**Question:** When gas filled cysts are found in subserosa or submucosa of small intestine or colon, it is called

A. Diverticulitis
B. Diverticulum
C. Giant Meckel's Diverticulum
D. Inflammatory Bowel Disease

**Correct Answer:** **C. Giant Meckel's Diverticulum**

**Core Concept:** A Meckel's diverticulum is a remnant of the embryonic vitelline duct, which is a normal variant in the human gastrointestinal tract. It is a blind-ending pouch, typically located in the mesentery of the small intestine, most commonly in the ileum. Meckel's diverticulum is usually asymptomatic but can lead to complications such as hemorrhage, obstruction, or infection.

**Why the Correct Answer is Right:** When a Meckel's diverticulum becomes infected, it can result in a condition known as Meckel's diverticulitis. In this case, the cysts filled with gas are found in the subserosa or submucosa of the small intestine or colon, leading to the diagnosis of a gas-filled cyst in the mentioned locations.

**Why Each Wrong Option is Incorrect:**

A. **Diverticulitis (Option A)**: Diverticulitis refers to inflammation of the diverticula, which are pouches in the colon, not the small intestine or associated with gas-filled cysts found in the subserosa or submucosa.

B. **Diverticulum (Option B)**: A diverticulum is a simple pouch-like outgrowth from the intestinal wall, typically in the large intestine, not associated with gas-filled cysts in the mentioned locations.

C. **Giant Meckel's Diverticulum (Option C)**: Meckel's diverticulum is a type of diverticulum, but the correct answer should be Meckel's diverticulitis as it represents an infection in Meckel's diverticulum, causing gas-filled cysts in the subserosa or submucosa.

D. **Inflammatory Bowel Disease (Option D)**: This option refers to conditions like Crohn's disease or ulcerative colitis, which are unrelated to Meckel's diverticulum or gas-filled cysts in the specified locations.

**Clinical Pearls:**

1. Meckel's diverticulitis is a rare entity but crucial to recognize due to its potential complications.
2. Intestinal infections can lead to gas production, which when present in the subserosal or submucosal layers can lead to diagnostic dilemmas.
3. The location of the gas-filled cysts is critical to differentiate it from other conditions like diverticulitis or inflammatory bowel disease.