Pet Columns, Office of Public Engagement, College of Veterinary Medicine at the University of Illinois at Urbana-Champaign

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Improper Blood Flow around the Liver Can Pose Serious Health Risks for Your Pet

Pet Column for the week of December 16, 1996

Office of Public Engagement
2001 S. Lincoln Ave.
Urbana, Illinois 61802
Phone: 217/333-2907
By Joseph Hahn
Information Specialist

In railroad tracks and electrical circuits, shunts are useful things, allowing train cars or the
flow of current to be diverted from one pathway to another. But a portosystemic shunt,
which allows blood to flow abnormally around instead of to the liver, is a serious health
problem in pets. Both dogs and cats can have portosystemic shunts, although it is much
more common in dogs.

Normally, the blood carries toxins and toxic by-products of metabolism from the stomach
and intestines to the liver, where the toxins are removed. "In animals with portosystemic
shunts, the blood bypasses the liver and is diverted to another blood vessel, allowing toxins
to circulate through the body," says Dr. Jennifer Brinson, a veterinarian who specializes in
internal medicine at the University of Illinois College of Veterinary Medicine Teaching
Hospital in Urbana.

Shunts can be either congenital--a condition the animal was born with--or acquired--a
condition that developed later in life. Congenital shunts are generally diagnosed in animals
less than one year old. Acquired shunts can occur at any age and are often caused by liver
disease. Shunts are also categorized as intrahepatic (within the liver) or extrahepatic
(outside the liver).

"Congenital shunts are most commonly seen in small breed dogs, such as Yorkshire terriers
or toy poodles. These dogs generally get single, extrahepatic shunts," says Dr. Brinson.
"This disease can also affect large breed dogs. Unfortunately, larger dogs typically get
intrahepatic shunts, which are much more difficult to treat."

Dogs with congenital shunts tend to be small for their age and breed. Other signs of shunts
include excessive drinking, frequent urination, and a condition known as hepatic
encephalopathy. This condition arises shortly after eating and may appear as depression,
muscular incoordination, coma, and seizures--signs caused by ammonia (a by-product of
protein digestion) reaching the brain instead of being cleared by the liver.

Diagnosis of a suspected portosystemic shunt is often done in three stages. The first stage is
checking a blood and urine sample. If these samples are suggestive of a shunt, second stage
tests, consisting of a pre- and post-bile acid test and an ammonia challenge test, are
performed. These two tests help determine the functional capacity of the liver. Finally, an
ultrasound or nuclear scan may be used to try to locate and determine the extent of the

Treatment and prognosis of shunts depend on their location and severity. "A congenital,
single, extrahepatic shunt that is caught early is a good candidate for surgery," says Dr.
Brinson. "Intrahepatic shunts commonly must be treated medically."

The medical treatment for portosystemic shunts is aimed at reducing the amount of ammonia
circulating in the body and decreasing the symptoms. A low-protein diet and lactulose to
reduce absorption of ammonia are prescribed. In emergency cases, enemas with water or
lactulose are used to reduce ammonia absorption immediately. If portosystemic shunts go
untreated, the symptoms will get progressively worse and eventually the pet may die.

If you would like further information, contact your local veterinarian.