Portsystemic (liver) shunts, their resolution and their more rare, extended realities

Patty Khuly, DVM
Vet Reviewed
By Patty Khuly, DVM on Mar. 7, 2009
Portsystemic (liver) shunts, their resolution and their more rare, extended realities

One of my patients will die within weeks. Her congenital portosystemic shunts, presumably the result of a pre-birth complication or genetic defect, have led to almost complete liver failure after three short years of life.

Lily is a pet shop Maltese. Her true origins are as unknown as the exact cause of her liver disease. But we do know her liver doesn’t work. And we know it’s the result of a variety of circulatory abnormalities that allow her blood vessels to bypass her liver, thereby limiting the ability of her liver to clear the blood of its toxins.

The Liver 101

The liver is an organ that functions to 1) aid in the digestive process by helping to break down food into digestible nutrients, 2) help the immune system, 3) produce important blood chemicals and 4) filter toxins through enzymatic reactions that eliminate their poisonous effects (among other wonderful functions).

It’s a multi-purpose organ that we think of mostly as one that secretes bile for digestion and biochemically breaks down bad stuff so that animals can survive the effects of toxins they’re regularly exposed to in their environments. 

When the liver doesn’t do its anti-toxic job or doesn’t get enough blood, it can’t do its other functions either. That’s when it curls up and dies. 

Luckily, the liver is one of those organs that has a surprising ability to regenerate. We don’t know exactly why that is, but we suppose it has something to do with its adaptation to occasional or chronic exposure to toxins. If it wasn’t able to absorb insults related to ingestion of or exposure to bad stuff, animals would never survive bouts of food poisoning or common encounters with other environmental toxins.

Portosystemic Shunts 101

Some dogs, unfortunately, (and some humans too) have a congenital malformation that leads blood vessels to bypass the liver. It’s called a “portosystemic shunt” but is also often referred to as a “hepatic shunt” or “liver shunt.” Others have the "acquired" form of the disease, which is typically secondary to severe, diffuse liver ailments in [usually] older dogs.

Here’s what happens: The abnormal vessel(s) allow blood to go around or through the liver without stopping to clear the blood of its toxins or feed the liver its normal quantity of blood. The toxins then move along to the rest of the body. Animals with portosystemic shunts eventually die of common toxins and infections normal bodies don’t stress over. But first, they usually show some or all of the following symptoms:

  • Abnormal behavior after eating
  • Pacing and aimless wandering
  • Pressing the head against the wall
  • Episodes of apparent blindness
  • Seizures
  • Poor weight gain
  • Stunted growth
  • Excessive sleeping and lethargy

Normally, we see the first sign of a portosystemic shunt in dogs when they’re very young––six months is common––but some dogs won’t show signs until a year of age or later. 

Some shunts are “simple.” A big vessel leading to the liver completely circumvents it. Instead of driving blood through the liver so that it can be “cleansed,” it gets “shunted” completely around it. The blood (in which all the bad stuff goes when it enters the body) just keeps circulating, taking the untreated toxic waste to all the organs and tissues. This is called an “extrahepatic shunt,” and it’s most common is small breed dogs.

Bad. But fixable––with surgery to clamp off or slowly constrict this “shunted” vessel. 

Back to Lily:

Lily’s problem was not so easy to handle. When she was an eight month-old pup, she came to me as a second-opinion case as a result of chronic vomiting. Sometimes she would stumble around as if she was drunk, stare at walls or press her head against them, but her owners thought this was a Lily-ism...not a sign of disease. 

Lily was easily diagnosed with a portosystemic shunt after some simple bloodwork (CBC, chemistry, urinalysis and a bile acids test) and X-rays (revealing a small liver because of poor circulation). Sometimes a test called nuclear scintigraphy is done to confirm the diagnosis of a shunt, but in many cases, as in Lily’s, exploratory surgery is a more immediate approach.

In surgery, the veterinary surgeon specialist found numerous vessels being shunted around the liver instead of just one. He clamped as many of these as he could, but assumed the worst: Lily’s liver might well have shunts that travel through it, too. In these cases, called “intrahepatic shunts,” the bad blood vessel is located in the liver but does not actually exchange blood with its tissues. 

Intrahepatic shunts are more common in large breed dogs and they’re especially tough to handle because they’re very difficult to find and in most cases can’t be clamped off the way easier to see extrahepatic shunts can be. This is especially problematic when multiple intrahepatic shunts are present.

Because Lily had numerous extrahepatic shunts, and because her liver was already in such bad shape, the surgeon assumed he had missed many small intrahepatic shunts as well. The only good news was that the slice of liver he biopsied in the process (a common practice for careful surgeons) showed a liver that was still capable of doing its job––for now, anyway.

Back to the Present:

It’s two years later and Lily’s had been doing well all this time. She’d been eating a low protein food, taking liver supplements and drinking lactulose (a sugar syrup that helps draw toxins into the colon for immediate expulsion). 

She’d had a few bouts of gastroenteritis, which were apparently always related to foods she’d managed to consume without her owners’ blessing, but otherwise had remained in great shape. Her liver enzymes had remained high on blood tests but they’d been stable, as had her bile acid levels (the blood test which often most specifically helps identify the degree to which the liver isn’t processing toxins). 

When I saw her last week, however, she’d been vomiting again. While her liver enzymes and bile acids were unchanged from previous tests, an ultrasound at the specialists’ two days later confirmed this was no mere bout of gastroenteritis. Lily’s liver was shot. Within these two days, her bile acids had skyrocketed and her liver enzymes actually plummeted, (a sign that the liver’s most basic functions were shutting down).  


Though 85% of dogs with portosystemic shunts do very well with surgery, Lily’s case was not among the typical success stories. Yes, two years of life beyond treatment is something of a success, especially given her numerous faulty vessels and the length of time her liver had lived with the disease before the surgical “fix,” but it’s nonetheless a heartbreaking story for her family. 

Lily's now living with her family at home for what will most likely be the last few weeks of her life. She’s receiving a diuretic that helps relieve the fluid that build up in the abdomen due to backed up blood (portal hypertension), lactulose to help remove toxins like ammonia and antibiotics to kill the bacteria her liver isn’t currently handling. 

So many of my cases do so perfectly well with liver shunts it’s a shame I’ve chosen Lily’s depressing case as an example. But Lily doesn’t so much seem to mind. Sure, she hates her meds and declines her prescription dog food (so would I) but for now she’s taking it as we all should...one day at a time. 

Patty Khuly, DVM
Vet Reviewed


Patty Khuly, DVM


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