In this case the major findings include; absent portal vein, giant inferior mesenteric vein and multiple hepatic focal lesions. 

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. 

Types

 Abernethy malformation is an anatomical classification of portosystemic anomalies consisting of:

•  Type 1 , there is complete diversion of portal blood into the systemic circulation (end-to-side shunt), with absent intrahepatic portal branches. Type 1 shunts are further subdivided into:
  • Type 1a: those in which the splenic vein (SV) and superior mesenteric vein (SMV) drain separately into a systemic vein.  
  • Type 1b:  those in which the SV and SMV drain together after joining to form a common trunk .
• Type 2, the intrahepatic PV is intact, but some of the portal flow is diverted into a systemic vein through a side-to-side shunt.

Clinical classification of congenital extrahepatic portosystemic shunts consist of:¹

• Type A,  In type A, the supramesenteric vein (SMV) and splenic vein (SV) drain directly into the inferior vena cava (IVC).
• Type B, the SMV and SV drain into the left renal vein.
• Type C, the SMV and SV drain into the iliac vein via a dilated inferior mesenteric vein. (As in this case)

In type C patients, collaterals can develop between the inferior mesenteric and iliac veins mainly via the hemorrhoidal plexus. ¹

Associations

Recognized associations include:

• 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 
• pulmonary arteriovenous fistulae
• other congenital abnormalities: particularly type I 1
  • congenital cardiac anomalies
  • biliary atresia
  • polysplenia