Portosystemic shunts in dogs and cats*

Portosystemic shunts in dogs and cats

Portosystemic shunts (“liver shunts”, PSS) are an important and relatively frequent disease of dogs and cats. Anatomically, a PSS is one or more venous connections between the portal vein and the systemic venous system, typically the caudal vena cava or azygous vein. Most PSS are macroscopic venous structures but in some breeds abnormalities of the microcirculation within the liver results in functional shunting without macroscopic vascular abnormalities (microvascular dysplasia, MVD). Clinical signs are often somewhat non-specific (unthriftiness, vomiting, anorexia) and also typically include either neurological abnormalities (hepatic encephalopathy) or urinary obstruction (urate urolithiasis). Shunts can be classified as congenital or acquired. Acquired shunts are a feature of chronic liver disease and secondary hypertension, and are of little surgical interest. Affected animals are treated for the effects of hepatic encephalopathy and for the underlying liver disease if possible. Animals with congenital shunts can be managed with medical treatments and dietary manipulation to reduce the signs of hepatic encephalopathy and in the majority there is a good or excellent short to medium term improvement in clinical signs. However, if surgical occlusion of the shunt is possible, the long term outcome is improved compared to those managed medically alone. For most animals, it is therefore logical to recommend surgical intervention following a period of medical stabilisation. PSS are seen in dogs and cats. In dogs, breed dispositions to both congenital macroscopic PSS and MVD are reported.