**Core Concept**
The "tail sign" refers to a radiographic feature observed on computed tomography (CT) scans, particularly in the context of abdominal imaging. It is characterized by a tapering or constricted segment of the small intestine, often associated with intussusception or other pathologies that lead to bowel obstruction.

**Why the Correct Answer is Right**
The tail sign is a specific radiologic finding that helps in diagnosing intussusception, a condition where a part of the intestine telescopes into another, causing bowel obstruction. This sign is typically seen on CT scans as a constricted segment of the intestine with a "tail" of bowel extending beyond the point of constriction. The presence of the tail sign, along with other clinical findings, aids in distinguishing intussusception from other causes of bowel obstruction.

**Why Each Wrong Option is Incorrect**
**Option A:** Intussusception is a condition where a part of the intestine telescopes into another, causing bowel obstruction. The tail sign is indeed associated with intussusception, making this option incorrect.
**Option B:** A Meckel's diverticulum is a congenital anomaly of the small intestine that can cause abdominal pain and bleeding. While it can cause intestinal obstruction, the tail sign is not specifically associated with this condition.
**Option C:** A volvulus is a twisting of the intestine, which can cause bowel obstruction. However, the tail sign is more specific to intussusception and not typically associated with volvulus.
**Option D:** A hernia can cause bowel obstruction, but the tail sign is not specifically associated with this condition.

**Clinical Pearl / High-Yield Fact**
The tail sign is a key radiographic feature of intussusception, and its presence should prompt further investigation, including CT scans and possibly surgical consultation. A classic mnemonic to remember the radiographic signs of intussusception is "Target, Crescent, and Tail" – the target sign refers to a target-like appearance on CT scans, the crescent sign refers to a crescent-shaped area of bowel wall thickening, and the tail sign refers to the constricted segment of the intestine.

**Correct Answer: D. A hernia can cause bowel obstruction, but the tail sign is not specifically associated with this condition.**