Portosystemic Shunts in Cats

Key takeaways

A portosystemic shunt (PSS) occurs in cats when abnormal blood flow from the digestive and ancillary organs bypasses the liver.

  • Blood from the digestive and enzyme-secreting organs normally flows through into the liver where toxins are processed before being eliminated by the kidneys
  • When blood bypasses the liver, toxins build up in the bloodstream, leading to symptoms of poisoning including drooling, vomiting, blindness, bloody urine, and incoordination
  • Symptoms of PSS are a medical emergency warranting immediate veterinary attention 
  • Shunts are either congenital or acquired; acquired shunts develop secondary to an underlying disease process
  • Treatment depends on the type of shunt present
  • Surgery is considered the gold standard treatment for congenital shunts
  • Acquired shunts are typically managed medically with diet and medications
  • Prognosis is generally good to excellent with surgical correction of congenital shunts
  • Prognosis for acquired shunts is poor
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A closer look: Portosystemic Shunts in Cats

A portosystemic shunt (PSS) describes when abnormal vessel/s allow blood flow from the stomach, intestines, pancreas, and spleen to bypass the liver and enter circulation to the rest of the body.

Blood from the above-mentioned organs normally flows through the portal vein into the liver where multiple functions, such as breaking down toxic substances like ammonia and urea, are performed. If these toxins are not metabolized by the liver, they enter the bloodstream and accumulate, leading to symptoms of poisoning.

Symptoms depend on the type of shunt, the location of the shunt, and the level of toxicity built up. Some pets have only a mild single symptom while other pets have multiple severe symptoms.

Risk factors

Pets with portosystemic shunts are either born with them or develop them slowly over time. Both types are uncommon in cats. Any cat showing excessive drooling, vomiting, blindness or incoordination needs urgent veterinary attention.

Eighty percent of shunts are congenital, meaning they are present at birth. Male cats are more commonly affected by PSS. One out of four affected male cats with a portosystemic shunt also have undescended testicle(s). Persian and Himalayan breeds have higher rates of PSS, suggesting a genetic component.

Kittens with congenital shunts typically have a history of failure to gain weight and are noted to be smaller in body stature. Pets with acquired shunts tend to be older and generally are in poor body condition. Symptoms generally get worse as the disease continues.

Possible causes

Congenital shunts are usually associated with a single abnormal vessel that develops improperly in the womb. Acquired shunts develop secondary to chronic high blood pressure in the portal vein.

Chronic elevations of portal vein blood pressure cause numerous smaller blood vessels to develop into functioning shunts. Common causes of chronic portal hypertension are portal vein hypoplasia, hepatic vessel malformations, and liver cirrhosis.

Main symptoms

Testing and diagnosis

Diagnostics include

  • Physical exam and detailed history
  • Blood work,
  • X-rays
  • Urinalysis

A CT scan is needed to confirm diagnosis and to determine the location and number of shunt(s) present. Abdominal ultrasound can be attempted if a CT scan is not readily available, but this form of imaging has lower resolution and results may not be conclusive.

Steps to Recovery

Surgical correction of PSS is the treatment of choice for the congenital form.

Acquired portosystemic shunts do not lend themselves to surgical correction due to the presence of an underlying disease process and (often) multiple shunts. Medical management can be attempted with acquired shunts.

Medical management consists of a highly digestible, high quality protein diet fed in multiple small meals throughout the day. Supplementation to lower levels of ammonia and urea in the bloodstream may also be beneficial. Antibiotics may also be prescribed for the same reason.

Congenital shunts persist until they are surgically corrected. Prognosis is good to excellent for about half of cats with surgical correction of their PSS if they survive the risk period before and after surgery. Approximately twenty-five percent of cats have a poorer long-term prognosis after surgery and recurrence is possible.

Cats with portosystemic shunts are prone to forming bladder stones; close monitoring for any symptoms such as bloody urine, difficulty urinating, or straining to urinate is needed after diagnosis.

Prognosis is poor for acquired shunts.


PSS is thought to be inherited, especially in Persian and Himalayan breeds, so selective breeding may help prevent the condition. Portosystemic shunts are not contagious.

Are Portosystemic Shunts in Cats common?

Portosystemic shunts are uncommon in cats.

Typical Treatment

  • Surgery
  • Feeding small, frequent meals with a highly digestible protein
  • Dietary supplementation
  • Antibiotics

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