**Beheaded Scottish Terrier Sign**

**Core Concept**
The beheaded Scottish terrier sign is a radiological finding associated with a specific condition of the gastrointestinal tract. It refers to the appearance of a barium-filled structure that is truncated or cut off, resembling a beheaded Scottish terrier. This sign is typically seen on barium studies of the upper gastrointestinal tract.

**Why the Correct Answer is Right**
The beheaded Scottish terrier sign is characteristic of a duodenal web, a congenital or acquired condition where there is a membrane or web-like structure in the duodenum. This web can cause partial obstruction of the duodenum, leading to the characteristic appearance on barium studies. The web acts as a barrier, preventing the barium from flowing distally, resulting in the beheaded appearance.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because the beheaded Scottish terrier sign is not typically associated with a gastric outlet obstruction, which would present with a different radiological appearance.

**Option B:** This option is incorrect because the beheaded Scottish terrier sign is not characteristic of a pancreatic pseudocyst, which would present as a rounded or oval mass in the pancreas.

**Option C:** This option is incorrect because the beheaded Scottish terrier sign is not typically associated with a Meckel's diverticulum, which would present as a small outpouching of the ileum.

**Clinical Pearl / High-Yield Fact**
The beheaded Scottish terrier sign is a classic radiological finding that should raise suspicion for a duodenal web. This condition can cause symptoms such as abdominal pain, nausea, and vomiting.

**Correct Answer: D. Duodenal web.**