If your dog or cat has ever received a “portosystemic shunt” diagnosis from your primary care veterinarian, you might have found the condition’s details hard to understand or remember. A portosystemic shunt (PSS) is an abnormal vessel that allows blood from the animal’s intestine to bypass the liver. As a result, toxins, proteins, hormones and nutrients absorbed by the intestines also bypass the liver, circulating throughout the body, and results in further deterioration of liver function.
There are two categories of congenital shunts – extrahepatic (outside the liver) and intrahepatic (inside the liver). While most are congenital (the dog or cat is born with it), under certain circumstances, PSS may be acquired secondary to another problem with the liver.
If a shunt is present, the liver is deprived of factors that enhance liver development and fails to reach normal size (hepatic atrophy). A common result of hepatic atrophy is hepatic insufficiency, which combined with the circulating toxins, proteins and nutrients, frequently results in hepatic encephalopathy, a clinical syndrome of altered central nervous system function due to failure of normal liver function.
The genetic basis of congenital PSS in dogs is unclear. Breeds commonly affected include miniature schnauzers, Yorkshire terriers, Irish wolfhounds, cairn terriers, Maltese, Australian cattle dogs, golden retrievers, Old English sheepdogs and Labrador retrievers. Single extrahepatic shunts are typically present from birth and affect small and toy breeds whereas single intrahepatic shunts typically affect large breeds. Cats nearly always have extrahepatic shunts.
Acquired PSS almost always presents as multiple abnormal vessels, which develop in response to an increase in blood pressure within the liver (hepatic hypertension). They can occur in any breed or age of the animal. Acquired PSS is one of the protective mechanisms that could reduce or offset unpleasant side effects of hepatic hypertension, to prevent or delay liver failure. As such, they cannot be closed off without causing severe symptoms, and medical management is the only option for treatment.
Signs and Symptoms:
Animals born with PSS may have small body stature, prolonged recovery following an anesthetic event and behavioral abnormalities.
The signs are often episodic and may be more noticeable after eating. Signs of abnormal neurologic function are due to hepatic encephalopathy and may include swaying as if intoxicated, seizures, blindness, head pressing, loss of appetite, vomiting, diarrhea, constipation, hypersalivation (which is most frequently seen in cats) or excessive urination/drinking. Some toxins that bypass the liver are excreted in the urine and can cause bladder stones. Therefore, animals affected by PSS may also present with difficulty urinating or blood in the urine.
If your primary care veterinarian suspects that your pet has PSS, a full diagnostic work-up is advised. Some of these diagnostics may be completed by your primary care veterinarian, but you may also be referred to an ACVS board-certified veterinary surgeon or veterinary specialty center for additional diagnostics. A full work-up may include blood work, urinalysis, liver function tests, radiographs, ultrasounds and potentially advanced diagnostics such as a CT scan with contrast or nuclear scintigraphy.
The goal of medical management is to improve your animal’s health to a point where the risk of anesthesia and surgery is low. Medical management of PSS consists of a low protein diet and oral administration of antibiotics and laxatives in order to decrease the bacterial population in the intestines and assist in excretion of toxins. If seizures are a part of symptoms, anti-seizure medication may also be used.
The treatment of choice for a single extrahepatic PSS is surgical attenuation (narrowing) or full ligation (tying off) of the abnormal shunt vessel. This surgery is technically challenging, and your primary care veterinarian may refer you to an ACVS board-certified veterinary surgeon. If a shunt cannot be readily identified at surgery, an intra-operative portogram (an image obtained in surgery to evaluate blood flow) is performed. Additionally, in some cases pressure in the portal vein may be measured to determine if the shunt can be safely attenuated, partially ligated, or completely ligated. Many intrahepatic PSS can now be treated using minimally invasive techniques (sometimes called Interventional radiology) and your surgeon may discuss this with you.
Aftercare and Outcome:
Routine postoperative management includes IV fluids and pain medications. Laxatives and diet modifications are continued, as it takes time for the liver cells to regenerate and adjust to the new circulation. Some dogs may need long term treatment whereas others may only need certain dietary restrictions or no medical restrictions.
Complications after surgery include portal hypertension, which can lead to loss of proper blood circulation to abdominal organs and death. Animals may also experience fluid distension in the abdomen, vomiting, diarrhea, depression, and respiratory distress.
The prognosis is excellent if the animal survives the immediate post-surgery period and full ligation of the shunt is achieved. In many cases, full ligation is possible in animals partially ligated 4–6 months prior, so follow-up tests should be done to monitor for liver function.
If you have concerns about your pet and need to locate a board-certified veterinarian, use the VetSpecialists.com search tool on the website’s homepage that allows you to search for a veterinary specialist in your area. Contact the hospital of your choice to discuss your pet’s symptoms and to review whether there is a need for a referral from your primary care veterinarian.