Abernethy malformation

Abernethy malformations are rare vascular anomalies of the splanchnic venous system. They consist of congenital portosystemic shunts and result from persistence of the embryonic vessels. 

Epidemiology

Type I malformations are thought to occur only in females, while type II have a male predominance ¹.

Pathology

Subtypes

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

• type I: end-to-side shunt7shunt; superior mesenteric and splenic vein drain separately into inferior vena cava
• type II: side-to-side shunts; superior mesenteric vein and splenic vein form a common trunk before draining into the inferior vena cava

In type I shunts (end-to-end), there is a congenital absence of the portal vein with a complete diversion of portal blood into systemic veins (inferior vena cava, renal veins, or iliac veins). These are further subdivided into:

• type Ia: separate drainage of the superior mesenteric vein and splenic vein into systemic veins
• type Ib: superior mesenteric vein and splenic vein join to form a short extra-hepatic portal vein which drains into a systemic vein (inferior vena cava, right atrium or iliac veins)

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 generate due to the absence of the portal vein
  • hepatocellular carcinoma
  • hepatoblastoma
• hepatopulmonary syndrome ²
• pulmonary arteriovenous fistulae
  • thought to arise due to hyperammonaemia
  • may lead to systemic emboli
• other congenital abnormalities, particularly associated with type I ¹ :
  • congenital cardiac anomalies
  • biliary atresia
  • polysplenia

History and etymology

Named after John Abernethy, who gave the first account of an absent portal vein with accompanying congenital mesentericocaval shunt ^1,5 in 1793.