Liver Disease in Dogs and Cats: Portosystemic Shunt

A liver shunt (portosystemic shunt) is a condition where the normal blood flow is diverted awayLiver Disease in Dogs and Cats: Portosystemic Shunt from the liver to the heart.  Congenital liver shunts in small breed dogs typically occur outside of the liver (extra-hepatic) and large breed dogs typically occur within the liver (intra-hepatic). Congenital liver shunts are typically single shunt vessels, while acquired liver shunts are often multiple shunt vessels.  Cats can also have liver shunts but they are much less common than in dogs.  All forms of liver shunts cause a reduction in blood flow to the liver and an inability of the liver to remove certain substances from the systemic circulation.

A dog with a congenital liver shunt will often develop abnormal neurologic signs (hepatic encephalopathy) in the first 2 years of life.   Some of the signs of hepatic encephalopathy are the following:  head pressing, walking into corners and unable to get out, blindness, seizures, less alert and responsive, and stumbling when walking.  Other potential signs of a liver shunt are stunted growth, gastrointestinal upset, and drinking and urinating larger volumes.

A dog with acquired liver shunts typically has severe liver disease that is irreversible.  The multiple

Portosystemic Shunt Liver Disease in Dogs and Cats

X-Ray showing a Liver Shunt Repair

liver shunts occur due to increased blood pressure in the portal vein secondary to severe liver disease.  This condition carries a poor prognosis.

The diagnosis of a liver shunt in dogs requires multiple diagnostic tests.  Blood tests to assess the liver function and enzyme profile.  A fasting and post-prandial bile acid blood test is an important diagnostic test because the results are often very elevated in a dog with a liver shunt.  If there is a strong suspicion of a liver shunt based on the history and blood tests then imaging needs to be performed to confirm the presence of a liver shunt.  The most commonly used imaging modality to visualize a liver shunt is ultrasonography.  Other imagining modalities that have been used toPortosystemic Shunt and Cats identify liver shunts are contrast radiography (portovenography), CT scans, MRI scans, and nuclear scintigraphy.

A dog with hepatic encephalopathy secondary to a liver shunt should be treated with a low protein diet, an antibiotic to reduce urease producing bacteria in the intestines, and lactulose to reduce the amount of ammonia in the blood.  These therapies will help reduce the signs associated with hepatic encephalopathy but will not treat the underlying liver shunt.

Congenital liver shunts can often be corrected surgically.  Surgically, a single extra-hepatic liver shunt in dogs is often the easiest to correct, whereas an intra-hepatic liver shunt in a large breed dog is more difficult.  Other forms of liver shunts, especially multiple acquired liver shunts, often can not be corrected surgically and carry a poor prognosis.

Click here to learn about chronic liver disease in dogs, or here to learn about fatty liver disease in cats.

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