[TLC]

The following was posted on my Dog Liver Disease. I thought it was good information so I am posting here.

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Porto-systemic Shunt (PSS) / LIVER SHUNT

Pathophysiology
Ammonia comes from bacteria in the intestines and when muscles utilize protein as a energy source. In a normal animal this ammonia gets delivered through the portal vein directly into the liver. The liver cells metabolize the ammonia to urea, which is excreted by the kidneys. The liver also detoxifies bacteria and drugs that are also absorbed from the intestines before they get into the general circulation and go to the rest of the body.

Shunts occur when the blood supply through the liver is abnormal. The abnormal blood vessel shunts blood around the liver instead of through the liver.. By bypassing the liver the toxins that are normally metabolized by the liver (especially ammonia) are allowed to enter the general circulation before the liver has a chance to detoxify them. It is this ammonia buildup that causes most of the symptoms observed with PSS. It is also know as hepatic encephalopathy (HE) because of its toxic effects on the brain.

Several factors can add to HE. A diet high in protein will add to blood ammonia levels, along with infection, cancer, and excess use of cortisone. Kidney disease along with constipation will also add to the problem. Some drugs, notably barbiturates, valium, and anesthetics can also be factors.

Shunts can be multiple or single. The shunt can occur within the liver (intrahepatic) or in the blood supply before it enters the liver (extrahepatic) .. Larger breed dogs are more prone to intrahepatic shunts, extrahepatic shunts are more common in small breed dogs and cats. It is important to differentiate them for therapeutic purposes.

There are other diseases that can mimic PSS. They include liver toxins, liver infection, liver cancer, and hepatic lipidosis (see previous description) . An organ as complex as the liver necessitates the need for a precise diagnosis before treatment can be instituted. Also, a pet with chronic liver disease leading to cirrhosis will sometimes get acquired shunts.

Causes
Congenital The congenital version of PSS occurs more commonly in dogs than in cats. Most of these shunts are extrahepatic, meaning the shunting vessels are located outside of the liver.

Acquired
Seen mostly in dogs, they occur when there is increased resistance to blood flow through a fibrotic liver. These shunts occur inside the liver and are not easily corrected.

Signalment
Congenital shunts tend to be found in younger dogs and cats, while acquired shunts tend to occur in older animals. In some situations the symptoms of this disease are so subtle that a diagnosis of congenital shunt is not made until a pet is much older. We tend to see it more often in male cats as opposed to female cats.


Several dog breeds are predisposed:
Irish wolfhounds
Maltese
Yorkshire terriers
Miniature schnauzers
Australian cattle dogs
Retrievers
Cairn terriers
Old English sheepdogs

Cat breeds might include:
Himalayan
Persian

History
Some of the symptoms of PSS can be subtle, and easily interpreted as a quiet puppy or kitten. Symptoms can wax and wane, thus they are easily missed. Some pets seem to have a preference for fruits and vegetables.

Hepatic Encephalopathy (HE) Behavior changes, particularly right after eating. These changes include depression, head pressing, blindness, lethargy, coma, seizures, and personality changes. anorexia, vomiting, diarrhea, and excess salivation (more so in cats) might be present. Excess urinating and drinking (PU/PD), blood in the urine (hematuria) and an increased incidence of ammonium urate bladder stones might also be present. Other symptoms might include inhibited growth, fever, and abnormally long recovery periods from anesthesia (ex.-when a spay or neuter is performed).

Physical Exam
Pets with PSS will commonly be stunted in growth, but usually exhibit no abnormalities on their neurologic exams. A small liver might be palpated on smaller animals. Hair coat might be unkempt and there might be ascites on abdominal palpation. Other occasional findings include cryptorchidism. (undescended testicles)

Diagnostic Tests
Several diseases mimic PSS. They include Distemper, FIP, toxoplasmosis, FeLV related diseases, toxicities, idiopathic epilepsy, and hypoglycemia. This emphasizes the importance of proper testing to come to an accurate diagnosis.

Blood Panel
In dogs, a blood panel might show anemia along with elevated levels of ALT and Alk Phos. The BUN might be low, cholesterol might be low, the protein level might be low (hypoproteinemia) , and the blood sugar might be low (hypoglycemia) in the smaller breed dogs. A bile acids tests will show an elevation, particularly after we feed a meal. If we suspect PSS as the cause to your pets problem we will run a blood ammonia level, which will come back elevated if PSS is present. An ammonia tolerance test might be needed for verification.

In cats the albumin, BUN, and cholesterol might be low or at the low end of the normal range.

Urinalysis
A urinalysis might show symptoms of urinary tract infection or abnormal crystals, particularly ammonium biurate.

Radiography
A radiograph of the liver might show a small liver (microhepatica) , particularly in the dog. The liver might be hard to evaluate because a lack of abdominal fat, due to emaciation or a young animal.
Kidney changes and bladder stones might be visible, although ascites might obscure vision of internal organs. ammonium urate bladder stones might not show up on a radiograph even though they are present.

Ultrasound
Ultrasound can give further information on the liver and its blood supply, and even detect ammonium biurate bladder stones which normally don't appear on a radiograph. Ultrasound is better at differentiated intrahepatic shunts as opposed to extrahepatic shunts.

Positive Contrast Portography
Some consider this test the gold standard for diagnosis. In this test a special dye is injected directly into one of the veins of the small intestines while a pet is under anesthesia. A radiograph is taken and the flow of the dye is followed. If a shunt is present this will show up on the radiograph.

Biopsy
A biopsy of the liver (usually performed when the ultrasound is done) will show microscopic abnormalities consistent with PSS. This usually includes small hepatocytes and a decrease in the blood vessels within the liver.

Laparotomy
Exploratory surgery to visualize the vessels directly, or to inject dye into the portal vessels, is also used to verify the diagnosis. After the dye is injected a radiograph is taken to assess absorption. Surgical repair can immediately be initiated.

Scintigraphy
A transcolonic nuclear scan can give a definitive diagnosis. In this test a small amount of radioactive (99technetium pertechnetate) material is put into the colon and its absorption is monitored. In pets with PSS this radioactive material will appear in the heart before it appears in the liver, the opposite of what should normally happen. This test does not require anesthesia like the Positive Contrast Portography test.