Computed Tomography Diagnostic Values of Acute Appendicitis in Different Patient Subgroups

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 appendicitis 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 Acute appendicitis in different patient subgroups 10 J Radiol Sci March 2013 Vol.38 No.1 In recent years, the negative appendectomy rate (NAR), defined as the proportion of pathologically normal appendices removed surgically in patients suspected of having acute appendicitis, has been used to evaluate the quality of diagnosis of acute appendicitis. Historically, an acceptable NAR has been set between 15% and 25% [4]. Several previous investigations have demonstrated a decrease in the NAR with use of preoperative CT [4]. McGory and colleague’s study demonstrated that the increased use of CT only reduced NAR in women [5]. However, some studies demonstrated that the use of CT significantly reduces the NAR in women ≤45 years of age but only subtle decline for men and women >45 years which may be owing to initially low NAR [6, 10]. Due to these inconsistent NAR reductions in the literature and the existence of only a few studies that have tried to analyze the discrepancies, we undertook this project to address the issues of the effects of age and gender on CT diagnostic values. MAteRiAlS And MethodS Subjects This retrospective study was approved by our institutional review board. Informed consent was waived. We included patients > 16 years of age with RLQ pain, fever and/or leukocytosis who had undergone abdominal CT examination at ER under a clinical suspicion of acute appendicitis. The CT data between January 1, 2008, and December 31, 2009, were retrieved from our radiological information system. Patients with an appendectomy history were excluded. A total of 226 patients were identified within this 2-year period. In total, 105 men and 121 women with a mean age of 44.0 ± 16.7 years (age range, 16-88 years) were included. Among them, 57 men (57/105, 54.3%) and 68 women (68/121, 56.1%) were ≤ 45 years. Their medical charts were reviewed for surgical records, pathology reports, and discharge diagnosis. ct data All intravenous contrast-enhanced CT examinations were obtained at the portal venous phase after administration of 100 mL of iodinated contrast material with 4-detector MDCT scanner (LightSpeed QX/i Scanner, General Electric Medical Systems, Milwaukee, WI, USA). No oral or rectal contrast was given for opacification of the bowels. All images were reconstructed with a 5-mm slice thickness and a 5-mm interval and were then sent to a Picture Archiving Communication System for viewing. Coronal and sagittal reconstructions were available if the radiologists had made a request at the time of reporting. All official CT reports were reviewed for the CT diagnosis of RLQ pain. In our department, positive diagnosis of acute appendicitis of CT is defined as a distended appendix (> 6 mm wall-to-wall diameter), appendicolith, fluid-filled lumen, enhancing appendiceal walls, and/or inflammatory changes around the appendix (Fig. 1, 2) [7]. If acute appendicitis was excluded, we recorded the alternative diagnosis provided by the CT report. Pathology records All pathology records were reviewed to determine whether the removed appendices were acutely inflamed. All acutely inflamed appendices were categorized as positive for acute appendicitis, whereas all other findings were categorized as negative. Figure 1. Axial contrast-enhanced CT scan demonstrates dilatation of appendix, enhancing appendiceal walls, and periappendiceal fat stranding (black arrow). Tip of appendix is also shown (white arrow). Figure 1 Acute appendicitis in different patient subgroups 11 J Radiol Sci March 2013 Vol.38 No.1 Final diagnosis of acute appendicitis The final diagnosis of acute appendicitis or alternative diagnosis (not acute appendicitis) was concluded based on pathological diagnosis in patients who had undergone surgery. For patients who had not undergone surgery, the discharge diagnosis based on clinical course and outcome served as the final diagnosis. Analyses and statistics The CT diagnosis was compared with the final diagnosis of acute appendicitis for sensitivity, specificity, accuracy, positive predictive value (PPV), negative predictive value (NPV), and the likelihood ratio (LR) of a positive CT test. The overall CT performance in all patients as well as the CT performances in the subgroups stratified by gender (men and women) and age (≤ 45 years and > 45 years) were computed. ReSultS Of the 226 patients, 122 (53.9%) had a CT diagnosis of acute appendicitis, and 14 patients (6.1%) had a normal CT scan. Ninety patients (39.8%) had an alternative CT diagnosis. Gastrointestinal system disorders were the most common and were attributed to 48 patients, followed by gynecological and urological disorders. The alternative CT diagnoses are summarized in Table 1. A total of 135 (59.7%) of 226 patients underwent surgery. Of these, 108 were diagnosed with acute appendicitis based on surgery and pathology, 16 had a gastrointestinal disorder, eight had a gynecological disorder, and three had another condition. The alternative surgical diagnoses are summarized in Table 2. Of the 226 patients, 114 (50.4%) had a final diagnosis of acute appendicitis. Among these, 108 final diagnoses were made based on the surgical pathology report, and six were based on the discharge diagnosis. Of these six patients, three underwent CT-guided drainage of a periappendiceal abscess. These periappendiceal abscesses were resulted from ruptured appendicitis because they contained a segment of a perforated appendix [8]. The other three Figure 2. Reconstructed oblique coronal image of contrastenhanced CT scan demonstrates dilated appendix (black arrow) owing to appendicolith impaction at the base of appendix (white arrowhead). Figure 2 table 1. the classification and types of ct alternative diagnoses in 90 patients ct alternative diagnoses 90 Gastrointestinal system 48 Diverticulitis/diverticulosis 29 Colitis/ enteritis 9 Colon/ appendix tumor 5 Small bowel ileus 3