To understand what a portosystemic shunt (or liver shunt) is, 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.
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, or present at birth.
Portosystemic shunts can also be acquired, and can occur at any age. These shunts are typically caused by liver problems, such as chronic inflammation or infection.
The reason liver shunts are dangerous is that they allow toxins to build up in the body. This leads to stunted growth (in congenital cases), vomiting and diarrhea, increased water intake with a corresponding increase in urine production, and neurologic signs such as seizures, a “spaced out” appearance, circling to one side, and pressing of the head against firm objects, such as a wall. Often, these symptoms are most obvious immediately after the affected pet has eaten a meal.
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:
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.
If you notice any of the signs and symptoms of a liver shunt mentioned above, whether in your very young puppy or older pet, be sure to talk to your veterinarian right away.