly, your vet may prescribe a specific diet to reduce the number of toxins in the bloodstream and help deal with some of the clinical signs. A low protein diet has been proven to be effective in cases, while an enema or IV fluids may also be given in order to remove toxins before they are absorbed.

Surgical treatment

During surgery, the shunted vessel is partially closed off, and the blood flow is redirected into the liver. Commonly, veterinary surgeons will use an ameroid constrictor, a stainless steel ring with a casein core, to close the shunt slowly. This works by absorbing abdominal fluid and swelling, putting pressure on the shunt and causing it to gradually close over a number of weeks. Similarly, cellophane bands may also be used. These also work by inducing inflammation – they are placed around the shunt vessel,

As the shunt closes, the liver will grow due to the influx of nutrients and is likely to function normally and be of normal size within 2 to 4 months. After surgery, your pet will need to remain calm and still for around a week, and once you take your pet home, it’s important to keep an eye on them in case any complications occur, however, your vet will provide you with further guidance following surgery. It is important, also, to note that sometimes, animals can suffer from seizures following surgery, but these can be managed with anti-seizure medication.

Will my pet recover from a liver shunt?

Typically, the prognosis for dogs and cats with a liver shunt depends on how early the condition is diagnosed, along with the treatment provided. For the majority of patients, when surgery is used and the shunt is fully closed, cats and dogs are likely to have a normal life expectancy with no need for additional medication or treatment.

We understand that surgery can be nerve-wracking, which is why we’re there to support you and your pet from start to finish, keeping you informed every step of the way.