Congenital portosystemic shunt

Congenital portosystemic shunts are rare anatomical abnormalities linked to abnormal embryological venous development. They can be extrahepatic or intrahepatic. In either case, the underlying abnormality is shunting of blood from the portal venous system to the systemic venous system thus avoiding passage through the hepatic acinus 1.

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 haptic sinusoids. The term “portosystemic shunt” is more frequently associated with secondary causes, such as portal hypertension or obstruction.

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. 

A Swiss study reported 5 cases out of 145,000 neonates. Seemingly higher incidence in Japan may be due to routine screening for hypergalactosaemia 1.

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 1

Presentation ranges from an incidental finding to hepatic encephalopathy and liver failure depending on the type of abnormality. The portovenous shunt ratio may be prognostic of progression to encephalopathy and cirrhosis. Decompensation may be precipitated by concurrent illness. Clinical features can include the following 1:

Being a congenital anatomic abnormality, the pathogenesis is linked to the complexity of embryological development of the Inferior vena cava and portal vein 2

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 the abnormal anatomy. General findings may include1:

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

Natural history is dependent on the portovenous shunt ratio, patient age, type of variant and associated congenital abnormalities. It is worth noting the following 1:

  • children are more resistant to 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 1:

  • 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
    • embolisation
    • surgical correction
  • removal of the shunt

John Abernethy first reported on extrahepatic portosystemic shunts in 1793 5.

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