Liver shunt, or portosystemic shunting (PSS), is one of several liver problems that affect dogs. Specifically, in this condition, blood from the intestines flows around the liver, thereby bypassing it. This results in toxins such as ammonia not being able to be metabolized or removed from the blood circulation.
Liver shunt in dogs can be a defect at birth (congenital), or it can be acquired, i.e. the result of some form of liver disease such as scarring of the liver (cirrhosis).
Most cases of liver shunts in dogs are congenital.
Congenital Liver Shunt in Dogs
When a dog fetus is in its mother’s womb, its liver is not developed and therefore not functioning. The fetus depends totally on its mother’s liver to do everything, including, among other things, the filtering out of toxins.
Blood is carried through the fetal liver to the heart by a large shunt (a fetal vein called “ductus venosus”).
Shortly before or after birth, the large shunt closes down and the puppy’s liver begins to function independently.
When the shunt in a puppy fails to close down, the puppy has an “intrahepatic shunt” (a shunt inside the liver).
In some other cases, a blood vessel outside of the puppy’s liver fails to develop normally and remains open after the fetal vein closes. When that happens, the puppy is said to have an “extrahepatic shunt” (a shunt outside the liver).
Large breed dogs, such as Irish Wolfhounds, Labrador Retrievers, Australian Shepherds, and others, are at higher risks of developing shunts inside the liver (intrahepatic shunts).
On the other hand, smaller dogs appear to be at higher risks of developing extrahepatic shunts. Breeds that are predisposed include the Yorkies, Maltese, Miniature Schnauzers, Dachshunds, Shih tzus, Jack Russell Terriers, Poodles, and others.
In general, female dogs are more susceptible to shunts than males.
Symptoms of Canine Liver Shunt
Most puppies with congenital liver shunts start showing signs by six months of age although some dogs may not develop any symptoms until middle age or even older.
Dogs with liver shunts develop symptoms of hepatic encephalopathy, which is a type of brain dysfunction caused by high levels of ammonia and other toxins in the blood.
These symptoms include:
- Weakness and lethargy
- Behavioral changes
- Mental dullness
- Head pressing against objects
In advanced cases, seizures and coma occur.
Diagnosis and Treatment of Canine Liver Shunt
Usually, blood tests on dogs with congenital liver shunts will show low levels of blood urea nitrogen (BUN) and albumin, increased blood bile acid concentrations, and increased liver enzymes.
Additional examinations that are needed to confirm diagnosis include the use of scintigraphy (a nuclear scan), ultrasound, portography (a special x-ray with contrast), CAT scan (“CT”), or MRI.
Depending on the type of canine liver shunt, it can be corrected surgically, and/or managed through a low-protein diet supplemented with lactulose (for the absorption of intestinal toxins such as ammonia by altering intestinal pH) and medications (antibiotics).
Generally speaking, most liver shunts cannot be treated by using a special diet and medications alone.
Surgery can correct extrahepatic shunts rather easily.
Intrahepatic shunts are much more complicated and surgery should best be performed by a board certified surgeon (ACVS Diplomate).
In some cases, since the liver has not developed normally, the shunt can only be partially closed. However, even by partially closing the shunt, it is usually sufficient to relieve the symptoms for the dog patient to live a normal life without medications.