9 J Radiol Sci March 2013 Vol.38 No.1 Acute appendicitis is one of the most common causes of right lower quadrant abdominal pain in emergency room (ER) and the most common indication for emergency abdominal surgeries [1]. The typical clinical presentation of appendicitis is initial periumbilical abdominal pain, which is progressively localized to a point in the right lower quadrant (RLQ), where the infamed appendix irritates the parietal peritoneum. The pain is usually associated with vomiting, fever, and leukocytosis. Therefore, American College of Radiology (ACR) Appropriateness Criteria demonstrates that acute appendicitis should be suspected in the patient with RLQ pain associated with fever or leukocytosis. However, the clinical diagnosis of appendicitis has both false-positive and false-negative rates of approximately 20%; thus, clinical diagnosis based on history taking and physical examination remains challenging [2]. Imaging diagnostic tests such as ultrasound and computed tomography (CT) have been employed to reduce misdiagnosis. Evaluation of the diagnostic performance of CT for acute appendicitis has revealed a sensitivity of 87-100%, a positive predictive value of 94-97%, a negative predictive value of 93-100%, and an accuracy of 93-98% [3]. The high accuracy of the CT scan has led to increased use of this modality for suspected cases of acute appendicitis. Computed Tomography Diagnostic Values of Acute Appendicitis in Different Patient Subgroups Chih-Chen Chang Y on-Cheong Wong Li-Jen Wang Cheng-hsien Wu huan-Wu Chen Chen-Chih huang Yung-Liang Wan Department of Medical Imaging and Intervention, Chang Gung Memorial Hospital at Linkou, Chang Gung University, Taoyuan, Taiwan AbStRAct To determine the diagnostic values for computed tomography (CT) in acute appendicitis in different subgroups of patients presenting with right lower abdominal pain at emergency room (ER). This was a retrospective study on 226 patients (105 men and 121 women) with mean age of 44.0 ± 16.7 years (age range, 16-88 years) who presented with right lower abdominal pain at ER from January 2008 to December 2009. All were suspected of having acute appendicitis and underwent CT examinations before therapy was instituted. Their medical charts were reviewed for initial CT report, surgical report, pathology report and final diagnosis. Subgroup analyses of CT diagnostic values of acute appendicitis were performed in patients with different gender (men or women) and age (≤ 45 years or > 45 years). Of 226 patients, 114 (50.4%) had a final diagnosis of acute appendicitis. Overall, CT accuracy of acute appen- dicitis was 94.7%. In subgroup analyses, CT accuracy was 94.7% (men ≤ 45 years), 93.8% (men > 45 years), 97.1% (women ≤ 45 years), 92.5% (women > 45 years), respectively. The likelihood ratio (LR) of positive CT for acute appendicitis ranged from 37.7 in women ≤ 45 years to 7.0 in men > 45 years. Overall, CT diagnosis of acute appendicitis at ER is accurate. Women ≤ 45 years benefit most from preoperative CT because positive CT in this subgroup is associated with a large chance in the LR for appendicitis. However, in elderly patients, appendiceal tumors and chronic appendicitis may mimic acute appendicitis on CT scan. Correspondence Author to: Yon-Cheong Wong Department of Medical Imaging and Intervention, Chang Gung Memorial Hospital at Linkou, Chang Gung University, Taoyuan, Taiwan No. 5, Fu-Hsing Street, Guei-Shan, Taoyuan 333, Taiwan J Radiol Sci 2013; 38: 9-14