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Can a shunt be diagnosed with a liver biopsy?
In animals with shunts, the liver is smaller than normal because it is atrophied from poor blood flow. On a liver biopsy, the tissues appear shrunken. Some of the vessels are very tiny, while others multiply in an attempt to improve the blood supply and drainage. These changes are called hepatic microvascular dysplasia. Hepatic microvascular dysplasia (HMD or MVD) can also occur in dogs without liver shunts; therefore, other tests are needed to be determine if a shunt is also present.

What medical management is needed for an animal with a shunt?
Dogs with shunts are usually stabilized with special diets and medications to reduce the amount of toxins that are produced and absorbed in the large intestines. Dogs that are severely ill may require intravenous fluids to restore blood sugar, an enema to remove intestinal toxins before they are absorbed, and medications such as valium to stop seizures.

Diet:
Because many of the toxins produced in the intestines come from protein, it is important to reduce the amount of protein in the diet. Dog food for adults and puppies usually contains 25% and 29% protein, respectively, and may have meat byproducts. Dogs with shunts need high quality proteins made from milk or vegetable, and are restricted to a protein content of 18% or less (on a dry matter basis). The diets should be easily digestible, rich in antioxidants and vitamins, and low in copper and iron.

Lactulose:
Much of the toxins absorbed from the intestines are produced by normal intestinal bacterial. Lactulose changes the pH in the large intestines, which decreases absorption of ammonia and other toxins and makes the environment unfavorable for the toxin-producing bacteria. It also encourages the intestinal contents to leave the area more quickly, so that toxins have less time to be absorbed. Lactulose is basically a sugar solution; its primary side effect is diarrhea. Because of this, veterinarians will instruct owners to adjust the dose so that the dog’s feces is soft but formed.

Antibiotics:
If clinical signs are not controlled with a protein-restricted diet and lactulose, veterinarians will often prescribe antibiotics to reduce the number of toxin-producing bacteria in the intestines. Antibiotics will also be needed if the animal has a urinary tract infection.

Can dogs with shunts be treated with only medical management?
Most animals improve immediately with proper diet and medicine, and about one third of the dogs treated medically will live a relatively long life. Unfortunately, over half of the dogs treated medically are euthanized, usually within 10 months of diagnosis, because of uncontrollable neurologic signs, such as seizures and behavior changes, or progressive liver damage. Dogs that tend to do well with long term medical management are usually older at the time of diagnosis, have more normal bloodwork, and have less severe clinical signs. Surgery provides the best chance for a long healthy life in most dogs.

How is a shunt corrected surgically?
Because shunts inside the liver are more difficult to find and close off, surgery of dogs with intrahepatic shunts is best performed by a board certified surgeon (ACVS Diplomate). Surgery for congenital extrahepatic liver shunts is slightly easier, particularly if the veterinarian has a lot of experience, and is performed at most veterinary surgery referral centers. The surgeon must find the abnormal blood vessel and close it off to force blood to flow back through the liver. Unfortunately, the blood vessels inside the livers of some dogs are so poorly developed that they will not open quickly. Therefore, most surgeons will use a device that slowly closes the shunt, such as an ameroid constrictor. Other options include placement of a suture or cellophane band around the shunt or coils inside of the shunt. Placement of coils can be performed through a catheter in the neck (“jugular”) vein; however, because they tend to cause rapid obstruction of the shunt in animals, their use is still being researched.

How does an ameroid constrictor work?
An ameroid constrictor is a metal band with an inner ring of casein, a protein found in milk. In the belly, the inner ring absorbs normal fluid and gradually swells, pressing on the shunt and encouraging it to scar shut. Shunts usually close within 3-4 weeks of ameroid constrictor placement. Because of the metal outer ring, the constrictor will always be visible on x-rays of the belly.

What are the complications of shunt surgery?
Surgery with ameroid constrictor placement is faster and complications are fewer compared to other techniques, but the puppies can still get very cold or develop low blood sugar during or after the procedure. Occasionally dogs will develop pain and bloating if the constrictor kinks the vessel or if a suture or a cellophane band is used. This can progress to shock and death, so animals must be watched carefully for several days after the procedure. A small percentage of dogs may also have seizures after surgery. Dogs with intrahepatic shunts are more likely to have complications and usually require several days of intensive care and possible blood transfusions.

What care is needed for dogs after shunt surgery?
Dogs are kept on a protein-restricted diet for atleast 6-8 weeks after surgery. Lactulose can be continued as well, or can be gradually decreased over 2-4 weeks. Most dogs do not need antibiotics unless they have infections in the urine or other sites. The liver will begin to grow as the shunt closes, and will often be normal sized in 2-4 months. To check liver function, blood tests (BUN, albumin, liver enzymes, and bile acids) are usually evaluated at 8-12 weeks after surgery. If these are still abnormal, they are repeated in another 3 months. If they are normal, the diet is gradually switched to an adult maintenance dog food. A scintigraphy can be performed at 3-6 months to confirm that the shunt is closed.

What is the prognosis for dogs after ameroid constrictor placement around a shunt?
Survival rate from the surgery is over 95% for dogs with shunts treated by ameroid constrictor placement, and our long-term prognosis is better with this technique than with most other methods. Many dogs are clinically normal within 4-8 weeks after the surgery. Long term, about 85% of dogs with liver shunts closed with ameroid constrictors do well clinically. About 15% continue to have problems, probably because the tiny blood vessels inside the liver were also abnormal. Usually these dogs develop multiple acquired shunts and must be managed with a protein restricted diet and lactulose for life.

Dr. Tobias is an Associate Professor in Small Animal Surgery at the University of Tennessee College of Veterinary Medicine.