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1
Department of Radiology, Founders House, Massachusetts General Hospital and
Harvard Medical School, 55 Fruit St., Boston, MA 02114.
2
Department of Pediatric Surgery, Massachusetts General Hospital and Harvard
Medical School, Boston, MA 02114.
3
Department of Pediatrics, Massachusetts General Hospital and Harvard Medical
School, Boston, MA 02114.
Received May 3, 2000;
accepted after revision June 22, 2000.
Presented at the annual meeting of the American Roentgen Ray Society,
Washington, DC, May 2000.
Abstract
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MATERIALS AND METHODS. Between November 1995 and July 1999, 199 pediatric patients (1-18 years old; mean age, 12 years) were examined with focused CT in the emergency division for suspected appendicitis. The findings on CT were compared with the findings at surgery, pathology, and clinical follow-up.
RESULTS. There were 64 true-positive CT scans, two false-negative, 128 true-negative, one false-positive, and four indeterminate. Seventy-four patients underwent appendectomy, with a negative appendectomy rate of 9%. One hundred twenty-five patients without appendicitis were treated nonoperatively. The true-positive rate was 32%, true-negative rate was 64%, sensitivity was 97%, specificity was 99%, positive predictive value was 98%, negative predictive value was 98%, and overall accuracy was 96%. Pediatric patients tolerated the procedure well. Colonic contrast material saved time and provided improved identification of the cecum and appendix. In 62 patients without appendicitis, focused CT provided alternative diagnoses.
CONCLUSION. Focused CT appears to be nearly as accurate in pediatric patients as in adults. Focused CT provided alternative diagnoses in 48% of the patients for whom CT findings were negative for appendicitis.
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Noninvasive imaging has been most commonly reserved for patients with unclear diagnoses; patients with a more typical clinical presentation of appendicitis are taken for appendectomy [9]. The use of abdominal sonography has been associated with sensitivities in the range of 75-95% in low and medium clinical risk groups and with slightly lower sensitivity in high-risk groups [10,11,12,13]. Sonography is an operator-dependent examination, and statistics vary according to the skills of the person performing the procedure. Investigations have reported that the use of abdominal sonography in this setting does not result in an early diagnosis of appendicitis or a reduction in complications, and moreover, has been associated with a delay to surgery and an increase in hospital charges [14]. Direct comparisons in adults favor CT over sonography [15].
In recent years, the use of CT for the diagnosis of appendicitis has been popularized [16] using a variety of techniques, including unenhanced CT [17,18,19], oral and IV contrast-enhanced CT [20,21,22], and rectal contrast-enhanced CT with or without oral contrast material [23, 24]. Our department has advocated the use of focused CT of the pelvis and abdomen with colonic contrast material and a helical technique, which has proven to be an accurate and effective method for the diagnosis of appendicitis in adults [23]. In certain settings, some authors recommend the use of abdominal sonography or unenhanced radiography of the abdomen before or in lieu of a CT examination [25]. The CT signs of appendicitis in adults that are reported in the literature include appendicolith, intramural or periappendiceal air, fat stranding, enlarged nonopacified appendix, focal cecal apical thickening, adenopathy, arrowhead sign, paracolic gutter fluid, abscess, cecal bar, phlegmon, and bowel wall thickening [26,27,28,29]. CT for the diagnosis of appendicitis is technically limited [30], especially when the appendix is borderline abnormal or is not well seen [31], although the operator dependence is thought to be less than with sonography.
In recent years, the use of CT in the diagnosis of suspected appendicitis in sick children has been increasingly reported in the literature [32, 33]. At our hospital, the use of focused CT with a helical scanning technique for the diagnosis of appendicitis in adults is routine and, recently, has been made routine for examining sick children with suspected appendicitis. Garcia-Pena et al. [2] recently described prospective results for 177 children with suspected appendicitis, of which 139 underwent sonography and 108, CT. CT achieved higher sensitivity and negative predictive value than sonography, although sonography had a high positive predictive value [2]. The use of appendiceal CT in adults and children has resulted in decreased negative appendectomies rates, decreasing the number of nontherapeutic operations on patients who do not have appendicitis [34]. The ability of CT to help radiologists make early diagnoses has decreased the rate of appendiceal perforation [34].
Recent publications have reported a high accuracy for focused appendiceal helical CT using colonic contrast material in the evaluation of suspected appendicitis in adults [23, 24] and, more recently, in smaller studies in children [2]. Evaluation of suspected appendicitis in children is also technically more challenging than in adults, in part because less intraabdominal fat is present. To determine the accuracy and feasibility of focused helical CT for children compared with adults, we carried out a retrospective investigation.
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Statistics
The findings on CT were compared with the findings at surgery, discharge,
or follow-up. If a child did not undergo surgery during the admission,
evaluation of medical records was obtained at follow-up. No children were
known to have later-diagnosed appendicitis in whom it was not diagnosed during
the initial presentation or admission. Patients with pathology-proven
appendicitis who were diagnosed with appendicitis on CT were categorized as
true-positive cases. Patients with pathology-proven appendicitis who were
diagnosed on CT as not having appendicitis were categorized as false-negative
cases. Patients without pathology-proven appendicitis who were diagnosed as
not having appendicitis on CT were categorized as true-negative cases.
Patients without pathology-proven appendicitis who were diagnosed as having
appendicitis on CT were categorized as false-positive cases. Values of
sensitivity, specificity, positive predictive value, and negative predictive
value were calculated. We found four equivocal CT interpretations, and these
patients were considered a separate group (but were counted as inaccurate
results for the determination of overall accuracy).
Technique for Performing Focused Helical CT
Rectal contrast material (40 mL of Gastrografin [meglumine diatrizoate];
Bristol-Myers Squibb, Wallingford, CT, diluted in 1000 mL of normal saline
solution) was administered through a soft pediatric rectal tube. Volume was
estimated according to the size of the child. An adult-sized child would
receive approximately 1000 mL as tolerated. A child of grade school age (5-13
years old) would typically receive 500 mL of rectal contrast material.
Contrast material was instilled with the patient in the right lateral
decubitus position to facilitate movement into the right lower quadrant.
Contrast material was allowed to fill the colon through gravity (3-4 feet
[90-120 cm] above the table) and was not forcefully instilled. If cramps
(bowel spasm) ensued, a recess was taken until relief of symptoms occurred.
Most patients tolerated the procedure well. Most children were accompanied by
a parent or guardian during the examination.
Focused abdominal CT (Hi-Speed helical CT Scanner; General Electric Medical Systems, Milwaukee, WI) was performed from the level of L3 on the scout image to the top of the acetabulum using 3- or 5-mm collimation with a pitch of 1.5 mm and image spacing at 3-5 mm, depending on the size of the patient. If contrast material was not seen in the right colon, saline was instilled through the rectum. In some cases, images were reformatted at 1-mm spacing to provide better identification of the appendix and to provide better quality sagittal and coronal images.
Review and Interpretation of CT Images
The findings on CT were tallied, including the final diagnosis, alternative
diagnosis (if any), and presence of signs of appendicitis: nonfilling
appendix, appendicolith, fat stranding in the right lower quadrant, fluid
collection in the right lower quadrant, appendix diameter greater than 6 mm or
appendiceal thickening, or cecal wall thickening or arrowhead sign. CT studies
were considered positive, negative, or equivocal for appendicitis on the basis
of the report. In instances in which a definitive result was not given in the
report or the evaluation was unclear, an assessment of "equivocal"
was given. CT images of patients with false-positive, false-negative, and
equivocal results were reviewed individually by two of the authors. Results of
5% of imaging examinations were compared at random with electronic reports to
ensure accuracy, which was 100%.
Notation was made of signs of appendicitis listed in the report. By convention, signs of inflammation or abscess—including phlegmon, fat-stranding, nonfilling of the appendix despite adequate filling of the cecum with contrast material, free fluid, and an enlarged or thickened appendix—are considered highly suspicious for appendicitis. If a sign was not listed, it was assumed to not be present. If the CT sign was listed as "possible" or "cannot exclude," it was assumed to be equivocal.
Review and Interpretation of Abdominal Radiography Results
Abdominal radiography studies were considered positive (i.e., helpful) if
they listed one of the following findings: appendicolith, right lower quadrant
adynamic ileus, or another cause identified to account for the patient's
symptoms and presentation. The remaining abdominal radiographic studies were
considered negative (i.e., not helpful). Patients who underwent only abdominal
radiography (who did not undergo CT) were not identified or evaluated. There
is no specific protocol for which imaging tests should be requested or in
which order they should occur. Rather, the inclusion of conventional
radiography before or after CT is based on the preference of the individual
referring physician.
Review and Interpretation of Abdominal Sonography Results
Abdominal and combined pelvic and abdominal sonography studies were
considered positive if an abnormal appendix was identified (classic
sonographic signs of appendicitis are noncompressible or enlarged appendix
> 6 mm in cross-sectional diameter). If a normal appendix was identified, a
negative result was ascribed. If the appendix was listed as "not
identified" or equivocal, the imaging study was determined to be
equivocal for appendicitis, and CT was then performed as in the algorithm
proposed by Garcia-Pena et al.
[2]. Patients who had only
abdominal sonography (who did not undergo CT) were not identified or
evaluated.
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CT was interpreted prospectively by the attending radiologist as positive for appendicitis in 65 children (33%), negative in 130 children (65%), and equivocal in four children (2%). On the basis of the comparison with surgical findings and follow-up, there were 64 true-positive CT scans (Fig. 1), two false-negative (Fig. 2), 128 true-negative (Fig. 3), one false-positive (Fig. 4), and four equivocal (Table 1). Of the four equivocal cases, one patient had acute appendicitis at surgery, one did not have acute appendicitis at surgery, and the remaining two did not undergo surgery.
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Seventy-four children underwent appendectomy, with a negative appendicitis rate of 9% (7 children). Of the seven children without appendicitis at surgery, one was evaluated as false-positive, five were true-negative, and one was equivocal. Sixty-seven children had acute appendicitis at surgery; 64 were true-positive, two were false-negative, and one was equivocal. Open appendectomy or laparotomy was performed in 66 (89%) of these 74 patients, and laparoscopic surgery was performed in the remaining eight patients (11%). One hundred twenty-five patients without appendicitis were treated nonoperatively, with 123 true-negative results and two equivocal results. The overall CT true-positive rate was 32%, true-negative rate was 64%, sensitivity was 97%, specificity was 99%, positive predictive value was 98%, negative predictive value was 98%, and overall accuracy was 96% (Table 1).
CT signs considered positive for appendicitis were evaluated individually on the basis of their communication in radiology reports. Table 1 lists the signs considered positive for appendicitis; the number of patients whose results were true-positive, true-negative, false-positive, and false-negative; and the sensitivity, specificity, positive predictive value, and negative predictive value of each sign. Results of CT with colonic contrast material for the evaluation of suspected appendicitis in sick children reveal accuracy and sensitivity of focused abdominal CT in pediatric patients to be only slightly less than that for adult patients. The most sensitive CT signs for acute appendicitis in children include nonfilling of the appendix, periappendiceal fat stranding, and an appendiceal diameter greater than 6 mm. The identification of a calcification that might represent an appendicolith and the finding of pelvic free fluid were less sensitive signs for acute appendicitis.
Other findings on CT that were considered suggestive of appendicitis but not diagnostic in the original reports were also noted, including right lower quadrant adenopathy (36 cases), small-bowel wall thickening (6 cases), and nonfilling of the distal appendix (suggesting distal or "tip" appendicitis, 4 cases). Seven patients were noted to have phlegmon or abscess at the time of initial CT, which are signs of appendiceal rupture.
In 62 patients (31% overall, 48% of CT studies with negative findings), focused helical CT provided alternative diagnoses (Table 2), including inflammatory bowel disease such as ileitis or colitis (22 patients, 35% of alternative diagnoses), mesenteric adenitis (17 patients, 27%), and ovarian cyst with (4 patients, 6%) or without (8 patients, 13%) rupture.
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Abdominal radiography with the patient in the supine position and with or without an upright view was performed in 98 children. The abdominal radiograph was considered helpful in six of the patients (6%; signs suggestive of appendicitis, including calcified stone in the right pelvis or a right lower quadrant focal ileus). None of the abdominal radiography results were considered diagnostic by radiologists or surgeons. The abdominal radiograph was considered "not helpful" in 92 patients (94%).
Abdominal or combined abdominopelvic sonography was performed in 32 children who also underwent focused helical CT. Three of the sonographic examinations were true-negative, two were false-positive, one was false-negative, none was true-positive, and 26 were indeterminate.
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The most sensitive CT signs for acute appendicitis in sick children include nonfilling of the appendix, periappendiceal fat stranding, and an appendiceal diameter greater than 6 mm. By comparison, the identification of a calcification that might represent an appendicolith and the finding of pelvic free fluid were less sensitive signs for acute appendicitis. All signs reviewed, with the exception of pelvic free fluid, had a high positive predictive value. Although some reports have indicated specific signs of appendicitis on CT [32, 33], to our knowledge this study is the first evaluation of CT signs of appendicitis in children.
Focused helical CT also provided several alternative diagnoses that avoided unnecessary surgery for several patients. Many of the children with alternative diagnoses received specific therapy based on the CT result, in many patients obviating further diagnostic workup. Because of the focused nature of the appendiceal CT protocol and to save radiation, the entire abdomen is not visualized, and diagnoses other than appendicitis may be overlooked in portions of the abdomen not included in the scan. Therefore, the focused scans should be extended when clinically indicated.
The use of CT in pediatric patients should not add to hospital costs. A recent report from our hospital indicated that before the use of CT, 208 pediatric patients were admitted with the diagnosis of suspected appendicitis [35]. Seventy percent of these patients had an appendectomy, and of those with appendectomy, 13% did not have acute appendicitis. Our investigation indicates that 9% of patients taken to surgery did not have acute appendicitis. Taking into account the reduced number of patients having nontherapeutic surgery, decreased observation time in the hospital, and the addition of CT to the patients' examination, there are small cost savings to the hospital. Specifically, using the costs previously reported, a nontherapeutic appendectomy costs $4749, 1 day in the hospital for low acuity nursing care and room costs $405, and CT for appendicitis costs $233. Before CT, the nontherapeutic surgery cost per 100 patients was $61,737 (13 patients x $4749 per patient). After CT, the nontherapeutic surgery cost per 100 patients was $42,741 (9 patients x $4749 per patient). Previously calculated savings in costs of observation would be approximately $7290 per 100 patients [35]. The CT cost per 100 patients was $23,300 (100 patients x $233 per patient). By considering only change in surgical, observation, and CT costs, almost $3,000 savings in hospital total costs (per 100 patients) should result from the use of CT. Garcia-Pena et al. [36] reported a cost savings of $2018 per patient when abdominal CT is performed on all patients with suspected appendicitis and those without appendicitis are discharged. CT of the entire abdomen was performed in that cohort, and the authors note that focused helical CT with colonic contrast material would likely increase sensitivity and decrease the patient's radiation dose [36]. A more complete investigation of cost savings when using focused helical CT with colonic contrast material for pediatric patients with suspected appendicitis is ongoing.
Our study suggests that abdominal radiography in this cohort was not particularly helpful in comparison with focused helical CT. There were no true-positive sonography results. The reason is unclear but may be related to operator variability in the performance of appendiceal sonography at various medical centers. Garcia-Pena et al. [2] reported a sensitivity of 44%, a specificity of 93%, and an accuracy of 76% in a larger sonography cohort than in our study. In that group, the equivocal rate for sonography was much smaller than in our study (13/139 patients).
Our study has some limitations. The data obtained are retrospective and depend on data provided in the medical record. The evaluation of abdominal sonography and radiography may be affected by selection bias. That is, in most cases these examinations were used for triage, and patients having definitive or alternative diagnoses would likely not have received CT as well as sonography and radiography. However, some patients received radiography or sonography after CT. Additionally, not all CT signs may have been commented on in all instances. This could theoretically impose bias on specificity and negative predictive value but likely has a small impact on sensitivity and positive predictive value because we hypothesize that the presence of signs is more likely to be mentioned than their absence.
In summary, focused helical CT appears to be as accurate in pediatric patients as in adults. Focused helical CT provided alternative diagnoses in 48% of patients with CT findings negative for appendicitis.
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