THE MERCK VETERINARY MANUAL
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Congenital and Inherited Anomalies of the Liver

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The most common congenital liver anomaly is portosystemic shunt (PSS). (see Portosystemic Vascular Malformations in Small Animals for a complete discussion.) Although this condition can occur in any dog breed, breeds with a reported increased incidence include Yorkshire Terriers, Cairn Terriers, Maltese, Pugs, Irish Wolfhounds, Labrador and Golden Retrievers, and Miniature Schnauzers. They are also known to occur in Himalayan and Persian cats. PSS results in portal blood bypassing the liver and gaining direct access to the systemic vascular system. Shunts may be single and intrahepatic (most often secondary to a patent fetal ductus venosus), single and extrahepatic (with various possible vascular routes between the portal and postcava or azygous vein), or multiple and secondary to intrahepatic arterioportal fistulas. Clinical signs generally manifest as metabolic neurologic disturbances (hepatic encephalopathy) and are usually seen in young animals after a high-protein meal. In the later stages, ascites may develop secondary to portal hypertension. Other concurrent clinical findings may include renomegaly and cystic urate calculi. Abdominal ultrasonography is reported to be 100% sensitive for intrahepatic PSS (although somewhat less for extrahepatic PSS), but sensitivity is dependent 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. 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. It is generally asymptomatic, with its predominant clinical significance being its differentiation from PSS, as bile acid testing is abnormal in both; this can be done only through the exclusion of a definable macroscopic shunting vessel(s). Dogs that progress to clinical disease are treated medically as described for PSS; with no definable macroscopic shunting vessel, surgery is not a therapeutic option.

Copper-associated hepatopathy is a metabolic derangement of hepatic copper storage resulting in progressive hepatocellular copper accumulation and the subsequent development of chronic hepatitis and hepatic cirrhosis. This condition is well defined in Bedlington Terriers, in which 3 clinical variations are described: acute hepatic necrosis in young (<6-yr-old) dogs; chronic progressive hepatic failure in older dogs; and asymptomatic but affected (carrier) dogs. Elevated copper levels have also been identified in the familial hepatic disease of Dalmatians, West Highland White Terriers, Skye Terriers, and Doberman Pinschers, although a causal relationship, as demonstrated in Bedlington Terriers, has not been defined. There are apparent geographic breed variations, with hepatic copper levels worse in Bedlington and West Highland White Terriers of North American descent. Treatment involves the use of copper chelators, low copper diets, and other supportive measures directed at animals with clinical hepatic disease.

Additional hepatic developmental anomalies include hepatic cysts, which are generally asymptomatic and of clinical significance only in that they must be differentiated from hepatic abscesses. Finding a hepatic cyst should also prompt the evaluation of renal architecture (especially in cats) as it may coexist with polycystic renal disease.

Primary or familial hyperlipidemia has been reported in both dogs and cats. Collies, Shetland Sheepdogs, and Briards appear to have a predisposition to hypercholesterolemia. Hypertriglyceridemia of Miniature Schnauzers reportedly affects up to 33% of the breed based on prevalence of hypertriglyceridemia on biochemical testing. Clinical signs in affected dogs are often vague and include abdominal discomfort, behavioral changes, seizures, ocular changes associated with lipid deposits, and an increased risk for pancreatitis.

Hyperchylomicronemia has been reported in domestic cats in New Zealand with clinical signs that include peripheral neuropathies and cutaneous xanthomas often manifesting at <9 mo of age. Treatment of primary hyperlipidemia is focused on feeding a low fat diet, supplementation with omega-3 fatty acids, and in more severe cases, the use of lipid lowering medications, although little information regarding their safety and efficacy in animals exists.

Last full review/revision March 2012 by Walter Ingwersen, DVM, DVSc, DACVIM

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