Acquired shunts are usually multiple, and are caused by portal hypertension in humans or in dogs with liver disease. Most commonly, extrahepatic shunts are found connecting the portal vein or left gastric vein to the caudal vena cava.Ĭongenital shunts are usually solitary. Toxins such as ammonia are not cleared by the liver. Thus in the juvenile and adult animal with PSS, blood from the intestines only partly goes through the liver, and the rest mixes into general circulation. On the other hand extrahepatic shunts usually result from a developmental abnormality of the vitelline veins, which connect the portal vein to the caudal vena cava. A failure of the ductus venosus to close causes an intrahepatic shunt. Normally, blood from the placenta bypasses the liver and goes into circulation via the ductus venosus, a blood vessel found in the fetus. Urate bladder stones may form because of increased amounts of uric acid in circulation and excreted by the kidneys.Ĭongenital PSS is caused by an anomaly in fetal liver circulatory system development. Symptoms of congenital PSS usually appear by six months of age and include failure to gain weight, vomiting, and signs of hepatic encephalopathy (a condition where toxins normally removed by the liver accumulate in the blood and impair the function of brain cells) such as seizures, depression, tremors, drooling, and head pressing. Īcquired PSS is uncommon and is found in dogs and cats with liver disease such as cirrhosis causing portal hypertension, which is high blood pressure in the portal vein. The shunts found mainly in small dog breeds such as Shih Tzus, Tibetan Spaniels, Miniature Schnauzers and Yorkshire Terriers, and in cats such as Persians, British Shorthairs, Himalayans, and mixed breeds are usually extrahepatic (outside the liver), while the shunts found in large dog breeds such as Irish Wolfhounds and Labrador Retrievers tend to be intrahepatic (inside the liver). Congenital portosystemic shunts (PSS) is a hereditary condition in dogs and cats, its frequency varying depending on the breed.
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