Feline Portosystemic Shunts (Liver Shunts) Study Guide

Overview and Clinical Importance

Portosystemic shunts (PSS), also known as liver shunts, are abnormal vascular connections between the portal and systemic venous circulation that allow blood to bypass the liver. In cats, this condition causes hepatic encephalopathy, stunted growth, and urinary tract abnormalities due to the accumulation of toxins that would normally be metabolized by the liver. While relatively uncommon in cats (reported incidence of 2.5 per 10,000 cats), PSS represents a critical topic for NAVLE examination due to its distinct clinical presentation and management challenges.

Understanding the pathophysiology, clinical signs, diagnostic approach, and treatment options for feline portosystemic shunts is essential for board success and clinical practice.

Pathophysiology

Normal Hepatic Circulation

In normal physiology, the portal vein carries nutrient-rich but toxin-laden blood from the gastrointestinal tract, spleen, and pancreas to the liver. The liver receives approximately 80% of its blood supply from the portal vein and 20% from the hepatic artery. This portal blood undergoes first-pass metabolism in hepatocytes, where ammonia is converted to urea via the urea cycle, and other toxins are detoxified or eliminated.