**Question:** A 27-year-old woman is admitted to the emergency department with markedly elevated temperature and abdominal pain. Physical examination initially indicates paraumbilical pain, but the site of origin of pain soon shifts to the right lower quadrant. A CT scan is shown. Which of the following structures is affected?

A. Omentum
B. Liver
C. Appendix
D. Cecum

**Core Concept:** Abdominal pain in relation to the sites of origin and the response to physical examination is crucial in narrowing down potential causes.

**Why the Correct Answer is Right:** In this scenario, the patient presents with fever and abdominal pain initially in the paraumbilical region but later shifts to the right lower quadrant. This indicates that the pain is originating from a structure situated in the right lower quadrant of the abdomen.

**Why Each Wrong Option is Incorrect:**

A. Omentum pain typically causes diffuse abdominal pain and is less likely to localize to a specific quadrant.
B. Liver pain is usually described as dull, central, and non-localizing, not shifting with physical examination.
C. Appendix pain is often localized and may shift with physical examination, but the right lower quadrant is a more common location for appendicitis.
D. Cecum pain would also be less likely to shift to the right lower quadrant, and the pain would be diffuse rather than localized.

**Clinical Pearl:** A shifting pain with marked fever is highly suggestive of appendicitis, which is why option C is correct. A CT scan is often performed to confirm the diagnosis and guide treatment decisions.

**Correct Answer:** C. Appendix

**Explanation:** In this scenario, the patient presents with fever and abdominal pain initially in the paraumbilical region but later shifts to the right lower quadrant. This indicates that the pain is originating from a structure situated in the right lower quadrant of the abdomen. Appendicitis is a common cause of acute abdomen and is characterized by fever, abdominal pain, and shifting tenderness in the right lower quadrant. The appendix is a small, finger-like projection of the large intestine that runs from the caecum to the rectum. Appendicitis is a common surgical emergency and requires urgent intervention due to the risk of rupture and sepsis.