Abernethy malformation

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

Epidemiology

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

Pathology

Subtypes

Two main types of Abernethy malformations have been described ⁶:

• type I: end-to-side shunt; 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 hyperammonemia

  • 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.