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Gastrointestinal Imaging |
1 From the Department of Medical Imaging, St Vincent’s Hospital, Sydney, Victoria St, Darlinghurst, NSW 2010, Australia. Received September 25, 2000; revision requested October 27; revision received March 26, 2001; accepted April 9. Address correspondence to B.D.D.
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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MATERIALS AND METHODS: One hundred patients (age range, 14–81 years; mean age, 30.6 years) with equivocal symptoms and signs of acute appendicitis were included in this prospective study. Patients were given 30 mL of diatrizoate meglumine and diatrizoate sodium and 60 mL of sorbitol mixed in 1 L of water orally over 1 hour. CT was performed 1.5 hours after the commencement of oral contrast material administration. The criteria used for the diagnosis of appendicitis were (a) appendix greater than 6 mm in maximum diameter, (b) no contrast material in the appendiceal lumen, and (c) inflammatory changes in the periappendiceal fat. CT results were compared with histopathologic findings at appendectomy. Patients with negative CT findings were followed up by telephone or clinically.
RESULTS: Of 100 cases, 30 were positive at CT and 70 were negative. There were 28 true-positive cases; two false-positive cases, one cecal diverticulitis and one pelvic peritonitis with periappendicitis; and two false-negative cases, one perforated appendix and one mucosal and submucosal inflammation of the appendix but no transmural inflammation. Sensitivity was 93%, specificity was 97%, and accuracy was 96%.
CONCLUSION: Focused appendiceal CT in which oral contrast material is used alone yields high levels of accuracy in clinically equivocal cases of acute appendicitis.
Index terms: Appendicitis, 751.291 • Appendix, CT, 751.12112, 751.12115
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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To reduce the error rate in the diagnosis of this potentially life-threatening condition, conventional radiography, barium studies, and ultrasonography (US) have been used with limited success (7–10). Computed tomography (CT) with and without contrast material has improved the success rate in the diagnosis of appendicitis. Some previous studies (11,12) used CT in all patients with suspected acute appendicitis, not just in patients who presented with equivocal signs. Others (13–16) used CT to aid in the diagnosis only in patients with equivocal symptoms and signs of appendicitis. To date, various investigators have used CT without contrast material (nonenhanced CT) (12), with contrast material administered orally and rectally together (11), with rectal contrast material only (17), or with oral and intravenous contrast material (13,14) to diagnose appendicitis.
Rao et al (11) described a focused appendiceal CT technique that involves contiguous thin-collimation helical scanning limited to the right lower quadrant after the administration of both oral and rectal contrast materials. We examined the diagnostic accuracy of focused appendiceal CT by using oral contrast material only to confirm the diagnosis of appendicitis in patients who presented without the typical symptoms and signs of appendicitis, described earlier in this article. We chose to investigate the accuracy of focused appendiceal CT with only oral contrast material to simplify the procedure described by Rao et al (11), thereby avoiding the administration of both rectal and intravenous contrast materials, which are invasive procedures. Our approach adds a further dimension to the already large body of studies aimed at improving the accuracy of the diagnosis of acute appendicitis. To our knowledge, no one has previously used CT with only oral contrast material to diagnose acute appendicitis in patients who present with equivocal symptoms and signs.
The purpose of our study was to determine the diagnostic accuracy of modified focused appendiceal CT technique to exclude or confirm appendicitis in patients who presented with equivocal symptoms and signs of appendicitis. We obtained levels of sensitivity, specificity, and accuracy similar to those achieved by other authors in this field (11,12), although an exact comparison is difficult because of the differences in patient selection.
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MATERIALS AND METHODS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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Any patient who met the inclusion criteria and presented with symptoms and signs between midnight and 8 AM was observed until morning and then underwent CT examination. All patients were referred by the surgeon on call for the emergency room that day. The surgeon saw all cases that did not display the typical signs and symptoms of acute appendicitis, and these were included in our study. Serum beta human chorionic gonadotropin levels were obtained in all female patients prior to CT examination. Female patients did not undergo pelvic US prior to CT, although 10 patients underwent pelvic US after CT examination for reasons such as cystic ovaries, adnexal masses, pelvic fluid, or continuing symptoms with negative CT findings for appendicitis. US images were interpreted by a staff specialist (including G.W.B.W., B.D.D.) in radiology. Our institutional review board did not require its approval for this study. Informed consent was obtained from all patients.
The patient preparation involved oral administration of a solution made up of 60 mL of sorbitol (70% British Pharmacopoeia noncrystallizing; Orion Laboratories, Welshpool, Australia) and 30 mL of diatrizoate meglumine and diatrizoate sodium (Gastroview; Mallinckrodt, St Louis, Mo) mixed in 1 L of water over 1 hour. No rectal or intravenous contrast material was administered. CT was performed 1.5 hours after the commencement of oral contrast material administration.
Each patient was examined in the supine position. First, a single section was obtained at the level of the cecum to check that the oral contrast material had reached the cecum. Thin-section helical CT (5-mm collimation, pitch of 1) was performed through a 12–15-cm region of the right lower quadrant of the abdomen to include the proximal ascending colon, cecum, appendix, and pelvis. Ninety-nine patients had adequate cecal distension; one showed poor distension. Seventy-seven of the 100 scans were interpreted immediately by a radiology resident (R.W., B.S.T., J.C.R.) with between 1 and 4 years of experience in radiology. Twenty-three scans were interpreted immediately by a staff specialist radiologist (including G.W.B.W., B.D.D.). Every report issued by a radiology resident was confirmed by a staff specialist radiologist. Twenty-four to 30 5-mm-thick images were reconstructed from the helically acquired data set. All studies were performed with a CT scanner (Twin Flash version 3.3; Elscint, Haifa, Israel). In five patients, the images were enlarged for improved interpretation.
CT scan interpretation was based on the positive and negative criteria described by Rao et al (11,18). CT scans were interpreted as positive for appendicitis if three or more of the following criteria were present: (a) the appendix was greater than 6 mm in maximum diameter; (b) there was no contrast material in the appendiceal lumen; (c) there were inflammatory changes in the periappendiceal fat, such as fat stranding or phlegmon, extraluminal gas bubbles, fluid collection, or enlarged lymph nodes; (d) appendicoliths (one or more) were present; and (e) there was thickening of the cecal wall (focal thickening, arrowhead sign, cecal bar) (11,19).
Abnormal cecal wall thickening was assessed by means of comparison with the normal ascending colon wall thickness distal to the cecum. An RIF abscess suggested the diagnosis of a ruptured appendix. It should be noted that waiting 1.5 hours after the administration of oral contrast material ensures that the contrast material reaches the cecum and the appendix. Because of severe nausea, five patients needed nasogastric tubes to assist in the introduction of oral contrast material. Because of adynamic ileus, three patients had no opacification of the cecum at 1.5 hours and needed up to 6 hours for contrast material to reach the cecum. Therefore, preliminary single-section CT was performed at the level of the cecum to ensure that oral contrast material had reached the cecum.
CT scans were interpreted as negative for appendicitis if the appendiceal lumen filled completely with contrast material or air, or if the appendiceal lumen contained air and contrast material and the appendix was less than or equal to 6 mm in maximum diameter, or if the appendiceal wall was less than 2-mm thick (11), or if no periappendiceal inflammation was present. When the appendix was not visualized, absence of appendicitis was diagnosed on the basis of absent periappendiceal inflammation.
CT results were compared with findings obtained at surgery, histopathologic examination, or follow-up. The final diagnosis of appendicitis was confirmed at histopathologic examination. CT scans were also evaluated for other disease, such as ovarian, cecal, sigmoid, ileal, and gallbladder diseases. All patients with negative CT findings who were not operated on were followed up over a period ranging from 1 to 8 months. Follow-up was conducted by means of review of hospital notes and telephone calls to the patients.
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RESULTS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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Of the 30 patients with positive CT findings, 28 (93%) had true-positive (Fig 1) and two (7%) had false-positive findings. Of the two patients with false-positive findings, one patient had cecal diverticulitis (Fig 2) and one had periappendicitis but no acute appendicitis at histopathologic examination. Of the 70 patients with negative CT findings, 68 (97%) had true-negative and two (3%) had false-negative findings. Of the two patients with false-negative findings, one had a perforated appendix with fluid and pus in the pelvis. The pelvic fluid could be seen at CT, but the appendix was not seen (Fig 3). Laparotomy was performed in this patient to assess the cause of the fluid. The second patient was operated on because he continued to have pain. Histopathologic examination revealed mucosal and submucosal inflammation only but no transmural inflammation. The false-negative cases were not related to the paucity of intraabdominal fat. In all but two of the 28 true-positive cases of acute appendicitis, there was an enlarged appendix (>6 mm in diameter), nonfilling of the lumen with contrast material, and inflammatory changes in the periappendiceal fat. In these two cases, the appendix had perforated, forming an abscess (Fig 4).
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Overall, sensitivity was 93.3% (28 of 30 patients), specificity was 97.1% (68 of 70 patients), and accuracy was 96% (96 of 100 patients) for the CT diagnosis of appendicitis.
In 23 (33%) of 70 patients with negative CT findings, an alternative diagnosis was made with focused appendiceal CT, including ovarian cysts with complications and adnexal masses (eight patients), cecal or sigmoidal diverticulitis (four patients), infectious or inflammatory ileitis with or without cecitis (eight patients), inguinal hernia (one patient), mesenteric adenitis (one patient), and cholecystitis (one patient).
Of the 30 patients with acute appendicitis, one (3%) had distal appendicitis; 23 (77%), nonobstructing appendicitis; seven (23%), appendicoliths; one (3%), local thickening of the cecal wall (the arrowhead sign); three (10%), ruptured appendix; and one (3%), mucosal and submucosal inflammation only. Two of the three ruptured appendices were diagnosed at both CT and histopathologic examination.
Nonobstructing appendicitis is a condition in which there is no demonstrable luminal obstruction. This condition was diagnosed histopathologically. The patient with distal appendicitis had an appendix that filled proximally with contrast material, did not fill distally, was enlarged at its distal end, and had associated periappendiceal fat stranding.
It is unusual for an appendicolith to be obscured by oral contrast material, because the appendicolith is of higher attenuation than the oral contrast material and is well circumscribed. However, we encountered one false-negative case due to cecal diverticulitis. The cecal wall was abnormally thickened and this is associated with a focal area of concentrated contrast material in the cecum, which had the appearance of an appendicolith (Fig 2).
In 65 of 70 cases with negative CT findings, a normal appendix was depicted at CT. In five cases, the appendix filled with contrast material and air, in 11 it contained no contrast material or air but was of normal size, in four it contained air only, and in 45 it filled with contrast material only.
Follow-up of the 70 patients with negative CT findings ranged from 1 to 8 months. Sixty-two (89%) patients experienced no further symptoms, while eight (11%) patients experienced recurrent or persisting symptoms. Of the eight patients, two had acute appendicitis (false-negative), one underwent appendectomy 2 months later but was found to have a histologically normal appendix, one had a left ureteric calculus and hyperparathyroidism, two had ovarian and/or pelvic endometriosis, one had a ruptured ovarian cyst, and one had polycystic ovarian disease.
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DISCUSSION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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CT scanning of the entire abdominopelvic region (nonfocused CT) after the administration of oral and intravenous contrast material (14) and CT scanning of the right lower quadrant of the abdomen with neither intravenous nor oral contrast material (20) have both been used to diagnose appendicitis. Sensitivities of 87%–96% and specificities of 89%–97% have been reported.
In a recent study, Kamel et al (15) also examined the value of nonfocused appendiceal CT. These authors performed a retrospective study of the value of standard nonfocused CT by examining 100 consecutive patients with right lower quadrant pain who were clinically equivocal for acute appendicitis. Helical CT of the abdomen and pelvis was performed at 7-mm increments after oral and intravenous contrast material administration. It was found that the most common CT findings in acute appendicitis were a dilated nonopacified appendix (22 of 23 positive cases), fat stranding (21 of 23 positive cases), and an appendicolith (10 of 23 positive cases). When the appendix was not depicted, appendicitis was excluded if other signs of appendicitis were absent. These authors found that with abdominopelvic (nonfocused) CT scanning, they achieved a sensitivity of 98%, a specificity of 100%, and an accuracy of 99%. If CT had been limited to the pelvis, the sensitivity would have decreased to 88%, the accuracy would have decreased to 92%, and the specificity would have remained the same at 100%. These authors did not encounter a case in which nonvisualization of the appendix impaired the ability to assess for possible appendicitis.
Other authors who used CT diagnosis only in patients with equivocal symptoms and signs of acute appendicitis include Balthazar et al (13,14) and Weltman et al (16). McClelland et al (21) commented that they believe that clinical examination is still the most important means of diagnosing acute appendicitis. They stated that adjunctive tests such as CT should be used only in clinically questionable cases.
Determination of an alternative diagnosis in 48% of patients without appendicitis has been reported (13,20). In a study by Rao et al (11), an alternative diagnosis was established in 33 (80%) of 41 patients in whom CT results were negative for appendicitis. In our study, we established an alternative diagnosis with CT in 23 of the 70 patients in whom CT results were negative for appendicitis.
Lane et al (12) examined 300 consecutive patients prospectively by using nonenhanced thin-section focused helical CT for the detection of suspected acute appendicitis. Their study yielded a sensitivity of 96%, a specificity of 99%, and an accuracy of 97%. An alternative diagnosis was established in 35% of patients in whom CT results were negative for appendicitis. Intraperitoneal fat is the intrinsic contrast medium in a nonenhanced CT examination. Identification of inflammatory changes in thin pediatric patients with little intraperitoneal fat may therefore be difficult. Three of five false-negative CT scans in the Lane et al study (12) were obtained in thin young women with little intraperitoneal fat. This is also evident in the series by Malone et al (20), in which eight of 10 patients with false-negative nonenhanced CT interpretations were slender with little intraperitoneal fat.
Rao et al (11) used a focused CT technique with oral and rectal contrast material. The technique used by us differed from that used by Rao et al (11) in several aspects. The Rao et al study included all patients clinically suspected of having acute appendicitis, while we examined only those patients who presented with equivocal symptoms and signs of acute appendicitis. Where the diagnosis was clinically obvious, CT was not performed in our study, because the referring surgeons did not believe that there was any advantage to scanning clinically typical cases, as this would have delayed diagnosis and increase complications and thus also increase costs. Rao et al also used pelvic US to exclude gynecologic abnormalities prior to CT. We did not, because we believed this would result in a high pretest probability that appendicitis would be found with whatever test was used next (22).
The Rao et al CT studies were always interpreted by the same board-certified fellow in radiology. Our CT studies were interpreted by either a radiology resident (n = 77) with between 1 and 4 years of experience in radiology or by a staff specialist radiologist (n = 23). All reports written by a radiology resident were confirmed by a staff specialist radiologist within 24 hours. Radiologic examination and interpretation by a radiology staff member with varying levels of experience is a standard practice in Australian teaching hospitals. The slightly lower sensitivity and accuracy achieved in our study compared with those of Rao et al may be due to our exclusion of straightforward cases, our use of several interpreters with varying levels of experience, and our inclusion of gynecologic cases.
We believe that our results are a realistic representation of the levels of sensitivity, specificity, and accuracy, which can be expected by any radiology department in a teaching hospital wishing to put our method of diagnosis of equivocal acute appendicitis to practice. In the day-to-day running of a large radiology department, it is unlikely that it will be possible to always have every study interpreted by a single experienced CT specialist. We believe that it was important not to artificially elevate our results by having a single gastrointestinal radiologist interpret all the CT scans. Our findings show that under conditions that may not be ideal, we can still obtain high levels of sensitivity, specificity, and accuracy with our technique.
Rao et al (11) used oral and rectal contrast material, while we used only dilute oral water-soluble contrast material. We chose to dispense with the rectal contrast material to simplify the procedure for radiologists and patients. Furthermore, diatrizoate meglumine and diatrizoate sodium with sorbitol given orally achieve good cecal distension and appendiceal filling, allowing the visualization of the entire appendix. A minor disadvantage of our technique is that patients must wait 1.5 hours after the commencement of oral contrast material before CT is performed. In the Rao et al study, CT was performed immediately once the contrast material had been administered.
The appendix was not always depicted (five [7%] of 70 negative cases at CT). Nonvisualization of the appendix with absence of any other inflammatory signs was interpreted as negative for appendicitis in accordance with other literature (12,13,15,16). This is the main point of the divergence between CT interpretation in our study and that of Rao et al (11), in which the appendix was depicted in every true-negative case of appendicitis. Rao et al (11) attribute their improved results to the use of helical thin-section scanning and bowel opacification with both oral and rectal contrast materials. However, Federle (22) stated that in his opinion, there is some doubt that rectal contrast material provides sufficient added benefit to warrant its use and that most investigators find that oral administration of up to 800 mL of contrast medium over 1 hour before CT scanning enables opacification of both the small bowel and the right colon in most patients. Water-soluble agents such as diatrizoate meglumine and diatrizoate sodium with sorbitol (an osmotic laxative) tend to stimulate peristalsis and move through the small intestine more quickly than do barium suspensions, as used by Rao et al (11). We, like Federle (22), have found that there is good cecal filling with water-soluble agents (oral diatrizoate meglumine and diatrizoate sodium) mixed with sorbitol. Federle questions whether the administration of 700–1,000 mL of rectal contrast material was well tolerated by the patients and quick, as stated by Rao et al (11).
In a separate study, Rao et al (17) also examined the use of rectal contrast material alone in the diagnosis of appendicitis. In that study, 13 (13%) patients underwent additional CT with the patient in a lateral decubitus position to clarify findings obtained in the initial CT series in which the patient was supine. Rao et al (17) found that with rectal contrast material only, in the 47 cases of normal appendix at CT, the appendix was visualized in 44 (94%) cases. Therefore, there were three cases where there was no appendicitis and nonvisualization of the appendix with only rectal contrast material, while the use of rectal contrast material with oral contrast material achieved 100% visualization of the appendix in cases negative for appendicitis (11). Therefore, it is difficult to argue that rectal contrast material increases the chance of visualization of the appendix. The disadvantage of using only rectal contrast material is that up to 15%–20% of normal appendices do not fill during fluoroscopic barium enemas (23). Another concern is that administration of rectal contrast material may cause a hydrolic pressure effect, which may result in rupture of the appendix with considerable detriment to the patient.
There is a wide variation in the rates of visualization of the normal appendix at CT with different routes of bowel opacification. Balthazar et al (13) found that oral and intravenous contrast material–enhanced CT of the entire abdominopelvic region demonstrated a normal appendix in 43% of patients without appendicitis. Weltman et al (16) found that by using helical CT with 5-mm sections, normal appendices were identified in 75% (39 of 52) of negative cases when rectal, oral, and intravenous contrast material were used. Rao et al (17) reported visualization of a normal appendix on CT scans in 94% of negative cases with rectal contrast material only. In our study, we saw 93% (65 of 70) of normal appendices with oral contrast material only. Therefore, rectal contrast material does not necessarily increase the rate of visualization of a normal appendix. Lane et al (12) reported 67% visualization of normal appendix when no contrast material was given; this is similar to the result obtained in the Weltman et al study (16). Since 88% of the true-negative cases in the Weltman et al study had adequate opacification of the cecum with oral and rectal contrast material, they (16) do not believe that the use of rectal contrast material could account for the higher rates documented in the series by Rao et al.
The CT interpretation used by us was based on the positive and negative criteria described by Rao et al (11,18). In the Rao et al study (11), there were 56 true-positive CT findings, all of which demonstrated three or more signs of appendicitis. The 41 true-negative CT results in the Rao et al study (11) showed the appendix filled with contrast material only, air only, air and contrast material, or neither air nor contrast material but with a maximal appendiceal diameter of less than 6 mm (11). In our interpretation of the CT studies, we required the presence of three or more signs to diagnose appendicitis. We chose these signs because they were the most frequently seen signs in true-positive CT findings in the Rao et al study. In all but two of our 28 true-positive cases of acute appendicitis, there was an enlarged appendix (>6 mm in diameter), nonfilling of the lumen with contrast material, and inflammatory changes in the periappendiceal fat. In these two cases, the appendix had perforated, forming an abscess.
Without the administration of oral contrast material, the identification of terminal ileum, cecum, and appendix is difficult (Wijetunga R, Doust BD, personal observation, 1998). In our experience, perforation without abscess formation, periappendicitis (serosal inflammation of the appendix due to disease outside the appendix), or inflammation limited to the mucosa and submucosa of the appendix makes the diagnosis of appendicitis at CT difficult. The usefulness of intravenous contrast material in the diagnosis of appendicitis is questionable. The advantages of using intravenous contrast material in addition to bowel contrast material are that intravenous contrast material allows assessment of appendiceal wall enhancement, differentiation of pelvic blood vessels from a retrocecal appendix, and identification of other pathologic conditions (11). The disadvantages of intravenous contrast material are the increased cost and the increased risk of contrast material reaction (24–26). The disadvantages of focused CT over nonfocused CT are the difficulty in identifying the cecum on the scans obtained in some patients and the failure to demonstrate other intraabdominal pathologic conditions outside the scanning field. Focused CT, however, has the advantage of minimizing the time required for diagnosis and radiation exposure while substantially improving the diagnostic accuracy over that available from clinical diagnosis alone.
Rao et al (11) had a sensitivity of 100%, a specificity of 95%, and an accuracy of 98%. In addition, CT helped to establish an alternative diagnosis in 33 (80%) of 41 patients in whom the results of CT were negative for appendicitis. Our study achieved a sensitivity of 93.3%, specificity of 97.1%, and accuracy of 96.0% for the diagnosis of appendicitis. In our study, CT helped to establish an alternative diagnosis in 23 (33%) of 70 patients in whom the results of CT were negative for appendicitis.
In conclusion, our technique greatly improved the accuracy of diagnosis of equivocal acute appendicitis over the accuracy of clinical diagnosis alone, as reported in the literature (1–5). The use of oral contrast material alone simplifies the procedure for both the radiologist and the patient and yields high levels of accuracy in the diagnosis of equivocal cases of acute appendicitis. We achieved high rates of sensitivity (93%), specificity (97%), and accuracy (96%) without the use of intravenous or rectal contrast material in the diagnosis of equivocal acute appendicitis. Although restricting the use of focused CT to those patients whose clinical diagnosis is equivocal was not formally assessed in our study, we believe that this may be more useful than CT scanning in all patients with suspected acute appendicitis and involves less radiation than does full abdominopelvic (nonfocused) CT (17). Our modified focused appendiceal CT study with oral contrast material alone has the potential to become the definitive investigation for the subgroup of patients who present with clinically equivocal acute appendicitis.
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FOOTNOTES |
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Author contributions: Guarantors of integrity of entire study, R.W., B.D.D.; study concepts, R.W., G.W.B.W.; study design, R.W., B.D.D., G.W.B.W.; literature research, R.W.; clinical studies, R.W., B.S.T., J.C.R.; data acquisition, R.W., B.S.T.; data analysis/interpretation, R.W.; statistical analysis, R.W.; manuscript preparation, R.W.; manuscript definition of intellectual content, R.W., B.D.D., G.B.W.W.; manuscript editing, revision/review, and final version approval, B.D.D.
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