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 2 3.
This anomaly results from failure of right sub-cardinal-hepatic anastomosis with atrophy of right sub-cardinal vein and shunting of blood from supra-cardinal-sub-cardinal anastomosis to cranial portion of supra-cardinal vein (retro-crural azygos vein) 2.
Imaging findings include: hepatic veins drain into right atrium. Renal veins drain into azygous (or hemi-azygous). This anomaly usually occurs with a right infra-renal IVC with azygos/hemi-azygos continuation (4), but it may also occur with other two variants:
(1) Left infra-renal IVC with azygos/hemi-azygos continuation 5 (as in this case).
(2) Double infra-renal IVCs with two possibilities: EITHER both IVCs join at the renal level and continue as azygos vein) 6 OR (the right IVC continues as the azygos vein and the left one continues as the hemi-azygos vein) 7.
The clinical importance of this anomaly is in misinterpretation as right para-tracheal mass or retro-crural adenopathy, in being associated with heterotaxy syndromes and other congenital heart diseases and in pre-operative knowledge of the anatomy prior to planning cardio-pulmonary bypass and to avoid difficulties in catheterizing the heart 8 9.