Liver shunts in dogs may go unnoticed in a dog, but if left untreated in time it can cause serious health problems. Severe liver shunts can cause seizures and can be fatal, so recognizing the signs of this congenital condition can save your dog’s life.
What is Liver Shunt (Portosystemic Shunt) in Dogs?
A liver shunt in dogs is a congenital condition in which vessels that are supposed to carry blood to the liver bypass the liver through an abnormal vein. This allows the blood to enter the body without undergoing the liver filtration process to remove toxins, drugs, and wastes from the blood. It also inhibits the absorption of critical nutrients that would normally occur in the liver. In veterinary terms, this condition is called a portosystemic shunt or PSS. Some dogs have more than one shunt, others have only one, and dogs may also have intrahepatic (inside the liver) or extrahepatic (outside the liver) shunts.
The portal vein is a large vein that collects blood from the gastrointestinal tract, pancreas, and spleen and transports it to the liver, where toxins and other byproducts are removed. A liver shunt occurs when an abnormal connection persists or occurs between the portal vein or one of its branches and another vein.
In most cases, the liver shunt is caused by a birth defect called a congenital portosystemic shunt. In some cases, multiple small shunts form due to serious liver disease such as cirrhosis. These are called acquired portosystemic shunts.
Symptoms of Liver Shunts in Dogs
Most signs of liver shunts in dogs appear in the first few weeks of life, but if the shunt is less severe others may not become apparent until later in life.
The most common sign that a dog has a liver shunt is slow growth. These tiny puppies are often diagnosed with liver shunts because this problem causes problems in assimilation of nutrients from food. These little puppies may be quieter or more reserved than their peers due to problems with energy regulation.
Chronic liver shunts, or in severe cases, can cause a dog to press his head against objects or people, stare at walls and doors, stumble as if intoxicated, go in circles or even have seizures. These neurological symptoms often get worse after the dog eats. Rarely, dogs with liver shunts may experience vomiting and diarrhea, especially if the kidneys and bladder are affected by toxins that build up in the body. In these cases, excessive thirst and urination may also occur.
Causes of Liver Shunts in Dogs
Congenital portosystemic shunts are present at birth and are the result of one of two things happening in the body:
- ductus venosus remains open: The ductus venosus, which comes from the placenta and bypasses the liver, remains open and intact even when the developing fetus no longer needs it in utero.
- Abnormal blood vessel development: An abnormal blood vessel develops in the body that remains open after the ductus venosus closes in utero.
Another type of liver shunt can occur in dogs due to severe liver disease, but this is not present at birth and is referred to as an acquired portosystemic shunt. This type of shunt is not seen in puppies, but more so in older dogs struggling with liver problems.
Breeds at Risk of Developing a Liver Shunt
There is no genetic testing for portosystemic shunts in dogs, but breeds commonly affected include:
Diagnosing Liver Shunts in Dogs
After a complete physical examination, your veterinarian will do blood tests to check the liver and blood. Complete blood count, liver enzyme analysis, and bile acid test are starting points for shunt diagnosis. A urinalysis may also be done to assess the health of the bladder and kidneys. Sometimes further diagnostic tests are recommended and these may include ultrasound, X-rays, CT scans, MRI, and even surgery to visualize the liver and blood vessels.
Diagnosis is based on medical history and clinical findings. Common diagnostic tests include:
- Complete Blood Count (CBC) and Serum Chemistry: Typical abnormal findings include mild anemia or smaller-than-normal red blood cells (microcytosis), low blood urea nitrogen (BUN), and increases in albumin and liver enzymes (AST, ALT).
- Urine test: Urine may be dilute (low urine specific gravity) or evidence of infection. Urine may contain tiny prickly crystals known as ammonium biurate crystals.
- Bile Acid Test: Bile acids are elevated in most dogs with liver shunts. If bile acids are slightly elevated or the dog appears clinically normal despite abnormal test results, tests are usually repeated in three to four weeks.
Additional diagnostic tests may include:
- Ultrasound with Doppler flow analysis.
- Computed tomography (CT) scan or nuclear scintigraphy, which is a nuclear scan that measures blood flow through the liver.
- Radiograph, an X-ray that shows blood vessels supplying and/or bypassing the liver using radio-opaque dye injected directly into the portal vein
- Magnetic resonance imaging (MRI).
- Exploratory surgery (laparotomy).
Some breeds such as Yorkshire Terriers, Old English Sheepdogs, Irish Wolfhounds, Cairn Terriers and Beagle Dogs have an increased incidence of portosystemic shunts. Small breed dogs usually have extrahepatic shunts (blood vessels outside the liver), while larger breeds have intrahepatic shunts (abnormal blood vessels inside the liver). Surgical repair of extrahepatic shunts is less difficult than intrahepatic shunts.
What are bile acids?
Bile acids are produced in the liver and stored in the gallbladder between meals. Normally, they are released into the intestines to help break down and absorb fats, then they are absorbed by the portal system and enter the liver, where they are removed and stored again until needed. Bile acid concentrations in the blood are increased in dogs with liver shunts because the liver does not have a chance to remove and store these chemicals once they are reabsorbed.
Tests that measure the amount of bile acids in the blood are used to screen for liver shunts. Two samples are usually taken to perform this screening test. The first sample is taken after fasting (before the meal). The second sample is usually taken two hours after a meal (post-meal). Actual technique may vary depending on the patient and your veterinarian’s preferences.
Liver Shunts in Dogs Treatment
Dogs with portosystemic shunts are often balanced with special diets and medications that try to reduce the amount of toxins produced and absorbed in the large intestines. Seriously ill dogs may need intravenous fluids to stabilize their blood sugar, an enema to remove intestinal toxins before they are absorbed, and medications such as diazepam to stop seizures.
The most common medical treatment regimen includes:
- Diet: The aim is to reduce the amount of protein in the diet and to feed only high-quality, highly digestible protein diets.
- Lactulose: Administration of this sugar changes the pH in the large intestine, which reduces the absorption of ammonia and other toxins and makes the intestinal environment unfavorable for toxin-producing bacteria.
- Antibiotics: In some cases, antibiotics are used to replace the bacterial population in the intestines and reduce intestinal bacterial overgrowth.
Surgical Treatment of Liver Shunts in Dogs
Surgical treatments in dogs include 1) cellophane tapes that induce inflammation, gradually closing the shunt with scar tissue, and 2) intravascular occlusive, clot-forming devices.
For most dogs with extrahepatic shunts, surgery provides the best chance for a long and healthy life. If an ameroid constrictor is placed, the survival rate is over 95%. Many dogs are clinically normal within four to eight weeks after surgery. A small percentage of dogs will develop more than one acquired shunt and should be managed with a lifelong protein-restricted diet and lactulose.
What is involved in the post-surgical management of patients with portosystemic shunts?
It is important to feed your dog a protein-restricted diet for at least six to eight weeks. After the blood test values return to normal, your dog can return to a high-quality maintenance diet. Lactulose is usually given a few weeks after surgery. As the shunt closes, the liver will begin to enlarge and will have normal size and function, usually within two to four months. Blood tests will be repeated at regular intervals to assess liver function.
Surgery is usually required to correct and close the shunt. This type of surgery is usually very successful in dogs with only one extrahepatic shunt, although some dogs may have multiple shunts or intrahepatic shunts that do not make surgery a therapeutic option.
If surgery isn’t an option financially, if a dog has multiple shunts or if the shunts are intrahepatic, then medications and diet can help manage symptoms. Special low-protein diets and medications to help a dog tolerate protein are often used as dogs with liver shunts cannot metabolize protein well. A veterinary nutritionist can assist in creating the ideal treatment plan for your dog.
Prognosis for Dogs with Liver Shunts
Most dogs respond well to treatment and continue to live normal lives. However, statistically speaking, surgery tends to yield better results than medical treatment. If there are neurological symptoms such as spinning, head-downing, and seizures, it is usually due to protein wastes that are not excreted from the body due to the liver shunt. Medications can help improve these symptoms. But in extreme cases, euthanasia is chosen if symptoms cannot be managed.
Most dogs recover almost instantly with the proper diet and medication. About a third of medically treated dogs will live relatively long lives. Unfortunately, more than half of medically treated dogs do not live long after diagnosis due to uncontrollable neurological signs such as seizures, behavioral changes or progressive liver damage. Dogs that tend to do well with long-term medical treatment are generally older at the time of diagnosis, have more normal blood test values, and have less severe clinical signs.
Dogs with single shunts, especially extrahepatic, have an excellent prognosis if surgical correction is performed.
How to Prevent Liver Shunts?
Since nearly all liver shunts are congenital abnormalities, there is little that can prevent them. In purebred dogs, conscientious breeders may try to minimize the occurrence of shunts by not breeding dogs whose puppies have been diagnosed with liver shunts.