liver shunts in dogs and cats

liver shunts in dogs and cats
Posted by Dr. Kim Smyth on May 29 2020

To understand how liver shunts affect pets, it helps to understand a little bit about the normal function of the liver.

In a healthy pet, venous blood from the intestines passes through the liver, where toxins are removed before the blood returns to the body. When a pet has a liver shunt, the blood from the intestines bypasses the liver. This is undesirable, because instead of getting “detoxed” in the liver, the blood returns to the body, allowing toxins to build up.

How liver shunts occur

In mammals, including dogs and cats, the mother’s liver does all of the toxin-filtering for the fetus, so before birth, the baby’s portal blood vessel purposely bypasses the liver. Normally, this vessel closes within a few days of birth, thereby allowing all of the venous blood to pass through the liver before being redistributed through the body. When it doesn’t close and the blood continues to bypass the liver, the resulting shunt is called a congenital shunt.

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Liver shunts can be congenital, meaning that they are present at birth, or they can be acquired at an older age. Most shunts are congenital in nature, but about 20 percent of shunts are acquired. Acquired shunts are most commonly secondary to liver problems, such as exposure to toxins or chronic hepatitis. In these cases, the body routes blood through whatever blood vessels are available, even if it means bypassing the liver.

When portosystemic shunts occur, hormones are not available to encourage liver growth, so the liver can begin to atrophy. Poor protein production and abnormal fat metabolism can also occur, as well as blood clotting disorders. And the toxins that are normally eliminated by the liver begin to accumulate in the body, causing what is known as hepatic encephalopathy.

Signs and symptoms of liver shunts in pets

Clinical signs of hepatic encephalopathy include seizures, spaciness and disorientation, circling, and “head pressing,” when pets press their heads against hard objects, such as a wall or the side of their crate.  Often, these symptoms are most obvious immediately after the affected pet has eaten a meal.

Pets with liver shunts may also have gastrointestinal signs, drink excessive amounts of water, and urinate excessively.

Commonly affected breeds

Because acquired shunts occur secondary to another condition, they can happen in any breed. Congenital shunts, however, are passed down genetically, and certain breeds (especially small breeds) are more commonly affected, including:

Diagnosis

Diagnosing liver shunts is relatively easy with blood tests and ultrasounds. In the case of congenital portosystemic shunts, surgical repair is the treatment of choice. Unfortunately, acquired shunts generally cannot be repaired surgically. Medical management, including diet change and oral medications, may be able to provide a good quality of life for these cases.

Prognosis is great for congenital cases where the shunt is completely repaired surgically, and even partially corrected shunts can have a good prognosis. The prognosis for acquired shunts depends largely on the location and severity of the shunt.

Treatment and management

Congenital liver shunts can often be managed surgically, as there tends to be only one anomalous vessel shunting blood, and it can be ligated easily. However, in most cases of acquired shunts, multiple small vessels are present, and surgical correction is not a viable option. Instead, medical management must be pursued, often at a high cost, reaching as much as  $12,634 according to Petplan pet insurance claims data. 

Diet change. A low protein, low magnesium diet should be started. Several prescription diets will fit the bill, with the added benefit of increased zinc and vitamin E levels. Prescription diets specific for liver disease lessen the burden on the liver.

Decrease ammonia production in the colon. Warm water enemas can be used during periods of severe hepatic encephalopathy to decrease the amount of ammonia producing bacteria present.

Decrease ammonia production in the gut. Antibiotics are used daily to reduce the amount of bacteria present in the gastrointestinal tract.

Lower the pH of the colon. An oral medication called lactulose is given to lower the colonic pH, resulting in lowered ammonia levels.

Medical management of portosystemic shunts is not corrective in nature. It is intended to lessen the clinical signs by targeting the factors that contribute to hepatic encephalopathy. Prognosis is good for pets with mild signs of hepatic encephalopathy, especially in the case of pets who are diagnosed with a liver shunt in their golden years.

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