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Published online before print October 30, 2001, 10.1148/radiol.2213010379
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(Radiology. 2001;221:755-759.)
© RSNA, 2001

Pediatric Imaging

Nonenhanced Limited CT in Children Suspected of Having Appendicitis: Prospective Comparison of Attending and Resident Interpretations1

Lisa H. Lowe, MD, Kimberly S. Draud, MD, Marta Hernanz-Schulman, MD, Martha R. Newton, Richard M. Heller, MD, Sharon M. Stein, MD and Theodore Speroff, PhD

1 From the Department of Radiology, Children’s Mercy Hospital and University of Missouri, 2401 Gillham Rd, Kansas City, MO 64108 (L.H.L.); and Department of Radiology and Radiological Sciences (K.S.D., M.H.S., R.M.H., S.M.S.), Center for Clinical Improvement (M.R.N., T.S.), and Department of Medicine (T.S.), Division of General Medicine Health Services Research, Vanderbilt Children’s Hospital and Medical Center, Nashville, Tenn. Received January 30, 2001; revision requested March 6; revision received April 23; accepted May 2. Address correspondence to L.H.L. (e-mail: llowe@cmh.edu).


   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
RESULTS
DISCUSSION
 REFERENCES
 
PURPOSE: To prospectively compare resident and attending radiologic interpretations of nonenhanced limited computed tomographic (CT) scans obtained in children suspected of having appendicitis.

MATERIALS AND METHODS: Seventy-five consecutive children underwent nonenhanced limited CT for suspected appendicitis. The scans were prospectively interpreted by a resident and an attending radiologist, each unaware of the other’s interpretation. The probability that the findings indicated a diagnosis of appendicitis, level of certainty in the interpretation, and presence of an alternate diagnosis were statistically analyzed.

RESULTS: Nineteen children (25%) had appendicitis. The area under the receiver operating characteristic curve was not significantly different between residents (0.97 ± 0.02) and attendings (0.95 ± 0.04). The percentage agreement between residents and attendings was 91% ({kappa} = 0.73 ± 0.095). The average level of certainty tended to be higher for attendings (93% ± 15) than residents (89% ± 12). The sensitivity, specificity, and accuracy of resident interpretations were 63%, 96%, and 88%, respectively, compared with those of attending interpretations—95%, 98%, and 97%, respectively. Residents and attendings noted alternate diagnoses in 30% of children without appendicitis.

CONCLUSION: A high level of agreement exists between resident and attending radiologists in the interpretation of nonenhanced limited CT scans in children suspected of having appendicitis. Residents, however, tend to be less confident in their interpretations.

Index terms: Appendicitis, 751.291 • Children, gastrointestinal tract, 751.291 • Computed tomography (CT), in infants and children, 751.12111


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
RESULTS
DISCUSSION
 REFERENCES
 
Cross-sectional imaging techniques, including ultrasonography (US) and more recently computed tomography (CT), have been successfully used to examine children suspected of having appendicitis (1). In highly trained hands, US has proved accurate up to 97% and has helped reduce the negative laparotomy rate from 23% to 9% in some studies (2,3). Because of operator dependence, however, its sensitivity has ranged from 40% to 100%, which has generated controversy throughout the general radiology community regarding its application (1,3,4). Helical CT with use of various combinations of intravenous, oral, and rectal contrast agents has yielded accuracies from 90% to 98% in the general and pediatric populations suspected of having appendicitis (5–11). Its use has decreased the negative laparotomy rate from 10%–20% to 4%–7% (12–14).

Nonenhanced limited CT has been evaluated in the general (mostly adult) population (15–19), and, more recently, in children, with the accuracy being similar to that of CT with contrast material (1). Issues unique to children must be taken into consideration when performing helical CT in this population. Many children do not possess the same ability to cooperate as adults and may be less able to tolerate intravenous, oral, or rectal contrast material. With the nonenhanced limited CT protocol, the scan is obtained quickly and no sedation is needed.

Accurate interpretation of helical CT scans in adults and children suspected of having appendicitis has obvious clinical ramifications (20–22). Comparing the interpretations of nonenhanced limited CT scans made by residents with those made by attending radiologists may help determine whether a difference related to level of experience and training exists, as is the case with US (4,10,23). This information in turn carries potential implications of the resident’s role in the interpretation of nonenhanced limited CT scans, performed on call, for appendicitis, as well as the broad application of nonenhanced limited CT (24,25).

The objective of this study was to prospectively compare resident and attending radiologic interpretations of nonenhanced limited CT scans obtained in children suspected of having appendicitis.


   MATERIALS AND METHODS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS
DISCUSSION
 REFERENCES
 
Subjects
Nonenhanced limited CT was performed in 75 consecutive children with atypical or equivocal clinical history and physical examination findings of suspected appendicitis over an 8-month period from February through September 2000. The study took place in a medium-sized urban setting, Vanderbilt Children’s Hospital, a university-based children’s hospital. Emergency room physicians, pediatric surgeons, and pediatricians referred children for nonenhanced limited CT. The 75 children (43 girls, 32 boys) ranged in age from 3 to 18 years (mean, 11 years; SD, 4 years 3 months). The study had institutional review board approval, although informed consent was not required because studies performed were for accepted clinical indications and were a part of routine clinical care.

Imaging Technique
Nonenhanced limited CT scans have been obtained for the evaluation of appendicitis at our institution since November 1997. Studies were performed without sedation or intravenous, oral, or rectal contrast material by using a commercially available scanner (Tomoscan AV; Phillips Medical Systems, Shelton, Conn) and 5-mm collimation, 180 mA, 120 kV, and a 1:1 table pitch from the inferior edge of the liver to the pubic symphysis. Images collimated to 3-mm thickness through the region of the appendix were obtained at the discretion of the on-site radiologist (resident or attending pediatric radiologist).

Study Design
All nonenhanced limited CT scans were initially interpreted by one of six radiology residents who were all at the same level of residency training. All six residents had completed 1 year of in-house diagnostic radiology call. The study was performed during their 2nd year of in-house call, which coincided with the last 6 months of their 2nd year and the first 2 months of their 3rd year of radiology residency. Each resident completed 1–2 months of pediatric radiology during each of the 1st and 2nd years of their residency training. For each child, the resident independently filled out a survey noting the findings of appendicitis, the percentage probability (1%–100%) that the findings indicated a diagnosis of appendicitis, their level of certainty (confidence, 1%–100%) in the nonenhanced limited CT interpretation, and the presence or absence of an alternate diagnosis. All resident surveys were filled out independently, without input or consultation from other resident or attending radiologists, surgeons, or emergency room physicians (Figure). An identical questionnaire was completed independently by one of four attending pediatric radiologists within 24 hours, without knowledge of the resident’s initial interpretation or the final clinical diagnosis.



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  		Figure 1. Sample questionnaire filled out by the resident radiologists during interpretation of the nonenhanced limited CT scans. An identical questionnaire was completed independently by the attending radiologists. RLQ = right lower quadrant.

 
Correlation of nonenhanced limited CT scan interpretations with follow-up data in children with and those without a diagnosis of appendicitis was performed by one of the authors (K.S.D.) who was unaware of the study results. In children who were proved to have appendicitis, we confirmed the diagnosis by reviewing surgical and pathology reports. In children who did not have appendicitis, we confirmed the diagnosis by reviewing surgical reports and pathology data and with telephone follow-up. Telephone follow-up was performed 4 months after the end of the study period in 52 (93%) of 56 children without appendicitis by one of the authors (K.S.D.) who was unaware of the nonenhanced limited CT findings and clinical diagnoses. The parents were asked specific questions to confirm that their child did not subsequently develop appendicitis. Review of the medical records of the four children whose families were unable to be contacted by telephone for follow-up confirmed that to our knowledge none of these children returned with recurrent symptoms and none later received a diagnosis of appendicitis.

Statistical Analyses
The performance of resident and attending radiologists was compared by using receiver operating characteristic (ROC) analysis for matched pairs (26,27). ROC analysis is nonparametric and is a pair-wise rank ordering. We used it to measure the ability of the physician to discriminate between appendicitis and nonappendicitis cases. A cutoff value is often used in testing to indicate a threshold that defines when a test should be considered positive or negative. For the purpose of our statistical analysis, the nonenhanced limited CT interpretation was defined as diagnostic for appendicitis when the radiologist’s percentage probability was recorded as equal to or greater than 90%. To determine the level of agreement between resident and attending radiologists, the percentage agreement and the {kappa} coefficient were calculated (28,29). Sensitivity, specificity, and accuracy were determined by using a probability cutoff of equal to or greater than 90% and 85%. All statistical analyses were performed with computer software (SPSS, version 10.0; SPSS, Chicago, Ill). Significance was inferred for P values less than .05.


   RESULTS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS
DISCUSSION
 REFERENCES
 
Subjects
Nineteen (25%) of the 75 children had appendicitis. The nonenhanced limited CT findings recorded by the resident and attending radiologists in children with appendicitis are shown in Table 1.


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  		TABLE 1. Summary of Nonenhanced Limited CT Findings of Resident and Attending Radiologists in 19 Children with Proved Appendicitis

 
Resident Radiologists
On the basis of a 90% or greater probability of appendicitis, the sensitivity, specificity, and accuracy of resident CT scan interpretations were 63% (12 of 19), 96% (54 of 56), and 88% (66 of 75), respectively. There were seven false-negative and two false-positive interpretations for the residents, which are detailed in Table 2. An alternate diagnosis was made in 17 (30%) of the 56 children who did not have appendicitis.


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  		TABLE 2. Resident Survey Results for False-Positive and False-Negative Interpretations of Nonenhanced Limited CT Scans

 
Attending Radiologists
On the basis of a 90% or greater probability of appendicitis, the sensitivity, specificity, and accuracy of attending CT scan interpretations were 95% (18 of 19), 98% (55 of 56), and 97% (73 of 75), respectively. There was one false-negative and one false-positive interpretation by the attending radiologists (Table 3), both of which were also incorrectly interpreted by the resident radiologists (by the last resident as false-negative and by the first resident as false-positive [Table 2]). For the false-negative interpretation, the resident and attending radiologists noted the same finding of a solitary appendicolith without other evidence of appendicitis. For the false-positive interpretation, the resident and attending both identified an enlarged appendix (11 mm and 12 mm) and a small appendicolith. However, the patient improved clinically, did not undergo emergency appendectomy, and had not developed appendicitis, per telephone follow-up. Attendings made the same number of alternate diagnoses as residents, that is, in 17 (30%) of the 56 children who did not have appendicitis.


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  		TABLE 3. Attending Survey Results for False-Positive and False-Negative Interpretations of Nonenhanced Limited CT Scans

 
Statistical Analyses
The mean area under the ROC curve, the measurement of the radiologist’s ability to discriminate presence or absence of appendicitis, was 0.97 ± 0.02 for residents and 0.95 ± 0.04 for attendings. The P value for the difference in ROC curves was .35, which was not statistically significant. The percentage agreement between the residents and attendings was 91%. The mean {kappa} coefficient was 0.73 ± 0.095, indicating a good to substantial level of agreement according to the guidelines of Fleiss (29) and of Landis and Koch (28). The average level of certainty (confidence) tended to be higher for attendings (93% ± 15) than residents (89% ± 12), although the difference was not statistically significant (P = .051).

The confidence of the attendings for correct interpretations (true-positive, 98%; true-negative, 92%) was similar to that for incorrect interpretations (false-positive and false- negative, 99.5%) (P = .30). The residents, however, were significantly less confident for false-negative (72%) interpretations compared with all other interpretations (true-positive, 96%; true-negative, 90%; false-positive, 90%) (P < .001).

With use of a 90% cutoff for the probability that the findings indicated a diagnosis of appendicitis, the sensitivity of the interpretations by the attendings of 95% was significantly greater than that by the residents, 63% (P = .031). When a cutoff of 85% was used, the sensitivity of the residents’ interpretations improved to 79% (15 of 19), which was not significantly different from the sensitivity of the attendings’ interpretations of 95% (P = .25). Changing the cutoff from 90% to 85% probability that the findings indicated a diagnosis of appendicitis did not change the specificity of the residents’ interpretations or the sensitivity or specificity of the attendings’ interpretations.


   DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS
DISCUSSION
REFERENCES
 
Despite a tendency to be less confident, the resident radiologists were able to reliably diagnose appendicitis on nonenhanced limited CT scans in children with abdominal pain who were suspected of having appendicitis, with statistical accuracy similar to that of attending radiologists. The high performance and similarity in ROC areas indicate that both residents and attendings were able to rank order and classify nonenhanced limited CT scan findings according to disease status. Residents, who are less experienced, tend to be less certain of their ability to discriminate; thus, they select a lower probability of appendicitis. Although the discrimination ability does not differ between residents and attendings, the cutoff value chosen to define a positive result can affect the interpretation as well as the radiologists’ sensitivity and specificity. The study results suggest that more lenient cutoffs may be appropriate for residents.

To our knowledge, no prior study has addressed the accuracy of residents’ interpretation of nonenhanced limited CT scans obtained in patients with suspected appendicitis. This study was limited to children, however, and the results may not be amenable to generalization to the adult population. Our study included image interpretations made by a limited number of resident and attending radiologists from a single institution, and we are not able to determine the degree to which the results may apply to other institutions. The number of cases per resident or attending was not sufficient to statistically analyze and compare the performance of individual residents and attendings. However, the false-negative and false-positive interpretations were distributed among several different residents and attendings. Our sensitivity, specificity, accuracy, and rate of alternate diagnosis (6,8,30) for interpretation of nonenhanced limited CT scans are similar to those of previous studies in the adult population (19,31–33).

The ability of the residents to make the diagnosis of appendicitis with a level of accuracy similar to that of the attending radiologists implies that nonenhanced limited CT is not operator dependent and does not require the extensive experience needed for accurate results with US documented in the literature (4,10,23).


   FOOTNOTES
 
Abbreviation: ROC = receiver operating characteristic

Author contributions: Guarantors of integrity of entire study, L.H.L., M.H.S., R.M.H.; study concepts and design, L.H.L., M.H.S., T.S.; literature research, L.H.L., M.H.S.; clinical studies, K.S.D., L.H.L., R.M.H.; data acquisition, K.S.D., L.H.L., S.M.S., R.M.H., M.H.S.; data analysis/interpretation, L.H.L., T.S., M.R.N.; statistical analysis, K.S.D., T.S., M.R.N.; manuscript preparation, L.H.L., T.S., M.R.N.; manuscript definition of intellectual content, L.H.L., M.H.S., R.M.H.; manuscript editing, L.H.L., T.S., M.R.N., M.H.S.; manuscript revision/review, L.H.L., T.S., M.H.S.; manuscript final version approval, all authors.


   REFERENCES
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS
DISCUSSION
 REFERENCES
 

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This Article
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