A portosystemic shunt (PSS) or liver shunt is a condition where the normal flow of blood, to and through the liver, is markedly reduced or absent. Normally, blood returning from the puppy's digestive tract is routed to the liver through the portal vein. The blood flows through the liver and then exits the liver and joins the venous blood flowing back to the heart. A liver shunt is a blood vessel that connects the portal vein with the main systemic blood stream. This causes the blood to bypass the liver. Without adequate blood flow to the liver, the puppy's body cannot thrive.
These shunts can occur as a result of a birth defect (congenitally). A liver shunt can be intrahepatic, when blood is diverted in a vessel within the liver, or it can be extrahepatic when blood is diverted in a vessel around the outside of the liver.
What are the results of a liver shunt in dogs?
When blood is shunted around the liver rather than to and through it, the liver is not able to perform its many important tasks and therefore, metabolic wastes such as ammonia, reach unhealthy levels in the animal and threaten the dog's health.
The degree to which blood is shunted around the liver is dependent on the size of the shunting blood vessel. Liver shunts may be large allowing a large amount of blood to bypass the liver, or they may be partially closed allowing only small amounts of blood to shunt around the liver. The extent of blood shunting varies with every dog.
What are the symptoms of liver shunts in dogs?
The symptoms of liver shunts vary and are directly related to the extent of blood by-passing the liver. If the liver is receiving and processing 95% or greater of the dog's blood, the symptoms may be few, if any. As the amount of blood by-passing the liver increases, the symptoms of this condition will become more pronounced.
The following symptoms may be evident in puppies at only a few weeks of age:
Poor growth rates
Lethargy
Vomiting
Diarrhea
Constipation
Drooling
Increased thirst
Increased urination
Walking in circles
Seizures
Death
Dogs with less severe liver shunts may not exhibit any clinical signs until the puppy is much older, even up to one year of age.
What are the risks of a liver shunt?
All liver shunts, whether mild or severe, are considered serious. Even dogs with mild liver shunts exhibit greater symptoms as they increase in body size. The larger the puppy grows, the more metabolic wastes are produced, and therefore, the more the liver is needed. Most affected dogs will not live a normal life expectancy unless the abnormality is corrected.
How are liver shunts treated in dogs?
The best and preferred treatment for liver shunts is to identify the abnormal blood vessel(s) and surgically close them; eliminating the shunt and returning normal blood flow to the liver. This is a complicated surgery. A minority of dogs can be treated with medical management that includes a protein restricted diet and the administration of certain medications are often beneficial. Restricted protein diets help reduce the production of toxic wastes such as, ammonia. The older a dog is at the time he starts showing symptoms, the more likely medical management can have some success.
What is the prognosis for puppies with liver shunts?
The prognosis for a dog with a PSS depends on the size and location of the shunting vessel(s). Owners and veterinarians should thoroughly discuss the seriousness, expense, and expected outcome associated with this condition. The cost and results of surgically correcting liver shunts are variable and depend on the anatomical location of the shunt, the degree of shunting and the age of the dog.
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