By Jennifer Coates, DVM
Liver shunts (technically called portosystemic shunts) are not that common in dogs, but if you are an aficionado of certain breeds or if your dog develops liver disease, you may find yourself in desperate need of information. Read on to learn all about liver shunts in dogs.
What Is a Liver Shunt?
First, we need to review some canine anatomy and physiology. A network of veins (called the portal system) drains blood away from the digestive tract. This blood carries nutrients, hormones, and waste material and is supposed to enter the liver before it travels to the rest of the body. The liver takes what it needs to function properly and also detoxifies the blood before sending it onward.
A shunt is defined as a passage “that allows the flow of materials between two structures that are not usually connected.” A portosystemic shunt is, specifically, an abnormal blood vessel (or vessels) that connects the “portal” system draining the digestive tract to the “systemic” circulatory system feeding the rest of the body, thereby bypassing the liver.
Causes of Liver Shunts in Dogs
Liver shunts can be divided into two categories: those that are present at birth (congenital shunts) and those that develop later in life (acquired shunts).
Congenital shunts are most common, being responsible for approximately 80 percent of cases. Dogs are usually quite young (less than 3 years old) when they start experiencing symptoms. A genetic cause is known for some breeds and suspected in others. Breeds at higher than average risk for congenital liver shunts include the Yorkshire Terrier, Dachshund, Maltese, Miniature Schnauzer, Lhasa Apso, Bichon Frise, Shih Tzu, Havanese, Toy and Miniature Poodle, Pekingese, Dandie Dinmont Terrier, Australian Cattle Dog, Australian Shepherd, Irish Wolfhound, Old English Sheepdog, Samoyed, Irish Setter, Labrador Retriever, Doberman Pinscher, Golden Retriever, and German Shepherd.
Acquired shunts typically develop when blood pressure within the veins connecting the digestive tract to the liver becomes elevated—most often because of diseases that cause liver scarring (cirrhosis). Dogs with acquired liver shunts tend to experience symptoms when they are older in comparison to those diagnosed with congenital shunts.
Symptoms of Liver Shunts in Dogs
Dogs with liver shunts generally have some combination of the following symptoms:
- Poor growth (congenital shunts)
- Poor appetite and/or eating unusual things
- Weight loss
- Increased thirst and urination
- Difficulty urinating or blood in the urine due to the formation of bladder stones
- Vomiting, which may contain blood
- Diarrhea, which may contain blood
- Behavioral changes like mental dullness, staring vacantly, poor vision, unsteadiness, circling, and head pressing
Diagnosing Liver Shunts in Dogs
These symptoms are obviously not unique to liver shunts. A veterinarian will start the diagnostic process by taking a complete health history, performing a physical examination, and running some basic tests such as blood work and a urinalysis. If he or she thinks that a liver shunt is likely, additional testing will be necessary to reach a definitive diagnosis. Possibilities include bile acid tests, blood ammonia levels, abdominal X-rays, abdominal ultrasound, and advanced imaging studies. Your veterinarian can discuss the pros and cons of each test with you based on the specifics of your dog’s case.
Treatment for Liver Shunts in Dogs
The type of liver shunt that a dog has and their age and overall condition determines what type of treatment is best. Most small breed dogs who have congenital shunts have just one abnormal blood vessel that is located outside of the liver. These are the most amenable to surgical correction. A single shunt that is located within the liver itself is more common in large breed dogs. These are still usually best treated with surgery, but the procedure is a little more difficult. Dogs with acquired shunts tend to have multiple, abnormal vessels and may be poorer candidates for surgery due to their underlying illness.
Surgery for liver shunts centers on blocking the flow of blood through the abnormal vessels so that more of it travels through the liver. This can involve the application of devices specifically designed to do this (e.g., ameroid constrictors or cellophane bands) or tying off the vessels with suture material. Oftentimes, the abnormal vessels cannot be completely blocked off all at once without the dog developing serious side effects like intestinal damage. Ameroid constrictors and cellophane bands are designed to get around this problem since they cause the vessel to narrow over time, which gives the body a chance to adjust.
Medical management for liver shunts can be used to improve a dog’s condition prior to surgery, when surgery is not in a dog’s best interests, or when surgery is unable to entirely correct the problem. Veterinarians typically prescribe a diet that has just enough protein for the dog but no “extra,” which reduces the byproducts of protein digestion (e.g., ammonia) that can make a dog’s symptoms worse. Research indicates that soy protein may be a better option in comparison to meat-based sources of protein. Feeding several smaller meals throughout the day is also beneficial.
Medications also play an important role in the medical management of liver shunts. Antibiotics are prescribed to reduce the number of bacteria in the gut, and enemas can be given to physically remove feces and bacteria from the colon. Oral lactulose, a type of indigestible sugar, is used to encourage rapid transit of stool through the intestinal tract and to lower the pH within the gut, which reduces the absorption of ammonia.
Prognosis for Liver Shunts in Dogs
Approximately one-third of dogs with liver shunts can be successfully managed with dietary changes and medications, according to Dr. Karen Tobias, professor of small animal soft tissue surgery and a board-certified surgeon at the University of Tennessee College of Veterinary Medicine.
Dogs who have liver shunts that are located outside of the liver and that are surgically corrected using ameroid constrictors or cellophane bands have the best prognosis, with around 85 percent being clinically normal several months after surgery, according to Tobias. In comparison, dogs with shunts that are located within the liver have a greater risk of complications although many still do very well after surgery.