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.

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.

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.

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.

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.

Portosystemic shunts are uncommon in cats.

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