Abernethy malformation

Abernethy malformations are an extremely rare anomalous group of the splanchnic venous system. They comprise of congenital portosystemic shunt and results from persistence of embryonic vessels. 

Epidemiology

Type I malformations are thought to only occur in females with type II having a male predilection ¹.

Pathology

Subtypes

There are two main types of Abernethy malformations have been described (initially devised by G Morgan and R Superina ⁶):

• type I: end-to-end shunts
• type II: side-to-side shunts

In type I shunts (end-to-end), there is congenital absence of the portal vein with complete diversion of portal blood into systemic veins (inferior vena cava, renal veins or iliac veins). These are further subdivided into those in which the splenic and superior mesenteric veins end up separately at the systemic veins, and those in which the splenic and superior mesenteric veins join to form a common trunk that ends up at the IVC, right atrium, or iliac veins.

• type Ia: separate drainage of the superior mesenteric and splenic veins into systemic veins
• type Ib: superior mesenteric and splenic veins join to form a short extra-hepatic portal vein which drains into a systemic vein

In type II shunts (side-to-side), there is a hypoplastic portal vein with portal blood diversion into the inferior vena cava through a side-to-side, extrahepatic communication.

Associations

• hepatic encephalopathy: from portosystemic shunting
• hepatic mass lesions 
  • focal nodular hyperplasia: thought to be due to the absence of the portal vein
  • hepatocellular carcinoma
  • hepatoblastoma
• hepatopulmonary syndrome ²
• pulmonary arteriovenous fistulae
  • thought to be due to hyperammonaemia
  • may lead to systemic emboli
• other congenital abnormalities: particularly type I ¹
  • congenital cardiac anomalies
  • biliary atresia
  • polysplenia

History and etymology

It was named after John Abernethy in 1793 who gave the first account of an absent portal vein and a congenital mesentericocaval shunt ^1,5.  

See also

• portosystemic shunts