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Pediatric Imaging |
1 From the Department of Radiology, Division of Pediatric Radiology, New York University Medical Center, 560 First Ave, New York, NY 10016. Received November 20, 2000; revision requested January 10, 2001; revision received February 12; accepted March 8. Address correspondence to N.R.F. (e-mail: nfeff@aol.com).
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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MATERIALS AND METHODS: Ninety-three abdominal-pelvic contrast material–enhanced CT scans obtained during 6 years in 54 girls and 39 boys (age range, 1–18 years) with right lower quadrant pain were retrospectively reviewed. The detected abnormal findings were recorded as being in the region above the upper pole of the right kidney, between the upper pole of the right kidney and the lower pole of the right kidney (RLP), or below the iliac crest. Sensitivity, specificity, and positive and negative predictive values were calculated. 
2 analysis was performed to determine whether there were significant differences among patient groups according to region of detected disease.
RESULTS: Fifty-five scans were abnormal: 38 showed appendicitis; and 17, other diseases. No scans, except two that showed pneumonia, had key findings above the RLP. Nineteen scans showed key findings between the RLP and the iliac crest. Thirty-three scans had diagnostic findings only below the iliac crest. The sensitivity (97%), specificity (93%), positive predictive value (90%), and negative predictive value (98%) of interpretation with all images for the diagnosis of appendicitis were the same as those of interpretation with only the focused images.
CONCLUSION: CT performed to diagnose appendicitis can be limited to the region below the RLP.
Index terms: Appendicitis, 751.291 • Appendix, CT, 751.12112, 751.12114, 751.12115
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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To our knowledge, there is no definitive CT technique for the evaluation of appendicitis in children. The findings of Rao et al (14) and Rhea et al (15) suggest that CT for evaluation of suspected appendicitis in adults can be limited to the right lower quadrant with use of rectal contrast material. Garcia Peña et al (4,11) obtained similar results in a pediatric population by using limited CT with rectal contrast material. However, many institutions continue to use oral and intravenous contrast materials rather than rectal contrast material. The purpose of our study was to determine the accuracy of limited CT with oral and intravenous contrast materials in the diagnosis of appendicitis without compromising the diagnosis of other substantial abdominal diseases, which, to our knowledge, have not yet been described in the literature.
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MATERIALS AND METHODS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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Of 163 patients in whom CT scans were obtained for assessment of abdominal pain during the study period, 98 fulfilled the selection criteria. Sixty-five patients were excluded from the study for the following reasons: findings positive for human immunodeficiency virus (n = 7), sickle cell disease (n = 3), nephrotic syndrome (n = 4), suspected malignancy (n = 12), congenital heart disease (n = 4), Crohn disease (n = 1), chronic anemia (n = 2), flank pain (n = 6), hematuria (n = 5), elevated amylase (n = 4), hepatobiliary disease (n = 9), and fever of unknown origin (n = 8). Of the remaining 98 patients who underwent CT, five had undergone CT without intravenous contrast material and thus were excluded from the study for consistency. Thus, the study population was reduced to 93 patients.
Of the 93 patients included in the study, 14 initially had undergone US of the right lower quadrant, and nine of these 14 patients were female adolescents in whom pelvic sonograms also had been obtained. The US examinations had yielded results that were inconsistent with the clinical presentation, so a CT scan was requested by the attending physician. At our institution, there has been a trend toward performing CT as the primary imaging modality for the evaluation of suspected appendicitis in patients with lower abdominal pain. This study was not meant to be a comparison of US and CT, but rather it was conducted to evaluate the accuracy of focused CT in patients in whom CT had been performed for clinical reasons.
Thirty-nine patients were male, and 54 were female. They ranged in age from 0 to 18 years. Their median age was 13 years (14 years for female patients and 10 years for male patients). Eleven (12%) patients (four male and seven female) were aged 4 years or younger. Thirty-five (38%) patients (23 male and 12 female) were aged 5–12 years. Forty-seven (51%) patients (12 male and 35 female) were aged 13–18 years (Figure).
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Seventy-six CT scans had been obtained with a helical technique, and 17 had been obtained with a nonhelical technique. In the nonhelical CT group, collimation had varied between 5 and 10 mm for the region above the iliac crest and 5 mm below the iliac crest at intervals of 8 mm. In the helical group, collimation in the upper abdomen had varied between 5 and 10 mm and between 5 and 7 mm in the region below the iliac crest, with a 0–1-mm section overlap. The helical CT examinations had been performed with pitches ranging from 1.0 to 2.0: 37 studies with a pitch of 1.0, 23 with a pitch of 1.6, 10 with a pitch 1.5, two with a pitch of 1.4, two with a pitch of 1.8, and two with a pitch of 2.0. Forty-nine of the helical images had been acquired by using 7-mm section thickness in the upper part of the abdomen and 5-mm section thickness in the lower part of the abdomen.
The images were independently interpreted by two experienced pediatric radiologists (N.B.G., K.J.R.), and discordant readings (n = 4) were resolved at consensus with a third pediatric radiologist (L.P.P.). The CT scans were divided into three anatomic regions: the area above the lower pole of the right kidney, the area between the lower pole of the right kidney and the iliac crest, and the area below the iliac crest. The images of each individual region were interpreted, beginning with the most inferior region, to simulate an examination that consisted of images of only those regions. Initially, only those images in the inferior region were available to the radiologist. After data were recorded, images of the middle region were added, followed by images of the most cephalad region. The importance of the findings in each region was assigned a grade from 1 to 4: Grade 1 meant the finding was necessary for diagnosis; grade 2, the finding was additional information to confirm impression; grade 3, the finding was nonspecific; and grade 4, the finding was normal.
Evaluation of the scans also entailed recording technical parameters, including opacification achieved with oral and intravenous contrast materials, identification and localization of a normal appendix, anatomic location of the lower pole of the right kidney according to vertebral body level, and diagnosis of other diseases in the studies that were negative for appendicitis. The diagnosis of appendicitis was based on standard CT criteria, including a peripherally enhancing fluid-filled tubular structure with a diameter greater than 8 mm in the absence of a normal appendix, the identification of an appendicolith in association with inflammatory changes, and/or inflammatory changes in the right lower quadrant without visualization of a normal or abnormal appendix (16). Correlations between the CT results and the surgical findings and pathology reports were performed by two authors (N.R.F., M.M.A.) who were not directly involved in the interpretation of the images. Patients who were discharged without surgical intervention were assumed not to have appendicitis, and thus, follow-up was not feasible in view of the retrospective nature of the study; none of these patients was readmitted to our hospital.
To validate our baseline accuracy for the diagnosis of appendicitis, sensitivity, specificity, accuracy, and positive and negative predictive values for the CT-based diagnosis of acute appendicitis in this series were calculated on the basis of the interpretation of the entire scan. Sensitivity, specificity, accuracy, and positive and negative predictive values were calculated also on the basis of the interpretation of scan findings in only the two most inferior regions. 2 analysis was used to ascertain whether there was a significant difference between the population in which disease was identified above the lower pole of the right kidney and that in which disease was identified below the lower pole of the right kidney. In addition, sensitivity and specificity values were calculated for studies performed with helical versus nonhelical CT.
One author (N.R.F.) subsequently reviewed the initial image interpretations and delayed images, if available, for those cases considered to be false-positive and false-negative. The radiologists were blinded to this information during the retrospective interpretations.
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RESULTS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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Thirty-four CT scans were true-positive for appendicitis, four were false-positive, and one was false-negative. These results yielded a CT accuracy of 95% (95% CI: 91%, 98%); sensitivity of 97% (95% CI: 93%, 100%), specificity of 93% (95% CI: 88%, 98%); positive predictive value of 90% (95% CI: 83%, 96%), and negative predictive value of 98% (95% CI: 96%, 100%). These values are similar to those reported in the literature (13). The results were the same for interpretation of the scans of only the region below the lower pole of the right kidney.
Of the 17 scans acquired with the nonhelical technique, six were true-positive for appendicitis, eight were true-negative, two were false-positive, and one was false-negative. The sensitivity and specificity of the nonhelical CT scans were 86% and 80%, respectively. Of the 76 scans acquired helically, 28 were true-positive, 46 were true-negative, two were false-positive, and none was false-negative. The helical CT scans had a sensitivity of 100% and a specificity of 96%. At 2 analysis, there was a statistically significant difference in the sensitivity (P < .005) and specificity (P < .01) of the scans acquired with nonhelical CT, as compared with these values for the larger group of scans acquired with helical CT.
On 20 CT scans, oral contrast material did not opacify the cecum. The single false-negative CT scan and the four false-positive CT scans showed no oral contrast material in the ileocecal region.
Review of the delayed CT scans obtained during the initial imaging examination, for analysis of one of the false-positive cases, demonstrated contrast material opacification in the structure recorded as an inflamed appendix. Review of the delayed scans for analysis of the false-negative case revealed an absence of contrast material opacification of the structure thought to represent nonopacified distal small bowel at retrospective scan interpretation for purposes of the study.
The distribution of the diseases according to anatomic region is shown in Table 2. For the 38 CT-based diagnoses of appendicitis, the findings that were sufficient to confidently make the diagnosis were located below the iliac crest in 26 cases. In the remaining 12 cases of appendicitis, imaging between the iliac crest and the lower pole of the right kidney was required to make the diagnosis. In these 12 cases, the two radiologists graded the findings as either necessary to make the diagnosis or additional information to confirm the impression. The relevant findings for seven of the 17 alternative CT-based diagnoses were located below the iliac crest. In another seven of the alternative diagnoses, the relevant findings were located between the iliac crest and the lower pole of the right kidney. One diagnosis of colitis required imaging above the lower pole of the right kidney, and two cases of pneumonia were diagnosed by using the most cephalad images that included the lung bases.
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2 analysis of these data revealed that there was a statistically significant difference (P < .001) between the population in which disease was identified above the lower pole of the right kidney and that in which disease was identified below the lower pole of the right kidney.
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Analysis of the scans for localization of the lower pole of the right kidney revealed that there was a slight variation based on age. The lower pole of the right kidney was located approximately at the level of the middle aspect of the L3 vertebral body in most patients younger than 10 years. In the patients older than 10 years, the location of the lower pole of the right kidney varied slightly between the top and the middle aspect of the L4 vertebral body.
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DISCUSSION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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The radiation exposure to the gonads remains unchanged with this technique. Further investigation regarding the usefulness of reduced milliampere levels for the evaluation of appendicitis may be a means of addressing this issue. To our knowledge, there have been no reported investigations of a limited CT technique with oral and intravenous contrast materials.
In our series, all of the cases of appendicitis were diagnosed by using images of the region below the lower pole of the right kidney. Conversely, no case of appendicitis would have been missed if the images had been limited to the lower part of the abdomen and pelvis beginning at the lower pole of the right kidney. We recognize that there may be unusual locations of the appendix, such as the right upper quadrant and the left lower quadrant in cases of malrotation or incomplete rotation. However, these are rare instances that probably should not be factors that limit the use of focused CT, because additional images should be obtained if the focused study proves to be nondiagnostic or suggests disease in the upper part of the abdomen.
CT has been advocated as a means of not only effectively diagnosing appendicitis but also establishing alternative diagnoses that may manifest in a similar manner (13,17). Some authors (13,17) have suggested that images of the middle and upper parts of the abdomen are necessary to depict all potential diseases in both adults and children. In our series, all but three cases of an alternative diagnosis were identified on images of the region below the lower pole of the right kidney. Two of these three cases were pneumonia, which should not require abdominal CT to make the diagnosis. Basilar pneumonias are known to mimic acute appendicitis secondary to patterns of pain referral (18). However, the presence of pneumonia does not exclude the possibility of concurrent appendicitis, and a limited CT scan of the lower part of the abdomen and pelvis may be warranted.
The third case that required imaging above the lower pole of the right kidney was that of diffuse colitis. Findings suggestive of this diagnosis were present on images obtained below the lower pole of the right kidney, and these data typically prompt additional imaging of the upper abdomen. We found an alternative diagnosis in 17 (29%) of the 58 patients who did not have appendicitis. However, our findings suggest that the alternative diagnoses also were located predominantly in the lower part of the abdomen. This disparity likely reflects the highly specific selection requirements applied in our series and demonstrates the importance of rigorous clinical patient screening for the optimal success of a limited CT study.
It seems that if CT is to become the primary imaging modality for the evaluation of suspected appendicitis in children, then the issue of radiation dose must be addressed, particularly in the adolescent female population. The age and sex distribution in our series suggests that a substantial proportion of the population of patients with suspected appendicitis comprises female adolescents; they represented greater than one-third of our study cases. Thirty-five of the 93 patients were female patients aged 13–18 years, and 74% of the overall adolescent population were female patients. The diagnoses were almost evenly split between appendicitis (eight cases) and adnexal cysts (six cases) in the female adolescent population. With this in mind, and with the ultimate goal of reducing exposure to ionizing radiation, it may be interesting to prospectively look more closely at the use of US as the initial means of imaging in the female adolescent population, with CT reserved for the more complex cases in these patients.
It is interesting that the four false-positive cases and one false-negative case did not result from interpreting CT scans of a limited region. Rather, the four false-positive scans and the single false-negative scan showed no oral contrast material in the ileocecal region. As has been reported in the past (2), fluid-filled loops of terminal ileum were misinterpreted as distended inflamed appendices in all four false-positive cases. This was confirmed in one of the cases in which delayed images of the right lower quadrant demonstrated contrast material opacification of the structure suspected to be an abnormal appendix. The delayed images were not included in the interpretations performed in this study, but they had been reviewed at the initial (prospective) image interpretations.
The four false-positive scans were initially interpreted (for clinical management) as normal, in contrast to the interpretation of abnormal in the retrospective reading. This explains the management protocol of observing patients with positive CT results and discharging them without surgery. Conversely, in the false-negative case, an abnormally dilated fluid-filled appendix was mistaken for unopacified loops of terminal ileum. Given the technical limitations of these five examinations, it is possible that the additional information obtained by conferring with the clinicians influenced the initial image interpretations. This observation, in conjunction with the relatively low sensitivity for consistent visualization of a normal appendix in children, raises questions regarding the use of CT without oral contrast material (19–21).
The majority of the CT examinations were performed by using a helical technique. The sensitivity and specificity of nonhelical CT for the diagnosis of appendicitis was lower: 86% and 80%, respectively. These numbers are lower than those reported in the literature (2,10,12,13) probably because of the small sample size (n = 17).
This study had several limitations. We had a relatively limited number of patients in our series. The majority of cases of suspected appendicitis during the initial portion of our 6-year study period were more often evaluated by using only US, with a more recent trend toward increased use of CT only. Second, patient follow-up for negative CT scans was not feasible in this retrospective study. Patients discharged without surgery were presumed not to have appendicitis. Since we cannot confirm that these patients were not readmitted to another hospital and treated for appendicitis, the sensitivities and specificities may be overestimated.
Another limitation may be the relatively small number of patients younger than 4 years (n = 11), who made up only 12% of the study population. Since young children with appendicitis may have difficulty describing their symptoms or localizing their pain, it could be difficult to apply the careful clinical screening that we believe is imperative to the success of a focused CT technique in this population. Although no disease above the lower pole of the right kidney was missed in these patients, additional investigation is probably warranted. Finally, the CT protocols assessed varied with the evolving technology of this modality, particularly with regard to section thickness and degrees of overlap. However, these variations should not affect the notable absence of disease in the region above the lower pole of the right kidney.
In conclusion, our data suggest that there is a role for focused CT with oral and intravenous contrast materials in the evaluation of suspected appendicitis in children. The caveat to this approach is the careful clinical screening of patients that is needed to exclude those with preexisting medical conditions or positive laboratory data suggestive of disease other than acute appendicitis. A more standardized prospective study may enable the findings in our study to be confirmed.
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FOOTNOTES |
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REFERENCES |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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