QMy Chihuahua puppy has been diagnosed with a liver shunt. I have been researching this condition and treatments and have discussed it with my vet. I would appreciate your opinion on how to proceed and the prognosis.

A: So what is a liver shunt anyway? In simple terms, blood flows from the intestines bearing both wastes and nutrients. Before this blood goes into our general circulation, it must be filtered by the liver so waste products and toxins can be removed, and nutrients can be processed.

A shunt is an abnormal blood vessel that goes around the liver, bypassing it like I-526 around Charleston. This unfiltered blood causes toxins to build up in the body to dangerous levels. About 80 percent of the blood flowing to the liver comes from the intestines. So a shunt also deprives the liver of blood, necessary for normal liver development.

We all know that the liver is the organ responsible for removing alcohol from the blood. It also is responsible for the breakdown and removal of many of the drugs we consume.

What many may not realize is that toxins are constantly being produced in our digestive tracts.

For example, ammonia is a biproduct of protein digestion, and there are compounds that are chemically similar to Valium being produced by bacteria in our intestines.

When the liver ceases to function normally, these chemicals build up to dangerous levels in the blood and have profound effects on the brain, producing stupor, dementia and even coma. This is known as hepatic encephalopathy, meaning that the liver has caused disease in the head or brain.

These are the type of symptoms that typically lead to the diagnosis of a shunt. A typical description is of a young dog, usually a puppy, that has intermittent bouts of depression and lethargy. In more severe cases, they may be disoriented, dazed or have for seizures.

Shunts are most commonly seen in small breed dogs such as the Yorkshire terrier, Shih-Tzu or Chihuahua. Shunts also are seen in large breed dogs and are also seen in cats.

When a shunt is diagnosed or suspected, the recommendation is to surgically close it, diverting the blood to its normal course through the liver. This is because, although medical management can significantly improve symptoms, the majority will not gain long-term control and symptoms will worsen with age, ultimately becoming more difficult, if not impossible, to manage effectively.

There is typically a major reduction in longevity and quality of life in patients with shunts afforded only medical management.

Shunts come in many shapes and sizes. In small breeds, shunts are usually a single vessel that goes around the liver. In large breed dogs, the shunting vessel often goes through the liver like a tunnel through a mountain, carrying the blood through, but not to, the liver. The surgical technique depends upon the type, but they all involve closing the vessel one way or another.

There are two major risks to surgery. One is that the liver cannot handle the added blood flow. This allows pressure to develop in the abdomen and can lead to shock and acute death or, if less severe, additional shunts will form to relieve the pressure. The other risk is that seizures will develop as the chemically tainted blood is filtered. These seizures can be intractable, severe, and often fatal.

Technological advances have improved the odds of surgical success. For example a device called an Ameroid ring can be placed around the shunt. This ring gradually closes off the vessel by constriction, allowing the liver to adapt slowly to the added blood flow. This may also allow the brain to gradually adjust to the withdrawal of certain chemicals, diminishing the odds of seizure development.

In our operating rooms, we use fluoroscopy, which are moving, real time X-rays that allow us to visualize the blood flow through the shunts so they can be identified during surgery, confirming the diagnosis and guiding accurate placement of closure devices.

Overall, the long term prognosis for surgically treated shunts is excellent. In the short term, the mortality rates are variable, between 5 percent and 25 percent, depending upon the type of shunt and the closure technique. For the vast majority of animals, the surgery is smooth, as experienced by Marley (pictured), one of our patients.

The prognosis is also greatly dependent upon the technical skill and experience of the surgeon. The statistics overwhelmingly favor surgical management.

Dr. Henri Bianucci and Dr. Perry Jameson are with Veterinary Specialty Care LLC. Send questions to petdocs@postandcourier.com.