Portosystemic Shunt In Dogs: Causes, Signs & Treatments

In terms of organs and body systems, humans actually share a lot of internal anatomy with dogs – lungs, heart, stomach, and so on. That’s why, in both pet parents and their canine companions, the liver serves the same purpose: to filter out toxins from the bloodstream and ensure overall health. When something interferes with that process, multiple serious health problems occur, many grave enough to endanger the life of a beloved pet. One of those threats is called a portosystemic shunt (PSS) in dogs, and it happens even before a puppy is born. 

Whether it’s a pet owner excitedly adopting a puppy or a breeder assisting with an at-home puppy birth, knowing the signs and symptoms of a canine portosystemic shunt is crucial to rendering timely assistance to a pup in need. 

What Is A Portosystemic Shunt In Dogs?

In a healthy and unaffected puppy, growth in the womb follows a very specific timeline as independent body functions are set up prior to birth. Earlier in the gestation, the mother dog’s liver takes on the task of filtering blood for all her puppies. This is no small feat, considering many larger dams birth litters in the double-digits: the Guinness Book record for a litter is a whopping twenty four pups. As the birth approaches, the dam’s body should automatically begin to close and eventually cut off a mother-to-puppy blood vessel known as the ductus venosus in each puppy, signaling to their individual livers that it’s time to take on the work themselves. This gives each puppy the biological nudge they need to start up their body’s filtering systems prior to the birthing process.

Sometimes, however, that process doesn’t go as smoothly as it’s supposed to and the puppy’s body makes a portosystemic shunt instead. This means an abnormal blood vessel is created that bypasses the liver entirely, connecting the vessel that’s supposed to travel to the liver to another vessel in his body, often connected directly to the heart. A normal, healthy blood vessel connection to the liver is important for filtering blood as well as keeping the liver healthy. That’s the reason that the unwanted shunt actually hurts the puppy in two ways: his body can’t filter out toxins normally, and the liver doesn’t receive the blood flow it should. 

When this happens, a host of symptoms arise in his puppyhood and adolescence, up to and including dire problems like liver failure. Knowing how and why shunts form is crucial to responsive treatment, and may even save his life.

What Are The Types Of Portosystemic Shunts?

The prognosis for a dog with a portosystemic shunt depends largely on the type of canine liver shunt he’s afflicted with. Because shunts can appear both inside (intrahepatic) and outside (extrahepatic) the liver, it’s important for a vet or animal health professional to narrow down the structure of the shunt before recommending treatment – in some cases, surgery is appropriate, in others, diet changes and symptom mitigation alone are prescribed.

  • Extrahepatic portosystemic shunts in dogs are the more treatable version of the two: a vet will usually perform surgery and implant a device to mimic what the dam’s body would normally have done in gestation. This device gradually closes off the shunt, giving the dog’s body time to adjust to the “new normal” and take over liver filtering functions without causing a shock to his system. These types of shunts appear most often in smaller-breed dogs, such as Yorkies and Jack Russell Terriers
  • Intrahepatic portosystemic shunts in dogs are, conversely, more common in larger breeds, such as Golden Retrievers and Labradors. These types of canine liver shunts are more difficult to treat, as they require more intensive surgery and more post-operative recovery time needed. Preoperative changes to diet and medication will likely be prescribed, with a goal of putting as little stress as possible on his compromised blood filtering systems beforehand to boost chances of surgical success. 

In some cases, multiple shunts appear, rather than simply one – this can happen both inside and outside of the liver. In most of these multi-shunt occurrences, surgery is unfortunately not usually an option. A vet team will generally recommend treating the symptoms medically or with a change in diet to keep their canine patient comfortable, as well as delay complete liver failure for as long as possible. These specialized diets are intended to reduce the toxins going into his system, hopefully minimizing the negative effects of buildup in the process.

When Do Portosystemic Shunts In Dogs Appear?

Shunts can appear in dogs in one of two ways: congenitally, which means they are born with it, and less commonly as an acquired portosystemic shunt. In the case of the latter, abnormally elevated blood pressure in digestive tract vessels triggers growth of a shunt. This phenomenon is most common in an older dog already afflicted by comorbid issues with his liver, such as cirrhosis (liver scarring). In these cases, the shunt is intended to compensate for the compromised liver by bypassing it entirely, but this obviously leads to separate and equally serious canine health issues.

Because shunts can, between the two emergent varieties, occur at any age, it means that pet parents have to be continually vigilant for symptoms in their dogs. These symptoms may include, but are not limited to:

  • Body stature on the small / underdeveloped side of his breed spectrum: This symptom may include a puppy being the “runt” of his litter: a substantial size difference compared to his littermates may be the first sign of a potential shunt. 
  • Issues with anesthesia: If a dog doesn’t tolerate anesthesia either during or after a procedure (neutering, for example), this can be a red flag for a portosystemic shunt in dogs. He may fail to “come to” in a normal window of time after a surgery or procedure, and appear sluggish for many hours, or even days afterward. This occurs because his liver cannot filter out the anesthesia as it normally does in a healthy dog with full liver function.
  • Swaying and/or difficulty walking: If there are no other obvious issues affecting his gait, such as an injured paw, swaying while walking (ataxia) can be a signal he’s having issues processing toxins. He will appear almost as if he is drunk, unable to navigate straight, familiar courses like hallways or frequented rooms of the home. 
  • Seizures: Absent any other cause, such as allergies or a traumatic injury, canine seizures can point to a buildup of toxins in his internal system. This buildup essentially “short circuits” his brain as his body struggles to cope with naturally-occurring but unfiltered substances, like ammonia, in the blood. 
  • Head-pressing: This is not a burrowing, cuddling, or curling maneuver, but rather exactly what it sounds like: a dog pressing his head up against a firm surface, like a wall. He will remain in this position for a noticeable period of time, even if it looks uncomfortable. Head pressing is a symptom of a neurological disorder, which in turn can be caused by toxin buildup. 
  • Blindness: Another off-shoot of neurological issues, a sudden and dramatic inability to see can be caused by toxin buildup as his body struggles to process toxins without the aid of the liver. 

How Do I Prevent Portosystemic Shunts In Dogs?

The best defense against congenital liver shunts in dogs is the same approach taken to breed afflictions such as Collie Eye Anomaly: selective breeding. Because congenital shunts are hereditary, most vets recommend spaying and/or neutering any dog found to have one, as they are likely to pass the genes to their puppies. 

For acquired shunts, the best defense is a periodic checkup schedule with a vet, who will be able to diagnose and treat liver issues before a shunt appears. Another way to avoid acquired portosystemic shunts in dogs is timely medical visits if symptoms are observed; in addition to those listed above, a reluctance or inability to urinate can also signal a need for a checkup. This behavior can result from bladder stones, which block the normal flow of urine and can make the elimination process uncomfortable or painful as well. Thankfully, veterinarians can perform various tests, including testing both blood and urine, to check for the presence of minerals, toxins, or bacteria that can point to a less-than-optimal liver function. 

In most cases, however, discovery of shunts of either variety are a result of investigating emergent symptoms, rather than proactive testing. Even the most vigilant pet parent can’t sense a shunt being formed, and should remember that outward symptoms are a dog’s way of communicating he’s in need of help. As long as he’s taken to a vet in a timely fashion when troublesome signs emerge, prognosis is typically positive, and healthy post-operative recovery points to a long, healthy life for a formerly shunt-afflicted pup.

Sources Cited:

1)      “Portosystemic Shunts.” American College of Veterinary Surgeons (ACVS.org), (no publish date), https://www.acvs.org/small-animal/portosystemic-shunts. Accessed May 26, 2020.

2)      Williams, Krista; BSc, DVM, CCRP; Ward, Ernest; DVM. “Portosystemic Shunt in Dogs.” VCA Hospitals.com, (no publish date), https://vcahospitals.com/know-your-pet/portosystemic-shunt-in-dogs. Accessed May 26, 2020.

3)      Zeltzman, Dr. Phil; DVM, DACVS, CVJ. “Liver Shunt in Dogs.” Pet Health Network.com, (no publish date), http://www.pethealthnetwork.com/dog-health/dog-diseases-conditions-a-z/liver-shunt-dogs. Accessed May 26, 2020.

4)      Sullivan, Megan. “Liver Shunts in Dogs: What You Need to Know.” PetMD.com, January 10, 2018, https://www.petmd.com/dog/general-health/liver-shunts-dogs-what-you-need-know. Accessed May 26, 2020.

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