Portosystemic Shunts

Nancy McDonald BSN, RN, retired

Portosystemic Shunts is a serious, congenital disease and may be known by many other names, liver shunts, portosystemic vascular anomaly, extrahepatic or intrahepatic liver shunts, congenital portosystemic shunts.

Normally, blood from the digestive tract flows to the liver via the portal vein. There the blood is cleansed of metabolic wastes then returned to the main systemic blood stream that flows back to the heart. In the fetus, the liver does not function so is bypassed in utero by the ductus venosus that should close after birth, thus directing blood to the liver. If the ductus venosus does not close completely the blood would be shunted around the liver. This is called a congenital intrahepatic liver shunt. An extrahepatic portosystemic shunt occurs when an anomalous vessel forms and connects the portal vein (it collects blood from the digestive tract) directly to the main systemic bloodstream and blood bypasses the liver. The amount of blood that shunts the liver depends on the size of the shunting blood vessel. The amount of blood by-passing the liver will determine and vary the symptoms.

Some puppies will develop signs and symptoms within a few weeks of age or if the shunts are small, severe clinical signs may not present until the dog is much older. Symptoms vary and may include stunted growth, lethargy, walk in circles or unsteadily, drooling, seizures, have excessive thirst, urination variations, vomiting, diarrhea, constipation, intolerance to anesthesia. Symptoms may increase after eating.

It takes sophisticated testing to accurately diagnose portosystemic liver shunt. Needed is a complete blood count , bile acid tests and urinalysis. Additional test may include ultrasound with Doppler Flow Analysis, CT scan with contrast, nuclear scintigraphy, MRI. After diagnosis, usually first treatments are a diet change to a low protein diet, administer lactulose that changes the pH in the large intestines to decrease absorption of toxin, and administer antibiotics to alter bacteria in the intestines. Pets usually improve quickly and about one-third can live a relatively long life if if seizures, behavioral changes or progressive liver damage does not occur. Success with long-term medical management are dogs diagnosed at an older age.

The best success for dogs diagnosed with extrahepatic liver shunt is surgery. One method is the shunt vessel is sealed causing normal blood to the liver. This is done by tying off the vessel, or sealing it with a special glue material. A complication with this procedure is portal hypertension, Procedures that slowly close the shunting vessel is a ameroid constrictor, cellophane band, and trans-venous coiling. The preferred method is the ameroid constrictor that closes the vessel within three or four weeks. There are reasons the procedure could fail or complications could occur after surgery but using the ameroid constrictor, survival rates are very good. All of these are technically challenging surgeries. Your local veterinarian will refer you to a board certified surgeon.

Although a rarity in the Bichon Frise, portosystemic shunts do occur and the female Bichon is about 12 times the chance of being born with portosystemic shunts than do the males. This is a congenital disease and any dog producing a portosystemic shunt should be removed from a breeding program.