Veins are part of the body’s circulatory system. The hepatic portal system consists of the numerous veins that drain blood away from digestive organs and deliver it to the liver. Small veins merge into one large one, called the portal vein, that feeds directly into the liver. The formation of these veins, however, can sometimes go awry.
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Portal vein hypoplasia (PVH), also known as portal venous hypoplasia, hepatic microvascular dysplasia, portal microvascular dysplasia, non-cirrhotic portal hypertension, and hepatoportal fibrosis, is a circulatory anomaly of the liver in dogs and cats. Hypoplasia indicates the incomplete development of a structure. With PVH, there is a microscopic malformation of the liver’s tiny blood vessels. The tiny abnormalities can lead to defective connections between circulation in the portal vein and that of the rest of the body.
PVH can occur alone, or it can be combined with portosystemic shunts (PSS). A shunt allows blood to flow between two structures that are not supposed to be connected. One study showed that 58 percent of dogs and 87 percent of cats with PVH had a concurrent PSS that they were born with. Cats are less commonly affected than dogs.
PVH is a nonprogressive disorder, meaning it does not get worse over time.
Pets with PVH should not be bred due to the possibility this is an inherited condition. This condition most commonly affects Yorkshire terriers and Cairn terriers, but it’s also seen in Maltese, dachshunds, miniature poodles, Shih tzus, Lhasa apsos, cocker spaniels, and West Highland white terriers. Dogs with PVH are usually older at time of diagnosis, compared to dogs with PSS. No gender predisposition has been noted.
Many pets that have PVH without portal hypertension don’t have any signs or have signs that are less severe than those with PSSs. Possible clinical signs include failure to grow, weight loss, small stature, lack of appetite, and behavioral changes.
Dogs rarely exhibit signs of hepatic encephalopathy (HE), but it is possible. Possible clinical signs of HE include circling, behavior changes, head pressing, ataxia, weakness, seizures, coma, stupor, pacing, blindness, and vocalization. HE is a consequence of liver failure.
Other clinical signs that can be seen in PVH dogs include excessive thirst and urination, vomiting, diarrhea, pica (eating abnormal and often undigestible items), bloody vomiting, bloody stools, blood in urine, straining to urinate, and drooling.
To diagnose your pet, your veterinarian will take a thorough history, give a physical exam, take a complete blood count, run a blood serum chemistry, do a urinalysis, run blood bile acids, radiograph/ultrasound the abdomen, and may take liver biopsies for analysis. The liver biopsy can provide the definitive diagnosis if it shows the abnormal vessels.
Therapy for PVH is aimed at controlling clinical signs. Therapy does not result in a cure, and no surgical correction is possible.
- Dogs that are affected with PVH, but don’t have any signs, do not necessarily require any therapy.
- If there are signs of HE, treatment is directed at controlling those clinical signs.
- Hepato-protective supplements can be given, but it is not known if they improve the lifespan of affected dogs. Supplements include s-adenosylmethionine (SAMe), vitamin E, milk thistle, and ursodeoxycholic acid.
- Patients that have concurrent PSSs may require surgical correction of the macroscopic shunt.
- Dogs may be placed on a low-protein commercial diet with high-quality protein, to reduce the protein levels in their system.
Monitoring And Prognosis
Patients with PVH are monitored with yearly biochemistry panels and bile acid tests to assess any abnormalities or changes in liver values. Monitoring is important even in dogs that do not have clinical signs, so that any elevated values can be acted on.
Overall, prognosis for patients with PVH is good, especially if the dog doesn’t have any signs. Most affected dogs have a normal life expectancy. Rarely, some pets have PVH so severe that they develop liver failure; their prognosis is poor.