Portosystemic shunts (PSS) are abnormal vessels that allow normal portal (liver) blood that is draining from the stomach, intestines, pancreas, and spleen to pass directly into systemic circulation without first passing through the liver. When this blood bypasses the liver, toxins enter the bloodstream that would have normally been deactivated by the liver. Also, substances meant for the liver that are released from the pancreas and intestines will not reach the liver, resulting in the failure of the liver to reach a normal size.
PSS are categorized as either intrahepatic or extrahepatic. Extrahepatic shunts can be acquired or congenital. Congenital extrahepatic shunts are usually a single abnormal vessel and account for 63% of single shunts in dogs. Acquired extrahepatic shunts are usually multiple abnormal vessels and account for 20% of all PSS cases in dogs. Intrahepatic shunts are usually congenital defects in which the ductus venosis (a major blood vessel) fails to close after birth.
Multiple shunts are most commonly associated with chronic/severe liver disease.
Single PSS are usually diagnosed in animals under a year of age. Extrahepatic shunts are usually diagnosed in miniature and toy-breed dogs. Intrahepatic shunts are usually diagnosed in large-breed dogs.
The presenting history for PSS varies greatly. The affected animal is examined due to growth failure, small body frame, or weight loss. Other symptoms may be intermittent anorexia, depression, vomiting, polydipsia/polyuria (increased drinking/increased urination), and behavioral changes.
Upon examination, the animal with PSS may have kidneys that feel very prominent or plump. Some neurologic abnormalities may be seen. There may also be a palpably enlarged liver or fluid in the abdomen.
The definitive diagnosis for PSS is made by surgical identification of the shunt, ultrasound, or portogram. Here at the VSRP, the patient will be under general anesthesia while a portogram is performed to view if a shunt is present. A portogram is a procedure in which a special dye (Renografin) is injected into a mesenteric vein. A radiograph is quickly taken while the dye is being injected and then viewed for traveling sequence. A normal radiograph will show the dye successfully traveling from the injection site into the branches of the liver. A PSS will show the dye completely bypass the liver. Once diagnosed, surgery is the treatment of choice for a PSS because liver function will continue to deteriorate with the continuation of blood being shunted away from the liver.
The goal of surgery is to identify and close off the abnormal vessel. A device called an ameroid constrictor is used with extrahepatic shunts to slowly close off the shunt vessel. The ring is placed around the shunt at the time of surgery. The ring will slowly close over 14-20 days. With the vessel slowly being shut off, this will keep the intestines from experiencing too much back pressure (portal hypertension).
Animals with multiple shunts are best managed medically to achieve long-term survival and quality of life though they may benefit from caudal vena cava banding (a constrictor placed around the lower major vessel of the heart).
After surgery, continuing medical management and feeding a low-fat diet may be recommended until the abnormal vessel is completely occluded. Your animal will need to be re-evaluated for his/her liver function 6-8 weeks after surgery.