Liver shunts, also known as porto-systemic shunts (PSS) are the most common porto-vascular anomaly in dogs. And one of the more common abnormalities of blood vessels in total. Thankfully, PSS are not that common in dogs but certain breeds of dogs are more likely to develop liver shunts than others. This article will cover what porto-systemic shunts are, the different types of shunts, how they are identified and treatment options available.
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What is a liver shunt?
A liver shunt (PSS) is a blood vessel abnormality that results in blood from other organs including the gastrointestinal tract (the small intestine, large intestine, and stomach) being diverted directly towards the heart and bypassing the liver. Consequently, this results in a build-up of toxins within the blood that the liver would normally eliminate.
So let’s quickly review a portion of the normal blood flow to and from the liver. (Which if you don’t know already, is an extremely important organ!). In a normally functioning liver with normal blood vessels, the hepatic portal vein carries blood (containing toxins) from the gastrointestinal tract to the liver to be “cleaned” and processed, before the blood proceeds to the heart and then to the rest of the body. There are other vessels too which provides circulation to and from the liver. But the hepatic portal vein supplies approximately 60-70% of the liver’s blood supply.
In a “shunt”, abnormal vessels form, which bypass the liver. These can either be intrahepatic (within the liver) or extrahepatic (outside of the liver) which is more common.
What causes liver shunts?
Liver shunts can be generally placed into two categories: congenital shunts vs acquired shunts.
Congenital shunts
These types of PSS are hereditary and are usually present from birth. Larger breeds such as golden retrievers and german shepherds are predisposed to intrahepatic shunts. Whereas smaller breeds such as Yorkshire terriers and poodles are predisposed to extrahepatic shunts. Dogs with congenital liver shunts are typically under 1 year of age. It is strongly not recommended to breed from dogs with liver shunts.
Acquired shunts
With these types of shunts, your dog is not born with a congenital abnormality but they can develop a PSS overtime, often secondary to liver disease and failure. Often acquired shunts occur in older patients.
Congenital shunts are much more common than acquired shunts. Additionally, individual dogs can have more than one liver shunt, sometimes there can be multiple PSS in one patient.
What are the clinical signs?
The severity and consequences of the liver shunts depend on the location of the shunt and the volume of blood which the shunt bypasses from the liver. Therefore, the clinical signs can vary depending on the severity of disease. The clinical history is also very important in helping to identify dogs with this condition.
Below lists some of the clinical signs in dogs with liver shunts (this list is not exhaustive):
Neurological signs
Often worse following a meal/protein ingestion, these neurological signs are usually associated with “hepatic encephalopathy”. This is a condition which occurs as a result of excessive ammonia build up in the bloodstream. In a normally functioning liver, this organ is responsible for converting ammonia into the protein urea, which is then excreted by the kidneys. These neurological signs include head pressing against walls, disorientation and sometimes seizure activity.
Slower recovery from sedation or anaesthesia
The liver has many vitally important roles including the metabolism and processing of drugs. Dogs with liver impairment do not metabolise the anaesthetic/sedative drugs as efficiently. And as a result of this they can take much longer to recover from its effects.
Gastrointestinal upset
Usually vomiting, and sometimes diarrhoea. This is due to toxins (especially ammonium) in the bloodstream, but also problems with digesting food.
Weight loss
Usually due to difficulty processing nutrients, and sometimes from difficulty in digesting them due to a failure of bile production.
Jaundice (yellow mucous membranes)
Icteric (yellow) mucous membranes often occur in advanced stages of liver damage. Another role of the liver is to remove bilirubin (a blood waste product) from the blood. However, in poorly functioning livers they are unable to remove the bilirubin from the blood; this results in yellowing of the skin, gums and sclera (white part of the eye).
Stunted growth/smaller size
Failure to thrive and grow is usually apparent in animals with congenital liver shunts.
How are liver shunts diagnosed?
Diagnosis of liver shunts is often via a multi-diagnostic approach and some shunts may be easier to diagnose than others depending on the location. Your Vet may recommend blood tests (assessing liver/kidney enzymes), liver function tests, abdominal ultrasound scans, urine tests, sometimes advanced imaging including CT scans and contrast studies (portovenogram) and liver biopsies.
What are the treatment options?
The treatment option and management plan for your canine friend is very dependent on the type and location of the shunt. Other factors also play an important factor including age and overall health of your dog and your Vet will be able to guide you on the most appropriate options and management plan most suitable for your dog.
Congenital shunts are sometimes corrected by surgery if this is possible and the surgical procedure involves ligating (tying off) the problematic vessel(s). Nowadays, alternative approaches involving keyhole surgery to insert a “plug” (coil embolisation) or a gradually closing ring (ameroid constrictors) are widely used. Extrahepatic shunts are generally easier to correct via surgery due to their location outside of the liver tissue. If surgery is an option, this would ideally be the treatment of choice alongside medical management.
Dogs with more complicated liver shunts including multiple intrahepatic liver shunts are often not surgical candidates due to the complexity of the procedure.
However, as acquired shunts are usually secondary to liver disease or failure, these patients are more often managed medically rather than surgery, due to the underlying liver disease. Also, as mentioned above these patients are usually older and are more likely to have underlying health conditions and the patient will fall into a higher anaesthetic risk group. Medical management usually involves supportive medication including antibiotics and a specific diet (lower protein). Antibiotics are usually prescribed to combat the bacteria and toxins accumulating in the blood.
Conclusion
To conclude, there are various types of liver shunts in dogs and the underlying cause of the PSS can affect the clinical outcome. Following successful surgical ligation of the liver shunt and restoration of normal blood flow, patients can be expected to lead a relatively normal life, providing there is no problematic long-term liver impairment.
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