Portosystemic shunts (PSSs) are the most common congenital liver anomaly (see Portosystemic Vascular Malformations in Small Animals). PSSs typically involve single extrahepatic or intrahepatic vessels, with extrahepatic shunts more common in toy breeds (Yorkshire Terriers, Cairn Terriers, Havanese, Maltese, Pugs, and Miniature Schnauzers), and intrahepatic shunts more common in large breeds (Irish Wolfhounds, Labrador and Golden Retrievers, Australian Cattle Dogs, and Old English Sheepdogs). They have also been reported in Himalayan and Persian cats. Commonly, extrahepatic shunts occur between the portal vein or its branches, and the caudal vena cava or azygous vein, whereas intrahepatic shunts may be due to failure of closure of the ductus venosus or connections between the portal vein branches and hepatic veins. Clinical signs generally manifest as neurologic disturbances (hepatic encephalopathy) and are usually seen in young animals. Cats may show ptyalism. In the later stages, GI signs (including vomiting, anorexia, and diarrhea) as well as ascites may develop secondary to portal hypertension. Other concurrent clinical findings may include renomegaly and urate urolithiasis. Laboratory tests may show increased liver enzymes and erythrocytic microcytosis. Abdominal ultrasonography is reported to be 100% sensitive for intrahepatic PSSs (although somewhat less for extrahepatic PSSs), but sensitivity depends on the skill of the ultrasonographer. Definitive diagnosis via positive-contrast portography can identify shunt location and whether the shunt is single or multiple. This procedure also allows assessment of feasibility for surgical correction. Multiple shunts have a poor prognosis, because they are often secondary to an underlying, progressive hepatic parenchymal disease (eg, cirrhosis).
Hepatoportal microvascular dysplasia is an intrahepatic circulatory disorder that results in the shunting of portal blood to the systemic circulation yet no discernible large vessel shunt is identified. The disorder has been classified as a variation of primary hypoplasia of the portal vein, which results in noncirrhotic portal hypertension. The syndrome is well defined in Cairn Terriers and Yorkshire Terriers, although it has also been reported in Maltese, Dachshunds, Toy and Miniature Poodles, Bichon Frise, Pekingese, Shih Tzus, Norfolk and Norwich Terriers, Tibetan Spaniels, Havanese, and Lhasa Apsos. Animals may be asymptomatic or show clinical signs similar to those of PSSs. Dogs that progress to clinical disease are treated medically as described for PSSs. Because there is no macroscopic shunting vessel, surgery is not a therapeutic option.
Copper-associated hepatopathy results either from a metabolic derangement of hepatic copper storage or secondary to hepatobiliary disease (mostly cholestatic disease). In Bedlington Terriers it has been identified as an autosomal recessive disorder, whereas in other breeds that have been identified as susceptible (Dalmatians, Skye Terriers, West Highland White Terriers, and Doberman Pinschers) no genetic basis has been identified. Primary copper toxicosis is very rare in cats. Affected animals may be asymptomatic or show acute signs of hepatobiliary disease, including vomiting, anorexia, depression, hemolytic anemia, and icterus. Older, chronically affected animals may show progressive end-stage liver disease. Treatment is based on dietary reduction of copper and either treatment with zinc salts to prevent GI absorption of copper in asymptomatic animals, or copper chelators to reduce copper in animals with clinical signs. Because copper chelators are not without adverse effects, treatment should be closely monitored.
Congenital hepatic cysts or congenital hepatic fibrosis is seen in both Persian and Persian-cross cats as an autosomal dominant trait and in the Swiss Freiberger horse (also called the Franches-Montagnes horse) as an autosomal recessive trait that can be traced back to one stallion. Both are features of a larger, polycystic organ syndrome that affects the kidneys, liver, and/or pancreas. Clinical signs in cats may not be apparent or manifest as chronic renal insufficiency. In horses, affected foals present in the first year of life with weight loss, jaundice, hepatic encephalopathy, abdominal distention, fever, and colic signs. A report of dogs with congenital hepatic fibrosis described ascites, vomiting, seizures, and portal hypertension but did not draw inferences on heritability.
Primary or idiopathic hyperlipidemias of dogs and cats have been reported. Miniature Schnauzers have a high prevalence of hypertriglyceridemia, up to 33% of animals in one study, with or without concurrent hypercholesterolemia and chylomicronemia. There was an effect of age, with higher prevalence in older animals, and a genetic basis is suspected. Hypercholesterolemia has been reported in Briards, Rough Collies, Shetland Sheepdogs, Doberman Pinschers, and Rottweilers. Also in dogs, a syndrome of idiopathic hyperchylomicronemia has been reported, with hypertriglyceridemia and normal serum cholesterol. Clinical signs may be absent or may include vomiting, diarrhea, pancreatitis, lipemia retinalis, seizures, peripheral neuropathies, and abdominal pain. Hyperlipidemias also occur secondary to other diseases, including hypothyroidism, diabetes mellitus, and hyperadrenocorticism, and treatment is aimed at the inciting disease as well as dietary modifications.
In cats, familial hyperlipidemia due to hyperchylomicronemia has been identified as due to an autosomal recessive defect in lipoprotein lipase. Secondary to this disorder, cutaneous and systemic xanthomatosis have been described, with deposition of lipid-laden macrophages in the dermis, usually around the head and ears. Peripheral neuropathy may develop secondary to nerve compression by the xanthomas, particularly on the limbs and paws.