The diagnosis of acute appendicitis is not always clear clinically since the specificities of the classic clinical symptoms (periumbilical pain migrat

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1 Note: This copy is for your personal, non-commercial use only. To order presentation-ready copies for distribution to your colleagues or clients, contact us at ORIGINAL RESEARCH n GASTROINTESTINAL IMAGING Courtney A. Coursey, MD Rendon C. Nelson, MD Mayur B. Patel, MD Courtney Cochran, BSRT, RDMS Leslie G. Dodd, MD David M. DeLong, PhD Craig A. Beam, PhD Steven Vaslef, MD, PhD Making the Diagnosis of Acute Appendicitis: Do More Preoperative CT Scans Mean Fewer Negative Appendectomies? A 10-year Study 1 Purpose: Materials and Methods: To determine the frequency of preoperative computed tomography (CT) in the evaluation of patients suspected of having appendicitis at one institution during the past 10 years and to determine whether changes in CT utilization were associated with changes in the negative appendectomy rate. Institutional review board approval was obtained, and a waiver of informed consent was granted for this HIPAAcompliant study. A surgical database search yielded medical record numbers of 925 patients (526 [ 56.9%] men and 399 [43.1%] women; mean age, 38 years (range, years]) who underwent urgent appendectomy between January 1998 and September Patients who were younger than 18 years of age at the time of surgery were excluded. CT, pathology, and surgery reports were reviewed. By using logistic regression, changes in the proportion of patients undergoing CT and in the proportion of patients undergoing each year appendectomy in which the appendix was healthy were evaluated. Subgroup analyses based on patient age ( 45 years or. 45 years) and sex also were performed. 1 From the Departments of Radiology (C.A.C., R.C.N., C.C., D.M.D., C.A.B.), Surgery (M.B.P., S.V.), and Pathology (L.G.D.), Duke University Medical Center, Box 3808, Erwin Road, Durham, NC Received December 24, 2008; revision requested February 5, 2009; revision received April 15; accepted June 3; fi nal version accepted August 20. R.C.N. is a medical consultant to GE Healthcare. Address correspondence to C.A.C. ( cours002@ mc.duke.edu ). Results: Conclusion: Prior to urgent appendectomy, 18.5% of patients underwent preoperative CT in 1998 compared with 93.2% of patients in The negative appendectomy rate for women 45 years of age and younger decreased from 42.9% in 1998% to 7.1% in However, the timing of the decline in negative appendectomy rates for women 45 years and younger could not be proved to be associated with the increase in CT use. There was no significant trend toward a lower negative appendectomy rate for men regardless of age or for women older than 45 years of age with increased use of preoperative CT. The shift from single-detector CT to multidetector CT and the use of decreasing section thickness also correlated with a reduction in false-positive diagnoses. Rising utilization of preoperative CT and advances in technology coincided with a decrease in the negative appendectomy rate for women 45 years and younger but not in men of any age or women older than 45 years. q RSNA, 2010 q RSNA, radiology.rsna.org n Radiology: Volume 254: Number 2 February 2010

2 The diagnosis of acute appendicitis is not always clear clinically since the specificities of the classic clinical symptoms (periumbilical pain migrating to the right lower quadrant, nausea, and anorexia) range from 37% to 53% ( 1 ). The consequences of missing appendicitis are severe, with increases in patient morbidity and mortality if the appendix perforates ( 2,3 ). Therefore, historically, negative appendectomy rates of 20% 25% and as high as 40% in women have been considered acceptable ( 4,5 ). Negative appendectomy rates are generally higher in women due to gynecologic disease, which can confound the diagnosis of appendicitis ( 5 ). Several previous investigations have demonstrated a decrease in the negative appendectomy rate from 12% 29% to 3% 11% with use of preoperative computed tomography (CT) ( 6 17 ). However, other studies, including a large populationbased study, found no significant change in the negative appendectomy rate with increased availability and use of preoperative CT ( ). Given the contradictory reports in the medical literature regarding whether increased preoperative CT use has resulted in a lower negative appendectomy rate, we undertook this project. The purpose of this study was to determine the frequency of preoperative CT in the evaluation of patients suspected of Advances in Knowledge n During the past decade at our institution, preoperative CT use increased from 18.5% to 93.2% in the evaluation of patients suspected of having acute appendicitis. n As preoperative CT use increased, the negative appendectomy rate in women 45 years of age and younger decreased from 42.9% to 7.1%. n As preoperative CT use increased, the negative appendectomy rate in male patients and in women older than 45 years of age did not change significantly. having appendicitis at our institution during the past 10 years and to determine whether changes in CT utilization were associated with changes in the negative appendectomy rate. Materials and Methods Institutional review board approval was obtained, and a waiver of informed consent was granted for this health insurance portability and accountability act-compliant study. A surgical database search by using the procedure code for appendectomy yielded patients who underwent an appendectomy from January 1, 1998, through September 30, 2007, and who were at least 18 years of age at the time of surgery. This study was performed at an urban university hospital. On the basis of review of surgical reports, patients who underwent incidental ( n = 387), interval ( n = 40), or elective ( n = 14) appendectomy were excluded, yielding a total of 925 patients (526 [56.9%] men and 399 [43.1%] women; mean age, 38 years (range, years) who underwent urgent appendectomy. Incidental appendectomy was defined as having occurred during the performance of another procedure (eg, gynecologic surgery), interval appendectomy was defined as having occurred following drainage of a periappendiceal fluid collection, and elective appendectomy was defined as having occurred in the nonurgent setting for primary appendiceal disease. The medical records of the 925 urgent appendectomy patients were reviewed to determine which patients underwent CT, appendiceal ultrasonography (US), magnetic resonance (MR) imaging, or abdominal radiography prior to appendectomy. CT examinations that took place within a 48-hour window prior to appendectomy ( n = 616) were included Implication for Patient Care n Use of preoperative CT in the evaluation of women 45 years of age and younger suspected of having acute appendicitis is associated with a lower negative appendectomy rate. in this study. CT reports were reviewed, and the radiologist s impression as to the presence or absence of appendicitis was recorded. CT images from the 515 studies available in our picture archiving and communication system or film hard-copy archive were reviewed to determine the type of CT scanner used, section thickness, section interval, type of contrast material used, and whether or not coronal reformations from isotropic voxels were obtained. Images from 101 CT studies had been purged from our film hard-copy archive due to at least 6 years of account inactivity and were no longer available for review. The presence or absence of appendicitis was determined on the basis of pathology reports for the 616 patients who underwent CT prior to appendectomy, as well as for the 309 patients who did not undergo preoperative CT. For patients who underwent a negative appendectomy, alternative diagnoses based on pathology reports, radiology reports, surgical findings, or clinical follow-up were recorded. Surgical reports were reviewed to determine if appendectomies were performed with open or laparoscopic techniques for those patients who did and did not undergo preoperative CT. Annual changes in the proportion of patients who underwent CT and in the proportion of patients undergoing negative appendectomy were evaluated by using logistic regression. Subgroup analyses based on patient age ( 45 years or. 45 years) and sex also were performed. The association of CT use Published online /radiol Radiology 2010; 254: Author contributions: Guarantor of integrity of entire study, C.A.C.; study concepts/ study design or data acquisition or data analysis/interpretation, all authors; manuscript drafting or manuscript revision for important intellectual content, all authors; approval of fi nal version of submitted manuscript, all authors; literature research, C.A.C., C.C.; clinical studies, C.A.C., R.C.N., L.G.D.; statistical analysis, D.M.D., C.A.B.; and manuscript editing, C.A.C., R.C.N., M.B.P., L.G.D., C.A.B., S.V. Authors stated no fi nancial relationship to disclose. Radiology: Volume 254: Number 2 February 2010 n radiology.rsna.org 461

3 rate and negative appendectomy rate was evaluated with the Mantel-Haenszel test controlling for year. Rates of negative appendectomy with those of laparoscopic and open surgery were compared by using Poisson regression. Whether age, sex, and year were related to the probability of a patient undergoing laparoscopic or open surgery was evaluated by using logistic regression. Differences in proportions of false-positive and false-negative CT reports were evaluated by using Fisher exact test and the x 2 test on the basis of the type of scanner used, section thickness, section interval, type of contrast material, and whether coronal reformations were obtained. A P value of less than.05 was considered to indicate a statistically significant difference. Results The percentage of patients undergoing CT prior to appendectomy increased from 18.5% (10 of 54) in 1998 to 94.2% (97 of 103) in 2007 ( P,.00001) ( Fig 1 ). During this same period, use of appendiceal US and abdominal radi- Figure 1 Figure 1: Preoperative imaging in patients suspected of having acute appendicitis. Preoperative CT ( ) use increased from 18.5% in 1998 to 94.2% in the fi rst 9 months of Preoperative appendiceal US ( ) and abdominal radiography ( ) decreased from 29.6% and 79.6% in 1998 to 1.0% and 10.7% in 2007, respectively. ography in the preoperative assessment of patients suspected of having acute appendicitis declined from 29.6% (16 of 54) to 1.0% (one of 103) and from 79.6% (43 of 54) to 10.7% (11 of 103), respectively ( Fig 1 ). Three patients underwent MR imaging prior to appendectomy. Two of these MR examinations were performed in pregnant patients (8 and 13 weeks estimated gestational age) after inconclusive appendiceal US findings, and one patient underwent preoperative MR to better characterize the appendix and neighboring right adnexal cysts following an inconclusive pelvic US and abdominopelvic CT findings. During this same time period, the negative appendectomy rate at our institution declined from 16.7% (nine of 54) in 1998 to 8.7% (nine of 104) in 2007 ( Fig 2 ) ( P,.0001). The reduction in the negative appendectomy rate was statistically significant for female patients 45 years of age and younger ( Table 1, Fig 2 ). From 1998 to 2007, the negative appendectomy rate declined from 42.9% (six of 14), when 14.3% (two of 14) of these patients underwent CT prior to appendectomy, to 7.1% (two of 28), when 92.9% (26 of 28) of these patients underwent CT before appendectomy ( Fig 2 ) ( P =.0001). There was no statistically significant trend toward a lower negative appendectomy rate for men regardless of age or for women older than 45 years of age ( Table 1, Fig 2 ). The association of the CT use rate and the negative appendectomy rate was evaluated with the Mantel-Haenszel test controlling for year. On a subgroup basis, only the subgroup of women 45 years of age and younger showed a statistically significant relationship ( P =.047); however, a Bonferroni adjustment for multiple subgroup testing yielded a nonsignificant result ( P =.2). The number of patients undergoing imaging with single, four-, eight-, 16-, or 64-detector CT is reported in Table 2. Section thickness, section interval, type of contrast material used, and whether coronal reformations from isotropic voxels were obtained are reported in Table 3. The proportion of false-positive and false-negative CT reports was greater for single-detector compared with multidetector CT ( P =.004). The differences in the proportion of false-positive and false-negative CT reports were not significantly different between four-, eight-, 16-, and 64-detector CT ( P =.7062 for four- vs eight-detector CT; P =.3022 for 16- vs 64-detector CT). The proportion of false-positive and false-negative CT reports was greater for 7-mm than 5-mm section thickness ( P =.002). Section thicknesses of 1.25, 3, and 10 mm were excluded from this analysis given the small number of patients who underwent imaging with these parameters ( n = 4). The proportion of false-positive and false-negative CT reports was greater for a section interval of 10 mm than that of 7 or 5 mm ( P =.001). There was no difference between a section interval of 7 or 5 mm ( P =.63). Section intervals of 3 and 1.25 mm were excluded from this analysis given the small number of studies with this parameter ( n = 2). The proportion of false-positive and falsenegative CT reports was not different ( P =.34) when patients were stratified on the basis of the type of contrast material used. The one patient who underwent imaging with intravenous contrast material only was excluded from this analysis. The proportion of false-positive and false-negative CT reports did not differ on the basis of whether coronal reformations from isotropic voxels were obtained ( P =.41). In Table 4, the number of patients who underwent laparoscopic or open appendectomy is reported for each year, stratified by age and sex. Age, sex, and year were all significantly related to the probability of a patient undergoing laparoscopic versus open surgery. Younger patients ( 45 years of age) were more likely than older patients to undergo a laparoscopic appendectomy ( P =.0003). Women were more likely than men to undergo a laparoscopic appendectomy ( P =.007). Patients were more likely to undergo a laparoscopic appendectomy during later years of the study compared with the earlier years ( P,.0001). Negative appendectomy rates are declining for laparoscopic procedures ( P,.0001) while they are slightly increasing for open surgery ( P =.0030). 462 radiology.rsna.org n Radiology: Volume 254: Number 2 February 2010

4 Table 1 Percentage of Patients Undergoing Negative Appendectomy Each Year from 1998 to 2007 Subdivided According to Age, Sex, and Whether the Patient Underwent Preoperative CT Parameter Men, 45 years 7.4 (2/27) 13.5 (5/37) 3.9 (1/26) 9.0 (5/55) 17.0 (9/53) 14.3 (6/42) 9.7 (3/31) 1.9 (1/53) 4.7 (2/43) 12.1 (4/33) Preoperative CT 25.0 (1/4) 28.6 (2/7) 7.1 (1/14) 8.0 (2/25) 16.7 (4/24) 8.7 (2/23) 13.6 (3/22) 2.3 (1/43) 5.4 (2/37) 10.7 (3/28) No preoperative CT 4.3 (1/23) 10.0 (3/30) 0 (0/12) 10.0 (3/30) 17.2 (5/29) 21.1 (4/19) 0 (0/9) 0 (0/10) 0 (0/6) 20.0 (1/5) Men. 45 years 11.1 (1/9) 0 (0/10) 28.6 (3/7) 18.1 (2/11) 6.7 (1/15) 7.1 (1/14) 12.5 (1/8) 0 (0/11) 0 (0/21) 5.0 (1/20) Preoperative CT (1/2) 0 (0/7) 50.0 (2/4) 28.6 (2/7) 0 (0/10) 0 (0/9) 14.3 (1/7) 0 (0/10) 0 (0/19) 5.0 (1/20) No preoperative CT 0 (0/7) 0 (0/3) 33.3 (1/3) 0 (0/4) 20.0 (1/5) 20.0 (1/5) 0 (0/1) 0 (0/1) (0/2) 0 (0/0) Women 45 years 42.9 (6/14) 58.3 (14/24) 37.5 (12/32) 23.5 (4/17) 20.7 (6/29) 32.1 (9/28) 23.1 (6/26) 11.4 (4/35) 14.0 (6/43) 7.1 (2/28) Preoperative CT 50.0 (1/2) 42.9 (3/7) 30.0 (3/10) 16.7 (1/6) 0 (0/15) 25.0 (5/20) 30.0 (6/20) 9.4 (3/32) 14. (6/42) 7.7 (2/26) No preoperative CT 41.7 (5/12) 64.7 (11/17) 40.9 (9/22) 27.3 (3/11) 42.9 (6/14) 50.0 (4/8) 0 (0/6) 33.3 (1/3) 0 (0/1) 0 (0/2) Women. 45 years 0 (0/4) 16.7 (1/6) 0 (0/4) 0 (0/3) 0 (0/9) 0 (0/16) 0 (0/21) 6.7 (1/15) 9.5 (2/21) 8.7 (2/23) Preoperative CT 0 (0/2) 20.0 (1/5) 0 (0/3) 0 (0/3) 0 (0/8) 0 (0/13) 0 (0/21) 6.7 (1/15) 9.5 (2/21) 8.7 (2/23) No preoperative CT 0 (0/2) 0 (0/1) 0 (0/1) 0 (0/0) 0 (0/1) 0 (0/3) 0 (0/0) 0 (0/0) 0 (0/0) 0 (0/0) Note. Data in parentheses are the numbers used to calculate the percentages. Figure 2 Figure 2: Graphs show the relationship between the rate of preoperative (preop) CT and that of negative (neg) appendectomy (appy) overall and based on patient sex and age: (a) women 45 years of age and younger, (b) women older than 45 years, (c) men 45 years of age and younger, (d) men older than 45 years, (e) overall. Decrease in negative appendectomy rate with increased use of preoperative CT is most pronounced for women 45 years of age and younger. Radiology: Volume 254: Number 2 February 2010 n radiology.rsna.org 463

5 Table 2 Number and Type of CT Reports Per Year and Number of Patients Undergoing Single- or Multidetector CT Per Year Parameter No. of CT reports True-positive 5 (50) 17 (65) 23 (74) 35 (85) 52 (91) 57 (88) 60 (86) 95 (95) 107 (90) 87 (90) True-negative 2 (20) 5 (19) 2 (6) 2 (5) 2 (4) 4 (6) 4 (6) 2 (2) 3 (3) 6 (6) False-positive 1 (10) 1 (4) 1 (3) 3 (7) 1 (2) 3 (5) 6 (9) 3 (3) 7 (6) 2 (2) False-negative 2 (20) 3 (12) 2 (6) 1 (2) 1 (2) 1 (2) (2) 1 (1) Indeterminate (10) 0 1 (2) (1) No. of detectors * One Four Eight Sixteen Sixty-four No. of purged CT reports Note. Data in parentheses are percentages. * Data are the number of patients. Table 3 Number and Type of CT Reports according to the Number of Detectors, Section Interval, Section Thickness, Contrast Material Administered, and Whether Coronal Reformations from Isotropic Voxels Were Obtained Parameter Total No. of CT Reports True-Positive True-Negative False-Positive False-Negative No. of detectors One (79) 1 (3) 4 (12) 2 (6) Four (92) 3 (6) 1 (2) 0 Eight (86) 3 (10) 1 (3) 0 Sixteen (91) 10 (3) 15 (5) 2 (1) Sixty-four (87) 6 (6) 5 (5) 2 (2) Section thickness (mm) (50) 0 1 (50) (50) 2 (20) 1 (10) 2 (20) (90) 20 (4) 24 (5) 4 (1) (100) (100) 0 0 Section interval (mm) (50) 2 (17) 2 (17) 2 (17) (93) 2 (3) 3 (4) (90) 18 (4) 21 (5) 4 (1) (100) (100) 0 0 Contrast material Intravenous and oral (90) 19 (4) 24 (5) 5 (1) Intravenous only (100) 0 0 Oral only (82) 2 (7) 2 (7) 1 (4) None (94) 1 (6) 0 0 Coronal reformations Yes (90) 16 (4) 19 (5) 3 (1) No (87) 7 (5) 7 (5) 3 (3) Note. Data in parentheses are percentages. A total of 515 CT reports were available for review; however, 101 had been purged from our hard-copy fi lm library and could not be reviewed. From 1998 to 2007, false-negative CT reports fluctuated between 0% (0 of 100) and 20.0% (two of 10), while falsepositive CT reports fluctuated between 1.7% (one of 57) and 10.0% (one of 10) ( Table 2 ). One of these false-positive CT scans is presented in Figure 3. The appendix was not visualized at CT in 3.7% (23 of 616) of patients who underwent CT. Of these patients, 30.4% (seven of 23) were found to have acute appendicitis at pathologic examination. The studies in these seven patients were performed in 1998 ( n = 2), 2000 ( n = 2), 2001 ( n = 1), 2002 ( n = 1), and 2006 ( n = 1). Images from studies in three of these patients were available for rereview, and those of the remaining four patients had been purged from our film library. (It is the policy of our film library to purge adult patient hard-copy film jackets after 6 years of inactivity.) Section thicknesses in these three studies were 5, 7, and 10 mm. Section intervals were 10 ( n = 2) and 5 mm. Intravenous and oral contrast material was used in one study, and no contrast material was used in two studies. In none of the seven studies were coronal reformations from isotropic voxels obtained. (Six of the studies were performed before we began obtaining coronal reformations at our institution, and one study was performed as a renal stone protocol without coronal reformations.) Four of these 464 radiology.rsna.org n Radiology: Volume 254: Number 2 February 2010

6 Table 4 Number and Type of Appendectomies according to Patient Age and Sex, Parameter * Total no. of appendectomies No. of negative appendectomies Laparoscopic appendectomies No. of appendectomies No. of negative appendectomies Open appendectomies No. of appendectomies No. of negative appendectomies Women 45 years No. of laparoscopic appendectomies No. of negative laparoscopic appendectomies No. of open appendectomies No. of negative open appendectomies Women. 45 years No. of laparoscopic appendectomies No. of negative laparoscopic appendectomies No. of open appendectomies No. of negative open appendectomies Men 45 years No. of laparoscopic appendectomies No. of negative laparoscopic appendectomies No. of open appendectomies No. of negative open appendectomies Men. 45 years No. of laparoscopic appendectomies No. of negative laparoscopic appendectomies No. of open appendectomies No. of negative open appendectomies * First 9 months of Figure 3: (a c) False-positive CT scans obtained with intravenous and oral contrast material in a 20-year-old woman with a 1-day history of abdominal pain that migrated to the right lower quadrant. Contiguous axial images going from (a) caudal to (c) cranial view. The appendix (arrow) measures up to 10 mm in diameter, and periappendiceal fat stranding is present. The appendix appeared somewhat infl amed and enlarged at surgery, but no infl ammation was noted at pathologic examination. An alternate cause of right lower quadrant pain was never established defi nitively. Figure 3 seven studies were reported as showing no acute intraabdominal process. Of the remaining three studies, one study was reported as showing perforated diverticulitis (perforated appendicitis at surgery), one study was reported as showing a right inguinal hernia with marked inflammatory changes (a gangrenous appendix was found in the right inguinal Radiology: Volume 254: Number 2 February 2010 n radiology.rsna.org 465

7 hernia at surgery), and one study was reported as showing a moderate amount of pelvic fluid in a 24-year-old man. The most common alternate diagnosis in patients undergoing negative appendectomy was a symptomatic right ovarian cyst (10.6%, 13 of 123). Discussion Our finding of an increase in the rate of preoperative appendiceal CT (from 18.5% to 93.2%) is in agreement with that in prior studies ( 14,24 ). For example, Raman et al ( 14 ) reported 20% of appendectomy patients undergoing preoperative CT in 1996 as compared with 85% in Our finding that increased use of CT prior to appendectomy was associated with a lower overall negative appendectomy rate is in agreement with those of several prior studies ( 6 13,15,16 ). For example, at the same institution Rao et al and Rhea et al found a decrease in the negative appendectomy rate from 20% to 7% ( 24 ) and then further to 3% ( 9 ) with increased use of preoperative CT. However, several prior studies, including a large population-based study, found no such reduction in the negative appendectomy rate with wider availability and use of CT ( ). The largest such study, published by Flum et al in 2001, reviewed the procedure codes reported in the Washington State Hospital discharge database from 1987 to 1998 and reported no change in the negative appendectomy rate (15.2% in 1987 and 15.6% in 1998) ( 22 ). However, in that study the authors did not actually determine which patients in the study group had actually undergone preoperative CT or US. In addition, most of the CT scans obtained during the time period of the study likely used axial images alone that were acquired with a single-section helical CT scanner. Authors of some studies ( 18,25 ), who have reported no change in the negative appendectomy rate with use of preoperative CT, compared the negative appendectomy rate in patients who underwent CT with that of patients who did not undergo CT during the same time period. Bias exists in such a com- parison. One would expect a low negative appendectomy rate in a group of patients undergoing surgery without CT when CT is widely available. Our finding that the negative appendectomy rate was lower in women of reproductive age in later years of the study when more patients underwent preoperative CT is consistent with several prior studies ( 12,13,24,26 ). Historically, higher negative appendectomy rates in women of reproductive age have been attributed in part to a variety of gynecologic processes that can confound the diagnosis of acute appendicitis. In our study, right lower quadrant pain was ultimately attributed to gynecologic disease in 38.7% (24 of 62) of patients who underwent a negative appendectomy and for whom a definitive alternative diagnosis was established. Seven of these 24 patients underwent preoperative CT. Of note, the timing of the decline of negative appendectomy rates could not be proved to be associated with the increases in CT use. That the negative appendectomy rate for men and women older than 45 years of age did not decline significantly as preoperative CT use increased was somewhat surprising. However, the negative appendectomy rate was 0% for women older than 45 years in 1998 and such that there could be no further decrease with increased use of CT. The lack of a decline in the negative appendectomy rates for men and women older than 45 years may be a consequence of the initially low rates resulting in low power. We suspect that CT findings (eg, epiploic appendagitis) that averted appendectomy were found in patients in these categories. Selective preoperative CT use in these patients is therefore likely beneficial. Whether the use of preoperative CT results in a lower negative appendectomy rate in male patients is a source of debate in the literature. Rao et al found that the negative appendectomy rate in men decreased from 11% to 5% with the introduction of appendiceal CT ( 24 ). Yet McGory et al studied all patients undergoing appendectomy in California in ( n = ) and reported that CT use did not result in a lower negative appendectomy rate in men ( 25 ). However, in the case of McGory et al, one would expect a lower negative appendectomy rate in those patients who did not undergo preoperative CT when CT was widely available as, presumably, clinical suspicion of appendicitis was so strong that CT was bypassed. Our false-positive CT report rate of 1.7% 10% (between 1998 and 2007) is in keeping with prior studies that have found false-positive CT report rates of 1% 10% ( 6,7,26 ). Our false-negative CT report rate varied between the later and early years of the study. Our falsenegative CT report rate of 0% 2.4% from 2001 to 2007 is consistent with prior studies that have found falsenegative CT report rates of 2% 3% ( 18,27,28 ). Our false-negative report rate was higher from 1998 to 2000 (6.5% 20.0%), which may reflect a learning curve in CT interpretation or the small number of patients ( n = 10 31) undergoing CT prior to appendectomy during those years. Furthermore, more liberal referral for CT in the later phase of the study may have meant that more typical, easy-to-interpret cases were included in the later phase of the study. A nonvisualized appendix on an otherwise normal multidetector CT scan is thought to exclude acute appendicitis ( 29 ) or make the likelihood of appendicitis low ( 30 ). We identified four patients (0.6% of 616 patients who underwent CT prior to appendectomy) in whom the appendix was not identified at CT, no acute abdominal process was identified at CT, and acute appendicitis was found at surgery and pathologic examination. These studies were not performed with the current protocol, which includes intravenous and oral contrast material as well as coronal reformations obtained from isotropic voxels. In our study, measures of report accuracy were not significantly different with the addition of coronal reformations from isotropic voxels. This is consistent with a prior investigation, which found that coronal reformations improved reader confidence but did 466 radiology.rsna.org n Radiology: Volume 254: Number 2 February 2010

8 not alter sensitivity or specificity ( 31 ). We also showed that the proportion of false-positive and false-negative CT reports was greater for 7- than 5-mm section thickness and for 10- than 7- or 5-mm section interval, which suggests that the accuracy of the CT diagnosis of appendicitis appears related to the use of thin sections with multidetector scanners. Similarly, Weltman et al ( 32 ) found that the use of thin-section CT (5 vs 10 mm) significantly improved the diagnosis of acute appendicitis. The risks of CT, most importantly, the risk of radiation exposure, should not be forgotten ( 33 ). Although it is a somewhat controversial topic, the estimated lifetime attributable risk of death from cancer has been estimated to be between 0.05% and 0.06% for a 25-year-old undergoing an abdominal CT with a tube current setting of 240 mas ( 34 ). The average mortality rates for a negative appendectomy, appendectomy for acute appendicitis, and appendectomy for perforated appendicitis have been found to be 0.14%, 0.24%, and 1.66% respectively ( 3 ). We believe that the risk of unnecessary surgery justifies the use of CT in patients in whom the clinical diagnosis of appendicitis is uncertain. Overutilization of CT is also a concern. In a study by Giuliano et al ( 35 ) in 2005, only 4% (21 of 525) of those undergoing pelvic CT to exclude acute appendicitis actually had appendicitis. US may also have a role in the evaluation of patients suspected of having acute appendicitis. It has been proposed by some ( 36,37 ) as the initial step in the imaging work-up of those patients. A recent study by Gaitini et al ( 36 ) reported a sensitivity and specificity of 74.2% and 97%, respectively, in the US evaluation of 420 adult patients suspected of having acute appendicitis. Further studies are needed to evaluate the role of US in the diagnosis of suspected appendicitis in adults, since its use may serve to reduce the number of negative CT examinations and patient radiation dose. Our study had a number of limitations. The study was retrospective and a number of important pieces of data were not available to us. However, a prospective, randomized study evaluating use of CT and the associated negative appendectomy rate would be difficult to perform in part because it would be considered unethical to randomize patients to the no-ct group in view of the existing data and community practice standards. Furthermore, we did not evaluate the effect of detector configuration on diagnostic performance. The proportion of appendectomies with prior CT scans we reported was a biased measure of CT use to diagnose appendicitis since it is missing the CT examinations that did rule out appendicitis. In conclusion, we found an increase (18.5% to 93.3%) in the percentage of adult patients undergoing CT prior to appendectomy at our institution during the past decade. This increase in preoperative CT use was associated with a decrease in the overall negative appendectomy rate. During this same time period, the shift from single-detector to multidetector CT and decreasing section thickness also significantly correlated with a reduction in false-positive diagnoses. The benefit from preoperative CT and the advances in CT technology that have directly improved image quality were greatest in women 45 years of age and younger in whom the negative appendectomy rate decreased from 42.9% to 7.1% during the period, though the timing of the decline of negative appendectomy rates could not be proved to be associated with the increases in CT use. We believe our study, along with the results of prior studies, supports the use of preoperative CT particularly in the evaluation of women of reproductive age suspected of having acute appendicitis. Furthermore, we believe the results of our study suggest that reconstruction section should be no more than 5 mm. References 1. Wagner JM, McKinney P, Carpenter JL. Does this patient have appendicitis? JAMA 1996 ; 276 : Kazarian KK, Roeder WJ, Mersheimer WL. Decreasing mortality and increasing morbidity from acute appendicitis. Am J Surg 1970 ; 119 : Velanovich V, Satava R. Balancing the normal appendectomy rate with the perforated appendicitis rate: implications for quality assurance. Am Surg 1992 ; 58 : Wen SW, Naylor CD. Diagnostic accuracy and short term surgical outcomes in cases of suspected acute appendicitis. CMAJ 1995 ; 152 : Lewis FR, Holcroft JW, Boey J, Dunphy E. Appendicitis: a critical review of diagnosis and treatment in 1,000 cases. 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