In animals with a portosystemic shunt (PSS) (commonly known as liver shunt) there is abnormal blood flow in the liver. Blood should flow from the digestive tract to the liver via the portal system into the blood vessels of the liver, and then to the caudal vena cava which is the large blood vessel carrying blood back to the heart. In a portosystemic shunt, as the name implies, portal blood by-passes the liver and goes directly to the systemic venous circulation (caudal vena cava). One important function of the liver is to clear toxins, many of which are by-products of protein digestion, from the blood. In PSS, these toxins are not cleared, and circulate in the body. This causes the clinical signs associated with PSS, many of which are neurological. The complex of neurological and behavioral signs caused by liver dysfunction is called hepatic encephalopathy.
Portosystemic shunts may be acquired secondary to another disease, or they may be congenital - that is the animal is born with a shunt. A congenital shunt usually occurs as a single abnormal blood vessel that is a remnant of normal embryonic development. These shunts are defined as intra-hepatic or extra-hepatic depending on the location of the blood vessel in relation to the liver.
Most animals with congenital portosystemic shunts show clinical signs before 6 months of age. Where signs are subtle, the condition may not be diagnosed until much later.
The mode of inheritance is not known. Affected individuals and their parents should not be used for breeding.
Generally the diagnosis of congenital PSS is suspected based on the history, clinical signs, and laboratory features. Typically an affected dog is young, of a breed with a predisposition for PSS, with clinical signs and laboratory findings relating to liver dysfunction. A special radiographic tool, contrast portal radiography, is the best way to confirm the diagnosis. Contrast dye is injected into one of the blood vessels going into the liver. In a normal liver, the contrast material disperses into the many blood vessels in the liver, but in congenital PSS, a large portion of the contrast bypasses those vessels and goes directly to the caudal vena cava, the large blood vessel that carries blood to the heart. Contrast radiography also helps in assessing the chances of successfully tying off the shunt surgically. The more contrast that is apparent in the liver, the higher the likelihood of success. Contrast radiography will also identify whether the shunt is intra- or extra-hepatic.
Signs of portosystemic shunts include:
- sensitivity to sedatives (especially diazepam)
- pushing the head against a solid object
- increased drinking and urinating
- frequent urinary tract disease or early onset of bladder stones.
If these signs increase dramatically after eating, it is a strong supportive sign of a portosystemic shunt. For more information visit Terri Shumsky Fanny Mae Liver Shunt Fund Dr. Tobias
