This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Small & Large Intestine, Subject name: Surgery
A 23-year-old lady presents with acute right sided lower abdominal pain since 4 hours. There is tenderness at McBurney's point. Which investigation is best suited to confirm the diagnosis of appendicitis 
Select and explain. 
A. CT scan, B. Plain X-ray, C. Serum ESR, D. MRI abdomen
A: CT scan
Answer: A: CT scan 
Explanation: Ans. (a) CT scanRef: Sabiston 20th edition, Page 1299Various investigations done for acute appendicitis:* X-ray abdomen erect -- Fecalith can be seen in 5% cases only* USG abdomen -- noncompressible appendix +sensitivity +78-83%, Specificity = 83-93%.* CECT abdomen with only IV contrast -- sensitivity and specificity is high (90-100%) -- Thickened appendix 7mm diameter+, most accurate imaging used.* MRI abdomen -- is 100% sensitive and, 98% sensitive. Used only in pregnant females. Operator dependent.