**Core Concept**
The epiploic foramen, also known as the omental foramen or foramen of Winslow, is a passage in the abdominal cavity that allows for the passage of structures between the greater and lesser sacs. The superior border of the epiploic foramen is formed by the caudate lobe of the liver and the first part of the duodenum.

**Why the Correct Answer is Right**
Injury to the superior border of the epiploic foramen would likely involve the portal vein, which is a major vein that carries blood from the gastrointestinal tract, spleen, and pancreas to the liver. The portal vein passes through the epiploic foramen and is closely related to the superior border. Injury to this area could lead to damage to the portal vein, which could result in bleeding or other complications.

**Why Each Wrong Option is Incorrect**
* **Option A:** The common bile duct is located in the lesser omentum, which is below the epiploic foramen. Injury to the superior border of the epiploic foramen is less likely to involve the common bile duct.
* **Option B:** The hepatic artery proper is located in the lesser omentum and is not directly related to the superior border of the epiploic foramen.
* **Option D:** The hepatic veins are located in the liver and are not directly related to the superior border of the epiploic foramen.

**Clinical Pearl / High-Yield Fact**
The portal vein is a high-risk area for injury during abdominal surgery, particularly when dissecting the superior border of the epiploic foramen. Surgeons should exercise caution when operating in this area to avoid damaging the portal vein.

**Correct Answer:** C. The portal vein.