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1
Department of Radiology, Pennsylvania State University College of Medicine,
Milton S. Hershey Medical Center, 500 University Dr., Hershey, PA 17033.
2
116 Racehorse Dr., Jonestown, PA 17038.
3
Department of Emergency Medicine, Pennsylvania State University College of
Medicine, Hershey, PA 17033.
4
Department of Pathology, Pennsylvania State University College of Medicine,
Hershey, PA 17033.
5
Department of Health Evaluation Sciences, Pennsylvania State University
College of Medicine, Hershey, PA 17033.
Received August 18, 2000;
accepted after revision October 2, 2000.
Address correspondence to S. W. Wise.
Abstract
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MATERIALS AND METHODS. One hundred patients with clinically suspected acute appendicitis were examined with sonography, unenhanced focused appendiceal CT, complete abdominopelvic CT using IV contrast material, focused appendiceal CT with colonic contrast material, and repeated sonography with colonic contrast material. Each sonogram was videotaped for subsequent interpretation by three radiologists and two sonographers. The mean sensitivity, specificity, positive and negative predictive values, inter- and intraobserver variability, and diagnostic confidence scores of all observers were used for comparative performance assessments. The three CT examinations were filmed and interpreted separately by four radiologists. Patient discomfort was assessed on a 10-point scale for each radiologic study. Diagnoses were confirmed by pathologic evaluation of resected appendixes or clinical follow-up for a minimum of 3 months after presentation.
RESULTS. Twenty-four of the 100 patients had positive findings for
acute appendicitis. Both sonographic techniques had high specificity (85-89%)
and comparable accuracy (73-75%) but low sensitivity (33-35%) and inter- and
intraobserver variability (
= 0.15-0.20 and 0.39-0.42, respectively).
Unenhanced focused appendiceal CT, abdominopelvic CT, and focused appendiceal
CT with colonic contrast material all significantly outperformed sonography
(p <0.0001), with sensitivities of 78%, 72%, and 80%;
specificities of 86%, 91%, and 87%; and accuracies of 84%, 87%, and 85%,
respectively. Abdominopelvic CT gave the greatest confidence in cases with
negative findings (p = 0.001), and focused appendiceal CT with
colonic contrast material gave the greatest confidence for cases with positive
findings (p = 0.02). In terms of inter- and intraobserver
variability, focused appendiceal CT with colonic contrast material yielded the
highest, and unenhanced focused appendiceal CT the lowest, agreement
(interobserver = 0.45 vs. 0.36 and intraobserver = 0.85 vs.
0.76, respectively) (p <0.05). Colonic contrast material was
unsuccessfully advanced into the cecum in 18% of patients and leaked in
another 24%. Patient discomfort was greatest with focused appendiceal CT using
colonic contrast material and least with unenhanced focused appendiceal CT
(p <0.05).
CONCLUSION. A standard abdominopelvic CT scan is recommended as the initial examination for appendicitis in adult patients. However, focused appendiceal CT with colonic contrast material material should be used as a problem-solving technique in difficult cases.
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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Some investigators have suggested an unenhanced technique in which thin-collimation (5 mm) CT is performed through the right lower abdominal quadrant with or without a general survey of the abdomen and pelvis [6, 7]. Other investigators have advocated using oral and IV contrast media and performing a similar CT assessment [8, 9]. Finally, Rao et al. [10, 11] have reported impressive results with focused appendiceal CT using rectally administered contrast material, with or without the use of additional oral contrast material. However, to our knowledge, a comparative assessment of the CT and sonographic techniques has not been performed on the same patient population with independent interpretations rendered by a group of radiologists. We undertook this investigation to evaluate the following five appendiceal imaging techniques: graded compression sonography, unenhanced focused appendiceal CT, standard abdominopelvic CT using IV contrast material, focused appendiceal CT using colonic contrast material, and sonography using colonic contrast material. The intent is to provide a comprehensive assessment of the diagnostic performance, diagnostic confidence, inter- and intraobserver variability, technical success, and patient comfort with each imaging technique.
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Oral contrast material (400-500 mL of 3% meglumine diatrizoate solution [Gastrografin; Bristol-Meyers Squibb, Wallingford, CT]) was given to each patient, who was instructed to drink the solution as tolerated for 30-60 min. The patients were taken to the emergency department CT scanner (PQ 5000; Picker International, Cleveland Heights, OH), and a predetermined array of examinations was performed. First, graded compression sonography (128XPIO scanner; Acuson, Mountain View, CA) of the right lower abdominal quadrant was performed (by one of two dedicated sonographers or one sonologist) using the graded compression technique described in the literature [12]. Second, unenhanced focused appendiceal CT was performed, obtaining an average of 21 consecutive 4-mm axial images over approximately 8.4 cm of the right lower abdominal quadrant (centered at the level of the cecal apex) using a small field of view centered over the right two thirds of the abdomen. Third, complete helical CT of the abdomen and pelvis was performed, obtaining 8-mm consecutive images using a field of view large enough to encompass the entire peritoneal cavity. Nonionic contrast material was administered for this study (125 mL of Optiray 320 [ioversol]; Mallinckrodt, St. Louis, MO), injected through a peripheral IV catheter at 2.5 mL/sec (65-sec scan delay). Fourth, focused appendiceal CT was performed after the administration of 800-1200 mL of colonic contrast material (3% meglumine diatrizoate solution) through a rectal catheter placed by the radiologist monitoring the study. Consecutive 4-mm small-field-of-view images were obtained focused on the cecal apex in a manner similar to the unenhanced focused appendiceal CT, with a mean anatomic coverage of 8.8 cm (mean, 22 images). A fifth study, repeated sonography of the right lower abdominal quadrant after administration of colonic contrast material, was performed. The technique used for each CT scan included 200-300 mA, 100-200 kVp, 1.5 pitch, and a 1.0 sec per revolution acquisition time. Standard (180°) linear interpolators and standard reconstruction kernels were used.
Patients were randomly assigned to one of two imaging sequences. Fifty percent of patients underwent the studies in the order just outlined. For the remaining 50%, the order of the abdominopelvic CT and focused appendiceal CT using colonic contrast material was reversed (the focused appendiceal CT with colonic contrast material in this sequence being performed before the abdominopelvic CT instead of after it).
A digital scout image of the abdomen and pelvis was obtained before each CT scan and was used to localize the cecum for the two focused appendiceal CT scans. If the cecum could not be localized on the scout image, the images were centered approximately 1 cm inferior to the iliac crest.
The CT scans were evaluated on the monitor before the second sonographic examination was performed. If the diagnosis of appendicitis remained uncertain to the radiologist monitoring the study, additional images (4-mm axial slices) of the right lower abdominal quadrant were obtained with the patient in the right or left lateral decubitus position. The right lateral decubitus position was chosen if the colonic contrast material did not initially opacify and distend the cecum. The left lateral decubitus position was chosen if the cecum was well filled with contrast material but the diagnosis was equivocal. These decubitus scans were used for both the prospective and retrospective interpretations.
The radiologist on duty for body imaging at the time of the studies interpreted all CT and sonographic studies as a unit, with the overall interpretation used for clinical treatment. The diagnosis of appendicitis and the alternative diagnoses were then documented using a confidence scale of 0-10. Findings related to appendicitis and findings that were nonappendiceal in nature were recorded as present, equivocally present, or absent. Ancillary findings were categorized according to the primary diagnosis (e.g., fluid collection, bowel obstruction) or incidental findings. In addition, the radiologists interpreting the studies prospectively recorded the specific examination that was considered most useful in the assessment of that particular case.
Each CT scan was filmed separately, with the only identification on the films being the patients' six-digit medical record number. At a later date, four observers independently interpreted each individual scan using the same scale described for documenting the prospective diagnosis. Unenhanced focused appendiceal CT, abdominopelvic CT, and focused appendiceal CT with colonic contrast material scans were interpreted separately and in random order (for 16 months), whereas the right and left lateral decubitus scans were interpreted only in conjunction with the focused appendiceal CT scans for which colonic contrast material was used (after the focused scans were first reviewed independently).
Three of the four CT observers were fellowshiptrained body imagers with various degrees of academic focus in gastrointestinal radiology. The fourth observer was a third-year radiology resident.
Two experienced sonographers performed 94 of the 100 sonographic studies (a sonologist performed the remaining six). Graded compression sonography of the right lower abdominal quadrant was performed in the presence of the sonologist. The sonographers were unaware of the CT results and performed the second right lower abdominal quadrant sonography after the final CT (while the colonic contrast material was still in place).
The real-time sonography was videotaped, with the only identification on the tapes being the six-digit medical record numbers and whether the scan was obtained before or after colonic contrast material administration. Body markers and annotation were added as appropriate. The videotaped scans were then interpreted separately and in a blinded fashion by three radiologists, including two staff sonologists and a third-year radiology resident.
Before the interpretative stage of the investigation, each observer reviewed the appendicitis-related radiology literature published in the preceding 4 years. Furthermore, prior clinical cases were available to review specific imaging findings and variations of appendicitis.
One observer interpreted each CT scan and sonogram twice to assess intraobserver variability. Given the multiplicity of the number of individual scans for 100 patients and the number of observers involved in the study, a total of 3110 interpretations were performed (Table 2).
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After each sonographic and CT technique was performed, the patient was asked to rate the level of discomfort for that procedure on a scale of 0-10 (0 being no discomfort and 10 being maximal discomfort), enabling an assessment of patient preference for techniques relative to one another.
An experienced emergency medicine physician established the clinical diagnosis for each nonsurgical case. Findings at pathologic assessment of resected appendixes were used as the gold standard for patients who underwent appendectomy. An experienced gastrointestinal pathologist reviewed each resected specimen to confirm the presence or absence of appendicitis. Patients who did not have surgery were contacted by telephone for clinical follow-up 1 week, 1 month, and 3 months after presentation. The final diagnosis for each patient incorporated information from the surgical and pathologic findings, clinical data at discharge, and the clinical follow-up.
In addition to parameters of diagnostic performance, we assessed diagnostic confidence with each imaging technique. A 10-point scale was used for the interpretations, and the mean scores for the cases with negative and positive findings were assessed as separate groups. In this analysis, a technique that is perfect would have a mean value of 0 for a case with negative findings and 10 for a case with positive findings. This assessment incorporated both relative accuracy and the diagnostic confidence level of the interpretations for each technique.
Several technical aspects of CT were assessed. First, the anatomic coverage of the appendix was assessed for the focused techniques using a 10-point scale. Second, the amount of colonic contrast material reaching the cecum was assessed for focused appendiceal CT using colonic contrast material. Cecal opacification and distention were assessed on a 10-point scale from no contrast in the cecum (0) to excellent opacification (10). If the degree of cecal opacification was considered poor (<5), the suspected reason for the failure (colonic stool, sigmoid redundancy, poor effort by radiologist, or other) was recorded. Third, for the second half of the study, the frequency of colonic contrast material leakage and problems related to the IV contrast material were assessed. The amount of colonic contrast leakage was assessed qualitatively (none, mild, moderately, and severe), whereas problems related to IV contrast material (e.g., extravasation) were recorded as they occurred. Last, the radiologist interpreting the studies prospectively was asked his or her preference among the three CT techniques and sonography.
Descriptive statistical analysis included means and standard deviations for continuous outcomes and frequency tables for categoric outcomes. Diagnostic parameters for each technique—sensitivity, specificity, positive predictive value, negative predictive value, and accuracy—were calculated separately for each observer. The means of all observers were used in the analyses unless otherwise indicated. Statistical comparisons among techniques with respect to categoric outcomes, such as diagnostic parameters, were made using the Cochran and Mantel-Haenszel tests, which accounts for the fact that all techniques were used on the same patients. Statistical comparisons among techniques with respect to continuous outcomes, such as diagnostic confidence score, were made using repeated measures analysis of variance with technique and observer as within-subject factors. Intra- and inter-observer agreement with respect to diagnostic confidence were quantified using the weighted kappa statistic. Values of the kappa statistic greater than 0.7 typically indicate good agreement, whereas values between 0.4 and 0.7 reflect moderate agreement. All analyses were carried out using the SAS statistical software system version 8.0 (SAS, Cary, NC).
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The prospective and retrospective sonographic interpretations had comparable accuracy, but the prospective assessment provided significantly higher sensitivity (p < 0.01). No differences were noted in the diagnostic performance of sonography with or without the use of colonic contrast material (p > 0.05). Both sonographic techniques were inferior to CT (p < 0.0001), with the greatest difference being a low sensitivity for sonography (range, 13-65% among observers).
Inter- and Intraobserver Variability
Table 4 shows the kappa
values for inter- and intraobserver variability with each imaging technique.
Regardless of the specific imaging technique, intraobserver variability was
significantly less than interobserver variability (p < 0.0001).
The sonographic techniques produced significantly worse inter- and
intraobserver agreement than the three CT techniques. Unenhanced focused
appendiceal CT was the CT technique with the greatest inter- and intraobserver
variability, whereas focused appendiceal CT with colonic contrast material had
the least variability (p = 0.04).
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Diagnostic Confidence
Figure
1A,1B
shows the mean confidence scores for each imaging technique. Again, the
prospective interpretations of CT produced the highest confidence scores for
both the negative and positive findings. For the retrospective CT
interpretations, abdominopelvic CT provided the greatest level of confidence
for negative findings (mean, 2.21) relative to the two focused appendiceal CT
techniques (mean, 2.75; p = 0.001). However, abdominopelvic CT
produced significantly lower confidence for the positive cases than did both
focused CT methods (p = 0.0001), with the greatest confidence seen in
positive cases with focused appendiceal CT using colonic contrast material
(p = 0.02).
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The retrospective interpretations of the sonograms were comparable to the CT scans for negative findings but were significantly inferior to all CT techniques for cases with positive findings (p < 0.0001). Prospective sonography produced comparable confidence to the retrospective interpretations of the negative findings but significantly greater confidence for the positive findings (p < 0.006).
During imaging, the appendix was identified with greater frequency on CT than on sonography, regardless of technique (p < 0.0001) (Table 5). Significant interobserver differences were noted for both CT and sonography (p < 0.01) but without significant trends among the techniques.
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Use of Colonic or IV Contrast Material for CT
The use of colonic contrast material did not improve the diagnostic
performance of CT (p > 0.33)
(Table 6). The addition of
colonic contrast material for focused appendiceal CT and abdominopelvic CT did
not alter diagnostic confidence for the cases with negative findings
(p = 0.30) but significantly improved confidence in cases with
positive findings (p = 0.02).
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Focused appendiceal CT using colonic contrast material was assessed between
the two imaging protocols. (Focused appendiceal CT with colonic contrast
material either preceded or followed abdominopelvic CT with IV contrast
material.) This comparison enabled assessment of the use of IV contrast
material, at least with delayed scanning. As seen in
Table 6, no significant
difference was noted between focused appendiceal CT scans with colonic
contrast material that also used IV contrast material and those that preceded
IV contrast administration (p 
0.18).
Other Analyses
When we used the discomfort scale of 0-10 (0 = least discomfort, 10 = most
discomfort), the mean patient discomfort scores for each technique were as
follows: sonography without colonic contrast material, 6.1; sonography with
colonic contrast material, 6.7; unenhanced focused appendiceal CT, 4.2;
abdominopelvic CT, 5.3; and focused appendiceal CT with colonic contrast
material, 6.7. Patients reported significantly less discomfort for unenhanced
focused appendiceal CT than for any other technique (p < 0.0001).
Focused appendiceal CT with colonic contrast material produced significantly
higher patient discomfort than the other CT techniques but did not
significantly differ from sonography (p < 0.0001 and p =
0.051-0.075 for CT and sonography comparisons, respectively).
The following technical problems were encountered during CT. Colonic contrast material leaked onto the table in 12 cases (six mild, one moderate, and five severe leakage) (24%), nausea or vomiting occurred in three patients (6%) during scanning, and one patient (2%) experienced extravasation of IV contrast material. In addition, cecal contrast opacification or distention was graded as suboptimal (<5 on the 10-point scale) in 18% of the 100 focused appendiceal CT scans with colonic contrast material, with 16 of the 18 failures caused by abundant stool in the right colon. (Of the two remaining failures, one case was related to excessive sigmoid redundancy and one was suspected to be inadequate effort by the radiologist.)
The accuracy of localizing the cecum and the appendiceal region using the scout topogram revealed that 8% of the unenhanced focused appendiceal CT scans and 4% of the focused appendiceal CT scans with colonic contrast material were graded as relatively poor for accuracy of scanning the appendiceal region.
The radiologists monitoring the cases were prospectively asked their preference among the techniques for establishing the diagnosis with greatest confidence. Abdominopelvic CT or focused appendiceal CT with colonic contrast material was preferred to sonography or unenhanced focused appendiceal CT in 87 of 100 cases (p < 0.0001). Focused appendiceal CT with colonic contrast material was preferred in 45 cases and abdominopelvic CT in 42 cases.
Alternative diagnoses were established using imaging in 30 cases. Specific diagnoses included ovarian cyst (n = 13), cecal diverticulitis (n = 3), sigmoid diverticulitis (n = 2), inflammatory bowel disease (n = 2), biliary colic (n = 1), mesenteric adenitis (n = 1), pelvic inflammatory disease (n = 2), pelvic hematoma (n = 1), endometriosis (n = 1), fibroid (n = 1), segmental omental infarction (n = 1), choledocholithiasis (n = 1), and ureteral calculus (n = 1). The latter three diagnoses required complete abdominopelvic scanning for identification.
The number of ancillary (incidental) findings (e.g., gallstones) identified was averaged for all observers to provide a relative (but fractional) assessment on a per-patient basis. For ancillary findings related to the diagnosis, sonography without colonic contrast material revealed 0.1 findings per patient; sonography with colonic contrast material, 0.1 findings; unenhanced focused appendiceal CT, 0.1 findings; abdominopelvic CT, 0.3 findings; and focused appendiceal CT with colonic contrast material, 0.1 findings. For incidental findings, sonography without colonic contrast material revealed 0.1 findings; sonography with colonic contrast material, zero findings; unenhanced focused appendiceal CT, 0.1 findings; abdominopelvic CT, 0.3 findings; and focused appendiceal CT with colonic contrast material, 0.1 findings. Abdominopelvic CT was superior to the other techniques in the identification of ancillary findings regardless of whether they were related to the primary diagnosis (p<0.01). Renal cysts, gallstones, diverticulosis, and one large hemangioma were incidental findings that were frequently identified on abdominopelvic CT.
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Several appendiceal imaging techniques have been advocated in the literature. Puylaert et al. [12] described a graded compression sonographic technique for appendiceal imaging reported to be 83-96% accurate for the diagnosis of appendicitis [8, 15, 16]. Complete CT of the abdomen and pelvis using oral and IV contrast material has also been advocated and shown to be 94% accurate in the examination of patients with possible appendicitis [8]. This technique, initially described by Balthazar et al. [8], entails the use of thin-section (5 mm) imaging through the cecal region, with thicker images in the upper and lower portions of the abdomen and pelvis. Unenhanced thin-section CT through the right lower abdominal quadrant with or without imaging the remainder of the peritoneal cavity has also been described [6, 7], yielding an accuracy of 93-97% without using oral, IV, or colonic contrast material.
Rao et al. [10, 11] developed the focused appendiceal CT technique in which a helical scan with 5-mm collimation is obtained through the appendiceal region after the administration of approximately 1 L of colonic contrast material. This technique, with or without the addition of orally administered contrast material, has a reported accuracy of 98% in the diagnosis of appendicitis [10, 11]. Furthermore, this technique enables a relatively quick diagnostic examination (there is no delay related to oral contrast material) while maintaining the benefit of enteric contrast material and cecal distention.
All these techniques offer promising results. However, few comparative studies have been performed [8]. We chose to undertake a comprehensive comparative study of appendiceal imaging techniques evaluating not only the diagnostic performance of each technique, but also the inter- and intraobserver variability, diagnostic confidence for negative and positive findings, number of normal appendixes identified, and relative patient discomfort with the various techniques.
The prospective interpretations of the CT scans in our study had the highest overall diagnostic performance, despite the fact that the initial observers were frequently residents at various stages of training with or without additional faculty input. This observation has two explanations. First, the combination of the various CT techniques with sonography is better than any individual study. The usefulness of performing tandem techniques has not been assessed to date and may warrant further investigation. Second, when examining a patient with abdominal pain, it is difficult to have prospective interpretations in which the diagnostician is completely unaware of clinical data. The influence of clinical correlation may have significant diagnostic impact in cases that are equivocal for appendicitis at imaging. Bias can be introduced from the impressions of referring clinicians, from laboratory data, or simply through patient observation during provocative imaging maneuvers such as compression with a sonographic transducer or the introduction of colonic contrast material. This effect may account for the overall poorer performance of the retrospective interpretations when compared with the performance data in the literature that consistently reports accuracies greater than 90%. This effect may also account for the overall higher sensitivity for prospective rather than for retrospective sonographic interpretations.
CT had significantly better diagnostic performance than sonography in our study, but no significant differences were noted among the individual CT techniques tested. Furthermore, the use of colonic or IV contrast material (at least in delayed scanning) had no effect on diagnostic performance. These findings support the conclusion postulated in the literature that comparable performances can be obtained regardless of the specific CT technique used [17] (Fig. 2A,2B,2C,2D,2E).
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The assessment of diagnostic performance in appendiceal imaging is undoubtedly important, particularly with a panel of observers who have a range of subspecialty clinical expertise and academic interest in the subject. Radiology investigations tend to emphasize diagnostic performance; however, diagnostic confidence and observer variability are also important in the diagnosis or exclusion of surgical conditions such as acute appendicitis. If surgeons recognize excessive interpretive variability or suboptimal diagnostic confidence of radiologists, they will be more likely to discount the efficacy of the imaging examination regardless of the accuracy reported in the literature.
The optimal imaging approach should have several key characteristics. Imaging tests should be sensitive, specific, and accurate; enable observers to be confident of both negative and positive findings with little inter- and intraobserver variability; and be easily performed with little risk and discomfort for patients. Rao et al. [11] addressed several issues that support the use of limited CT for appendiceal imaging rather than CT of the entire abdomen and pelvis. First, considerable cost savings can be realized by limiting the CT and reducing the cost and charge for the study to that for a pelvic CT. Second, the amount of radiation exposure for patients is significantly less with limited CT than with CT of the entire abdomen and pelvis. Most patients referred for appendiceal examination are relatively young, and gonadal radiation should be minimized, particularly for young women. Third, the use of IV contrast material has some inherent risk and intrinsic cost that is best avoided if a clearcut clinical advantage is not seen. Fourth, the study can be performed rapidly (without delay), resulting in quick diagnoses.
IV contrast material was used in each abdominopelvic CT examination. When assessing the focused appendiceal CT studies, no statistical influence was seen for the use of IV contrast material on the use of IV contrast material on the diagnostic performance of the focused appendiceal CT with colonic contrast material that followed the abdominopelvic CT (even though appendiceal mural enhancement can be indicative of appendicitis). This use of IV contrast material, however, combined with full coverage of the abdomen and pelvis during CT, does raise the cost of the study and may negatively influence the reported cost-effectiveness of CT for the examination of patients with possible appendicitis. The technique of helical abdominopelvic CT using prospectively planned thin sections through the appendiceal region (during dynamic enhancement) was not specifically tested in this study. However, this approach in theory takes advantage of dynamic enhancement IV contrast material as well as thin sections.
The limited scope of focused CT may result in pathologic disorders not being fully imaged. Rao et al. [10] reported in their initial investigation that 8% of patients underwent extended scanning (beyond the focused appendiceal CT anatomic coverage) "to follow the cranial or caudal extent of pathologic abnormalities noted on the initial limited scan." In a subsequent study, the same group reported the need to extend scanning into the upper abdomen or pelvis in 5% of cases [11].
Our study evaluated this issue by performing focused appendiceal CT with less overall coverage than was used in prior studies. The technique used in these prior investigations entailed 5-mm images with approximately 15 cm of coverage using a field of view encompassing the entire peritoneal cavity. Conversely, we used 4-mm images with 8.4-8.8 cm of coverage and a field of view encompassing the right two thirds of the peritoneal cavity. (We chose this technique to limit the amount of patient radiation and to magnify the performance differences of focused appendiceal CT vs. standard abdominopelvic scanning.)
Despite this focused approach to the focused appendiceal CT studies, we had good anatomic coverage of the appendix in most patients. However, three alternative diagnoses (choledocholithiasis, ureteral calculus, and segmental omental infarction) were encountered that would have required additional imaging of the upper abdomen or lower pelvis for detection. In addition, ancillary findings were more frequently identified on abdominopelvic CT than on either focused CT or sonography. Although most of these findings would probably not have altered clinical treatment of the patients, abdominopelvic CT provided a more complete assessment of the peritoneal cavity.
These observations, along with the superior level of observer confidence in cases with negative findings and relatively good inter- and intraobserver variability, lead us to conclude that abdominopelvic CT may be the best initial examination for suspected appendicitis in adult patients. Other observations also support this conclusion. The patients experienced a relatively low degree of discomfort with the technique. Radiologists preferred interpreting the abdominopelvic CT much more than the unenhanced focused appendiceal CT scans or sonograms. The identification of normal appendixes using 8-mm abdominopelvic images was comparable to identification on thin-section scans. (The latter observation differs slightly from a previous investigation that reported significantly higher frequency of normal appendix identification with 5-mm as opposed to 10-mm image collimation [18].)
The patients themselves were proponents for excluding the use of colonic contrast material, which became apparent through several observations. First, most patients refusing to enroll in the study did so to avoid receiving colonic contrast material. Second, the technique with the greatest relative patient discomfort was the one using colonical contrast material. Finally, the colonic contrast material could not be advanced successfully into the cecum in 18% of patients and was associated with leakage onto the CT table in 24%. Clearly, if an examination produces greater patient discomfort and offers greater technical challenges than rival techniques, its use should be justified through a significant improvement in diagnostic performance, greater degrees of diagnostic confidence, or lower inter- and intraobserver variability.
The diagnostic benefits of colonic contrast material for appendiceal CT relate to the ability to identify specific cecal apical findings (e.g., "arrowhead" and cecal bar signs) and to exclude appendicitis when colonic contrast material fills the appendiceal lumen. Focused appendiceal CT with colonic contrast material offered the greatest diagnostic confidence for cases with positive findings and the least intra- and interobserver variability. The significant advantage of diagnostic confidence in positive cases was also seen when the interpretations of the abdominopelvic CT scans were divided as to the presence or absence of colonic contrast material and were included in the analysis. However, focused appendiceal CT with colonic contrast material did not yield a higher diagnostic performance than the other CT techniques and resulted in greater patient discomfort and technical challenges. Therefore, we conclude that focused appendiceal CT with colonic contrast material is probably best used as a problem-solving technique for equivocal appendiceal cases after an initial assessment with standard abdominopelvic CT.
Sonography had a lower diagnostic performance and observer confidence than CT. Furthermore, the tenderness evoked by the transducer pressure produced the second highest rating of patient discomfort among the imaging techniques.
Before the investigation, we theorized that distending the cecum with contrast material could provide a useful window for the sonographic examination of appendixes, particularly those in a retrocecal location. Initial in vitro sonography with diluted iodinated colonic contrast material revealed it to be a primarily anechoic solution with scattered specular reflectors. However, the technique was unsuccessful in improving the accuracy of appendiceal sonography (Fig. 3A,3B). If the cecum is not completely fluid-filled and retains a small amount of gas, the retrocecal region can still be obscured.
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The primary limitation of this study is the possibility of spontaneously resolving appendicitis in a few patients. In three patients in our series, one of the CT techniques raised the possibility of mild appendicitis, but the patient did not undergo surgery and subsequently the symptoms resolved (Fig. 4A,4B,4C). Resolution of mild appendicitis has been widely recognized during the past several years [19, 20], and appendicitis may recur in approximately 38% of cases [21]. One case of apparent mild appendicitis was missed prospectively in the early stage of our study, but the patient was reenrolled 7 weeks later when symptoms recurred. Repeated imaging of this patient showed classic findings of appendicitis.
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Our study has unique limitations to the evaluation of appendiceal sonography. Sonographic interpretations were limited by the study design in that there was no communication between the sonographer and the reviewing physician (for the retrospective interpretations) and no opportunity for the reviewing physician to personally perform a real-time examination. These factors, plus the inability to correlate sonographic findings with patient tenderness during the examination, may explain the poor performance of sonography. (Patient body habitus, which may have been a significant limiting factor, is being evaluated separately). Our study specifically excluded pediatric patients—a subgroup of patients considered ideal for appendiceal sonography—which is another factor that likely contributes to the improved performance of CT over sonography. The predominance of female patients (with relatively greater differential diagnoses) in our series likely added to the diagnostic challenge of the imaging techniques.
In conclusion, our results suggest that abdominopelvic CT with a standard protocol should be the initial approach to imaging patients being examined for appendicitis. Focused appendiceal CT using colonic contrast material should be used for further examination of equivocal cases. This approach enables maximum diagnostic confidence and reduction in intra- and inter-observer variability.
Acknowledgments
We appreciate Doreen Katzaman's assistance in the preparation of this
manuscript. Additionally, we thank the Penn State College of Medicine
residency classes of 1998, 1999, and 2000 for their contributions to our
investigation.
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A. S. Doria, R. Moineddin, C. J. Kellenberger, M. Epelman, J. Beyene, S. Schuh, P. S. Babyn, and P. T. Dick US or CT for Diagnosis of Appendicitis in Children and Adults? A Meta-Analysis Radiology, October 1, 2006; 241(1): 83 - 94. [Abstract] [Full Text] [PDF]
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J. E. Jacobs CT and Sonography for Suspected Acute Appendicitis: A Commentary. Am. J. Roentgenol., April 1, 2006; 186(4): 1094 - 1096. [Full Text] [PDF]
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N. Pinto Leite, J. M. Pereira, R. Cunha, P. Pinto, and C. Sirlin CT Evaluation of Appendicitis and Its Complications: Imaging Techniques and Key Diagnostic Findings Am. J. Roentgenol., August 1, 2005; 185(2): 406 - 417. [Abstract] [Full Text] [PDF]
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C. Keyzer, M. Zalcman, V. De Maertelaer, E. Coppens, M.-A. Bali, P. A. Gevenois, and D. Van Gansbeke Comparison of US and Unenhanced Multi-Detector Row CT in Patients Suspected of having Acute Appendicitis Radiology, August 1, 2005; 236(2): 527 - 534. [Abstract] [Full Text] [PDF]
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C. P. Daly, R. H. Cohan, I. R. Francis, E. M. Caoili, J. H. Ellis, and B. Nan Incidence of Acute Appendicitis in Patients with Equivocal CT Findings Am. J. Roentgenol., June 1, 2005; 184(6): 1813 - 1820. [Abstract] [Full Text] [PDF]
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 T. Noguchi, K. Yoshimitsu, and M. Yoshida Periappendiceal Hyperechoic Structure on Sonography: A Sign of Severe Appendicitis J. Ultrasound Med., March 1, 2005; 24(3): 323 - 327. [Abstract] [Full Text] [PDF]
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 T. Terasawa, C. C. Blackmore, S. Bent, and R. J. Kohlwes Systematic Review: Computed Tomography and Ultrasonography To Detect Acute Appendicitis in Adults and Adolescents Ann Intern Med, October 5, 2004; 141(7): 537 - 546. [Abstract] [Full Text] [PDF]
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C. Keyzer, D. Tack, V. de Maertelaer, P. Bohy, P. A. Gevenois, and D. Van Gansbeke Acute Appendicitis: Comparison of Low-Dose and Standard-Dose Unenhanced Multi-Detector Row CT Radiology, July 1, 2004; 232(1): 164 - 172. [Abstract] [Full Text] [PDF]
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N. Kessler, C. Cyteval, B. Gallix, A. Lesnik, P.-M. Blayac, J. Pujol, J.-M. Bruel, and P. Taourel Appendicitis: Evaluation of Sensitivity, Specificity, and Predictive Values of US, Doppler US, and Laboratory Findings Radiology, February 1, 2004; 230(2): 472 - 478. [Abstract] [Full Text] [PDF]
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P. Poortman, P. N. M. Lohle, C. M. C. Schoemaker, H. J. M. Oostvogel, H. J. L. J. M. Teepen, K. A. H. Zwinderman, and J. F. Hamming Comparison of CT and Sonography in the Diagnosis of Acute Appendicitis: A Blinded Prospective Study Am. J. Roentgenol., November 1, 2003; 181(5): 1355 - 1359. [Abstract] [Full Text] [PDF]
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S. E. Bendeck, M. Nino-Murcia, G. J. Berry, and R. B. Jeffrey Jr Imaging for Suspected Appendicitis: Negative Appendectomy and Perforation Rates Radiology, October 1, 2002; 225(1): 131 - 136. [Abstract] [Full Text] [PDF]
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 P J Shorvon Imaging of appendicitis: a cautionary note Br. J. Radiol., September 1, 2002; 75(897): 717 - 720. [Full Text] [PDF]
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