Portosystemic Shunt (Hepatic Shunt) in Dogs

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Portosystemic Shunt (Hepatic Shunt) in Dogs

By: Dr. Erika De Papp

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Section: Information In-depth

A congenital portosystemic shunt is a condition that exists when your pet is born. This is a serious disorder because the liver does not receive adequate blood flow, and therefore does not grow normally. Most animals with shunts have livers that are smaller than normal. Because of the inadequate blood flow and improper growth, the liver does not function properly.

The liver is an enormously important organ that has many functions. The most notable abnormalities that result from a shunt are those affecting:

The central nervous system (CNS). The neurologic disorders are collectively referred to as hepatic encephalopathy and can range from lethargy and dullness to seizures, blindness, and erratic behavior.

The gastrointestinal system. The most common gastrointestinal signs are anorexia, vomiting and diarrhea.

The urinary tract. The most frequently documented urinary signs are straining to urinate and blood in the urine.

The urinary problems are a result of ammonium biurate bladder stones that occur secondary to liver dysfunction. Some pets also drink more and urinate more than normal. Your pet may show many of these signs or only a few.

Although the CNS problems are the most common, some pets show only urinary tract or gastrointestinal signs. Some animals may show a failure to grow normally as the only obvious abnormality. Because the clinical signs can be quite varied, there are a number of other conditions that can cause similar signs, including:

Infectious diseases. Distemper is a common viral illness of young dogs. Infections with protozoal organisms such as Toxoplasma and Neospora can occur in dogs . All of these diseases may cause abnormalities of the CNS and gastrointestinal tract, causing signs similar those seen in patients with portosystemic shunts.

Toxicities. Ingestion of, or exposure to, certain toxins may produce multiple neurologic abnormalities that can mimic the signs seen with hepatic encephalopathy. Toxins may include ethylene glycol (antifreeze), lead, flea products (organophosphates) and prescription medications. These animals often present with vomiting and/or diarrhea as well.

Hydrocephalus. This is a congenital brain defect that may cause seizures or abnormal behavior in young animals.

Epilepsy. This is a seizure disorder most commonly seen in dogs, with no known cause.

Hypoglycemia. Low blood sugar will often cause weakness and seizures, if severe. Young animals are prone to developing hypoglycemia if they are not eating normally.

Urea cycle enzyme deficiency. This is a rare metabolic disorder in which the animal is missing an enzyme necessary for normal ammonia processing. Build-up of ammonia causes encephalopathy, but the patient does not have a shunt.

Hepatic microvascular dysplasia. This disorder has only been described in dogs. It is another congenital disorder that causes abnormal liver function and can therefore cause many of the same signs that are seen with shunts. This is not a surgically correctable disorder.

Urinary tract infections. Bladder infections or inflammation will cause blood in the urine and straining to urinate. A simple urinary disorder would not cause the other clinical signs often seen in patients with shunts.

Gastroenteritis. There are multiple causes of vomiting and diarrhea. Although some pets with hepatic shunts will show only gastrointestinal signs, this is less common.

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