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Original Report |
1 Department of Radiology, University of Medicine and Dentistry in New Jersey,
150 Bergen St., Newark, NJ 07103.
2 Department of Radiology, Tel Aviv Sourasky Medical Center, 6 Weizman St., Tel
Aviv 62469, Israel.
3 Department of Obstetrics and Gynecology, Lis Maternity Hospital, Tel Aviv
Sourasky Medical Center, Tel Aviv 62469, Israel.
Received February 17, 2004;
accepted after revision June 30, 2004.
Address correspondence to C. D. Levine.
Abstract
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CONCLUSION. Increased awareness of the underlying factors common to most cases of the missed diagnosis of appendicitis on CT and increased radiologic vigilance in cases of atypical abdominal pain may enable us to further improve our diagnostic accuracy.
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Institutional review board approval for the retrospective review of the patients' reports and images was obtained. Patient informed consent was not required or obtained.
Imaging
The CT scans in 12 patients were obtained with a single-detector CT scanner
(CT Helicat, Elscint) and in 48 patients with a dual-detector CT scanner (CT
Twin, Elscint). A collimation of 5–7 mm, an increment of 5 mm, and a
pitch of 1 were used. All patients received 750 mL of meglumine ioxitalamate
(Telebrix, Guerbet) orally. The protocol for both groups was similar. Unless
clinically contraindicated, patients received 120 mL of IV iohexol (Omnipaque
300, Nycomed Amersham), administered via a mechanical injector (Medrad) at
2.5–3 mL/sec with a scanning delay of 60–70 sec. The number of
patients that eventually underwent contrast material–enhanced CT was
evaluated in both the control and case groups.
Evaluation of Images and Clinical Findings
The radiology request forms were evaluated for the patients' age, sex, and
relevant clinical history. The pathology reports were evaluated to compare the
relative rates of perforated appendicitis in the two groups.
All 60 CT examinations were evaluated randomly and individually in consensus by two reviewers who were blinded to all clinical information and had knowledge only of a possible diagnosis of acute appendicitis. The two reviewers were experienced in abdominal CT interpretation. Neither reviewer had been involved in the prospective evaluation of the CT scans. The diagnosis was considered positive for appendicitis if four or more of the following signs were present: a maximal appendiceal diameter greater than 6 mm, periappendiceal inflammatory changes, thickening of the appendiceal and cecal walls, and presence of extraluminal fluid collection or gas bubbles. The appendix was considered to be abnormally distended if it had a caliber of 7 mm or more. The maximal diameter of the appendix was measured in all cases in which it could be identified. Cecal wall thickening was assessed by comparing it with the normal thickness of the wall of the ascending colon immediately proximal to the cecum. Periappendiceal inflammatory changes were defined as stranding and infiltration of the periappendiceal fat. The presence of an appendicolith, free fluid, free air, and small-bowel dilatation were also noted. We also evaluated the degree of intraabdominal fat content in each patient.
Because there is no existing objective classification of abdominal fat content, we classified abdominal fat content subjectively as minimal, moderate, or marked, on the basis of the amount of intraperitoneal fat. The adequacy of small-bowel opacification in the region of the cecum was also noted. Lack of any contrast opacification or incomplete opacification was considered to be "inadequate," whereas complete opacification of the terminal ileum and cecum was considered "adequate."
A biostatistician participated in the study design and review of the data. The cohort and control groups were compared; statistical analysis was performed using the Fisher's exact test.
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Examination of the clinical history noted on the radiology request forms revealed that in the control group, 32 (89%) of the 36 requests mentioned "right lower quadrant abdominal pain" or "rule out appendicitis" as the reason for the CT. This type of history was obtained in only eight (33%) of the 24 patients in the case group (p < 0.0001), with most CT requests providing nonspecific clinical data (Fig. 3).
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Review of the CT scans showed that the typical radiologic signs of appendicitis were often lacking in reports of patients in whom the diagnosis of appendicitis was missed. The abnormal appendix was not visualized even retrospectively in 16 (67%) of the 24 patients in the case group, compared with identification of the abnormal appendix in 33 (92%) of the 36 patients in the control group (p < 0.0001). In those cases in which an appendix could be retrospectively identified, the mean appendiceal diameter measured 1.4 cm (SD, ± 0.54) and 1.2 cm (± 0.51) in the case and control groups, respectively. This difference was not statistically significant (p = 0.33). Furthermore, focal cecal wall thickening was noted in only seven (29%) of the 24 patients in the case group, as opposed to 25 (69%) of the 36 patients in the control group (p = 0.003). Infiltration of the pericecal fat was observed in only 14 patients (58%) in the case group and in 34 patients (94%) in the control group (p < 0.0001). Finally, appendicoliths were not found in any of the patients of the case group but were noted in 12 patients (33%) in the control group (p < 0.001).
Appendiceal inflammation may result in small-bowel dilatation mimicking small-bowel obstruction. In our control group, only two (6%) of the 36 patients showed a small-bowel obstruction pattern, however, in the case group, nine (38%) of the 24 patients had CT signs of small-bowel obstruction (p < 0.002) (Figs. 4A and 4B).
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Intraperitoneal free fluid was noted in only two patients (6%) with correctly diagnosed appendicitis, and intraperitoneal free air was noted in only one patient (3%) in this group. In the patients in whom diagnosis of appendicitis was missed, intraperitoneal free fluid was seen in 10 patients (42%) (p < 0.0001), and intraperitoneal free air was seen in three patients (13%) (p = 0.29).
Evaluation of the pathology reports showed that eight (33%) of the 24 patients in the case group had a perforated appendix, whereas in the control group, only four (13%) of 30 patients had a perforated appendix (p = 0.11).
Cecal and distal small-bowel opacification was graded to be adequate on the scans obtained in 34 (94%) of the 36 control group patients (Fig. 5), whereas bowel opacification was considered adequate on the scans obtained in only 12 (50%) of the 24 case group patients (p < 0.001) (Fig. 6). Administration of IV contrast material was slightly more common in the control group (34/36, 94%) than in the case group (21/24, 88%), although the difference was not statistically significant (p = 0.04).
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The usefulness of CT as a tool with which to diagnose appendicitis effectively and accurately has been shown in several studies [1–3]. These include studies evaluating a multitude of techniques such as abdominal CT with and without the use of orally and rectally administered gastrointestinal contrast material [5, 6], CT with IV-administered contrast material [7–9], scanning the patient in a decubitus position, and focused evaluation of the right lower quadrant [2, 8] versus a complete abdominal and pelvic CT [8]. Increasing evidence suggests that nonfocused CT performed with IV-injected contrast material is more accurate than focused studies [8]. All studies, no matter the technique utilized, have shown high sensitivities and specificities for CT in the diagnosis of appendicitis. The reported sensitivity and specificity for diagnosis of acute appendicitis range from 91–100% and 91–99% [1–3, 10], respectively. Although a plethora of articles exist espousing the virtues of CT in the evaluation of appendicitis, scant attention has been given in the literature to evaluation of cases in which the CT diagnosis of acute appendicitis was missed.
A review of the literature shows that the most common reason for a false-negative diagnosis of appendicitis is related to a paucity of intraabdominal fat [5, 11]. Intraabdominal fat serves as a natural contrast agent, allowing inflammatory changes to be easily noted, even when subtle. These CT findings may be much more difficult to visualize in patients with a lean body habitus. Malone et al. [5] found that eight of 10 cases of missed appendicitis were in slim patients. Lane and Mindelzun [11] also noted that three of five cases of false-negative diagnosis of appendicitis were due to a paucity of intraabdominal fat. In addition, diagnosis of appendicitis is notoriously difficult in the pediatric population [12, 13]. Similarly, we also noted a significantly higher percentage of false-negative diagnoses in patients with less intraabdominal fat. In our study, a patient's body habitus was noted to play a statistically significant role in the radiologists' ability to diagnose appendicitis.
Radiologists generally rely on a typical constellation of CT findings to diagnose appendicitis. These include distention of the appendix, inflammatory changes in the periappendiceal fat, focal cecal wall thickening, and an appendicolith. In any given case, most of these findings are present, allowing confident diagnosis. Comparison of patients from the case and control groups showed that each of these CT findings was absent in a significant number of patients in our case group. The lack of these findings undoubtedly played a major role in the failure to diagnose appendicitis in the case group population.
Appendicitis with its secondary inflammatory changes in the right lower quadrant may cause reactive dilatation of the small bowel. This small-bowel dilatation may be significant enough to mimic a small-bowel obstruction, resulting in a missed diagnosis of the underlying problem—the inflamed appendix causing the small-bowel dilatation. In addition, the dilated small bowel impedes the flow of oral contrast, so that opacification of the cecal region is often suboptimal, creating increased difficulty in diagnosis. Many of the patients with a missed diagnosis of appendicitis had small-bowel dilatation. Therefore, patients with an apparent small-bowel obstruction who have no prior history of surgery and no cause for obstruction seen on CT should raise an internal alarm for radiologists. In these cases, especially in younger patients, appendicitis should be suspected, and this diagnosis should be actively excluded.
Another important factor was that of the clinical history. Most patients (90%) in whom appendicitis was correctly diagnosed had specific clinical information raising the suspicion of possible appendicitis. The radiologist therefore specifically sought to diagnose or exclude this possibility while interpreting the CT scan. On the other hand, in our case group, only 33% had any mention of appendicitis or right lower quadrant pain in their records. Many had a history of epigastric pain that led the clinicians to suspect pancreatitis or peptic ulcer disease. Others had diffuse abdominal pain without localization to the right lower quadrant. This fact reinforces the necessity to carefully evaluate the cecal and appendiceal region not only in patients with right lower quadrant pain but in all patients with unexplained epigastric or diffuse abdominal pain.
Technical factors also played a role in cases of missed diagnosis of appendicitis. Our study showed that the case group had significantly fewer patients with adequate bowel opacification compared with those patients whose appendicitis was correctly diagnosed. Contrary to some reports noting high sensitivity and specificity of CT in the diagnosis of appendicitis even without any oral contrast material [5], we believe oral contrast material is of benefit, especially when imaging lean patients lacking many of the typical findings of appendicitis, as discussed earlier.
Although CT represents an excellent technique in the diagnosis of appendicitis, missed diagnoses still occur. We found that recurrent factors underlie most cases of a missed diagnosis that result in a suboptimal CT examination or a lower radiologist index of suspicion. These factors include a misleading clinical history, paucity of intraabdominal fat, incomplete contrast opacification of the cecum and distal small bowel, presence of a small-bowel ileus, and lack of the typical CT signs of appendicitis. Knowledge of these factors, which act as pitfalls to correct diagnosis, may enable us to avoid misdiagnosis of appendicitis and improve our diagnostic accuracy.
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