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Letters to the Editor |
Department of Radiology, University of Chicago Hospitals, MC 2026, 5841 South Maryland Avenue, Chicago, IL 60637, e-mail: bfunaki@midway.uchicago.edu
Editor:
The recent article by Dr Lane and associates in the November 1999 issue of Radiology (1) regarding the use of nonenhanced helical CT for the diagnosis of appendicitis continues to fuel the debate over the need for enterically administered contrast material in the evaluation of right lower quadrant pain. The authors report excellent sensitivity and specificity without the benefit of intravenous or enteric contrast enhancement. They state, "As with other authors, we have not found it necessary to administer rectal contrast material to achieve excellent results." While their observations are interesting, I believe that the implications of this article should be treated cautiously.
Comparing appendiceal CT techniques is problematic, and the need for enteric contrast material administration is controversial. In my experience, enteric contrast material administration facilitates diagnosis of early appendicitis and enables me to interpret any study finding more quickly and with greater confidence. I have found that nonenhanced CT with enteric contrast material administration is much more user friendly than nonenhanced CT without enteric contrast material administration for general radiologists and residents who may not have expertise in the subspecialty of abdominal CT. A learning curve for the interpretation of right lower quadrant CT studies definitely exists. Indeed, the authors state that their improved accuracy in the current study compared with that of an earlier one is partially attributable to their increased experience with the technique. Unfortunately, as many referring clinicians become aware of the excellent results reported in this article, they may expect similar accuracy with the use of this same technique in their own hospitals. I doubt that radiologists who do not have the authors’ extensive experience with this technique will be able to duplicate the authors’ accuracy. Since most cases of appendicitis are seen in community hospitals where individual experiences may differ, this technique must be studied in this setting. Nonenhanced helical CT with enteric contrast material administration for the evaluation of appendicitis in a community hospital has already been validated as an excellent technique in at least one such study (2).
Interestingly, in the time since this letter was first submitted, a scientific abstract (3) addressing this issue was presented at the 2000 American Roentgen Ray Society annual meeting. In a study of more than 600 consecutive patients suspected of having appendicitis who were evaluated in a community hospital, the sensitivity and specificity of nonenhanced helical CT without enteric contrast material administration was 84% and 92%, respectively (3). Dr Lane and associates reported a sensitivity of 96% and a specificity of 99% (1).
In the current series, the percentage of patients referred directly from the emergency room for CT versus the percentage of patients referred after admission was not stated. Since appendicitis is a dynamic process, images in patients with appendicitis who undergo imaging soon after the onset of symptoms may show only appendiceal enlargement without surrounding inflammation. If patients undergo scanning later, then nearly all images would be expected to show periappendiceal inflammatory changes. In general, later findings of even clinically equivocal appendicitis tend to be flagrant and easily diagnosed with practically any type of CT technique. The absence of periappendiceal inflammation does not reliably exclude early appendicitis in patients with enlarged appendices. One of the strengths of nonenhanced helical CT with enteric contrast material administration is the ability to diagnose appendicitis in patients who do not exhibit periappendiceal inflammation. While nonfilling of a normal appendix with a diameter of greater than 6 mm can occur, in my experience, this finding is unusual and occurs much less than 10%–20% of the time with good cecal opacification (ie, larger appendices fill with contrast material more readily than do smaller appendices).
In my initial experience with helical CT, most of the patients referred for imaging came directly from the emergency room, and four (13%) of 30 patients with pathologically proved appendicitis did not have periappendiceal inflammation (2). All of these patients would have had incorrectly negative diagnoses with the current technique. Furthermore, as the authors correctly state, periappendiceal inflammation may be very difficult to appreciate in thin individuals due to lack of periappendiceal fat. The use of enteric contrast material also facilitates CT evaluation in these patients.
Finally, I am unclear as to why the authors used 6 mm as the upper limit of normal appendiceal diameter in this study when they recently reported contradictory findings. Specifically, they reported that the normal appendix measures 6.88 mm ± 1.7, with a range of 4.3–10.8 mm (4). Do they now use different criteria for an enlarged appendix?
REFERENCES
Department of Radiology, Brooke Army Medical Center, 3851 Roger Brooke Drive, Fort Sam Houston, TX 78234-6200*, e-mail: drslane@yahoo.com, Winthrop University Hospital, Mineola, NY, e-mail: DSK2928@pol.net
We thank Drs Funaki and Rao for their letters regarding our recent article (1). Both of these authors would agree with us that thin-section helical CT is the initial study of choice for confirming the diagnosis of acute appendicitis in adults suspected of having it and that the intravenous administration of contrast material is not required. However, they disagree with our contention that the specific technique of choice in patients with normal or obese body habitus is a nonenhanced examination (1), and they favor the enteric administration of contrast material (2,3). Regardless of the specific technique used, however, the accuracy of helical CT in these studies ranges from 95% to nearly 100% (1–3). The more important message is, therefore, that thin-section helical CT—as opposed to clinical judgment, especially in equivocal clinical cases—is the method of choice for establishing or excluding the diagnosis of acute appendicitis.
Regarding Dr Funaki’s comments, we definitely agree that there is a learning curve with helical CT studies for suspected acute appendicitis. We also do not dispute the fact that the learning process may be more difficult with the interpretation of nonenhanced CT images than with the interpretation of CT images obtained with rectal contrast enhancement. However, although Dr Funaki considers helical CT with enteric contrast enhancement to be more user friendly for general radiologists and residents, we agree with the author of a relatively recent editorial in Radiology (4) in that the use of routine rectal contrast enhancement at CT for suspected acute appendicitis is not necessarily well tolerated by patients or user friendly for the radiologist and CT technologist performing the study. In addition, Dr Funaki’s comments regarding community radiologists are somewhat unsettling, as well as unintentionally ironic, as the first description of nonenhanced CT for suspected appendicitis originated from a community hospital practice (Malone et al [5,6]). At this 400-bed community hospital, nonenhanced CT, which has been in use since 1991, has "won the support of literally every physician" who deals with acute abdominal conditions; the technique has been found to be efficient and safe, without patient discomfort (6). Dr Funaki’s implication that community hospital–based radiologists might have trouble with CT for suspected acute appendicitis (3), regardless of the exact protocol used, is troubling and without a scientific basis, to the best of our knowledge.
All of the patients in our study were referred from either the department of emergency medicine (the vast majority) or the acute care clinics, as opposed to an inpatient service, following surgical evaluation. We agree with Dr Funaki that acute appendicitis is a dynamic process, but we decided to use a combination of periappendiceal inflammation and appendiceal size (>6 mm) as the primary criteria for the diagnosis of acute appendicitis, and the application of those criteria proved to be successful in our study (1).
Similarly, Dr Rao has confirmed the high sensitivity of these two signs for acute appendicitis, particularly periappendiceal inflammation, which was present in 93 (100%) of 93 cases of acute appendicitis in one of his studies (7). The administration of oral contrast material, rectal contrast material, or both does not aid in the detection of either of these two signs of acute appendicitis. The "contrast agent" of choice for detection of periappendiceal inflammation and visualization of the appendix is the degree of intraperitoneal fat (1).
Dr Funaki’s point regarding the 13% of patients in his study who had appendicitis without periappendiceal inflammation has not been our experience. In addition, the incidence of an "unopacified lumen (of the appendix), diameter greater than 6 mm" in his study was 100% (30 of 30 patients); so, the lack of periappendiceal inflammation in four patients did not lead to any false-negative diagnosis (3). We do, however, agree with Dr Funaki that in very select cases in which these two signs are equivocal, it would be preferable to repeat the CT examination in the very near future, as opposed to immediate surgical exploration (3).
Concerning Dr Funaki’s final comment with respect to our recent abstract on the size of the normal appendix, this study was performed following our data collection for the article published in the November 1999 issue of Radiology (1) and was in fact prompted by our initially anecdotal observation that, on average, the size of normal appendix may be larger than that reported in the literature. The subsequent study findings (8) confirm our belief that periappendiceal inflammation is the most important indicator of acute appendicitis, although we continue to recommend the identification of both periappendiceal inflammation and an enlarged appendix to ensure the correct diagnosis of acute appendicitis on nonenhanced helical CT images.
Regarding Dr Rao’s letter, we thank him for his kind remarks, and we agree that there are situations where rectally administered contrast material might be helpful in helical CT studies of the acute abdomen (eg, in cases selected for further evaluation of suspected diverticulitis and complications of diverticulitis). Anecdotally, use of rectal contrast enhancement in thin patients may facilitate identification of the normal or abnormal appendix, but, to our knowledge, there is no literature about direct comparisons of nonenhanced CT and CT performed with rectal contrast enhancement in this group of patients to support this contention.
Again, as Dr Funaki points out, there is a learning curve for all that we do. The purpose of our article was to provide a protocol for the accurate diagnosis of this very common disorder. We believe that radiologists should perform the specific imaging protocol with which they are most comfortable and with which they have produced accurate results in the recent past.
REFERENCES
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