Introduction

• Cause: congenital vascular anomaly connecting the portal blood system to the systemic circulation. This allows blood from the gastrointestinal tract to bypass the liver. 
• Primarily young cats.
• Signs:
  • Variable and non-specific, can be intermittent.
  • Central nervous system - depression/hyperactivity, head pressing, pacing/circling, stupor, ataxia, blindess, seizures, coma, ptyalism.
  • Gastrointestinal - vomiting, diarrhea, anorexia.
  • Other - small or stunted, poor body condition score,  polyuria/polydipsia, intolerance to sedatives and anesthetic drugs, urolithiasis.
• Diagnosis: history, age, clinical signs, pre and postprandial bile acids, ultrasonography, intra-operative mesenteric portovenography, CT angiography, MRI angiography.
• Treatment: surgical attenutation of shunt (ligation, ameroid constrictor placement, cellophane banding). Medical management prior to surgery or, in long-term cases where surgery impossible/failed/declined by owners.
• Prognosis: good if surgery successful.
  Print off the owner factsheet on Congential portosystemic shunt  Congenital portosystemic shunt  to give to your client.

Pathogenesis

Etiology

• Congenital anomalies that can take two forms:
  • Extrahepatic:
    • More common.
    • Abnormal vessel branches from portal vein or tributary before it enters the liver.
    • Left gastric vein to vena cava most common in cats. Other forms include portocaval and porto-azygous.
    • Represents an abnormal functional communication between the vitelline and cardinal venous systems.
  • Intrahepatic:
    • Arises from an intrahepatic portal vein branch and thus lies wholly or partly within the liver parenchyma.
    • Classified according to division of the liver that is affected - left, right or central.
    • Left is most common and takes the form of a patent ductus venous (PDV) which results from failure of the ductus venosus to close following birth.
    • The origin of other forms of intrahepatic shunts is unclear.

Pathophysiology

• Abnormal communication between portal and systemic blood systems allows blood containing toxic or harmful substances to bypass liver where they would normally be metabolized. This results in increased levels of toxins in the systemic circulation leading to hepatic encephalopathy:
  • Clinical signs relating to central nervous system.
  • Multifactorial - factors act synergistically.
  • Ammonia is major factor in hepatic encephalopathy. Produced from urea by anaerobic bacterial in gastrointestinal tract (colon).
  • Other factors include aromatic amino acids (phenylalanine, tyrosine, tryptophan and methionine), central nervous system inhibitors (GABA and GABA receptors), mercaptans and short chain fatty acids.
  • Signs of hepatic encephalopathy can be triggered by a high protein meal, gastrointestinal bleeding or the use of sedative or anesthetic drugs.

• Reduced hepatic blood supply results in a failure of normal liver growth and development and results in functional hepatic insufficiency:
  • Ability to metabolize uric acid reduced. This results in increased serum ammonia and uric acid which is excreted in the urine. Ammonium biurate crystals form and can cause lower urinary tract signs.
  • Hypoalbuminemia Hypoproteinemia.
  • Intermittent hypoglycemia.
  • Electrolyte abnormalities.
  • Stunted growth.

Diagnosis

Treatment

Prevention

Outcomes