Anomalous insertion of the inferior vena cava in the portal vein.

The ultrasonographic findings of anomalous insertion of the inferior vena cava in the portal venous system were evaluated and correlated with angiographic features. The ontogenic development of the relevant venous system is revisited, and the most important anomalies of the inferior vena cava are presented. An attempt is made to integrate our findings into the relevant classifications following the literature available. Possible developmental mechanisms of the malformation are discussed.