Complete regression of which of the following veins causes this anomaly in the development of IVC (Figure).
**Core Concept**
Incomplete regression of the right supra-cardinal vein leads to the development of a persistent left-sided superior vena cava (SVC) or a duplicated IVC system. Normally, the right supra-cardinal vein should regress during embryonic development, allowing the left supra-cardinal vein to form the IVC.
**Why the Correct Answer is Right**
The right supra-cardinal vein is responsible for forming the IVC in the early stages of embryonic development. However, if it fails to regress, it can lead to the development of a duplicated or anomalous IVC system. This is because the left supra-cardinal vein and the common iliac veins will form the left-sided IVC, while the right supra-cardinal vein will persist as a separate IVC. This anomaly can result in a duplicated or duplicated-incomplete IVC system.
**Why Each Wrong Option is Incorrect**
**Option A:** The right vitelline vein contributes to the formation of the hepatic veins and the inferior vena cava (IVC) but is not directly responsible for the development of the IVC anomaly described.
**Option B:** The left vitelline vein is involved in the formation of the hepatic veins and portal system but does not contribute to the development of the IVC.
**Option D:** The left supra-cardinal vein should form the IVC in the absence of regression of the right supra-cardinal vein.
**Clinical Pearl / High-Yield Fact**
Incomplete regression of the right supra-cardinal vein can lead to a duplicated or anomalous IVC system, which can increase the risk of thrombosis and other complications. This anomaly is often associated with other congenital anomalies, such as horseshoe kidney or renal agenesis.
**✓ Correct Answer: C. Right supra-cardinal vein**