Portosystemic Shunts in Dogs
Portosystemic shunts, or PSS, are vessels that bypass the liver allowing the blood that is draining from the stomach, intestines, spleen, and pancreas to go directly into circulation without getting detoxified by the liver first. The rest of the body is then exposed to these toxins which cause the majority of the clinical symptoms. Continue reading to learn more about liver shunts, clinical symptoms, diagnostic tests, and treatment options for your dog.
Portosystemic Shunts Can Be Congenital or Acquired
Congenital PSS is the most common form in dogs, representing 80% of the cases. This means the dog was born with the liver shunt. The abnormal vessels can go through the liver directly without allowing the blood into smaller vessels to filter out the toxins, or the vessel can be outside the liver altogether.
Congenital PSS located outside the liver is more commonly diagnosed in dogs under 1 year of age. Small and toy breeds are more commonly affected, including Maltese, Cairn terrier, mini and toy Poodles, miniature Schnauzer, Yorkie, Lhasa Apso, Bichon, Shih Tzu, Havanese, and Pekingese.
Congenital PSS located inside the liver is more common in large breed dogs including German Shepherd, Golden Retriever, Doberman, Labrador, Irish setter, Samoyed, Old English Sheepdog, and Irish Wolfhound. Aussies and Australian cattle dogs are also over-represented.
Acquired shunts make up the other 20% of cases. These shunts most commonly develop as a result of chronic high blood pressure in the portal vein. This high blood pressure causes small vessels to reopen that should remain closed after birth. These vessels are typically located outside of the liver near the kidneys. Liver cirrhosis and liver vessel malformations are the other common causes of acquired PSS.
With both forms of PSS, the liver misses out on blood that usually supplies it with hormones to grow and be healthy. This causes further liver damage, along with abnormal fat and protein metabolism. This can lead to damage to the central nervous system, intestinal upset, slow body growth, urinary symptoms, and abnormal clotting ability in some patients.
What symptoms may I see if my dog has a liver shunt?
Dogs with congenital PSS are often younger when symptoms develop. Acquired PSS is most often seen in older dogs and may have worse symptoms compared to congenital PSS. Behavior/neurologic changes are seen in about 80% of dogs with PSS, 75% have GI symptoms, 39% had urinary symptoms.
- Poor body condition (very thin, poor muscle tone)
- Failure to thrive in puppies - poor weight gain, small body stature
- Behavior/neurologic changes such as pacing, vocalizing, head pressing, ataxia, circling, blindness, muscle tremors, seizures, deafness, and extending the neck upward
- Prolonged recovery from anesthesia
- GI symptoms such as vomiting with or without blood, diarrhea with or without blood, eating abnormal things
- Ascites - fluid accumulating in the abdomen
- Urinary symptoms such as straining to urinate, blood in the urine, increased frequency of urination, increased water intake, and difficulty urinating.
- Cryptorchidism (retained testicle) has been reported to be present in over 30% of dogs with PSS
How can my vet diagnose a liver shunt?
Since the symptoms can vary and involve multiple organ systems, your vet will likely start with blood work and a urine test. Dogs with liver shunts often are mildly anemic with small red blood cells. They often have low albumin, cholesterol, BUN, and glucose levels. The liver enzymes may or may not be mildly to moderately elevated. The urine is often dilute and may contain ammonium biurate crystals.
The next test is often a Bile Acid Assay. This test involves obtaining a blood sample after a 12 hours fasting period, feeding the dog, then obtaining another blood sample about an hour or so later. This test assesses liver function. If this test is normal, there is a 97% likelihood that your pet does NOT have a shunt. If this test is abnormal, there is a 67% chance a PSS is the cause.
Ammonia level is another common test to perform. High ammonia levels are suggestive of a PSS, but any form of severe liver disease can result in high levels.
Radiographs (x-rays) can show a small liver.
Abdominal ultrasound by an experienced individual can detect liver shunts in about 75% of cases.
Nuclear Scintigraphy involves administering a nuclear medicine called technetium-99 into the colon via the rectum. The drug is absorbed through the intestinal vessels and then moves toward the liver. The test detects how much technetium bypassed the liver. This test cannot differentiate between shunts through or outside of the liver.
Finally, advanced imaging with a CT scan is the preferred imaging method. It is more accurate than ultrasound and can help with surgical planning.
Exploratory surgery may be offered. The vet will go into the abdomen and search for abnormal vessels in and around the liver.
My dog has a portosystemic shunt. What can we do now?
Surgery is the treatment of choice for PSS. A vessel-occluding device is typically placed to slowly close down the abnormal vessels, allowing for the liver and other vessels to adjust to the new blood flow route.
There is even a type of surgical correction where a coil is inserted into the jugular vein, the large veins in the neck, and is directed to the liver shunt to occlude the abnormal vessel. This is called percutaneous transverse coil embolization, or PTCE.
If surgery is not possible, medical management can be started to help control clinical symptoms, but this will not cure or treat the shunt itself. Medical management includes liver supportive medications, lactulose, enemas to reduce the number of bacteria in the colon that produce toxins, and a highly digestible protein diet. Other potential treatments include zinc supplementation, antibiotics, and probiotics. In dogs that are having seizures, an anticonvulsant may be needed.
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