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Portosystemic Shunt (Liver Shunt)

In the normal animal, the blood supply draining the intestines travels through the portal vein into the liver where it is filtered, and then returned to the heart via the caudal vena cava. A portosystemic shunt (PSS) is an abnormal vein connecting the blood supply returning from the intestines to a vein returning blood to the heart, thus bypassing the liver. Because of this bypass (shunt), the liver does not filter the blood, and substances from the intestine gain access to the bloodstream. Moreover, due to decreased blood supply, the liver becomes dysfunctional. Portosystemic shunts can be either congenital (present at birth) or acquired. Acquired PSS can develop in pets that have severe chronic liver disease. Congenital PSS can be found within the liver (intrahepatic) or before the liver (extrahepatic). Intrahepatic shunts are more commonly found in large-breed dogs. Extrahepatic shunts are more commonly found in miniature and toy breed dogs such as Yorkshire terriers, Havanese, Miniature Schnauzers, poodles, Lhasa Apsos, and Pekingese, as well as in cats.

Portosystemic Shunt (Liver Shunt)

PSS symptoms

A patient with a PSS may show symptoms such as poor weight gain, increased thirst and urination, increased salivation (more common in cats), vomiting, diarrhea, straining or difficulty urinating due to bladder stone development, decreased or excessive appetite, and neurological symptoms such as tremors, disorientation, depression, circling, blindness and seizures.

Diagnosis of PSS

Diagnostic workup for a PSS usually includes blood tests, liver function testing, and urinalysis to evaluate liver function and look for other causes. Definitive diagnosis of a PSS requires imaging (visualization) of the shunt. This can sometimes, but not always, be achieved via abdominal ultrasonography. Where this is not possible, other imaging modalities, such as contrast enhanced radiographs, computed tomography (CT) scan, MRI, or nuclear scintigraphy, may be necessary. In some cases, definitive diagnosis is made at the time of surgery.

Surgery for extrahepatic PSS

Portosystemic Shunt (Liver Shunt) surgery is considered the treatment of choice for extrahepatic PSS, and is commonly performed. At surgery, our goal is to locate and close the abnormal shunt vessel. Rapid closure, however, can be problematic as the liver cannot accommodate the sudden increase in blood supply. As such, the preferred method of closure is via gradual occlusion (using ameroid constrictor or cellophane banding).

Surgery for intrahepatic PSS

Surgery for intrahepatic PSS

Although an intrahepatic shunt can be addressed as an abdominal surgery, the risks and complications during and after surgery are higher. Exposing these shunts may require dissection into the liver, and the shunts tend to be larger, making it more difficult to occlude. Newer minimally-invasive procedures have been developed to allow occlusion of the shunt with the aid of catheters and interventional radiology.

Surgical outcome

Based on the current literature, and in our experience, 80-90% of dogs with an extrahepatic PSS will have an excellent outcome. About 10% of dogs will have a recurrence of signs and will require continued medical management. About 7% of dogs will have severe problems after surgery, such as seizures or other systemic problems that can be life-threatening.

Perioperative care

Medical management is usually initiated presurgically to stabilize the pet prior to surgery, and is usually continued for a period after surgery until liver function is normalized.