Congenital anomalies of the venae cavae: embryological origin, imaging features and report of three new variants.

Due to the complexity of their developmental stages, the venae cavae may undergo a very large number of congenital anomalies. All the possible abnormalities which, to our knowledge, have been observed in the literature are reported, differentiating those of the superior vena cava and the azygos system, those of the inferior vena cava and the complex anomalies that concern the venous system as a whole. Moreover, we present three new variants: a right double inferior vena cava with azygos continuation of the posterior-medial vein; an agenesis of the superior vena cava with drainage through the azygos and hemiazygos veins to the inferior vena cava; and a double inferior vena cava with hemiazygos and azygos continuation of the left one.