A liver shunt in cats is a blood vessel abnormality that allows blood from your cat’s intestines to bypass the liver and go straight to their heart. The condition is uncommon in cats and is usually a birth defect. Other names for liver shunts include portosystemic shunts or porto-caval shunts. Most liver shunts are diagnosed in cats under 1 year old, but they can affect cats of any sex or breed. 

Liver shunts let toxins and unprocessed nutrients from the gut flow all around the body. It’s as if the liver isn't working, so symptoms resemble those of liver disease. They vary in severity from mild to life-threatening. In the short term, symptoms can be managed with medicine and a special diet. Curing liver shunts usually requires complex surgery.

What are liver shunts in cats?

Liver shunts in cats are blood vessels that bypass the liver. That’s fine when a kitten is in the womb. Their blood has been through their mother’s liver first. But when a kitten is born, the vessel should close. The kitten starts to feed, and its own liver gets to work.

• The liver is the body’s processing plant.

• Blood from the intestines is full of ‘raw’ nutrients. The liver turns these into fuel for the body. Without help from the liver, most nutrients are unusable. And they can be very harmful.

• Blood from the intestines will also carry toxins. 

• Lack of nutrition and the build-up of toxins make your cat very sick.

• A toxic chemical called ‘ammonia’ causes some of the most severe symptoms. It’s produced by bacteria in the intestine when they digest proteins. Increasing ammonia harms your cat’s entire body, especially their brain.

Shunt blood vessels can be outside the liver (extrahepatic) or inside the liver (intrahepatic). In both cases, shunted unfiltered blood gets past the liver.

• Congenital shunts happen because of a genetic (birth) defect. We don't always know why they happen. Around 80% of liver shunts are congenital. 

•  Acquired shunts result from severe and advanced liver disease. Cats with acquired liver shunts will be very ill because of the underlying illness.

What are the symptoms of liver shunts in cats?

Cats with liver shunts show a wide range of symptoms. These include:

• Poor body condition: failure to gain weight, stunted growth, and weight loss

• Neurological symptoms: head-pressing, tiredness, depression, unsteadiness, walking in circles, blindness, and seizures

• Gastrointestinal upsets: vomiting, diarrhoea, and not eating

• Urinary changes: drinking more, urinating more, difficulty passing urine, and bladder stones

Symptoms may be present all the time, and they can get worse after your cat eats something.

Which cats are most at risk of having a liver shunt?

• Liver shunts in cats are most commonly congenital and often extrahepatic.

• Certain pedigree cats, including Siamese and Persians, may be overrepresented.

• Liver shunts usually appear in kittens and young cats less than a year old. But sometimes blood can flow through the liver as well as the shunt. In these cases, symptoms may be milder and show up later in older cats.

How do vets diagnose liver shunts?

Shunts are not always easy to diagnose. Especially partial shunts, where some blood from the gut does pass normally through the liver. This means your cat may still get enough nutrition and have less severe or only intermittent toxic effects.

Aside from the symptoms, vets diagnose liver shunts from:

• General blood tests: to check organ health and red and white blood cells.

• Urine tests: to check for urate crystals and stones, which form in the urine when liver shunts develop.

• Special blood tests: for ammonia, and the bile acid stimulation test.

• Advanced imaging: including ultrasound and CT scans.

• Advanced imaging with ‘contrast studies’: using special dyes and imaging to ‘see’ how blood travels through the body. Sometimes surgery is carried out at the same time if the abnormal blood vessel is located.

How do vets treat liver shunts in cats?

As soon as a vet suspects your cat may have a liver shunt, they’ll start your cat on medical treatment to control the symptoms. But treatment for a liver shunt usually means a complicated operation to close the abnormal vessel.

Medical treatment

Aims to reduce ammonia production and ensure your cat gets enough energy:

• Special diet: provides essential nutrition, even for kittens

• Lactulose: a liquid medicine that stops bacteria from making ammonia

• Antibiotics: to control gut bacteria

• Anti-seizure medicines: to control neurological symptoms

Some cats can be managed with medical treatment alone. These are usually older cats with ‘partial’ shunts and some normal blood flow through the liver.

Surgical treatment

Involves closing off the abnormal blood vessel to allow blood flow through the liver:

• It’s not safe to close a shunt completely straight away. The liver needs time to develop and adjust to its new workload. So it’s partially closed to start with, then gradually seals over with time. This might mean another operation later on.

• Your cat has a general anaesthetic, so they sleep through the procedure.

• The vet uses a silk suture material or a special type of cellophane band to partially close the shunt.

• Shunts inside the liver that can't be reached by a surgeon can be sealed from inside the blood vessel. This uses a spring coil threaded into the shunt vessel. A blood clot forms on the coil and gradually seals the shunt.

What are the possible complications of surgery?

Surgery is often successful for shunts that are present at or shortly after birth. Some cases will need further operation(s) or medical management. Unfortunately, a small percentage of cats may not recover from the operation.

Caring for a cat with a liver shunt at home

There are no home remedies for liver shunts. But good home care is an essential part of treating and managing liver shunts in cats.

• Give all medicine prescribed by your vet at the correct time and dose.

• Ideally, feed a prescription diet to safely provide your cat with the nutrition they need. This is especially important for kittens and young growing cats.

• If a prescription diet isn’t an option for your adult cat, feed easily digested, high-quality proteins as advised by your vet.

• For treats, stick to vet-approved options.

• Always get advice from your vet before feeding home-cooked diets or treats to your cat.

Quality of life

Surgery isn’t suitable for every type of patient and every type of shunt. And sometimes surgery is not successful. Your cat may deteriorate in the days immediately after surgery, or continue to suffer from severe symptoms. Worsening seizures and neurological problems are particularly devastating. Medical treatment alone may not keep them comfortable and able to enjoy a happy life. If this happens, it may be kindest to discuss euthanasia with your vet.

It’s a heart-wrenching decision to make at any time, and especially with a young cat. But all we can focus on is what’s best for them. Always talk to a vet for support.

Are other pets at risk?

Liver shunts affect individual cats. Other cats and pets are not at risk.

Can liver shunts in cats be prevented?

• Congenital liver shunts are present at birth and can't be prevented.

• Cats with a liver shunt should not be used for breeding, even if surgery appears to have cured them.

• Some acquired shunts can be prevented if the underlying liver disease is identified early and is treatable.

Liver shunts in cats – when to worry

Find your nearest emergency vet if your cat is:

• Suddenly blind

• Not responding to you

• Unconscious

• Looking weak, vacant or unsteady

• Having a fit or seizure