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A portosystemic shunt is an abnormal vascular anomaly which diverts blood around the liver instead of into it. In the body the liver acts as a filter, to cleanse toxins and impurities from the blood. The blood which feeds the digestive organs drains into the portal vein. This vein transports this blood to the liver to be filtered and then released back to the rest of the body. A portosystemic shunt is named so because it connects the portal vein to the systemic circulatory system, bypassing the liver. This leads to underdevelopment of the liver and blood which is not filter properly, if at all.
Portosystemic shunts may be present at birth or acquired later in life. The shunts may be found either inside (intrahepatic) or outside (extrahepatic) the liver. Intrahepatic portosystemic shunts are normally found in large dog breeds while extrahepatic shunts are found in small dog breeds.
While portosystemic shunts can be seen in any breed of dog at any age certain breeds are at a higher risk of being affected by the condition than others. These breeds include Miniature Schnauzers, Yorkshire Terriers, Cairn Terriers, Maltese, Scottish Terriers, Irish Wolfhounds, Golden Retrievers, Labrador Retrievers, and Poodles. For more information about portosystemic shunts contact your local veterinarian.
Additional information about PSS is also available here from researcher Dr. Karen M. Tobias at the University of Tennessee Knoxville.
Congenital portosystemic shunts are thought to be inherited while acquired shunts are normally seen secondary to severe liver disease. The exact mode of inheritance in congenital shunts is not known but research continues to be done to determine it. In many cases congenital portosystemic shunts are specifically caused by the failure of a fetal shunt to close. In the fetus blood is diverted around the liver because the mother filters the fetal blood. This fetal shunt is programmed to close at birth. When it does not the result is a portosystemic shunt. Acquired shunts normally develop when the liver can no longer handle the amount of blood being sent to it. The shunts help relieve the increasing blood pressure there in an effort to delay liver failure.
The symptoms associated with portosystemic shunts are nonspecific and normally will come and go. Signs include poor growth, and overall poor condition. In many cases behavioral changes are the best indication of a shunt. The behavioral changes care caused by hepatic encephalopathy. Hepatic encephalopathy causes neurological disorders such as swaying, interrupted gait, head pressing, and seizures. Hepatic encephalopathy is a result of toxins in the blood affecting the brain. These toxins are normally filtered by the liver but because the shunt diverts the blood away from the liver these toxins removed and can have an effect on the dog. In many cases abnormal behavior will be seen frequently after meals.
Diagnosing portosystemic shunts is done based on the dog's history along with testing. Blood work will most likely be done to look for signs common with liver failure. Two tests which are commonly used in diagnosing these shunts are the blood ammonium concentration and bile acid concentration tests. Other tools used to confirm portosystemic shunts are ultrasound and scintigraphy. A scintigraphy is a nuclear scan of the liver after radioisotopes have been added to the blood. The scan will show if a portosystemic shunt is present.
Portosystemic shunts can be treated by surgical or medical means. In most cases medical means are used to stabilize the dog until they are healthy enough for surgery. Medical management consists of a low protein diet, lactulose, and in some cases antibiotics.
The preferred treatment is surgery. Surgery is done to narrow or completely close the shunt. Correcting extrahepatic shunts with surgery is normally done with ameroid constrictors. An ameroid constrictor is a ring which slowly closes over time. The constrictor is placed around the shunt and over a period between 4-6 weeks, the constrictor will close the shunt. Surgery to correct intrahepatic shunts is much more complicated. As these shunts are normally seen in large dogs the shunts seen are normally large as well. An ameroid constrictor can be used to close these shunts inside the liver, but in most cases two surgeries are needed.
A complication which can occur after surgery is done on any type of shunt is an increase in the blood pressure in the liver. Because the liver is underdeveloped, it cannot handle the new volume of blood being directed into it. This causes the blood pressure in the liver to rise dramatically. If this complication is not recognized it can be fatal. For this reason dogs are normally monitored closely for 24 to 48 hours after surgery.
Dogs with portosystemic shunts will need a special diet before surgery. Once surgery has been performed a low protein diet should been fed until blood tests have returned to normal. In some cases a low protein diet along with lactulose will always be needed even after surgery. Your veterinarian?s instructions should always be followed and any changes in your dog?s health should be reported to them.
The AKC Canine Health Foundation is currently funding three active grants dealing research on portosystemic shunts. The research is focused on new diagnostic methods, treatment methods, and finding a genetic marker for the condition. In the past there have been 5 other grants that have been funded which have helped researches get to where we are today in terms of knowledge and treatments of portosystemic shunts. With your help we can continue to further fund this research and hopefully one day come up with a cure for this condition.
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