In gallstone ileus, obstruction is seen at
**Core Concept**
Gallstone ileus is a rare complication of gallstones that occurs when a gallstone enters the small intestine through a fistula, typically between the gallbladder and the duodenum (choledocho-duodenal fistula). The stone acts as a mechanical obstruction, causing bowel distension and potentially life-threatening complications.
**Why the Correct Answer is Right**
In gallstone ileus, the obstruction usually occurs at the terminal ileum, which is the last portion of the small intestine. The stone becomes lodged in the narrow lumen of the ileum, causing bowel obstruction. The ileum is more susceptible to obstruction due to its smaller diameter compared to other parts of the small intestine. This obstruction can lead to severe abdominal pain, vomiting, and constipation.
**Why Each Wrong Option is Incorrect**
* **Option A:** This option is not relevant to gallstone ileus. The duodenum is the first portion of the small intestine, and obstruction here is not typical of gallstone ileus.
* **Option B:** While the jejunum is a part of the small intestine, it is not the typical site for obstruction in gallstone ileus. The jejunum is wider than the ileum, making it less susceptible to mechanical obstruction.
* **Option D:** The stomach is not a typical site for obstruction in gallstone ileus. The stone would need to pass through the pylorus and into the small intestine to cause an obstruction.
**Clinical Pearl / High-Yield Fact**
Remember that gallstone ileus is a surgical emergency that requires prompt diagnosis and treatment to prevent bowel ischemia and perforation. A high index of suspicion should be maintained in patients with a history of gallstones and symptoms of bowel obstruction.
**Correct Answer:** C.