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1
Department of Radiology, Rainbow Babies and Children's Hospital, University
Hospitals of Cleveland and Case Western Reserve School of Medicine, 11100
Euclid Ave., Cleveland, OH 44106-5056.
2
Department of Surgery, Rainbow Babies and Children's Hospital, University
Hospitals of Cleveland and Case Western Reserve School of Medicine, Cleveland,
OH 44106-5056.
3
Department of Pediatrics, Rainbow Babies and Children's Hospital, University
Hospitals of Cleveland and Case Western Reserve School of Medicine, Cleveland,
OH 44106-5056.
Received November 19, 1999;
accepted after revision March 17, 2000.
Address correspondence to C. J. Sivit.
Abstract
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SUBJECTS AND METHODS. Between June 1996 and April 1999, 386 pediatric and young adult patients with suspected appendicitis were examined using sonography, CT, or both: 233 underwent sonography only, 71 underwent CT only, and 82 underwent sonography and CT. All sonograms and CT scans were prospectively interpreted as showing positive or negative findings for appendicitis by one of six pediatric radiologists. CT and sonographic findings were correlated with surgical and histopathologic findings or findings at clinical follow-up.
RESULTS. Helical CT had a significantly higher sensitivity (95% versus 78%, p = 0.009) and accuracy (94% versus 89%, p = 0.05) than graded compression sonography for the diagnosis of appendicitis in children, adolescents, and young adults. The specificity of both techniques was 93%. Twenty of 82 patients who underwent both sonography and CT had discordance between the findings of the two examinations. The CT results were correct in a significantly greater number of patients with discordant examinations (17/20 patients [85%]).
CONCLUSION. Helical CT has a significantly higher sensitivity and accuracy than graded compression sonography for the diagnosis of appendicitis in a pediatric and young adult population, particularly in children more than 10 years old.
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The decision to examine a patient with suspected appendicitis with graded compression sonography, CT, or both during the study period was based on the clinical judgment of the referring pediatric surgeon or emergency department physician. Patients with clinically unequivocal appendicitis underwent immediate laparotomy without imaging studies, whereas those with equivocal clinical findings underwent graded compression sonography, CT, or both at the discretion of the referring physician. During the study period, 137 (52%) of 262 patients who underwent laparotomy for suspected appendicitis underwent sonography, CT, or both before surgery.
All sonographic examinations were performed using a 5.0- or 7.5-MHz linear array transducer (model XP10; Acuson, Mountain View, CA). Oblique, transverse, and longitudinal scans of the right lower quadrant were obtained using the graded compression sonographic technique. The cross-sectional diameter of the appendix was measured after the application of graded compression.
Appendicitis was diagnosed on sonography if the appendix was noncompressible with a maximal cross-sectional diameter exceeding 6 mm or if an appendicolith, adjacent complex fluid collection, or mass was noted. All other cases were considered normal. The identification of a normal appendix versus not identifying an appendix had no significance on our examination results. In fact, in most "normal" cases, we did not identify the appendix.
All CT examinations were performed using a helical CT scanner (PQ 5000; Picker International, Cleveland, OH). Helical scanning was performed from the diaphragm to the pubic symphysis in all patients. IV contrast medium (iothalamate meglumine [Conray 43], Mallinckrodt, St. Louis, MO; or iohexol [Omnipaque 240], Sanofi Winthrop, New York, NY) was administered at a dose of 3 mL/kg body weight (maximum dose, 120 mL) in 145 of 153 CT examinations. Opacification of the gastrointestinal tract was achieved through oral or rectal administration of a 3% meglumine diatrizoate solution (Gastrografin; Bristol-Meyers Squibb, Wallingford, CT) in 151 of 153 CT examinations. One hundred twenty-six patients received oral contrast material only, 21 received rectal contrast material only, and four received both oral and rectal contrast material. Collimation and image reconstruction through the upper abdomen ranged from 4 to 10 mm on the basis of patient age (<18 months, 4-mm collimation; 18 months-5 years, 8-mm collimation; >5 years, 10-mm collimation). Variable collimation and image reconstruction were used through the lower abdomen and pelvis. In 101 CT examinations, the collimation and image reconstruction through the lower abdomen and pelvis were 8-10 mm, dependent on age. In 52 CT examinations, a 4-mm collimation and a 4-mm image reconstruction were used to scan the lower abdomen and pelvis, originating approximately 3 cm above the iliac crest as identified on the initial digital radiograph. The route of contrast medium administration for each examination was selected by the attending radiologist monitoring the procedure. The collimation and image reconstruction through the lower abdomen and pelvis were changed from 8-10 to 4 mm during the study period because we found the thinner collimation allows better visualization of anatomic structures in the right lower quadrant.
Appendicitis was diagnosed on CT if the appendix did not fill completely with contrast material or air and exceeded 6 mm in cross-sectional diameter or if an appendicolith, adjacent extraluminal air, complex fluid collection, or mass was noted. The identification of a normal appendix on CT versus not identifying an appendix had no significance on our examination results. In many "normal" cases we did not identify the appendix.
All sonograms and CT scans were obtained under the supervision of and interpreted immediately by one of six pediatric radiologists. The examinations were prospectively interpreted as showing either positive or negative findings for appendicitis, and these findings were made immediately known to the treating physicians. The interpretation was both the official study result and the official radiology report for each patient.
The decision for operative intervention was made by the pediatric surgeon. The final diagnoses were established by surgical and histologic evaluation of the appendix in patients who underwent laparotomy and by clinical follow-up in patients treated nonoperatively.
Measures of test validity (sensitivity, specificity, and accuracy) and
their 95% confidence intervals (CI) were determined for the diagnosis of
appendicitis using graded compression sonography and helical CT. Generalized
estimating equations logistic regression models were used to simultaneously
estimate and compare the sonographic and CT test results. To examine possible
interactions with sex and age, data were stratified by age (
10 years and
>10 years), and this model was run for both strata. The use of 10 years was
an arbitrary decision based on the median age for the study group, which was
between 10 and 11 years. In addition, the patients who underwent both
sonography and CT (n = 82) were stratified into two groups on the
basis of the presence or absence of appendicitis. The McNemar test for paired
data was used to compare either the sensitivity or specificity of sonography
and CT within each of these groups.
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Graded compression sonography had a sensitivity of 78% (95% CI, 69-87%; 65/83), specificity of 93% (95% CI, 90-96%; 215/232), and accuracy of 89% (95% CI, 86-92%; 280/315) for the diagnosis of appendicitis (Table 2). CT had a sensitivity of 95% (95% CI, 90-100%; 58/61), specificity of 93% (95% CI, 89-97%; 86/92), and accuracy of 94% (95% CI, 90-98%; 144/153) for the diagnosis of appendicitis (Table 2). CT had a significantly higher sensitivity (p = 0.009) and accuracy (p = 0.05) than graded compression sonography for the diagnosis of appendicitis in the overall population. The difference in the specificity of the two modalities for the diagnosis of appendicitis was not significant (p = 0.69).
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A comparison of the sensitivity, specificity, and accuracy of graded compression sonography with CT in patients 10 years old or younger versus patients older than 10 years is listed in Table 2. The comparison of patient groups stratified by age showed CT has a significantly higher sensitivity (p = 0.01) and a trend for a higher accuracy (p = 0.09) when compared with sonography for the diagnosis of appendicitis in patients more than 10 years old (Table 2). The difference in specificity between CT and sonography in this age group was not statistically significant. In patients 10 years old or younger, the findings of the two imaging modalities were not significantly different.
The sensitivity, specificity, and accuracy for graded compression sonography and CT in the subgroup of 82 patients who underwent both examinations are listed in Table 3. Analysis of this subgroup of patients revealed discordance between sonography and CT in 20 (24%) of 82 patients (Table 4). The CT diagnosis was correct in 17 (85%) of 20 of these instances when the graded compression sonographic and CT findings were discordant. In the patients with appendicitis (n = 15), the CT results were correct in a significantly greater number of patients when there was discordance between CT and sonography (14/15 [93%], p = 0.002). In addition, CT findings were negative for appendicitis in three (75%) of four patients who did not have appendicitis but who had an initial sonogram with positive findings for appendicitis (Table 4).
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In our patient population, CT was particularly useful in patients with discordant examinations. Discordance between CT and sonographic findings occurred in 20 (24%) of 82 patients undergoing both examinations. The CT diagnosis was correct in 17 (85%) of these cases, whereas the sonographic diagnosis was correct in only three (15%). CT was particularly useful in the diagnosis of appendicitis in patients with normal findings on a sonographic examination. Fifteen patients for whom sonographic and CT findings were discordant had a histopathologic diagnosis of appendicitis. The CT diagnosis was correct in 14 (93%) of these 15 patients.
An important issue that should not be overlooked when evaluating the positive impact of an imaging examination on the assessment of patients with suspected appendicitis is the value of normal findings on an examination using a modality such as CT with a high sensitivity for diagnosing disease. The higher the sensitivity of the imaging examination, the lower the number of false-negative examinations, and, consequently, more trust can be placed on normal findings from that examination by caregivers. It is clear on the basis of the data presented that because of the significantly higher sensitivity of CT when compared with sonography for the diagnosis of appendicitis, a negative CT examination instills greater diagnostic confidence for the exclusion of appendicitis than do negative sonographic findings.
The principal imaging technique for evaluating children with suspected appendicitis over the past decade has been graded compression sonography [2,3,4,5,6,7,8,9,10,11,12]. Sonography can be performed quickly, is generally well tolerated, and uses no ionizing radiation. However, a wide range of values for the sensitivity and specificity of graded compression sonography has been reported for the diagnosis of appendicitis because of the large degree of operator dependency inherent to the technique, and the varied methodology of prior reports [2, 4,5,6, 8,9,10,11,12]. The sonographic diagnosis of appendicitis can be difficult in obese individuals because visualization of the appendiceal region may be limited. In addition, other reported potential pitfalls in the sonographic diagnosis of appendicitis include focal appendicitis limited to the distal appendix, retrocecal appendicitis, and perforated appendicitis [21]. An important factor accounting for the variability in diagnostic accuracy reported with graded compression sonography is that many sonographic examinations are not performed by radiologists having dedicated expertise with the procedure. At many university hospitals, after-hours imaging studies may be obtained and interpreted by residents or fellows. Moreover, many patients with appendicitis are treated at community hospitals and the sonographic examination is performed by a general radiologist. For sonography to be successful on a large scale, a high degree of accuracy must be seen when performed by radiologists with various degrees of expertise. On the basis of the wide range of reported sensitivity and specificity values of sonography for the diagnosis of appendicitis in various series, this does not appear to be the case. Another factor that likely accounts for the wide range in reported sensitivity and specificity of graded compression sonography for the diagnosis of appendicitis across various series is that in some reports all patients with suspected appendicitis were examined on sonography, whereas in others only patients with an equivocal clinical diagnosis underwent imaging [2, 4,5,6, 8,9,10,11,12]. This practice may result in a larger percentage of atypical, early, or more subtle cases of appendicitis in the population undergoing selective imaging, thereby decreasing the apparent accuracy of the test.
The superiority of helical CT over graded compression sonography for the diagnosis of appendicitis in the present study was principally noted in patients more than 10 years old. CT showed a significantly higher sensitivity than sonography (97% versus 71%, p = 0.01) in this subgroup of patients, whereas the two imaging modalities were not significantly different in patients 10 years old or younger. This finding is not surprising given that graded compression sonography is typically easier to perform in individuals with a smaller body habitus, a subgroup one would expect to see more frequently in a younger age group. Conversely, it could be speculated that the paucity of body fat in younger patients may result in increased difficulty diagnosing appendicitis because of the inability to readily separate the appendix from adjacent structures. However, caution should be used in speculating that graded compression sonography should be the study of choice in younger children. Even though no statistically significant differences were seen between the sensitivity of graded compression sonography versus that of CT for the diagnosis of appendicitis in children less than 10 years old, the sensitivity of CT was higher than that of sonography in this age group (93% versus 84%). One possible reason that these values are not significant in the present series is that by stratifying the study group by patient age, the sample size was decreased. Therefore, a greater difference in the value between the two modalities is required to reach statistical significance.
A limitation of this study is that it did not permit a true comparison of sonography versus CT for the diagnosis of appendicitis because all patients did not undergo both imaging examinations. In addition, in the subgroup of patients who underwent sonography and CT, sonography was always performed first, and the radiologist monitoring the CT examination may have been the same person who performed the sonographic examination. Therefore, the radiologist interpreting the CT examination was not blinded to the sonographic findings. However, this procedure reflects how these two imaging examinations are used in our clinical practice. An additional limitation of the present study is that the scanning protocol for CT was not standardized in all children during the study period. The CT protocol was altered during the study period to include the use of a thin collimation through the lower abdomen and pelvis and the use of rectal rather than oral contrast material for gastrointestinal tract opacification.
There are several valid concerns regarding the use of helical CT as the primary imaging modality in children with suspected appendicitis. These concerns include the greater cost of CT versus sonography, the exposure to ionizing radiation, and the exposure to contrast agents. However, these concerns may be better addressed by placing more emphasis on the use of clinical variables for stratifying risk of disease and allowing more selective use of imaging [22]. Most patients with suspected appendicitis undergoing cross-sectional imaging do not have the disease. In the present study, only 26% (83/315) of patients undergoing graded compression sonography and 40% (61/153) of patients undergoing helical CT for suspected appendicitis had appendicitis. The patients who can be considered, on the basis of physical examination or laboratory findings, as having a very low or very high risk of disease should not require cross-sectional imaging [7]. Rather than using a less expensive but potentially less sensitive modality such as sonography, selective CT may improve clinical decision-making because of its higher accuracy. With the implementation of a more selective system for imaging, the utilization, cost, and patient risk would presumably decline because of reductions in the number of imaging examinations being performed.
In conclusion, helical CT has a high accuracy for the diagnosis of appendicitis in a pediatric and young adult population. CT was superior to graded compression sonography for the diagnosis of appendicitis particularly in patients more than 10 years old, for whom CT had a significantly higher sensitivity and accuracy than sonography.
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