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Letters to the Editor |
Lansing Radiological Associates, 271 Woodland Pass, Suite 120, East Lansing, MI 48823, e-mail: rao@tcimet.net
Editor:
In the November 1999 issue of Radiology, Dr Lane and colleagues (1) report the accuracy of nonenhanced computed tomography (CT) in patients suspected to have acute appendicitis. I applaud this quality addition to the growing body of literature that shows CT to be the most accurate way to diagnose or exclude appendicitis (2,3). Their work makes a case for using nonenhanced CT in average-sized to large patients when the radiologist has considerable experience with appendiceal CT. However, there are situations where the use of rectal contrast material can be of substantial benefit.
Contrast material administered rectally confers three main advantages in appendiceal CT; it aids in defining the right lower abdominal quadrant anatomy (ileocecal valve, cecal apex, proximal appendix, and inferior cecal tip), it shows patency of the lumen in most patients with a normal appendix, and it highlights cecal apical changes in most patients with appendicitis (4). In thin patients, particularly when the radiologist is just gaining experience with appendiceal CT, initial rectal contrast material administration can be the difference between error and correct diagnosis. After equivocal nonenhanced CT findings (nondepicted or borderline-sized appendix), repeat imaging of the right lower abdominal quadrant after rectal contrast material administration can allow for definitive diagnosis.
Despite considerable experience with appendiceal CT, my colleagues and I still encounter difficulty in making definitive diagnoses with nonenhanced appendiceal CT. It may well be that we will eventually use this nonenhanced technique for average-sized to large patients, but so far we have remained more comfortable with the high accuracy and definitive diagnoses routinely achieved with focused appendiceal CT with contrast material administered rectally (4,5).
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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