Congenital portosystemic shunt

​Congenital portosystemic shunts are rare, extrahepatic or intrahepatic, anatomical abnormalities shunting blood from the portal venous system to the systemic venous system and, thus, avoiding passage through the hepatic acinus.

Terminology

The term “portosystemic shunt” can be used to refer to any pathology where blood from the splanchnic venous circulation is shunted to an alternate venous drainage pathway without passing through the hepatic sinusoids. When used by itself, the term “portosystemic shunt” is more frequently associated with secondary causes, such as portal hypertension or obstruction. The term "congenital portosystemic shunt" applies when there is no history of cirrhosis, portal hypertension, previous portal vein thrombosis, liver biopsy, or trauma .

The term “Abernethy malformation” is frequently used and typically refers to extrahepatic congenital portosystemic shunts similar to those first described by J Abernethy in 1793. Therefore care should be taken when referring to intrahepatic shunts.

Epidemiology

A Swiss study reported 5 cases out of 145,000 neonates. Seemingly higher incidence in Japan may be due to routine screening for hypergalactosemia .

Risk factors have not been well-defined. Shunts may be associated with other congenital abnormalities but are also found incidentally as isolated aberrancies. Extrahepatic type 1 shunts are more common in girls .

Clinical presentation

Presentation ranges from an incidental finding to hepatic encephalopathy and liver failure depending on the type of abnormality. The portosystemic shunt ratio may be prognostic of progression to hepatic encephalopathy and cirrhosis. Decompensation may be precipitated by concurrent illness. Clinical features can include the following :

• hypergalactosemia 
• hyperammonemia
• hyperglycemia
• hepatic encephalopathy
• liver failure
• hepatopulmonary syndrome
• heart failure

Pathology

Being a congenital anatomic abnormality, the pathogenesis is linked to the complexity of the embryological development of the inferior vena cava and portal vein.

These patients may develop benign regenerative liver lesions, mainly large focal nodular hyperplasia-like lesions, but hepatocellular adenomas have also been described .

Classification systems

• congenital extrahepatic portosystemic shunt classification
• congenital intrahepatic portosystemic shunt classification

Radiographic features

Findings will vary depending on the anatomical anomaly. Doppler ultrasound is used to determine the portovenous shunt ratio. CT and MRI are used to further define abnormal anatomy. General findings may include :

• absence of portal vein, notably only two tubular structures - hepatic artery and common bile duct present at the hepatic hilum
• decreased liver size

Ultrasound

• anechoic tubular or cystic structures communicating between portal venous branches and hepatic venous branches 
• increased intrahepatic peribiliary echogenicity
• elevated portosystemic shunt ratio

Treatment and prognosis

Natural history is dependent on the portovenous shunt ratio, patient age, type of variant and associated congenital abnormalities. It is worth noting the following:

• children are more resistant to hepatic encephalopathy with higher shunt ratios
• shunts often close in the first 2 years of life
• surgical correction is generally considered in shunt ratios >60%

Management may incorporate a combination of the following :

• observation
• correction of metabolic abnormalities
  • may be addressed with lifestyle modifications and medical therapy e.g protein-free diet, lactulose, branch-chain amino acids
• correction of the shunt
  • embolization
  • surgical correction
• removal of the shunt
  • local excision of the shunt
  • liver transplant

History and etymology

John Abernethy (1764-1831), an English surgeon, first reported on extrahepatic portosystemic shunts in 1793 .