A portosystemic shunt (PSS), or liver shunt in dogs is a vascular anomaly of the liver and is one of the most common congenital defects in dogs. If your dog is suffering from a liver shunt, it's important to get it the treatment it needs. In this blog post, we will discuss what causes liver shunts in dogs, the symptoms to look out for, and how to help manage the condition.
What is a liver shunt in dogs?
Portosystemic shunt (PSS), or liver shunt in dogs are abnormal vessels that allow normal blood, which drains from the digestive system (stomach, intestines, pancreas), to bypass the liver and flow directly into the systemic circulation.
Normally, blood from the digestive system enters the liver through the portal vasculature system. Hepatic portal blood transports trophic hormones such as insulin and glucagon, as well as toxins and bacteria derived from the intestinal tract. A portosystemic liver shunt bypasses the hepatic circulation and enters directly into the systemic circulation. Consequently, hepatic growth cannot be encouraged by these trophic hormones, which results in an underdeveloped liver, a deficient protein supply, and abnormal fat and protein metabolism. In the body, exogenous and endogenous toxins that are normally metabolized or eliminated by the liver accumulate.
What are the types of a liver shunt in dogs?
Portosystemic liver shunts can be either congenital or acquired.
Congenital liver shunt
Congenital shunts are most common, occurring in 80% of patients with a portosystemic liver shunt. A congenital portosystemic shunt typically occurs as a single extrahepatic or single intrahepatic anomalous vessel. During the fetal stages, there is a duct that normally diverts blood from the digestive system away from the liver and directly into systemic circulation. This occurs normally while in the fetus as there is no oral consumption of food in the mother's womb. This duct will resolve after birth but it is the persistence of this duct that leads to a congenital liver shunt in dogs. In the Yorkshire terrier and Cairn terrier, the portosystemic liver shunt is hereditary but there are many other breed predispositions such as the Maltese.
Acquired liver shunt
Acquired liver shunts occur in up to 20% of affected animals. It is common for them to develop secondary to chronic portal hypertension (more prevalent among dogs). Multiple acquired shunts are usually located extrahepatically (outside the liver) near the kidneys, are tortuous, and are numerous in number. Among the most common causes are cirrhosis of the liver (uncommon in cats) and portal vein hypertension.
What are the clinical symptoms of a liver shunt in dogs?
Dogs with a portosystemic liver shunt may have a history of failure to grow, weight loss, lack of appetite, small stature, anorexia, and behavioral changes. Many of the clinical signs associated with a liver shunt are related to hepatic encephalopathy. Hepatic encephalopathy is a condition that occurs secondary to a liver shunt as ammonia from the digestive system cannot be delivered to the liver. The ammonia subsequently enters the systemic circulation where it causes severe clinical signs, especially neurological symptoms. Other common clinical symptoms that dogs with a liver shunt may display include:
- Increased thirst and urination
- Vomiting
- Pica
- Drooling
- Ataxia (lack of coordination), circling and pacing, especially after eating
How is a liver shunt in dogs diagnosed?
A liver shunt in dogs is typically diagnosed with a combination of clinical signs, medical history, and diagnostic tests. Baseline lab work includes a complete blood count (CBC) and biochemical profile where the liver enzymes can be assessed and interpreted. The changes are often consistent with underlying liver insufficiency or illness.
More specific blood tests may be recommended by your veterinarian such as bile acid assays and blood ammonia levels. These tests evaluate liver function and the liver function in dogs with a liver shunt is reduced. Urinalysis may also be recommended as dogs with liver shunts often have increased protein and blood in their urine as well as ammonia urate urinary crystals.
Ultrasound is the most common diagnostic imaging tool used to diagnose a liver shunt in dogs. The ultrasonographic appearance of a liver shunt can vary depending on the location and type of shunt, but typically there is increased liver echogenicity (liver appears brighter than normal) and dilation of the portal vein.
What is the treatment for a liver shunt in dogs?
Medical therapy cannot correct the underlying condition whereas surgery can provide better management. The goals of medical management, however, are to correct factors contributing to the symptoms of hepatic encephalopathy as mentioned above. In cases where surgical correction is not possible or declined and for older dogs with mild clinical signs, medical therapy can be considered.
Surgery is often the treatment of choice for most dogs with a portosystemic liver shunt. As a result of surgery, the abnormal vessel is attenuated so that blood can be redirected to the liver, and blood flow is restored.
What is the prognosis for dogs with a liver shunt?
The prognosis for dogs with liver shunts depends on a number of factors, including the severity of clinical signs, underlying cause and whether surgery is performed. Dogs that have surgery generally have a good prognosis but those that do not may eventually die from the liver shunt. A liver shunt can be managed with medical treatment alone in approximately 1/3 of dogs. The older the dog is when it first shows signs of the disease, the longer it will live with medication alone. In one study of 126 dogs with a congenital portosystemic liver shunt, surgically treated patients had a significantly longer survival time than medically treated patients. 90% of those who had undergone surgery and 63% of those who had undergone medical treatment were still alive after 1500 days.
Can a portosystemic liver shunt in dogs cause seizures?
Yes, seizures can occur as a result of hepatic encephalopathy. The build of toxins and ammonia in the blood resulting from the liver shunt can cause seizures.
Do dogs with a portosystemic liver shunt require a special diet?
As of now, veterinarians recommended feeding rate is 4 g/100 kcal of highly digestible protein. Increases in protein may gradually be introduced if tolerated. Protein tolerance can also be promoted by eating small, frequent meals. Dietary restrictions are also recommended for manganese and copper.
What preventative measures should a dog owner take with a dog that has a liver shunt?
Dog owners should avoid situations that might precipitate signs of hepatic encephalopathy such as restricting excess dietary protein. Dog owners should also avoid giving dogs certain medications that are metabolized by the liver such as NSAIDs and barbituates.
Do liver shunts change a dog's behavior?
Yes, they can change a dog's behavior as a result of a portosystemic liver shunt. This is due to secondary hepatic encephalopathy where there is a buildup of toxins and ammonia in the bloodstream.
This article provides an overview of liver shunts in dogs, including the causes, symptoms, and treatment. Surgery is often the treatment of choice for most dogs with a liver shunt, as it can correct the underlying problem. The prognosis for dogs with liver shunts depends on a number of factors but is generally good when surgery is performed. If you have any questions or if you're concerned that your dog may have a liver shunt, please contact your veterinarian.