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Published online before print November 13, 2002, 10.1148/radiol.2261011612
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(Radiology 2003;226:101-104.)
© RSNA, 2002

Pediatric Imaging

US as a Primary Diagnostic Tool in Relation to Negative Appendectomy: Six Years Experience1

Stefan Puig, MD, Marcus Hörmann, MD, Winfried Rebhandl, MD, Rosemarie Felder-Puig, MSc, Mathias Prokop, MD and Kurosh Paya, MD

1 From the Departments of Radiology (S.P., M.H., M.P.) and Surgery (W.R., K.P.), University of Vienna, Währinger Gürtel 18-20, 1090 Vienna, Austria; and St Anna Children’s Hospital, Vienna, Austria (R.F.P.). From the 2001 RSNA scientific assembly. Received October 3, 2001; revision requested December 11; final revision received April 22, 2002; accepted May 24. Address correspondence to S.P. (e-mail: stefan.puig@univie.ac.at).


   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 
PURPOSE: To evaluate the effect of ultrasonography (US) on the rate of appendectomy after false-positive diagnosis of acute appendicitis (negative appendectomy).

MATERIALS AND METHODS: Data were analyzed in 736 pediatric patients (mean age, 13.2 years) who had undergone appendectomy between 1995 and 2000. Histologic data were compared in patients who underwent US with those who did not undergo imaging prior to surgery. US was performed by a radiologist or a pediatric surgeon or both.

RESULTS: A total of 643 (87.4%) of the 736 pediatric patients underwent preoperative US, and 93 (12.6%) of the 736 did not undergo preoperative US. Of the 736 patients, 97 (13.2%) underwent negative appendectomy. Thirty-four (36.6%) of the 93 patients who underwent appendectomy with no preoperative US and 63 (9.8%) of the 643 patients who underwent preoperative US underwent negative appendectomy. There was a significant association between US and positive appendectomy (P < .001).

CONCLUSION: US in pediatric patients suspected of having appendicitis can significantly lower the negative appendectomy rate.

© RSNA, 2002

Index terms: Appendicitis, 751.291 • Appendix, US, 751.12981


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 
Acute appendicitis is the most common cause of urgent abdominal surgery (1,2). About 250,000 cases of appendicitis occurred in the United States annually between 1970 and 1984 (3). Since clinical diagnosis of appendicitis is difficult, appendectomy after false-positive diagnosis of appendicitis (hereafter, negative appendectomy) is performed in up to 20% of cases (4). Some authors (5–7) have even reported negative appendectomy rates of up to 40%. Such negative explorations have been accepted as an unavoidable consequence of the principle of early exploration to prevent perforation of the appendix, but this practice is being increasingly questioned (8–10).

In 1986, Puylaert (11) reported on graded-compression ultrasonography (US) for diagnosis of acute appendicitis. Since then, numerous studies (12–21) have been presented about US as a diagnostic tool. The conclusion of these authors was that US is a valuable modality in the investigation of appendicitis. However, recently, Applegate and colleagues (4) published their results on the effect of cross-sectional imaging on negative appendectomy and perforation rates in children. Despite a decrease in negative appendectomy after computed tomography (CT), the number of negative appendectomies performed after US was greater than that in patients who did not undergo preoperative imaging. Nevertheless, increase in the accuracy of the diagnosis of appendicitis is, of course, the main target of US, and its use should reduce negative appendectomy rates. If US in individuals suspected of having appendicitis does not increase the accuracy of diagnosis or makes the diagnosis even more uncertain, it should no longer be a part of presurgical evaluation, especially in children. In addition to economic factors, an additional examination adds more time when urgent surgery is indicated. Furthermore, graded-compression US can be painful and should therefore be avoided if unnecessary.

These new data provided the impetus for us to explore our databases, since US is part of the standard evaluation protocol at our institution (University Hospital, Vienna, Austria) in pediatric patients suspected of having appendicitis. The purpose of this study was to evaluate the effect of US on the negative appendectomy rate.


   MATERIALS AND METHODS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS
 DISCUSSION
 REFERENCES
 
Three authors (S.P., M.H., K.P.) reviewed data from 736 patients who underwent appendectomy between 1995 and 2000 in the pediatric surgery division of our hospital. These data files are stored in a commercially available database (File Maker; Apple Computer, Cupertino, Calif) and include information about patient sociodemographic status; clinical examination, laboratory test, and histologic results; clinical and US diagnosis; names of physicians who performed US and surgery; details regarding surgery; and postoperative complications and therapy. Our institutional review board did not require its approval or informed consent for our study according to our institutional scientific guidelines.

The mean age of the subjects was 13.2 years (median, 10.8 years; age range, 3 days to 33 years). The age breakdown and number of male and female patients in each age group are displayed in Table 1. The three patients aged older than 20 years specifically requested surgeons from the pediatric surgery department; therefore, they were included in the pediatric surgery database.


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  		TABLE 1. Patient Age Breakdown and Number of Male and Female Patients in Each Age Group

 
Of 736 patients, 643 (87.4%) underwent preoperative US. In 207 (32.2%) of the 643 patients, US was performed by one of two pediatric surgeons (including K.P.) who both have approximately 15 years of experience in US of the pediatric abdomen. Of 643 patients, 251 (39.0%) were referred to the radiology department, where one of the radiologists on duty performed the US examination. This was not necessarily a pediatric radiologist but someone who had at least several years of US experience. Of 643 patients, 185 (28.8%) underwent preoperative US twice by both a pediatric surgeon and a radiologist. These cases occurred when, at the first US examination, the US report did not match the clinical symptoms or the sonographer was uncertain of the diagnosis. In some cases, a US examination by a pediatric surgeon was repeated by a radiologist because of legal reasons. When findings of the two US reports were not concordant, the final US diagnosis was made after another review of the findings with consensus of a radiologists or a pediatric surgeon.

Of the 736 patients, 93 (12.6%) did not undergo US prior to surgery, either because the clinical symptoms were unambiguous, in the surgeon’s opinion, or because there was no one available who had substantial US experience.

In both departments (radiology and pediatric surgery), US was performed according to the recommendations of Puylaert (11), that is, with graded compression of the right lower quadrant. Criteria for the US diagnosis of appendicitis included identification of the appendix as a fluid-filled, noncompressible, blind-ended tubular structure with a diameter of 6 mm or more. The radiologists used a 5–10-MHz linear-array transducer (HDI Ultramark 9 or HDI 5000; ATL, Bothell, Wash), and the pediatric surgeons used a 5-MHz linear-array transducer (Sonoline Versa; Siemens, Erlangen, Germany). Reports were written by the sonographer immediately after the examination, and hard-copy images were produced for each patient.

For statistical comparison of the frequencies of positive (appendectomy after true-positive diagnosis of appendicitis) and negative appendectomies and of examinations with and without US, we used a {chi}2 test in a 2 x 2 contingency table format. This is a test of association between mutually exclusive categories of one variable, given in the rows of the table, and mutually exclusive categories of another variable, given in the columns of the table (21). Our hypothesis was that an inverse relationship exists between the use of US and negative appendectomy.


   RESULTS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
DISCUSSION
 REFERENCES
 
Of the 643 (87.4%) patients who underwent preoperative US, 63 (9.8%) underwent negative appendectomy (Table 2, Figure). One hundred thirty-four (20.8%) of the 643 appendixes were perforated. In the 93 (12.6%) subjects who did not undergo US, the rate of negative appendectomy was 36.6% (34 of 93). Perforation was not observed in the group that did not undergo US. Statistical analysis revealed a significant association between the use of US and positive appendectomy ({chi}2 = 42.55, df = 1; P < .001).


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  		TABLE 2. Comparison of Numbers of US Examinations and Positive or Negative Appendectomies

 


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  		Figure a. Pie charts depict the relationship between findings of negative and positive appendectomy in (a) patients who underwent presurgical US and in (b) patients who underwent appendectomy without prior US.

 


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  		Figure b. Pie charts depict the relationship between findings of negative and positive appendectomy in (a) patients who underwent presurgical US and in (b) patients who underwent appendectomy without prior US.

 
The 97 (13.2%) of 736 patients who underwent negative appendectomy had a variety (n = 17) of final diagnoses (Table 3). In total, 160 types of abnormality were found in these 97 patients.


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  		TABLE 3. Final Diagnoses in 97 Patients Who Underwent Negative Appendectomy

 
Misdiagnoses in the group that underwent US and negative appendectomy (n = 63) occurred in 22 (34.9%) of the 63 patients examined by the radiologist and in 20 (31.7%) of the 63 patients examined by the pediatric surgeon. In the US reports, 21 (33.4%) of 63 false-positive diagnoses were made by the surgeon and radiologist in consensus. Comparison of the rates of US misdiagnosis for our three examiner groups revealed no significant differences.

In 576 (89.6%) of 643 preoperative US examinations, findings were positive for appendicitis. In the remaining 67 (10.4%) examinations, US findings were negative for appendicitis, a diagnosis that was also reported when the appendix could not be visualized. According to histologic reports, appendectomy was positive in 580 (90.2%) of 643 patients who underwent US prior to surgery. Of these, 42 (7.2%) had a negative US report. Appendectomy was negative in 63 (9.8%) of 643 patients who underwent US. Of these, 25 (39.7%) had had a negative appendectomy finding (Table 2).


   DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
REFERENCES
 
Although acute appendicitis is a diagnosis based primarily on history and physical examination findings, US is a cost-efficient adjunct to the diagnostic evaluation. However, the utility of US is a subject of controversy in the literature (22,23). In our hospital, US in pediatric patients suspected of having appendicitis is part of the diagnostic algorithm. After reviewing the data files of 736 subjects who underwent appendectomy in our pediatric surgery unit, we found an overall negative appendectomy rate of 13.2% (97 of 736 subjects), which is comparable to rates in the most recent studies published on this topic (4,24). The negative appendectomy rate of 36.6% in patients who did not undergo presurgical US is equivalent to that in studies presented by Andersson et al (5,6) and Baigrie et al (7). The negative appendectomy rate of 9.8% in patients who underwent presurgical US is similar to data published by Karakas et al (24) in 2000. In their investigation, 182 pediatric patients underwent preoperative US. The sensitivity was 74%, the specificity was 99%, and the negative appendectomy rate was 8%. In the study by Applegate et al (4), 126 patients who did not undergo imaging prior to surgery were reported to have a negative appendectomy rate of 14%, while 121 subjects who underwent US had a rate of 17%. When only false-positive US diagnoses were compared with histologic outcomes, the negative appendectomy rate decreased to 8% for US. This discrepancy was due to the surgeons not acting on the results of the US examination in 10 cases. Still, these data suggest that preoperative US might not have a substantial effect on the negative appendectomy rate at their institution.

In a recently published population-based study of 63,707 patients undergoing appendectomy, Flum et al (25) found no reduction in misdiagnosis of appendicitis in a 12-year period from 1987 to 1998, despite the use of US, CT, and laparoscopy. The authors started their survey with the hypotheses that misdiagnosis has decreased since the introduction of advanced diagnostic techniques and that the greatest decreases in the misdiagnosis rate would be identified in populations at increased risk for misdiagnosis. However, the data set from which the authors extracted their findings contained no information about whether patients actually underwent imaging prior to appendectomy. Thus, their work was based on the assumption that with the increased availability of advanced diagnostic techniques, these techniques are actually used for the diagnosis of appendicitis. In many institutions, however, referral for appendectomy is still based on clinical diagnosis only.

Another major difference between our work and that of Flum et al (25) is seen in the study populations. We analyzed data from pediatric patients (mean age, 13 years), while Flum et al (25) included patients from all age groups (mean age, 32 years). For children younger than 5 years, the authors reported a decrease in misdiagnosis from 1.01 cases per 10,000 individuals in 1987 to 0.59 case in 1998, although this decrease did not represent a significant change.

The question of who should perform US in patients suspected of having appendicitis is another issue that merits consideration, specifically since Applegate et al (4) argued that surgeons may lack confidence in US reports. At our institution, US is performed by either a pediatric surgeon or a radiologist. A US examination is repeated if a patient has typical symptoms at presentation but the US report is negative, the appendix is not visualized, or the sonographer is uncertain about his or her diagnosis. With such a diagnostic algorithm, performance of surgery despite a negative US report is, of course, rare and in most cases occurs only if clinical symptoms are unambiguous and the appendix cannot be visualized at two consecutive examinations. In fact, it has been reported that 98% of false-negative US examination findings occur because of nonvisualization of the appendix (17).

The advantages of performing US prior to surgery cannot be discussed without considering the problem of perforation. In the current study, the perforation rate in patients who underwent US was 20.8%. This is comparable with rates in another study (13), in which the overall incidence of perforation was 16%–39%. Perforation rates are related to age, with the first peak (40%–57%) occurring in very young patients and the second peak (55%–70%) occurring in elderly patients (12,24,26–28). There is evidence that an inverse relationship exists between a negative appendectomy rate and a perforation rate (13). Applegate et al (4) reported 72 (24%) perforations in 299 children, with the lowest perforation rate (20%) occurring after CT; the rate was 27% after US and 42% after US and CT (4). In the patients in the current study who did not undergo US, there were no perforations. These data may suggest that additional examinations such as US delay surgery and therefore increase the risk of perforation. On the other hand, perforation rates of 20%–30% were also reported for pediatric patients who underwent appendectomy without prior imaging (4,24). Therefore, one may speculate that a certain perforation rate is unavoidable in the age-associated risk groups, whether or not surgery is delayed as a result of additional diagnostic evaluation.

The limiting factors in the use of US include retrocecal appendiceal location and obesity in the patient. In such patients, high-frequency transducers may fail to reach the necessary depth; thus, low-frequency transducers must be used, which makes diagnosis more difficult because of the lower spatial resolution (29). In these cases, further evaluation with CT may be considered, as suggested in a number of studies (4,24,30–34). Magnetic resonance imaging has also been used as a diagnostic modality in patients suspected of having appendicitis (35), an alternative that will probably receive more attention in the future.

Because of the retrospective design of our study, we were not able to control our data for other variables, such as equivocal clinical findings, symptom duration, or sonographer skill level. Furthermore, the sample size of patients who did not undergo US was small. Nevertheless, we have shown that US can significantly lower the negative appendectomy rate in pediatric patients. This conclusion is based on the premise that US examinations should be performed by highly trained sonographers and with close communication between surgeons and radiologists, which leads to confidence in negative US findings.


   FOOTNOTES
 
Author contributions: Guarantor of integrity of entire study, S.P.; study concepts and design, S.P., K.P.; literature research, M.H.; clinical studies, K.P., W.R., S.P., M.H.; data acquisition, K.P., W.R.; data analysis/interpretation, S.P.; statistical analysis, R.F.P.; manuscript preparation, S.P., R.F.P.; manuscript definition of intellectual content, S.P., M.P.; manuscript revision/review, R.F.P.; manuscript editing and final version approval, S.P.


   REFERENCES
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 

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