AJR:168, February 1997 405 Unenhanced Helical CT for Suspected Acute Appendicitis Michael J. Lane1 Douglas S. Katz Barbara A. Ross Traci L. Clautice-Engle Robert E. Mindelzun R. Brooke Jeffrey, Jr. OBJECTIVE. The purpose of this study was to determine the diagnostic accuracy of unenhanced helical CT scans in patients with a suspected acute appendicitis. SUBJECTS AND METHODS. Over a 20-month period. 10#{176}) adult patients with sus- pected acute appendicitis were referred by the emergency department for an unenhanced heli- cal CT scan. Each scan was obtained in a single breath-hold from the I I2 vertebral body to the pubic symphysis using a 5-mm collimation and a pitch of I .6. No) patients were given oral or IV contrast media. The primary CT criteria for diagnosing acute appendicitis was the iden- tification of an appendix with a transverse diameter larger than 6 mm with associated periap- pendiceal inflammatory changes. The presence of an appendicolith was considered a secondary finding as was isolated periappendiceal inflammation: however. appendicitis was not diagnosed in such patients unless an enlarged appendix was definitely identified. Final diagnoses were established by surgical or clinical follow-up and were compared with the original CT reports. RESULTS. We found 66 true-negatives. 37 true-positives. four false-negatives. and two false-positives that yielded a sensitivity of 90%. a specificity of 97%. a positive predictive value of95%, a negative predictive value of95%. and an accuracy of94%. An alternative diag- nosis was established by an unenhanced helical CT scan in 24 patients (22% h which included cecal diverticulitis (seven patients). urinary tract disease (five patients). adnexal pathology (fbur patients). sigmoid diverticulitis (two patients). small bowel disease (three patients). right lower quadrant tumor (two patients). and an infected dialysis catheter (one patient). CONCLUSION. Unenhanced thin-section helical CT is an accurate, effective technique for diagnosing acute appendicitis. Received May 15, 1996; accepted after revision July 16, 1996. ‘All authors: Department of Radiology, Stanford University School of Medicine, Rm. H-i307, 300 Pasteur Dr., Stanford, CA 94305-5105. Address correspondence to A. B. Jeffrey, Jr. AJR i997;i68:405-409 0361-803X/97/i 682-405 © American Roentgen Ray Society I n 1991. Balthazar et al. I I I used CT to prospectively evaluate 100 patients suspected of having acute appendicitis: they used both oral and IV contrast medium. CT had a sensitivity of 98C/c, a specificity of 88%. and an accuracy of 93%. In 1993. Malone et al. [2] prospec- tively studied 21 1 patients with suspected acute appendicitis using unenhanced CT. Malone et al. found the technique to be 87% sensitive, 97% specific. and 93% accurate in diagnosing appendicitis. To our knowledge, the study by Malone et al. [2] has not been reproduced. We attemp- ted to confirm the results of Malone et al. by prospectively obtaining an unenhanced heli- cal CT scan on 109 adult patients with sus- pected acute appendicitis who were referred to us by the emergency department. The potential advantages of performing unen- hanced CT compared with enhanced CT include the ability to immediately scan a patient without any preparation such as oral contrast material, the elimination of the risk ofan adverse reaction to IV contrast material. and the monetary savings when contrast material is not used. Also, helical CT scans performed in a single breath-hold eliminate the potential risk of not visualizing the appen- dix because of image misregistration. Downloaded from www.ajronline.org by 54.163.42.124 on 05/26/20 from IP address 54.163.42.124. Copyright ARRS. For personal use only; all rights reserved