Complete regression of which of the following veins causes this anomaly in the development of IVC (Figure).

Ans: (c) Right supra-cardinal veinRef: Essentials of Human Embryology, A.K.Datta, 5th edition, 2005, Page 205-208 4The anomaly shown in picture is Retrocaval ureter (right ureter) passes at first behind the IVC, and then appears in front of it after winding the medial margin of IVC.Retrocaval ureter occurs when the post-renal segment of the IVC is developed from the right posterior cardinal vein and the right supra-cardinal vein regress entirely.Development of IVCIVC developed from the following sources from below upwards1. Persistent caudal part of the right posterior cardinal vein2. Right supra-cardinal vein (this part receives 3rd and 4th pairs of lumbar veins)3. Anastomosis between right supra-cardinal and right sub-cardinal veins (this part receives the right gonadal vein).4. Upper part of the right sub-cardinal vein (this part receives both renal veins and right supra-renal vein).5. A new vessel grows dorsal to the liver and communicates the right sub-cardinal vein with the common hepatic vein (intrahepatic part of IVC).6. Common hepatic vein-which is developed from the suprahepatic part of the right vitelline vein (terminal part of IVC).Anomalies of IVC1. Double IVC - IVC persist on both sides below the level of renal veins. This occurs when the left common iliac vein fails to develop and the infra-renal segment of the left supra-cardinal vein fails to regress.2. Retro-caval ureter (as explained earlier).