Canine Portosystemic Shunts: An Overview of Diagnosis and Treatment Options

Introduction

Portosystemic shunts (PSS) are vascular communications taking blood directly from the portal circulation to the systemic circulation, bypassing the liver in the process. Anomalous vessels have been identified connecting between the portal circulation and a wide variety of vessels including the caudal vena cava, the azygous vein, and the renal veins (Figure 1). Animals with PSS may have single, double or multiple shunts and may have concurrent abnormalities such as complete portal vein atresia or portal vein hypoplasia (1). PSS may be acquired or congenital, intrahepatic or extra-hepatic. Congenital PSS are diagnosed more commonly in purebred dogs than crossbreeds, with a reportedly high incidence in cairn terriers, dachshunds, miniature schnauzers, golden and Labrador retrievers, Irish wolfhounds (IWH), Maltese terriers and Australian cattle dogs (2). There is evidence to suggest that left division intrahepatic PSS in the IWH and extra-hepatic PSS in cairn and Yorkshire terriers are inherited and there is a suspicion that PSS may be inherited in Australian cattle dogs and other over-represented breeds. However there are no firm or consistent recommendations regarding breeding policies for affected individuals. Clinical signs caused by PSS can be both variable and vague but neurological signs are the most common presentation. However, some cases have no neurological signs at all and instead may present with a history of recurrent urinary tract infections, crystalluria and urate urolithiasis (3). In others the clinical signs are sufficiently vague that the diagnosis is not immediately obvious; for example, recurrent unexplained infections, ongoing nausea and vomiting, or failure to thrive. Diagnosis is based on combining the history and clinical findings with the results of appropriate laboratory tests and diagnostic imaging. A period of stabilization with medical management is typically recommended prior to surgery to attenuate or close the shunt vessel but surgery should be considered the treat- ment of choice unless there is a specific contra-indication present, such as absence of a portal vein or multiple secondary acquired shunts (2,4,5). [...]

Key Points

• Congenital portosystemic shunts are the most common congenital anomaly of the hepatobiliary system in dogs.
• Hepatic dysfunction results from the presence of a portosystemic shunt, leading to a wide variety of clinical presentations of which hepatic encephalopathy is the most common.
• Signalment, history and clinical signs may be strongly suggestive of portosystemic shunt as a diagnosis, but they are by no means conclusive.
• Definitive diagnosis, and identification of concurrent or complicating problems, requires a combination of laboratory data and diagnostic imaging.
• Medical and dietary management is generally instituted to stabilize patients prior to surgery. 
• In the absence of a known contraindication to surgery, surgical attenuation or ligation is the treatment of choice.