The reported incidence of this anomaly is estimated to be 0.6-2% of patients with congenital heart diseases and less than 0.3% in otherwise normal individuals ^1-3.

This anomaly results from failure of right subcardinal-hepatic anastomosis with atrophy of right subcardinal vein and shunting of blood from supracardinal-subcardinal anastomosis to cranial portion of supracardinal vein (retrocrural azygos vein) ².

Imaging findings include: hepatic veins drain into right atrium. Renal veins drain into azygos (or hemiazygos). This anomaly usually occurs with a right infra-renal IVC with azygos/hemiazygos continuation ⁴, but it may also occur with other two variants:

1. left infrarenal IVC with azygos/hemiazygos continuation ⁵ (as in this case).
2. double infrarenal IVCs with two possibilities: either both IVCs join at the renal level and continue as the azygos vein) ⁶ or (the right IVC continues as the azygos vein and the left one continues as the hemiazygos vein) ⁷. 

The clinical importance of this anomaly is the risk of misinterpretation of it as a right paratracheal mass or retrocrural adenopathy, in being associated with heterotaxy syndromes and other congenital heart diseases and in preoperative knowledge of the anatomy prior to planning cardiopulmonary bypass and to avoid difficulties in catheterizing the heart ^8,9.