True regarding common bile duct is all except
**Core Concept**
The common bile duct is a vital structure in the digestive system, responsible for transporting bile from the liver and gallbladder to the small intestine. It is formed by the union of the right and left hepatic ducts, which drain the liver, and the cystic duct, which drains the gallbladder.
**Why the Correct Answer is Right**
The common bile duct is approximately 7-8 cm long and is located behind the first part of the duodenum. It is a retroperitoneal structure and becomes intraperitoneal at the level of the pancreatic head. The common bile duct joins the main pancreatic duct to form the ampulla of Vater, which opens into the second part of the duodenum.
**Why Each Wrong Option is Incorrect**
**Option A:** The common bile duct is not formed by the union of the right and left hepatic ducts and the cystic duct. This is incorrect because the common bile duct is indeed formed by the union of the right and left hepatic ducts and the cystic duct.
**Option B:** The common bile duct is a retroperitoneal structure. This is correct.
**Option C:** The common bile duct does not join the main pancreatic duct to form the ampulla of Vater. This is incorrect because the common bile duct does indeed join the main pancreatic duct to form the ampulla of Vater.
**Option D:** The common bile duct is not located anterior to the first part of the duodenum. This is incorrect because the common bile duct is actually located behind the first part of the duodenum.
**Clinical Pearl / High-Yield Fact**
The ampulla of Vater is a critical point for the diagnosis of pancreaticobiliary disorders, and its anatomy is essential for the performance of endoscopic retrograde cholangiopancreatography (ERCP).
**Correct Answer:** A.