**Question:** All of the following form boundary of Calot's triangle EXCEPT?

A. Hepatic artery
B. Cystic artery and duct
C. Truncus coeliacus
D. Spleen

**Core Concept:**
Calot's triangle is a triangular region located between three major structures in the abdomen: the head of the pancreas, the common bile duct, and the gastro-duodenal artery. These structures form the base and sides of the triangle. A further understanding of the vasculature and biliary system is essential for identifying and avoiding complications during surgical procedures in this region.

**Why the Correct Answer is Right:**
The correct answer, **D. Spleen**, is not part of Calot's triangle because the spleen is located on the posterior aspect of the stomach, away from the triangle formed by the aforementioned structures. The spleen is part of the splenic hilum, which is located in the left hypochondrium (left upper quadrant) and is connected to the posterior surface of the stomach, while Calot's triangle is situated on the anterior surface of the stomach.

**Why Each Wrong Option is Incorrect:**

A. **Hepatic artery (Correct answer)** - The hepatic artery is a major vessel that supplies blood to the liver and is included in the triangle.

B. **Cystic artery and duct (Correct answer)** - The cystic artery and duct are structures associated with the bile duct system and are part of the biliary tree. They form the bottom of the triangle.

C. **Truncus coeliacus (Correct answer)** - The truncus coeliacus is a major blood vessel that supplies blood to the abdominal organs and is located within the triangle.

**Clinical Pearl:**
Understanding the anatomy of Calot's triangle is crucial for safe laparoscopic cholecystectomy, as it helps surgeons identify and protect the critical structures during surgery in this region. Distinguishing between the correct and incorrect options helps prevent complications such as bile duct injuries and bleeding.