Portosystemic shunts (PSSs) are vascular communications between the portal and systemic venous systems that allow portal blood to reach the systemic circulation without first passing through the liver. Signs of HE dominate the clinical picture because of inadequate hepatic clearance of enterically derived toxins such as ammonia, mercaptans, short-chain fatty acids, gamma-aminobutyric acid, and endogenous benzodiazepines.