By Dial A Vet Veterinary Team
Some puppies seem fine one moment and then, an hour after dinner, stand with their head pressed against the wall, wander in circles, or appear temporarily blind. Others are simply the smallest of the litter and never catch up. A portosystemic shunt is one possible reason. It is an abnormal blood vessel that lets blood from the intestines skip the liver, so toxins the liver would normally remove reach the rest of the body, including the brain. The good news is that many dogs do very well with treatment, especially when the shunt is found early.
Key takeaways
- A portosystemic shunt (PSS, or liver shunt) is a blood vessel that diverts blood around the liver.
- Most shunts are congenital and found in young dogs, often under one to two years old.
- Signs include stunted growth, unusual behaviour after meals, seizures, increased thirst and urinary stones.
- Diagnosis involves blood tests (including bile acids), urine tests and imaging, often CT.
- Treatment includes diet and medication to manage signs, and often surgery or an interventional procedure to close the shunt.
How a shunt affects the body
Blood from the stomach and intestines carries nutrients and toxins, including ammonia from protein digestion. Normally this blood flows through the portal vein into the liver, which processes nutrients and removes toxins. In a dog with a shunt, much of that blood bypasses the liver and goes straight into general circulation. The liver also receives less blood flow, so it stays small and does not develop or function normally.
The build-up of toxins can affect the brain, causing a condition called hepatic encephalopathy.
Types of shunt
- Extrahepatic shunts sit outside the liver and are most common in small and toy breeds, including Yorkshire Terriers, Maltese, Shih Tzus, Miniature Schnauzers, Pugs, Havanese and Bichon Frises.
- Intrahepatic shunts sit inside the liver and are more common in large breeds, including Irish Wolfhounds, Labradors, Golden Retrievers, Australian Cattle Dogs and Old English Sheepdogs.
- Acquired shunts develop later in life as a result of high blood pressure in the portal vein, usually from chronic liver disease. They are managed differently and are not usually closed surgically.
Signs to watch for
Neurological signs, often worse after meals:
- Head pressing, circling, aimless wandering or pacing
- Disorientation or apparent blindness
- Weakness, wobbliness or trembling
- Drooling (particularly common in affected cats)
- Seizures, or dullness and unresponsiveness in severe cases
Other signs:
- Small size, poor growth or failure to gain weight
- Poor appetite, vomiting or diarrhoea
- Increased thirst and urination
- Blood in the urine, straining, or urinary blockage from ammonium urate stones
- Slow recovery from anaesthetic or sedation, sometimes noticed after desexing
- Unusual reactions to certain medications
Signs can be subtle and may come and go, so many owners do not realise anything is wrong until their dog has bloods taken before an anaesthetic.
When it is an emergency
Go to a vet immediately if your dog:
- Has a seizure or a cluster of seizures
- Is collapsed, very dull or unresponsive
- Is straining to urinate with little or nothing coming out
- Is vomiting repeatedly or has bloody diarrhoea
How vets diagnose a shunt
- Routine blood tests may show low protein, low urea, low glucose, low cholesterol and small red blood cells.
- Bile acid testing, taken before and after a meal, is a key test of liver function. Abnormally high results support a shunt or other liver problem.
- Ammonia levels in the blood may be raised.
- Urine testing can reveal ammonium urate crystals.
- Imaging: abdominal ultrasound can find many shunts and a small liver. CT angiography is now commonly used to map the shunt precisely before surgery.
Your vet may refer you to a specialist internal medicine or surgery team for advanced imaging and treatment.
Treatment options
Medical management
Used to stabilise dogs before surgery, or long term for dogs who cannot have surgery. It typically includes:
- A liver-supportive diet, with moderate amounts of high-quality, easily digested protein, prescribed by your vet
- Medications to reduce ammonia production and absorption in the gut
- Anti-seizure medication if needed
- Treatment of urinary stones if present
Surgical or interventional treatment
For many congenital shunts, closing the abnormal vessel gradually offers the best long-term outcome.
- Extrahepatic shunts are commonly closed with a device that slowly narrows the vessel over weeks, such as an ameroid constrictor or a cellophane band. Gradual closure gives the liver time to adapt.
- Intrahepatic shunts are more complex and may be treated by specialist surgery or by interventional radiology, where coils are placed through a catheter.
Dogs are closely monitored after surgery, as complications such as seizures or high portal pressure can occur, usually in the first few days.
Outlook
Many dogs with a single extrahepatic shunt that is successfully closed go on to live normal lives, often without long-term medication. Outcomes for intrahepatic shunts and dogs managed medically vary more. Your vet or specialist can give a specific outlook.
Living with a dog with a shunt
- Feed exactly the diet your vet prescribes, and avoid high-protein treats.
- Give medications as directed.
- Avoid known triggers, such as large protein meals.
- Keep a diary of any neurological episodes.
- Tell any vet, groomer or boarding kennel about your dog's condition, as some sedatives and medications need adjusting.
FAQ
Is a liver shunt hereditary?
Congenital shunts are more common in certain breeds, suggesting a genetic component. Affected dogs are usually not recommended for breeding.
Can a dog live without surgery?
Some dogs are managed medically for years, though surgery generally offers a better long-term outcome for suitable congenital shunts.
Can older dogs have a shunt?
Yes. Some congenital shunts are found in older dogs with mild signs, and acquired shunts develop later in life.
Can cats get liver shunts?
Yes, though less commonly. Drooling and behaviour changes after meals are typical signs.
Talk with a vet
If your puppy is not growing well or acts strangely after meals, a Dial A Vet veterinarian can talk through the signs and help you plan the right tests with your local vet. Book a Dial A Vet consult. Seizures or collapse need an emergency vet straight away.
References
- Berent AC, Tobias KM. Portosystemic vascular anomalies. Veterinary Clinics of North America: Small Animal Practice. 2009;39(3):513-541.
- Merck Veterinary Manual: Congenital portosystemic shunts in small animals
- Merck Veterinary Manual: Hepatic encephalopathy in small animals
- American College of Veterinary Surgeons (ACVS): Portosystemic shunts
Disclaimer: Educational only. This page does not replace an examination or advice from your own veterinarian. If you are worried about your pet right now, contact your local vet or nearest emergency animal hospital.