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1
Department of Radiology and Radiological Sciences, Vanderbilt University
Children's Hospital and Medical Center, D-1120 Medical Center North,
Nashville, TN 37232-2675.
2
School of Medicine, Meharry Medical College, 1005 D.B. Todd Jr. Blvd.,
Nashville, TN 37208.
3
Department of Biostatistics, Vanderbilt University Children's Hospital and
Medical Center, Nashville, TN 37232.
Received December 3, 1999;
accepted after revision March 17, 2000.
Address Correspondence to M. Hernanz-Schulman.
Abstract
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MATERIALS AND METHODS. A retrospective review of children who underwent abdominal CT for suspected appendicitis over a 25-month period was performed to identify patients with an appendicolith. An age-matched group of patients examined for trauma served as controls.
RESULTS. CT was performed in 104 children. Appendicitis was present in 60 (58%) of 104 children; 39 (65%) of 60 had an appendicolith. Appendicitis was not present in 44 (42%) of 104; six (14%) of 44 had an appendicolith. An appendicolith detected on CT had a sensitivity of 65% and a specificity of 86% for the radiologist diagnosing appendicitis. An appendicolith had a positive predictive value of 74% and a negative predictive value of 26%. Among the control population, two (3%) of 74 children had an appendicolith. This number was statistically significant compared with children in the study group with an appendicolith and abdominal pain, but without appendicitis (p = 0.02).
CONCLUSION. Although an appendicolith is significantly associated with appendicitis, the detection of an isolated appendicolith on CT is not sufficiently specific to be the sole basis for the diagnosis of acute appendicitis.
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The objective of this study was to determine the significance of an appendicolith detected on CT in children with abdominal pain by determining its sensitivity, specificity, and positive and negative predictive values for the diagnosis of appendicitis.
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In the study population, helical abdominal CT was performed at 5-mm collimation without sedation and oral or rectal contrast material on a Tomoscan AV (Philips Medical Systems, Shelton, CT) or Somatom Plus (Siemens Medical Systems, Iselin, NJ). IV contrast material was not part of the routine protocol, but was given in two patients.
An attending pediatric radiologist reported initial CT findings regarding the presence or absence of appendicitis. Positive diagnostic criteria included an enlarged appendix (>6 mm) or inflammatory changes in the right lower quadrant (including periappendiceal inflammation, phlegmon, or abscess). After an initial false-positive finding of an isolated appendicolith found not to be associated with appendicitis surgically and pathologically, we did not consider an appendicolith alone as diagnostic. Negative diagnostic criteria included absence of an enlarged appendix and lack of periappendiceal inflammation, phlegmon, and abscess. Visualization of a normal appendix was not required for a negative diagnosis.
A positive diagnosis of appendicitis was confirmed by surgical and pathologic findings. A negative diagnosis was confirmed by surgery or chart review until discharge and subsequent telephone follow-up, ranging from 6 to 16 months after the CT (mean time, 9.2 ± 3.9 months). Telephone follow-up included questions to determine if the patient had a subsequent appendectomy, was seen by another physician for similar symptoms, or had recurrence of symptoms. We could reach all patients in the study group with an appendicolith without appendicitis who did not have surgical confirmation of the negative diagnosis. Chart review to discharge in both patients in the control group with an appendicolith showed no evidence of abdominal pain or appendicitis. We could confirm a negative diagnosis by telephone follow-up in one of these two patients in the control group who did not have appendicitis at 6-months follow-up. However, the other patient moved and was lost to follow-up.
Original CT reports identifying children with an appendicolith were correlated with the discharge diagnosis of appendicitis or no appendicitis by chart review. All CT scans of patients with an appendicolith, but without appendicitis, were pulled from files and reviewed by four attending pediatric radiologists; the presence of an appendicolith was confirmed by consensus. An appendicolith was defined as high-density material in the appendix with similar attenuation to that of adjacent bone. For an appendicolith to be defined for the purpose of the study, reviewers could not find radiodense material outside the appendix in adjacent bowel loops. In all children with an appendicolith, but without appendicitis, agreement was found between the initial report and the retrospective CT review.
The sensitivity, specificity, positive predictive value, negative predictive value, and odds ratio for diagnosing appendicitis in the setting of an appendicolith revealed on CT were calculated and subjected to statistical analysis by a biostatistician. We analyzed these data using Fisher's exact test for categoric variables. We calculated the 95% confidence interval (CI), using binomial proportions for the difference between experimental and control groups. All tests of significance were two-tailed tests, and differences were considered statistically significant when a p of greater than 0.05 (SAS version 7.0; SAS Institute, Cary, NC) was used for all analyses.
The institutional review board approved this study.
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Conversely, of all children in the study group examined for suspected appendicitis, an appendicolith was identified on CT in 45 (43%) of 104. Among these patients, 39 (87%) of 45 had surgically and pathologically confirmed appendicitis; all 39 had associated appendiceal distention and periappendiceal inflammation (Fig. 1). However, six (13%) of 45 did not have appendicitis; in these six patients, the appendicolith was an isolated finding (i.e., no appendiceal distention or periappendiceal inflammation) (Fig. 2). These six cases were confirmed by surgery (n = 1) or by chart review with telephone follow-up (n = 5). Among these five patients, one received 10 days of oral trimethoprim sulfamethoxazole (Bactrim; Roche Labs, Grafton, WI) for presumed shigella infection; the others did not receive any antibiotic treatment. The difference between children with an appendicolith accompanied by appendicitis compared with those with an appendicolith, but without appendicitis, was statistically significant (p < 0.001).
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An appendicolith detected on CT had a sensitivity of 65% (95% CI, 53-77%) and a specificity of 86% (95% CI, 76-96%) for the diagnosis of appendicitis. The positive predictive value was 74% (95% CI, 66-82%), and the negative predictive value was 26% (95% CI, 18-34%). The prevalence of appendicitis in our series was 60 (58%) of 104 children; given the presence of an appendicolith, we found the odds ratio for having appendicitis was 6.4.
In the control group, two patients (3%) of 74 had an appendicolith without appendiceal distention or inflammation (Fig. 3). The difference between six (14%) of 44 children who had an appendicolith without appendicitis in the study group compared with two (3%) of 74 in the control group was statistically significant (p = 0.02).
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The frequency of appendicoliths detected on CT and their specificity for the diagnosis of appendicitis differ in our study compared with previous reports [4,5,6,7,8,9]. In our series, 65% of children with proven appendicitis had an appendicolith on CT without oral contrast material; this percentage is greater than in previous reports of 43-50%. The specificity of an appendicolith on CT for the diagnosis of appendicitis in our series was 86%. This percentage differs from a specificity of 100% found by Rao et al. [8], the only other study addressing the specificity of an appendicolith identified on CT. However, unlike our series, Rao et al. performed their study on the general (mostly adult) population, and all patients received rectal contrast material.
The explanation for the higher detection rate and decreased specificity of appendicoliths in our pediatric series compared with CT studies performed with enteric contrast material on the general population could be related to an increased frequency and diminished significance of appendicoliths in children. However, we believe that a more likely explanation is absence of enteric contrast material in our patients. Because enteric contrast material may accumulate in the appendix, an appendicolith may be obscured to the degree that visualization is not possible. In patients without appendicitis, an appendicolith in an otherwise normal appendix may not be easily differentiated from enteric contrast material and, therefore, may not be detected.
Our data raise interesting questions regarding the pathophysiologic basis for an appendicolith in a child with abdominal pain but without appendicitis. Three possible explanations are suggested. First, an appendicolith may be the initiating event in developing appendicitis in some patients, resulting in abdominal pain, but this initial event may resolve before appendiceal distention and inflammatory changes ensue. Second, calcified material in the appendix may be a transient finding in healthy children. Third, a combination of the first and second explanation could be true. Calcified material could be a normal, and at times a transient finding, but with the potential to obstruct the appendiceal lumen and initiate appendicitis.
We did not believe we were justified in performing follow-up CT in asymptomatic patients to determine whether the appendicoliths resolved spontaneously. This resolution could have been correlated with the cessation of abdominal pain. However, to further explore this intriguing question, we identified an age-matched control population without acute abdominal pain. The identification of an appendicolith in 3% of children in the control population suggests that a small amount of calcified material in the appendix of an asymptomatic child may be a normal finding. However, children with abdominal pain but without appendicitis were significantly more likely to have an appendicolith than those without abdominal pain in the control group (p = 0.02). Furthermore, children with abdominal pain and an appendicolith on CT were significantly more likely to have appendicitis (p < 0.001). Thus, although none of our patients with or without abdominal pain and an isolated appendicolith developed appendicitis, the significant association of an appendicolith with abdominal pain and appendicitis suggests that the third alternative may be correct. A small, isolated appendicolith may be a normal finding in pediatric patients, but, in some patients, appendicoliths may be associated with abdominal pain and perhaps represent one of several possible initiating events in the eventual development of appendicitis.
In conclusion, in our series of 104 pediatric patients, an appendicolith detected on CT had a sensitivity of 65%, a specificity of 86%, a positive predictive value of 74%, and a negative predictive value of 26% for the diagnosis of appendicitis. An appendicolith was seen in 65% of CT scans of children with proven appendicitis and in 14% of children with abdominal pain but without appendicitis. Though the presence of an appendicolith is significantly associated with appendicitis, our data indicate that an appendicolith alone is insufficient to diagnose acute appendicitis on CT.
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