Portal Vein Hypoplasia and Secondary Portal Hypertension
Portal vein hypoplasia with portal hypertension and ascites occurs as a fibrosis variant. It is generally regarded that dogs
having congenital portosystemic vascular anomalies with a single intra or extrahepatic shunting vessel have signs associated
with hepatic encephalopathy but do not have portal hypertension or ascites. However there is a subgroup of dogs with portal
vein hypoplasia that have moderate to marked fibrosis of the portal tracts, sometimes resulting in portal to portal fibrosis
and a varying proliferation of arterioles and bile ductules, particularly at the periphery of the portal area. Ascites, portal
hypertension and secondary acquired portosystemic shunts occur. This condition has also been referred to as idiopathic noncirrhotic
portal hypertension or congenital hepatic fibrosis because there is significant fibrosis in the portal areas.
The hepatic histology demonstrates portal tracts associated with multiple arterioles, small or absent portal veins with variable
portal fibrosis, lymphatic distention and variable bile duct proliferation. The pathology is void of inflammatory infiltrates.
There are also increased amounts of hepatic iron deposited in the liver. The fibrosis and bile duct replication may be a non-specific
reaction from increased growth factors promoting arterial proliferation.
This latter condition is observed in dogs are under 2.5 years of age and there is no breed prevalence however Doberman Pinschers,
Cocker Spaniels and Rottweilers may be over represented.
The clinical presentation is similar to dogs having either congenital intra or extrahepatic shunts except most dogs have
ascites. The liver enzymes are generally increased with a hypoalbuminemia and very high bile acid concentrations. Work up
of these patients fails to identify a single shunting vessel, but rather these cases have marked portal hypertension associated
with multiple acquired portosystemic shunts. These dogs present with ascites and signs of hepatic encephalopathy. Ultrasound
is often helpful showing microhepatia, hepatofugal portal blood flow and multiple abnormal extrahepatic collateral shunts.
Portal contrast studies demonstrate acquired portal shunts and pressure measurements document portal hypertension. The prognosis
for this condition is generally guarded but some dogs are reported to have a prolonged survival using anti-fibrotic agents
and hepatic encephalopathy therapy.
Hepatocutaneous syndrome, better known as superficial necrolytic dermatitis or metabolic dermatosis is an uncommon disease
observed in middle aged to older dogs. The skin lesions have characteristic histological changes (superficial necrolytic dermatitis
or necrolytic migratory erythemia) and when combined with the hepatic changes typify this syndrome. The liver has mistakenly
been described by some as cirrhotic because of the nodular appearance of the liver. The hepatic changes are best described
as an idiopathic hepatocellular collapse with nodular regeneration. Changes are generally devoid of major inflammation. The
hepatic nodular regeneration consists of vacuolated hepatocytes. To date the pathogenesis of the hepatic disease is still
controversial. In humans other types of liver disease have been noted to produce the similar cutaneous lesions however the
hepatocellular collapse described in the canine hepatocutaneous syndrome has not been reported. It is not known if the liver
dysfunction is the major mediator of the necrolytic skin lesions or whether another metabolic disease produced both the skin
and hepatic lesions. Affected dogs almost all have pronounced reductions in amino acid and albumin concentrations. Some authors
believe this condition to be the result of exaggerated amino acid catabolism. Uncommonly some dogs and humans have hyperglucagonemia
secondary to a glucagon-secreting tumor. Diabetes mellitus occurs in some dogs. Recently hepatocutaneous syndrome has also
been associated with chronic long-term phenobarbital therapy.
Most dogs are presented because of the skin disease. Abnormal liver enzymes are identified and in most, ALP and bile acids
are increased. The albumin is typically below normal and almost every affected dog is hypoaminoacidemia. The liver has a characteristic
ultrasound appearance looking like "Swiss cheese" due to the hypoechoic nodules.
It is thought that the necrolytic skin lesions are directly related to the hypoaminoacidemia. The hypoaminoacidemia may be
responsible for the hepatic changes as well. This is supported in part by observations that dogs fed a protein deficient diet
for prolonged periods develop hypoalbumenia and hepatic changes that resemble hepatic changes described in the hepatocutaneous
syndrome, however skin lesions were not observed. The importance of hypoaminoacidemia in this disease is further supported
in that administration of intravenous amino acid solutions transiently improved the lesions in many but not all dogs. The
cause of the amino acid deficiency is unknown. The affected dogs appear to have been feed adequate protein content diets.
The reported prognosis for this disease is grave and invariably most succumb either due to liver dysfunction or to the severity
of the skin lesions, or both.