**Core Concept:** Meckel diverticulum is a vestigial pouch in the wall of the small intestine, usually located at the mesenteric border of the distal ileum. Inflammation of Meckel diverticulum can lead to complications like diverticulitis, which may present with symptoms resembling appendicitis.

**Why the Correct Answer is Right:** Inflammation of Meckel diverticulum (also known as Meckel's diverticulitis) can cause symptoms that mimic appendicitis due to the anatomical similarity between the two conditions. Both involve inflammation in the abdominal wall, and the differential diagnosis becomes crucial in such cases to avoid unnecessary surgery like appendectomy.

**Why Each Wrong Option is Incorrect:**

A. **Option A (Inflammation of Ileum)**: This option is incorrect because appendicitis typically affects the appendix, not the ileum. Inflammation of Meckel diverticulum is a more plausible diagnosis when symptoms resemble appendicitis, as both involve the abdominal wall.

B. **Option B (Diverticulitis)**: This option is also incorrect because diverticulitis typically affects the colon (diverticulosis and diverticulitis) and not the Meckel diverticulum. Inflammation of Meckel diverticulum is a more plausible diagnosis when symptoms resemble appendicitis.

C. **Option C (Inflammatory bowel disease)**: This option is incorrect because inflammatory bowel disease (e.g., Crohn's disease) usually involves the entire gastrointestinal tract, rather than a localized area like Meckel diverticulum. Inflammation of Meckel diverticulum is a more plausible diagnosis when symptoms resemble appendicitis.

D. **Option D (Acute appendicitis)**: This option is incorrect because appendicitis primarily affects the appendix, not the Meckel diverticulum. Inflammation of Meckel diverticulum is a more plausible diagnosis when symptoms resemble appendicitis.

**Clinical Pearl:** In cases of suspected appendicitis, a thorough clinical examination and history along with imaging studies like ultrasound or CT scan are crucial to differentiate between appendicitis and other potential causes like Meckel diverticulitis, inflammatory bowel disease, or other differential diagnoses. This helps guide appropriate management and prevent unnecessary surgeries like appendectomy.

**Correct Answer:** Inflammation of Meckel diverticulum (Meckel diverticulitis)

In summary, when faced with a patient presenting with right lower quadrant pain, fever, and signs of peritonitis, the correct answer lies in the differential diagnosis of appendicitis and Meckel diverticulitis (inflammation of Meckel diverticulum). A thorough clinical examination, history, and imaging studies are essential to make an accurate diagnosis and guide appropriate management.