Congenital and Inherited Anomalies of the Liver in Animals

Portosystemic shunts are the most common congenital liver anomaly (see Portosystemic Vascular Malformations in Small Animals). Typically, portosystemic shunts involve single extrahepatic or intrahepatic vessels. Extrahepatic shunts are more common in toy breeds (eg, Yorkshire Terriers, Cairn Terriers, Havanese, Maltese, Pugs, and Miniature Schnauzers); intrahepatic shunts are more common in large breeds (eg, Irish Wolfhounds, Labrador and Golden Retrievers, Australian Cattle Dogs, and Old English Sheepdogs). Portosystemic shunts have also been reported in 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 the failure of the ductus venosus or connections between the portal vein branches and hepatic veins to close.

Clinical signs of portosystemic shunts generally manifest as neurologic disturbances (hepatic encephalopathy) and are usually evident 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 shunts (although somewhat less sensitive for extrahepatic shunts); however, sensitivity depends on the skill of the ultrasonographer.

Definitive diagnosis via positive-contrast portography can identify shunt location and show whether the shunt is single or multiple. This procedure also enables assessment of the feasibility for surgical correction. The existence of multiple shunts has a poor prognosis, because they are often secondary to an underlying, progressive hepatic parenchymal disease (eg, cirrhosis). Nonsurgical treatment options for a single congenital portosystemic shunt may include feeding a protein-restricted diet with or without lactulose. Nonsurgical treatment is reported to have a median estimated survival time of ~3 years, with owners reporting an increase in quality of life and decrease in clinical signs.1

Hepatoportal microvascular dysplasia is an intrahepatic circulatory disorder that results in the shunting of portal blood to the systemic circulation, even though 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; it has also been reported in Maltese, Dachshunds, Toy and Miniature Poodles, Bichons Frises, Pekingese, Shih Tzus, Norfolk and Norwich Terriers, Tibetan Spaniels, Havanese, and Lhasa Apsos. Animals may be clinically normal or show clinical signs similar to those of portosystemic shunts. Dogs that progress to clinical signs of disease are treated medically as described for portosystemic shunts. Because there is no macroscopic shunting vessel, surgery is not a treatment 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; in other breeds that have been identified as susceptible (Dalmatians, Skye Terriers, West Highland White Terriers, and Doberman Pinschers), no genetic basis has been determined. Mutations in the copper transport genes ATP7A and ATP7B have been associated with hepatic copper accumulation in Labrador Retrievers and Dobermans.

Gene mutations resulting in primary copper toxicosis in cats has also been reported.2 Affected animals may be clinically normal or show acute clinical 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 clinically normal animals, or with copper chelators to reduce copper in animals with clinical signs. Because copper chelators do have some adverse effects, treatment should be closely monitored.

Congenital hepatic cysts or congenital hepatic fibrosis occur 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 they may manifest as chronic renal insufficiency. Clinical signs may also include abdominal distention, vomiting, abdominal pain, and jaundice.

Foals with either of these disorders present in the first year of life with clinical signs of weight loss, jaundice, hepatic encephalopathy, abdominal distention, fever, and colic. Dogs with congenital hepatic fibrosis may develop ascites, vomiting, seizures, and portal hypertension; heritability is unknown. Laparoscopic removal of hepatic cysts in a Persian cat has been described and has potential as a minimally invasive technique for treatment.3

Primary or idiopathic hyperlipidemias of dogs and cats have been reported. Miniature Schnauzers have a high prevalence of hypertriglyceridemia, with or without concurrent hypercholesterolemia and chylomicronemia. An effect of age was noted, 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. In cats, familial hyperlipidemia due to hyperchylomicronemia has been identified as resulting from 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.