If you are not raising an Asian cat, for example, if you are raising a British Shorthair, American Shorthair or Maine Coon cat, when their pupil color is copper, and they have severe liver disease or are smaller than cats of the same breed, If they are too young, you should be aware that they may have a disease that is very difficult to treat - feline congenital portal vein short circuit.

Cause and pathogenesis

Portal blood substances bypass the liver through abnormal blood vessels and enter the circulation directly. The pathophysiological reaction is the result of toxic substances that are not removed by the liver (such as ammonia and other brain toxins, absorbed bacteria, endotoxins) and the total hepatic blood flow is less than 80% of the normal portal blood flow. Since portal blood carries 50% of the oxygen required by the liver and contains important nutritional factors, especially insulin, the reduction in portal blood flow will lead to a decrease in liver cell regeneration and function. Several types of portal circulation abnormalities have been reported in dogs, but the most common abnormality in cats is a single extrahepatic short circuit, an anastomosis of the gastric, splenic, or portal vein to the posterior vena cava. Occasionally, complete portal venous short-circuiting may occur due to intrahepatic portal vein hypoplasia or incomplete closure of the ductus arteriosus. These defects may be due to a failure to regulate fetal vein degeneration or may be due to a lack of appropriate metabolic signals to promote fetal vein closure. Because intrahepatic portal pressure is usually higher than posterior vena cava pressure, blood flow preferentially passes through these abnormal unsealed channels.

Clinical features

Male cats less than 3 years old are susceptible to this disease, and hybrid cats, Persian cats and Himalayan cats have a higher incidence rate. The typical clinical manifestation of congenital portal vein short circuit in dogs and cats is hepatic encephalopathy. Behavioral and overt neurological abnormalities (eg, dementia, convulsions, visual impairment, ataxia) are most common in affected dogs and cats. Affected cats have multiple episodes of intermittent salivation, which may be a sign of mild hepatic encephalopathy. This performance usually occurs when eating halfway. The severity of other clinical symptoms, such as developmental delay, may be related to the location and size of the malformed vessels. A less common medical feature is recurrent urate stones. Recovery from anesthesia or sedation takes longer due to prolonged drug degradation. Behavioral and neurological symptoms improve with antibiotic treatment. Most affected cats are thin, but physical examination findings are nonspecific. Other congenital defects are sometimes seen, such as a heart murmur or cryptorchidism. Some veterinarians have noticed copper-colored irises in non-Asian breed cats with congenital portal vein short circuit.

　Diagnostic methods

Based on the results of routine examinations and liver-specific laboratory tests, congenital portal vein short circuit can be suspected. The most common clinicopathological abnormalities are hyperammonemia after provocation testing (administration of food or ammonium chloride) and elevated serum bile acid concentrations after fasting and/or feeding. Decreased serum urea nitrogen and creatinine concentrations, mild changes in liver enzyme activity, microcytosis, anisocytosis,Decreased urine specific gravity is a less common finding. It is unreliable to look for other clinicopathological abnormalities typical of hepatic insufficiency, such as hypoalbuminemia and diuretic acid ammonium crystalluria. Because congenital portal vein shunting is a simple vascular abnormality, significant hepatocellular damage is not a typical feature of it unless accompanied by liver damage. The mild increase in serum phosphatase activity may be the result of accelerated bone metabolism in cats younger than 6 months of age. Subclinical liver organelle damage may also be a factor.

Congenital portal short circuit is diagnosed by ultrasound, transcolonic portal scintigraphy or portal venography, as well as measurement of portal venous pressure and liver biopsy. Affected cats have normal or small livers. A liver biopsy sample must be obtained to confirm the liver histological features of congenital portal vein short circuit: hepatic lobular atrophy, inconspicuous portal vein branches, overlapping arterioles, and sometimes mild fat deposition and vacuolation changes. If necrosis or inflammation is present, it is mild.

　Treatment methods

The definitive treatment for congenital portal vein short-circuit is to assume that there is enough portal vein in the liver to accept the re-inflow of blood and to completely ligate the short-circuited blood vessel. This surgical approach is commonly used in referral centers and veterinary schools. After blood vessel ligation, the portal vein pressure should not exceed 18cmH2O (normal = 6~15), and the abdominal organs should be observed for 5~10 minutes to prevent congestion or congestion. If the above situation occurs, the ligature needs to be loosened or the blood vessel must be partially ligated to reduce its diameter to 50% to 75% of its original size. After ligating the short-circuited blood vessels, portal venography should be performed repeatedly to determine whether the perfusion of the portal vein is sufficient. After incomplete ligation, the condition will partially improve, and the clinical manifestations of completely ligated cats are usually normal. For cats with congenital portal vein short circuit that cannot be completely ligated, you can choose to use a device that can gradually narrow the short-circuited blood vessel within 30 days.

It is important to emphasize that symptomatic treatment is not a suitable long-term alternative to surgical treatment. Symptoms of hepatic encephalopathy will decrease, but portal blood flow is not restored, liver condition continues to worsen, and central nervous changes with refractory hepatic encephalopathy may become permanent.