Liver Shunts in Dogs

One of the most important functions of the liver in dogs is to detoxify the blood. When the items your dog ingests make it to the small intestine, it absorbs both nutrients and toxins into the bloodstream. Luckily, the blood passes through the liver, where it is detoxified before going to the rest of the body.

But what happens if the blood bypasses the liver, and those toxins aren’t filtered? When your dog has a liver shunt, this is exactly what occurs. Here, we’ll explain what a liver shunt is, signs to watch for, and treatment options.

What Is a Liver Shunt?

The vessels that carry blood from the intestines, spleen, and pancreas to the liver make up the portal venous system. When a vein is connected abnormally in a way that allows blood to bypass the liver, it is called a portosystemic shunt. Blood is “shunted” from the portal venous system to another vessel, bypassing detoxification in the liver. These shunts can be present at birth (congenital) or acquired later in life.

When a dog has a congenital venous shunt, around 75 percent of the time they have only one abnormal vessel. In the remaining 25 percent, they have multiple abnormal connections, resulting in multiple shunts. Shunts can occur outside of the liver (extrahepatic) or within the liver (intrahepatic).

Acquired shunts usually develop later in life as a response to other issues. With acquired shunts, your dog will typically develop multiple abnormal connections, meaning they have multiple shunts.

When the liver can’t detoxify blood, these toxins will go to the rest of the body, causing significant health concerns for your pup.

Causes of Liver Shunts in Dogs

Congenital liver shunts have different causes than acquired liver shunts. Let’s break down the origin of both. 

Causes of Congenital Liver Shunts

When your dog was a developing fetus inside their mother, they didn’t need their liver to detoxify blood from the intestinal tract because they weren’t eating anything. While in their mother’s uterus, puppies have a large shunt called the ductus venosus that allows blood to bypass the liver. This shunt is supposed to collapse after birth. 

If this vessel remains open after birth or your puppy develops another abnormal venous connection while growing within their mother, it is considered a congenital liver shunt.

Genetics play some role in the development of portosystemic shunts, with some breeds more likely to be affected than others. However, this condition is considered a complex trait that isn’t simply inherited from a dog’s parents.

Breeds that have a higher risk of developing congenital portosystemic liver shunts include:

• Yorkshire Terrier
• Old English Sheepdog
• Irish Wolfhound
• Cairn Terrier
• Maltese
• Labrador Retriever
• Miniature Schnauzer

Small and toy breeds tend to develop single extrahepatic shunts. Single intrahepatic shunts are more common in large breeds.

Causes of Acquired Liver Shunts

Acquired liver shunts occur later in life. If your dog develops significant liver disease, they can experience scarring (cirrhosis) of the liver. Because of the scarring, the blood vessels in the portal venous system may have high blood pressure (portal hypertension). Blood in the portal venous system will attempt to follow the path of least resistance, causing the dog to develop multiple abnormal connections that shunt blood around the liver. These shunts can occur in any breed or age of animal.

Symptoms of a Liver Shunt in Dogs

A dog with a large congenital liver shunt will develop symptoms earlier in life than a dog with a small, less severe shunt. Signs of a liver shunt in dogs can include:

• Stunted growth
• Poor muscle development
• Abnormal behaviors (appears disoriented, stares into space, walks in circles, presses head against walls), which sometimes develop after eating meals
• Seizures
• Drinking and/or urinating too much
• Vomiting
• Diarrhea
• Prolonged recovery after anesthesia

The signs of acquired shunts are similar (minus stunted growth), but your dog may also have signs of the underlying disease that’s causing portal hypertension. For example, a dog with severe liver cirrhosis may also have jaundice (yellow gums, eyes). Symptoms of acquired shunts are most often seen in middle-aged or older canines.

Diagnosing Liver Shunts in Dogs

To diagnose this condition, the veterinarian will start with a physical exam and routine lab work.

The blood work may show that the puppy is mildly anemic, and the blood chemistry may have changes in values that suggest a liver shunt. Urinalysis can show diluted urine and spiky crystals called ammonium biurate crystals. Although routine lab work may suggest a shunt and rule out other conditions, it’s unlikely to give a definitive diagnosis of liver shunt.

As most dogs with liver shunts will have elevated bile acids, your veterinarian will almost certainly want to run a bile acids test, which helps determine if the liver is functioning appropriately. This test involves taking blood from a dog who has not eaten in at least 12 hours (preprandial sample), feeding them a meal, and then drawing a second blood sample two hours after eating (postprandial sample). In a normal dog, bile acids enter the intestine and remain there until food has been digested. The intestines will absorb the bile acids, which will move through the portal venous system back to the liver. If the dog has a shunt, their bile acids will bypass the liver, so the levels remain elevated.

Other testing may include:

• X-rays of the abdomen, which may show a small liver
• Ultrasound of the abdomen, especially if the ultrasound machine allows examination of blood vessels (Doppler flow analysis)
• CT scan with contrast that allows the study of vessels
• MRI
• Exploratory surgery to see if an abnormal vessel is present

Liver biopsy may also be recommended if the dog has acquired portosystemic shunts or during surgical correction of congenital portosystemic shunts. 

Treatment for a Dog Liver Shunt

Depending on the situation, there are a variety of treatment options for congenital liver shunts.

Medical Treatment

If your dog is having significant clinical signs from their congenital liver shunt, initial stabilization should be completed with special diets and medications. Your pet may also receive a rectal enema to remove intestinal toxins before they are absorbed. Intravenous fluids may be administered to stabilize blood sugar. If your dog is having seizures, they will also be started on an anti-seizure medication such as diazepam.

Diet changes will aim to reduce the amount of protein in the diet and ensure that proteins are high quality and highly digestible. High levels of protein typically worsen the signs of liver shunts.

Your pet may be given a medication called lactulose. This decreases the absorption of ammonia and other toxins from the intestines, making the environment of the intestines less favorable to bacteria that produce toxins. Your veterinarian may also recommend specific antibiotics that reduce populations of toxin-producing bacteria.  

Surgical Treatment

In most cases of congenital liver shunts, surgery will be recommended. Most surgeons now use a metal band with an inner ring of casein (milk protein) called an ameroid constrictor, which slowly closes the shunt over time. The inner ring of casein absorbs normal abdominal fluid and gradually swells, pressing on the shunt and encouraging it to scar shut. 

Survival with this surgery is over 95%, and most dogs are clinically normal within 4-8 weeks after placement. The shunt is typically closed within 3-4 weeks. In dogs whose shunt does not completely close, the remaining shunt is usually less severe and can often be managed with diet and medication. Dogs with a single shunt have an excellent prognosis after surgery, especially if the shunt is extrahepatic.

About 1/3 of dogs treated medically will live a long life, but these tend to be dogs who are diagnosed later in life, meaning their shunt is less severe. Over half of dogs treated medically will be euthanized within 10 months of diagnosis because they continue to have uncontrollable neurologic signs, changes to their behavior, or liver damage.

Surgery is not typically recommended for acquired liver shunts. Instead, these dogs must be managed with a protein-restricted diet and lactulose for the remainder of their life.

Liver Supplements 

Pet parents often question if liver supplements will help their pets. Generally, they may help and are unlikely to hurt. Examples of liver supplements to speak to your veterinarian about include milk thistle and SAM-e (S-adenosyl-L-methionine), and active ingredients in these supplements vary. 

Supplements alone will not be enough, however, and most of these pets will still benefit from surgery or medical management.

Cost to Treat Liver Shunts in Dogs

Treating your pet’s liver shunt can be very expensive, but the positive outcomes make it worth it for many pet parents. Cost varies by the size of your dog and the type of shunt. The workup for diagnosing liver shunts can be around $1,500 to $2,000, sometimes more. Surgery for an extrahepatic congenital shunt (usually a small breed dog) can range from $3,500 to $5,000.

Both diagnosis of and treatment for intrahepatic shunts, which are more common in large breed dogs, are usually more complicated. Cost can range from $4,500 to $7,500 for workup and open abdominal surgery, but it can reach $8,000 to $9,500 for more complex procedures, like using a coil within the shunt to close the abnormal venous connection.

Overall, the price ranges from $2,000 to up over $10,000 for the treatment of liver shunts in dogs. 

In cases where medical management is acceptable, the workup can still be costly but long-term management with a medication like lactulose is usually affordable.

How to Prevent Liver Shunts in Dogs 

While it’s recommended not to breed dogs with portosystemic shunts due to the role genetics play, there is nothing you as a pet parent can do to prevent your puppy from developing a congenital liver shunt. They usually have them before they’ve even entered your home!

Acquired liver shunts can be prevented in some cases by keeping your pet’s liver healthy. Long-term or inappropriate usage of some medications, such as paracetamol or phenobarbital, can damage the liver. Keep your dog vaccinated against diseases that can affect the liver, such as leptospirosis or adenovirus.

Other cases may occur due to conditions you cannot prevent, such as idiopathic hepatitis, which is inflammation of the liver that occurs without a known cause. Annual or biannual lab work may help you and your veterinarian detect liver diseases early, allowing treatment to slow progression and keep your pet healthier for longer.